(12) Global Catastrophes

The cost of catastrophes

Five Global Catastrophes That Could Happen Tomorrow


How would you like to die?

If supporters of the Taurid Complex model are to be believed, and I should say now that their views remain very much in the minority amongst advocates of the impact threat, then we may have only another thousand years or so before a series of blinding flashes and crashing sonic booms heralds the arrival of the next batch of fragmented comet. Alternatively, we could face oblivion tomorrow or have to wait 100,000 or more years before a city is obliterated or a thousand millennia before the world plunges into cosmic winter beneath a cloud of pulverized rock. But whenever the skies next fall, how will it affect us? This will depend on three things: (i) the size of the object, (ii) how quickly it is travelling, and (iii) whether it hits the land or the ocean. Everything else being equal, the larger the impactor the more devastating and widespread will be its effects. To reiterate, a body in the 50-100-metre size range carries enough destructive power to wipe out a major city or a small European country or US state. The level and extent of associated devastation will increase progressively with larger impactors until the critical 2-kilometre size is reached. In addition to causing appalling destruction on a regional or sub-continental scale, the arrival of an object of this size will affect the entire planet through engendering a period of dramatic cooling and reduced plant growth. For impactors larger than 2 kilometres the effects on the planet’s ecosystems become progressively more severe until mass extinctions wipe out a significant percentage of all species. The 10-kilometre object that struck the Earth off the Mexican coast at the end of the Cretaceous period, 65 million years ago, not only finished off the dinosaurs but also two-thirds of all species living at the time. Even more disturbingly, there is evidence of a major impact event at the end of the Permian period some 250 million years ago that left fewer than 10 percent of species alive. In all, at least 7 out of 25 major extinctions in the geological record have been linked with evidence for large impacts, although as I mentioned in the previous chapter there is a school of thought that plays down the environmental effects of impact events and prefers to implicate huge outpourings of basalt lava in the great extinctions of the past.

The destructive potential of a chunk of rock hurtling into the Earth is directly related to the kinetic energy it carries, and this reflects not only the size of the object but also the velocity of the collision. Because they travel substantially faster, therefore, impacts by so-called long-period comets, whose orbits carry them far out into interstellar space, cause more destruction than either NEAs or local comets that follow orbits confined to the heart of the solar system. Both the nature and scale of devastation also depend upon whether the impactor hits the land or the sea. Two-thirds of our planet’s surface is covered by water, so statistically, this is where the majority of asteroids and comets strike. In such cases, the amount of pulverized rock hurled into the atmosphere might be reduced, compared to a land collision. However, this small benefit is likely to be at least partly countered by the formation of giant tsunamis capable of wreaking havoc across an entire ocean basin. Furthermore, the gigantic quantities of water and salt injected into the atmosphere may severely affect the climate and even temporarily wipe out our protective ozone shield. Most of the evidence for the environmental effects of impacts comes from studies of just two events, one small and the other enormous.

At the low end of the scale, in 1908 a small asteroid, estimated at around 50 metres across, penetrated the Earth’s atmosphere and exploded less than 10 kilometres above the surface of Siberia in a region known as Tunguska. This huge blast, which expended roughly the energy equivalent of 800 Hiroshima atomic bombs, was heard over an area four times the size of the UK and flattened over 2,000 square kilometres of full-grown forest. The blast registered on seismographs thousands of kilometres distant and the atmospheric shock wave was picked up by barographs time and again as it travelled three times around the planet before dissipating. The gas and dust generated by the explosion led to exceptionally bright night skies over Europe, sufficient – according to one contemporary report – to allow cricket to be played in London after midnight. Because of its inaccessibility, the first Russian expedition did not reach Tunguska until a quarter of a century later, when Leonid Kulik and his team were perplexed by the absence of the huge crater they were expecting. Instead, they found a circular patch of badly charred and flattened trees 60 kilometres across, formed by the airburst as the rock disintegrated explosively due to the huge stresses caused by entry into the atmosphere. As the region was sparsely inhabited, casualties due to the impact were small, with perhaps a few killed and up to 20 injured, although reports are understandably sketchy. Four hours later, however, and the Earth would have rotated sufficiently to bring the great city of St Petersburg into the asteroid’s range and the result would have been catastrophic.

The Tunguska event pales into insignificance when compared to what happened off the coast of Mexico’s Yucatan Peninsula 65 million years earlier. Here a 10-kilometre asteroid or comet – its exact nature is uncertain – crashed into the sea and changed our world forever. Within microseconds, an unimaginable explosion released as much energy as billions of Hiroshima bombs detonated simultaneously, creating a titanic fireball hotter than the Sun that vaporized the ocean and excavated a crater 180 kilometres across in the crust beneath. Shock waves blasted upwards, tearing the atmosphere apart and expelling over a hundred trillion tonnes of molten rock into space, later to fall across the globe. Almost immediately an area bigger than Europe would have been flattened and scoured for virtually all life, while massive earthquakes rocked the planet. The atmosphere would have howled and screamed as hypercanes five times more powerful than the strongest hurricane ripped the landscape apart, joining forces with huge tsunamis to batter coastlines many thousands of kilometres distant.

Even worse was to follow. As the rock blasted into space began to rain down across the entire planet, so the heat generated by its re-entry into the atmosphere irradiated the surface, roasting animals alive as effectively as an oven grill, and starting great conflagrations that laid waste the world’s forests and grasslands and turned fully a quarter of all living material to ashes. Even once the atmosphere and oceans had settled down, the crust had stopped shuddering, and the bombardment of debris from space had ceased, more was to come. In the following weeks, smoke and dust in the atmosphere blotted out the Sun and brought temperatures plunging by as much as 15 degrees Celsius. In the growing gloom and bitter cold, the surviving plant life wilted and died while those herbivorous dinosaurs that remained slowly starved. Life in the oceans fared little better as poisons from the global wildfires and acid rain from the huge quantities of sulphur injected into the atmosphere from rocks at the site of the impact poured into the oceans, wiping out three-quarters of all marine life. After years of freezing conditions the gloom following the so-called Chicxulub impact would eventually have lifted, only to reveal a terrible Sun blazing through the tatters of an ozone layer torn apart by the chemical action of nitrous oxides concocted in the impact fireball: an ultraviolet spring – hard on the heels of the cosmic winter – that fried many of the remaining species struggling precariously to hang on to life. So enormously was the natural balance of the Earth upset that according to some it might have taken hundreds of thousands of years for the post-Chicxulub Earth to return to what passes for normal. When it did the age of the great reptiles was finally over, leaving the field to the primitive mammals – our distant ancestors – and opening an evolutionary trail that culminated in the rise and rise of the human race. But could we go the same way? To assess the chances, let me look a little more closely at the destructive power of an impact event.

At Tunguska, destruction of the forests resulted partly from the great heat generated by the explosion, but mainly from the blast wave that literally pushed the trees over and flattened them against the ground. The strength of this blast wave depends upon what is called the peak overpressure, that is the difference between ambient pressure and the pressure of the blast wave. In order to cause severe destruction, this needs to exceed 4 pounds per square inch, an overpressure that results in wind speeds that are over twice the force of those found in a typical hurricane. Even though tiny compared with, say, the land area of London, the enormous overpressures generated by a 50-metre object exploding low overhead would cause damage comparable with the detonation of a very large nuclear device, obliterating almost everything within the city’s orbital motorway. Increase the size of the impactor and things get very much worse. An asteroid just 250 metres across would be sufficiently massive to penetrate the atmosphere; blasting a crater 5 kilometres across and devastating an area of around 10,000 square kilometres – that is about the size of the English county of Kent.

Raise the size of the asteroid again, to 650 metres, and the area of devastation increases to 100,000 square kilometres – about the size of the US state of South Carolina. Terrible as this all sounds, however, even this would be insufficient to affect the entire planet. In order to do this, an impactor has to be at least 1.5 kilometres across, if it is one of the speedier comets, or 2 kilometres in diameter if it is one of the slower asteroids. A collision with one of these objects would generate a blast equivalent to 100,000 million tonnes of TNT, which would obliterate an area  500 kilometres across – say the size of England – and immediately kill perhaps tens of millions of people, depending upon the location of the impact.

The real problems for the rest of the world would start soon after as dust in the atmosphere began to darken the skies and reduce the level of sunlight reaching the Earth’s surface. By comparison with the huge Chicxulub impact, it is certain that this would result in a dramatic lowering of global temperatures but there is no consensus on just how bad this would be. The chances are, however, that an impact of this size would result in appalling weather conditions and crop failures at least as severe as those of the ‘Year Without a Summer’, which followed the 1815 eruption of Indonesia’s Tambora volcano. As mentioned in the last chapter, with even developed countries holding sufficient food to feed their populations for only a month or so, large-scale crop failures across the planet would undoubtedly have serious implications. Rationing, at the very least, is likely to be the result, with a worst case scenario seeing widespread disruption of the social and economic fabric of developed nations. In the developing world, where subsistence farming remains very much the norm, widespread failure of the harvests could be expected to translate rapidly into famine on a biblical scale. Some researchers forecast that as many as a quarter of the world’s population could succumb to a deteriorating climate following an impact of a 2-kilometre object. Anything much bigger and photosynthesis stops completely. Once this happens the issue is not how many people will die but whether the human race will survive. One estimate proposes that the impact of an object just 4 kilometres across will inject sufficient quantities of dust and debris into the atmosphere to reduce light levels below those required for photosynthesis.

Because we still don’t know how many threatening objects there are out there nor whether they come in bursts, it is almost impossible to say when the Earth will be struck by an asteroid or comet that will bring to an end the world as we know it. Impact events on the scale of the Chicxulub dinosaur-killer only happen every several tens of millions of years, so in any single year, the chances of such an impact are tiny. Any optimism is, however, tempered by the fact that – should the Shiva hypothesis be true – the next swarm of Oort Cloud comets could even now be speeding towards the inner solar system.

Failing this, we may have only another thousand years to wait until the return of the dense part of the Taurid Complex and another asteroidal assault. Even if it turns out that there is no coherence in the timing of impact events, there is statistically no reason why we cannot be hit next year by an undiscovered NEA or by a long-period comet that has never before visited the inner solar system. Small impactors on the Tunguska scale pose less of a threat because their destructive footprints are tiny compared to the surface area of the Earth. It would be very bad luck if one of these struck an urban area, and most will fall into the sea. Although this might seem a good thing, a larger object striking the ocean would be very bad news indeed. A 500-metre rock landing in the Pacific Basin, for example, would generate gigantic tsunamis that would cause massive damage to every coastal city in the hemisphere within 20 hours or so. The chances of this happening are actually quite high – about 1 percent in the next 100 years – and the death toll could be in the tens of millions if not higher.

The most recent estimate of the frequency of 1-kilometre impacts is 600,000 years, but the youngest impact crater produced by an object of this size is almost a million years old. Of course, there could have been several large impacts since, which either occurred in the sea or have not yet been located on land. Fair enough, you might say, the threat is clearly out there, but is there anything on the horizon? Actually, there is. A dozen or so asteroids – mostly quite small – could feasibly collide with the Earth before 2100. Realistically, however, this is not very likely as the probabilities involved are not much greater than 1 in 10,000 – although bear in mind that these are pretty good odds. If this was the probability of winning the lottery then my local agent would be getting considerably more of my business. Most worrying is the 320-metre Near Earth Asteroid, MN4, discovered late in 2004 and recently named Apophis, the Greek name for the Egyptian God Apep – the destroyer. At one point, the probability of Apophis striking the Earth on 13 April 2029 was thought to be as high as 1 in 37. Now, to everyone’s relief, those odds have increased to 1 in 8,000. Again, these may sound very long odds, but they are actually only 80 times greater than those offered during summer 2001 for England beating Germany 5–1 at football. A few years ago, scientists came up with an index – known as the Torino Scale – to measure the impact threat, and so far Apophis is the first object to register and sustain a value greater than zero. At present, it scores a 1 on the scale – defined as ‘an event meriting careful monitoring’. The object is the focus of considerable attention as efforts continue to better constrain its orbit, and it is perfectly possible – as we find out more – than it could rise to 1 on the Torino Scale, becoming an ‘event meriting concern’. It is very unlikely, however, to go any higher, and let’s hope that many years elapse before we encounter the first category 10 event – defined as ‘a certain collision with global consequences’. Given sufficient warning, we might be able to nudge an asteroid out of the Earth’s way but due to its size, high velocity, and sudden appearance, we could do little about a new comet heading in our direction.

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(11) Global Catastrophes


How natural catastrophes cripple global supply chain

Harvey and Irma Could Have a Silver Lining

Is It Insensitive To Discuss Climate Change Right Now? No.



When worlds collide


It has been something of a struggle over the last few centuries for exponents of the theory to convince both scientists and the public that the millions of craters that pockmark the face of the Moon are the result not of volcanic explosions but of collisions with objects from space. As long ago as the early nineteenth century, the German natural philosopher Baron Franz von Paula Gruithuisen’s declaration that the lunar craters were a consequence of ‘a cosmic bombardment in past ages’ was treated with contempt by ‘serious’ scientists. (No doubt his further claims to have uncovered evidence for the existence of humans and animals on the surface of the Moon had a little to do with this.) At the other end of the nineteenth century, the US geologist Grove Karl Gilbert tried to simulate in the laboratory the formation of the lunar craters by firing objects into powder or mud. Gilbert was perplexed, however, by the observation that only objects fired vertically produced circular craters like those that cover the lunar surface. In light of this, W. M. Smart proclaimed, in 1927, that the craters of the Moon could not be caused by impacts because ‘there is no a priori reason why meteors should always fall vertically’. It was only after observing the effects of the billions of tonnes of bombs dropped in the Second World War that it began to dawn on geologists that given a violent enough explosion, a circular crater would always be formed – whatever the angle of the trajectory. In other words, the tremendous blast generated when an object hit the Moon virtually always resulted in a circular crater. Remarkably, it took another quarter of a century for the impact origin of lunar craters to gain widespread acceptance, and even today one or two maverick scientists still support a volcanic origin in the face of overpowering evidence to the contrary. Getting any new paradigm accepted in science is a battle, and geology is no exception. Just as the proponents of the revolutionary theory of plate tectonics had initially to fight hard against reactionary forces, so those scientists who claimed that the Earth, as well as the Moon, had also taken a battering found the going difficult.


As long ago as 1905, Benjamin Tilghman proposed that Arizona’s famous Barringer Crater (also now known as Meteor Crater) was the result of ‘the impact of a meteor of enormous and hitherto unprecedented size’. This suggestion failed to convince, however, because a quarter of a century of excavation by Tilghman and his engineer colleague D. M. Barringer failed to find the impactor itself.


We now know that this had been essentially vaporized by the enormous heat generated by the collision, but at the time the absence of a ‘smoking gun’ simply lent credence to those who suggested an alternative mechanism of formation. Until well after the end of the Second World War, many Earth scientists suffered an extraordinary failure of the imagination, accepting an impact origin for the lunar craters but grabbing at any straw in order not to support an impact origin for crater structures on the surface of our own planet. Given that, due to the Earth’s much greater size and stronger gravity field, it must have been struck perhaps 30 times more frequently than its nearest neighbour, this denial is even more extraordinary. Perhaps not entirely surprising, however, when we consider that the enormously dynamic nature of our planet is far from suited to the preservation of impact craters, particularly those of any great age. Because of plate tectonics, and in particular the process of subduction, through which the basaltic oceanic plates are continuously being consumed within the Earth’s hot interior, some two-thirds of the Earth’s surface is only a few hundred million years old. Bearing in mind that the most intense phase of bombardment occurred during the first few billion years of our planet’s history, evidence for this can now only be found in the ancient hearts of the granite continents that are immune to the subduction process. Because they have succumbed to erosion and weathering, perhaps for aeons, these craters are notoriously difficult to spot. Also, the oldest rocks, which are likely to support the most craters, are in remote areas such as Siberia, northern Canada, and Australia, and some craters are so big that their true form can only be seen from space. Today, satellites have helped in the identification of over 172 impact craters all over the world, and the idea that the Earth is susceptible to bombardment from space is now as accepted as plate tectonics.


Controversy has certainly not gone away, however, and the argument continues amongst the scientific community, particularly about the frequency and regularity of impacts and – probably of most interest to the layman – about the effects of the next large impact on our civilization. The question of frequency is far from straightforward and serious disagreement exists between schools of thought that, on the one hand, support a constant flux of impactors and, on the other, advocate so-called impact clustering. Notwithstanding the very heavy bombardment of the Earth’s early history, followers of impact uniformitarianism support a strike rate that is uniform and invariable. This is at variance with rival groups of scientists who are promoting an alternative theory of coherent catastrophism, within which the Earth, for one reason or another, periodically comes under attack from increased numbers of asteroids or comets.


If we are realistic to assess the threat of future impacts to our civilization, then clearly it is vital that we resolve as soon as we can whether the number of collisions continues at its current rate or whether we have a nasty shock in a store somewhere down the line. If the former proves to be correct, we can expect business as usual, meaning a collision with a 50-metre potential city-destroyer every few centuries or so, a half-kilometre small-country obliterator every several tens of millennia, and a 1-kilometre global consequence impact event every 600,000 years. Fortunately for us, gigantic extinction level events (ELEs), such as that caused by the 10-kilometre monster that ended the reign of the dinosaurs 65 million years ago, appear to happen every 50 to 100 million years, so the chances of one striking the Earth soon are tiny. Based upon the above impact or strike rates, proponents of the threat from asteroids and comets come up with probabilities of dying due to an impact that really makes one think. If you were able to construct a time machine and hurtled forwards to the year 1,000,2005 where you sought out and consulted the Centre for Planetary Records you would come up with a fascinating fact. The number of people killed in the air (and no doubt space) crashes during the intervening million years – probably between 1 and 1.5 billion – would be just twice that killed by impact events, which could total 500 to 750 million or more, assuming one or two collisions with two 1 kilometre objects.


What this amounts to is that during your lifetime your chance of dying due to an asteroid or comet impact could be as great as half that of being killed in an air crash; a pretty sobering thought if ever there was one. Looked at another way, if you gamble, your chance of being killed during an asteroid or comet strike is 350 times more likely than winning the UK lottery. Maybe this scares the wits out of you, but the true situation may actually be worse. If the coherent catastrophists are correct then there are certain periods in the Earth’s history when our planet, or perhaps even our entire solar system, travel through a region of space containing substantially more debris than normal, resulting in a significant increase in impact events on all scales.


A number of theories lay the blame for this periodic increase in Earth-threatening space debris on the episodic disruption of the so-called Oort Cloud, a great spherical swarm of comets that envelops the entire solar system far beyond the orbit of Pluto. Typically, comets in the cloud travel along such huge orbits, which take some a quarter of the way to the nearest star, that they rarely visit the inner solar system, and then only in ones and twos. However, if some external influence were to interfere with the cloud, so the thinking goes, hundreds or thousands could have their orbits changed encouraging them to plunge Sunwards, greatly raising the threat of collision with the planets – including our own. A number of suggestions have been put forward for how the Oort Cloud might be periodically disrupted, including due to the passage through the cloud of the mythical and much sought after planet X, which some scientists think may be orbiting far beyond frozen Pluto and the recently discovered planetoid, Sedna, or to a dark and distant stellar companion of our own Sun.


An alternative and intriguing theory, known as the Shiva hypothesis after the Hindu god of destruction and renewal, has been vigorously promoted by Mike Rampino of New York University and his colleagues, who believe that the great extinctions recognized in the Earth’s geological record are the result of major impact events that happen pretty regularly every 26–30 million years. Rampino and his colleagues link this to the orbit of our solar system – including the Earth – about the centre of our Milky Way galaxy, an orbit that moves up and down in a wave-like motion. Every 30 million years or so, this undulating path takes the Sun and its offspring through the plane of our disc-like galaxy, when the gravitational pull of the huge mass of stars at the galaxy’s core provides an extra tug.


This, say the Rampino school, is sufficient to disturb the orbits of the Oort Cloud comets to an extent sufficient to send an influx of new comets into the heart of the solar system, dramatically raising the frequency of large impacts on the Earth. It is just a few million years now since our system last plunged through the galactic plane – could a phalanx of comets be heading for us at this very moment?


By the time we find out it might very well be too late. The Shiva hypothesis calls for a periodicity operating on truly geological timescales, and for this reason, is rarely addressed in discussions of the immediate threat from impact events. Much more relevant to considerations of our own safety and survival – and that of our immediate descendants – is a proposal by UK astronomers Victor Clube and Bill Napier that the Earth is struck by clusters of objects every few thousand years, and that our planet took a serious pounding as recently as the Bronze Age – just 4,000 years ago. To find out what might cause such a worryingly recent bombardment we need to return to the Oort Cloud in deepest space. Leaving aside disturbance of the cloud due to the passage of the solar system around the galaxy, normality sees a new comet from the cloud every now and again falling in towards the inner solar system – maybe as frequently as every 20,000 years. The newcomer is rapidly ‘captured’ and torn apart by the strong gravitational fields of either the Sun or Jupiter, forming a ring of debris spread out along its orbit, but concentrated particularly around the position of the original comet itself. A large comet, broken up in this way, can ‘seed’ the inner solar system with perhaps a million 1-kilometre sized lumps of rock, dramatically increasing the number of Earth-threatening objects, and significantly raising the chances of our planet being hit. Clube, Napier, and others of this particular coherent catastrophist school propose that the last giant comet from the Oort Cloud entered our solar system towards the end of the last Ice Age – a mere 10,000 years or so ago – breaking up to form a mass of debris known as the Taurid Complex. Every December the Earth passes through part of this debris stream, resulting in the sometimes spectacular light show put on by the Taurid meteor storm, as small rocky fragments and gravel-sized stones burn up in the upper atmosphere. These innocuous bits and pieces only represent the tail end of the Taurid Complex, however, the heart of which contains a 5-kilometre wide Earth-crossing comet known as Encke and at least 40 accompanying asteroids any one of which would create global havoc if it struck our planet.


The distribution of debris along the Taurid Complex orbit about the Sun is rather like that of runners in a 10,000-metre race; while the majority are clustered together in a pack, the rest are dotted here and there around the track. Most years – according to the coherent catastrophists – the Earth’s orbit crosses that of the Taurid Complex at a point where there is little debris, resulting in a pre-Christmas spectacle and little else. Every 2,500–3,000 years or so, the Earth passes through the equivalent of the runners’ pack – and finds itself on the receiving end of a volley of rocky chunks perhaps up to 200–300 metres across. Benny Peiser, a social anthropologist at Liverpool’s John Moores University, thinks that just such a bombardment around 4,000 years ago led to the fall of many early civilizations during the third-millennium bc. He and others have interpreted contemporary accounts in terms of a succession of impacts, too small to have a global impact but quite sufficient to cause mayhem in the ancient world, largely through generating destructive atmospheric shock waves, earthquakes, tsunamis, and wildfires. Many urban centres in Europe, Africa, and Asia appear to have collapsed almost simultaneously around 2350 bc, and records abound of the flood, fire, quake, and general chaos. These sometimes fanciful accounts are, of course, open to alternative interpretation, and hard evidence for bombardment from space around this time remains elusive. Having said this, seven impact craters in Australia,


Estonia and Argentina have been allocated ages of 4,000–5,000 years and the search goes on for others. Even more difficult to defend are propositions by some that the collapse of the Roman Empire and the onset of the Dark Ages may somehow have been triggered by increased numbers of impacts when the Earth last passed through the dense part of the Taurid Complex between 400 and 600 ad. Hard evidence for these is weak and periods of deteriorated climate attributed to impacts around this time can equally well be explained by large volcanic explosions. In recent years there has, in fact, been a worrying tendency amongst archaeologists, anthropologists, and historians to attempt to explain every historical event in terms of a natural catastrophe of some sort – whether asteroid impact, volcanic eruption, or earthquake – many on the basis of the flimsiest of evidence. As the aim of this volume is to shed light on how natural catastrophes can affect us all, I would be foolish to argue that past civilizations have not suffered many times at the hands of nature. Attributing everything from the English Civil War and the French Revolution to the fall of Rome and the westward march of Genghis Khan to natural disasters only serves, however, to devalue the potentially cataclysmic effects of natural hazards and to trivialize the role of nature in shaping the course of civilization.


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(10) Global Catastrophes

What to do if an asteroid comes our way

Study Determines Which Effects Of An Asteroid Strike Would Result In Most Casualties

What would happen if that massive asteroid zipping by actually hit us? Study reveals exactly how millions would die


The Threat from Space

Asteroid and Comet Impacts

The astronomical event of the century

In 1993 a discovery by Carolyn Shoemaker, wife of the late and greatly lamented planetary scientist Eugene Shoemaker, and colleague David Levy, was to change forever our perception of the Earth as a safe and cosy haven insulated from the whizzes and bangs of a violent and capricious universe. The Shoemaker team had spotted 21 huge chunks of rock that had once been part of a comet torn apart by the enormous gravitational field of the planet Jupiter - a giant sphere mainly made up of hydrogen and helium gas that is large enough to contain over 1,300 Earths. Instead of orbiting the Sun, like most comets, however, this one had been captured by Jupiter’s gravity and the rocky fragments now orbited the King of Planets himself. As Jupiter already had a large retinue of moons, the addition of a few more would have been mildly interesting, if not surprising. What was extraordinary, however, was that these new ‘moons’ were very much ephemeral. The following year they would end their lives by crashing into the surface of Jupiter, providing scientists on Earth with a grandstand view of just what happens when a planet is struck by large hunks of space debris.

On 16 July 1994 - appropriately the 25th anniversary of the launch of Apollo 11, the first manned lunar landing mission - the first fragment of Comet Shoemaker-Levy struck the planet, sending up a gigantic plume of gas and debris and blasting outwards a rapidly expanding shock wave. As fragment after fragment hammered into the planet, spectacular images were gathered by the Hubble Space Telescope in Earth orbit and by the unmanned Galileo probe on its way to Jupiter. Two days after the initial impact, a chunk of rock 4 kilometres across and rather unromantically named fragment G smashed into the planet with the force of 100 million tones of TNT - roughly the equivalent of eight billion Hiroshima-sized atomic bombs. The flash generated by the collision was so brilliant that many infra-red telescopes trained on the event were temporarily blinded. The glare soon faded, however, to reveal an enormous dark impact scar wider than the Earth. Inevitably, everyone who saw this awesome image had the same thought. What would have happened if fragment G had struck the Earth instead of Jupiter?

Almost overnight our planet seemed a much more vulnerable place and the hold of our race upon it that much more tenuous. Suddenly both scientists and the public, and even politicians began to take the threat from space seriously. Two Hollywood blockbuster films fed growing interest in impact events by showing - with various degrees of scientific rigour - what we might all be in for if a comet or asteroid headed our way.

In 1996, just two years after the Jupiter impacts, an international body is known as the Space-guard Foundation was formed, with the dedicated aims of promoting the search for potentially dangerous asteroids and comets and raising the general level of awareness of the impact threat. In the United States, NASA and the Department of Defence began, albeit at a low level, to fund Space guard-related projects and the UK government established a task force to examine the risk of asteroids and comets hitting the Earth. All of a sudden everyone wanted to know what the chances were of the Earth being struck at some point in the future and what effect such a collision would have on our planet and our race. The answer to the first question is easy: the chances are 100 per cent. The Earth has been bombarded by space debris throughout its long history, and although such collisions are now far less common than they were billions of years ago, our planet will be struck again. The vital question is - when? And as regards how bad this will be for the human race: that depends largely on how big a chunk of rock hits us.

The cosmic sandstorm

To get a better idea of how frequently the Earth is likely to be hit, we need to find out how many rocks are hurtling around our solar system and, in particular, how many of these come close enough to the Earth to start us worrying. Although a vast amount of debris was swept up by the embryonic planets during the early solar system, countless dregs remain, ranging upwards in size from tiny specks a few millimetres across to gigantic rocks, such as the minor planet Ceres, over 1,000 kilometers in diameter. Like someone battling through a desert sandstorm, the Earth is constantly bombarded in the course of its journey through the solar system.

Fortunately for us, most of the billions of colliding fragments are tiny and flash into oblivion as soon as they come into contact with our planet’s atmospheric shield. Every now and again, however, the Earth collides with something larger.

A fragment of debris the size of a pea burns up in the Earth’s atmosphere every five minutes, while a soccer-ball sized lump will light up the sky with its death throes around once a month. Larger objects may run the gauntlet of the atmosphere and reach the surface, but this is rare and only happens a few times a year. Perhaps every few centuries, the Earth collides with a rock in the 40-50-metre size range - an object large enough to obliterate a city if it scores a direct hit. The last well-documented impact of this size occurred as recently as 1908 – of which more later.

While the entire solar system teems with debris, from a hazard point of view we are only really interested in those fragments that threaten to end their existence through collision with our planet. The majority of these Earth-threatening objects are rocky asteroids that have orbits around the Sun that approach or intersect the Earth’s. The true numbers of these Near Earth Asteroids (NEAs) are impossible to determine, but current estimates are pretty frightening.

In all, up to 20 million pieces of rock over 10 metres across may be hurtling across or close to our planet’s path during its journey around the Sun. Up to 100,000 of these are thought to be over 100 meters in diameter - big enough to obliterate London or New York gave a direct hit -and maybe 20,000 are half a kilometre across, sufficient to wipe out a small country if they strike land, or generate devastating tsunamis if they impact in the ocean. Fewer in number, but enormously more destructive if they hit, are those asteroids 1 kilometre or more in diameter, which have the potential to obliterate a country the size of England and - if 2 kilometres or more across - wreak havoc across the globe. Although barely equivalent in diameter to 20 soccer pitches laid end to end, such is the tremendous level of kinetic energy - or energy of motion - involved in the collision that a 2-kilometre objects striking land would leave a crater 40 kilometers or so across and loft sufficient pulverized debris into the atmosphere to block out the Sun’s rays and plunge the Earth into a freezing cosmic winter for years.

A range of estimates has been published for the number of NEAs in the 1 kilometre and above size range, with the most recent suggesting, there are around 1000. As of August 2005, 794 of these had been identified – perhaps three-quarters of the total – and their orbits projected forward in time to see if they pose a threat to the Earth in the medium term, and the search continues to find them all – a task that will take at least a couple more decades. Once this has been accomplished and assuming that one does not have our name on it, we can sleep a little safer in our beds. The problem does not, unfortunately, end there. We still have the comets to worry about. Comets are enormous masses of rock and ice that can be up to 100 kilometres or more across. In contrast to the near-circular orbits of the asteroids, most comets follow strongly elliptical paths that carry them from the freezing outposts of the outer solar system, or beyond, in close to the Sun and then out again. In the depths of space, comets are enigmatic objects and not easy to spot. As they enter the inner solar system, however, they undergo a remarkable transformation as sunlight starts to evaporate gas and dust particles from the central nucleus to form a spectacular tail that can stretch across space for 100 million kilometres or more. The stunning apparition of a comet’s tail was long regarded as a portent of doom and disaster, and in a way, this is not too far from the mark. Comets have typical velocities of 60–70 kilometres a second - a hundred times faster than Concorde, and around three times that of the typical NEA. As a result, a collision between a comet and the Earth is hugely more energetic and therefore tremendously more destructive.

Another problem with comets is that, unlike their asteroid cousins, their orbital parameters are often poorly known and therefore difficult to project into the future to see if they pose any threat.

Halley’s Comet, undoubtedly the most famous of all, follows an orbit around the Sun that takes only 76 years to complete. Consequently, it has been observed dozens of times over thousands of years and its orbit is well enough known to make it possible to calculate its path far into the future. This shows that, at least until 3000 ads, Halley’s Comet will not even come close to threatening the Earth. Other comets, however, follow parabolic orbits that take them on immeasurably long journeys far beyond the limits of the solar system. Some of these may have been observed once or twice by our distant ancestors, but others may be making their first ever visit the inner solar system. In these circumstances, there has been no opportunity to predict their orbits on the basis of earlier visitations, and our first view of one of these objects heading our way may provide us with just six months respite before an unavoidable and calamitous collision. Furthermore, because such comets have been confined to deep space, they are huge - perhaps 100 kilometres or more across. This is because they have not suffered attrition from the solar wind, the hurricane of solar particles that evaporates parts of a comet to produce the characteristic tail, as it forges its way through the inner solar system

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(9) Global Catastrophes

5 world ending disasters which could happen TOMORROW according to science

The Toba Super-Eruption: The Global Catastrophe that Creationists Ignore


The Toba supereruption

The city waiting to die

It is extraordinarily difficult to get across to someone who has never experienced it the sheer, mind-numbing terror of being caught in a major earthquake. Even in California, where the population is constantly bombarded with information about what to do in the event of a quake, coherent, sensible thought ceases when the ground starts to tremble. Following the Loma Prieta quake that struck northern California in 1989, a survey by the United States Geological Survey revealed that only 13 per cent of the population of Santa Cruz sought immediate protection, while close to 70 per cent either froze or ran outside. This is a perennial problem with earthquakes; however well-informed the people, when the ground starts bucking like a bronco and the furniture starts to hurl itself across the room, blind instinct takes over and tells them to ‘get the hell out of there’. Unfortunately, this serves only to increase the death toll as terrified homeowners rushing screaming into the street provide easy targets for falling masonry and other debris crashing down from above. What they should be doing is diving beneath the nearest piece of heavy furniture or sheltering under the lintel of a convenient doorway.

Earthquakes are immensely destructive, mainly because most cities in regions of high seismic risk are dominated by buildings that are simply not built well enough to withstand the severe ground shaking of a major quake. Modern construction methods in California follow stringent building codes that ensure they can withstand earthquakes that would be devastating elsewhere, and this policy has borne considerable fruit by dramatically limiting death, injury, and damage during major quakes in the last 15 years. Even so, the Northridge earthquake that struck southern California in 1994 is credited with losses totalling US$35 billion, largely accruing from damage to older structures. Other earthquake-prone countries also have in place building codes designed to minimize damage due to ground shaking, but often these codes are simply not enforced. The terrible legacy of such a lack of commitment by government and local authorities became all too apparent when a magnitude 7.4 quake struck the Izmit region of Turkey in 1999, obliterating 150,000 buildings and taking over 17,000 lives. Many apartment blocks simply pancaked; successive floors collapsing to form a pile of concrete slabs beneath which opportunities for survival were minimal. In January 2001, a severe earthquake shook the Bhuj region of Gujarat state in northwestern India, flattening 400,000 homes and killing perhaps 100,000 people. Many of the deaths resulted from the traditional construction methods used in the region, which involved the building of homes with enormously thick walls made of great boulders held together loosely with mud or cement, beneath heavy stone roofs. When the ground started to shake these buildings offered little resistance, collapsing readily to crush those inside. More recently, in 2003, a moderate earthquake in southern Iran took 26,000 lives in the city of Bam, as the traditional adobe (mud brick) buildings put up little or no resistance to the ground shaking, while in 2005 more than 80,000 died in a huge quake in Pakistan. During the last millennium, earthquakes were responsible for the deaths of at least 8 million people. Terrifying as this sounds, the rapid growth of megacities in regions of high seismic risk is set to ensure that this figure is surpassed, maybe in just the next few centuries, and some seismologists are already warning of the potential, in the near future, for a single large quake to take 3 million lives. If the unfortunate target were Karachi or Mexico City, although the catastrophe would have appalling consequences for the host countries, the global impact would be minimal and would barely impinge upon the lives of most of the world’s population. On the other hand, if ground zero were to be the Japanese capital, Tokyo, then the story would be very different. Projections to 2015 suggest that by this time the Tokyo-Yokohama conurbation will be the greatest urban concentration on the planet, with a population a shade over 36 million. The city is located in one of the most quake prone parts of the planet, where the Pacific and Philippine plates to the east plunge beneath the giant Eurasian plate, and was obliterated by a massive earthquake less than 80 years ago. While things have been ominously quiet since, it can’t be long now before another huge quake devastates one of the world’s great industrial powerhouses. When it does, the economic shock waves will hurtle out across the planet, bringing country after country to its knees. In order to provide an impression of the fate awaiting the Japanese capital, let me take you on a trip back to one of the great disasters of the twentieth century, the terrible event the Japanese call the Great Kanto Earthquake.

September 1st, 1923, dawned like any other day for the inhabitants of Tokyo and Yokohama, but for many it would be their last. The quake struck just before noon, when the cafés and beer halls were packed with hungry workers and as families sat down at home to their midday meal. A low, deep rumbling grew rapidly to a monstrous roar as a fault below Sagami Bay ripped itself apart and sent shock waves tearing northwards towards the twin cities, crashing first into Yokohama and then – a bare 40 seconds later – into the heart of the capital itself. The quake registered a massive 8.3 on the Richter Scale, and so severe was the ground shaking that it was impossible even to stand. Within seconds, thousands of buildings, many with the traditional wooden walls and heavy tiled roofs, collapsed into heaps of rubble, bringing sudden oblivion to those inside. The great cacophony of grinding rock and falling buildings eventually gave way to the quieter but equally terrifying crackling of flames as fires started by thousands of overturned stoves began to devour the wood out of which many of the buildings were constructed. Whipped up by a brisk wind, a million small fires swiftly merged to form unstoppable walls of flame that marched across the ruins. Shocked men, women, and children cowered before them in open spaces, but to no avail. The firestorms roasted them alive. In one area of waste ground 40,000 were immolated by the conflagration, so packed together that their charcoaled bodies were found still upright. The fires continued to consume what remained of the cities for two days and nights, before finally burning themselves out to reveal a post-apocalyptic scene of utter devastation. The true total will never be known but up to 200,000 people may have lost their lives in the quake itself and the fires that followed. The cost to the Japanese economy was phenomenal – around US$50 billion at today’s prices – and a combination of the quake and the Great Depression six years later led to economic collapse and severe hardship. Some have even suggested that these circumstances, as in the German Weimar Republic, helped stoke the fires of nationalism and the rise of the military, leading to conquest, imperialism, and ultimately war.

In the early years of the new millennium, the twin cities of Tokyo and Yokohama again await their fate, only this time it will be far, far worse, both for Japan and the rest of the world. Now the industrial and commercial might of the region constitutes one of the major hubs of the world market, with spokes reaching out to the far corners of the Earth, helping to bind together a global economic machine upon which the wealth of all nations now depends. When Tokyo falls, so will Japan, and the rest will follow – but when? Strains have now been accumulating in the rock beneath and around the capital for 78 years and, apart from a relatively small – magnitude 5.9 – quake in 1992, and another in 2005, the region has been seismically silent. Both the government and the population know, however, that this can’t last and money is being poured into constructing earthquake-proof buildings, improving education and emergency planning, and even trying to determine the precise timing of the next ‘big one’. So far, however, the accurate prediction of earthquakes has proved to be out of reach, and prospects for a breakthrough in the near future are slim. Furthermore, a substantial proportion of the older building stock remains vulnerable, and an estimated one million wooden buildings continue to provide an excellent potential source of fuel for the post-quake fires. Just ten years ago, 6,000 people died in the Kobe earthquake, 400 kilometres south of Tokyo, which can be viewed, perhaps, as a mini version of the catastrophe awaiting the capital. At Kobe serious fire damage contributed significantly to the overall destruction and to the huge economic losses of US$150 billion, and it was clear that emergency preparedness and response were far from effective, and certainly well below the rest of the world’s expectations, given the general perception of Japanese society as a model of efficiency. For one reason or another, the authorities were simply unable to cope with the chaotic aftermath of the event. Plans were not in place to ensure transport of emergency supplies and equipment to where they were needed, once roads were blocked by debris and railways out of commission, and many of the city’s hundreds of thousands of homeless received little or no help for several days after the quake. It is fair to say that some at least of the problems encountered at Kobe reflect the hierarchical structure of Japanese society, which stifles independent decision making and action and hinders rapid response in emergency situations. Without significant changes it is difficult to see how any earthquake emergency plan for the Tokyo region could function effectively within the straitjacket imposed by such a deeply ingrained and restrictive social etiquette.

The geological setting of Tokyo and Yokohama is complex, with three of the Earth’s great tectonic plates converging here. The enormous strains associated with the relative movements of these plates are periodically relieved by sudden displacements along local faults, which in turn lead to destructive earthquakes. In fact, there are so many active faults in the vicinity that the region is at risk from major quakes occurring at four different locations, all of which are thought by seismologists to be overdue or at least imminent. Some 75 kilometres south of Tokyo and Yokohama, close to the city of Odawara, earthquake scientists expect a magnitude 6.5–7 quake to strike at any moment. Although causing serious damage locally, and moderate damage in the twin cities, this is unlikely to hit the capital with the force of the 1923 quake. Similarly, another so-called Tokai earthquake is imminent beneath Suruga Bay, 150 kilometres to the south-west. Scientists forecast that this will be a huge, magnitude 8 event that will undoubtedly batter the coastal city of Shozuoka but will probably again be too far from the capital to have a serious impact. Far more worrying are two other expected quakes that pose a much greater threat to the Tokyo region, and which are awaited with much trepidation. Seismologists predict that a quake as large as magnitude 7 could strike at any time – directly beneath the capital. This event, known locally as a chokka-gata quake, will cause severe damage in the capital, although Yokohama is likely to be less badly hit. Worst of all, a repeat of the 1923 Great Kanto Earthquake itself may be less than a century away. This is likely to take the form of a massive magnitude 8 event resulting from the tearing open of a fault beneath Sagami Bay to the south. As was the case almost 80 years ago, the shock waves will race northwards, rolling first into Yokohama and barely half a minute later into Tokyo itself.

The national government still maintains that its scientists will detect in advance the warning signs that the ‘big one’ is on its way. Such faith in science is both rare and touching, but in this case entirely misplaced. Retrospectively, it has been noted that some earthquakes have been preceded by falls in the water levels in wells and boreholes, and in elevated concentrations of radioactive radon gas issuing from the rock, but this is not always observed. Furthermore, such changes can occur without the following quake, making them notoriously unreliable for prediction purposes. A group of Greek scientists claim that they can detect electrical signals in the crust prior to an earthquake, but there is no convincing evidence for this and the method is derided by most seismologists. On the other hand, there does appear to be something in the idea that animals, birds, and fish behave strangely before an earthquake, and the Japanese are actually undertaking serious research to find out if catfish – amongst other organisms – can help them forecast the next big one. The problem here is that no one knows how animals can detect a quake before it happens, although it has been suggested that strain in the rocks generates electrical charges in fur and feathers, and perhaps even scales, that trigger small electric shocks, making the animals understandably restless and irritable. But this begs the question, how do you decide if a pig, for example, is behaving strangely?

In the absence of an alert from a precognizant catfish, it is likely then, that the next great quake will strike the Tokyo region with no warning whatsoever. Recently constructed buildings will fare reasonably well, but many older properties will crumble. Notwithstanding an automatic gas shut-off device that is fitted to some buildings, exploding fuel tanks, fractured gas mains, and oil and chemical spills will ensure no shortage of fires to feed on a million wooden buildings. As in 1923, huge conflagrations are expected to cause at least as much destruction as the quake itself and to inflate the likely death toll – which is estimated at 60,000, substantially. While it is difficult to estimate in advance the economic losses resulting from the next big one, a modelling company that services the insurance industry has come up with the extraordinary figure of US$3.3 trillion. This would make the cost of the next Tokyo quake close to 20 times greater than Kobe, so far the most expensive natural disaster ever, and 60 times more than California’s 1994 Northridge quake – the costliest natural catastrophe in US history.

The impact on the Japanese economy is widely expected to be shattering. Japan is enormously centralised, and the Tokyo region hosts not only the national government but also the stock market and 70 per cent of the headquarters of the country’s – and the world’s – largest companies. Japan has the second largest economy on the planet, accounting for 51 per cent of Asia’s GDP and 13 per cent of the world’s GDP, and despite its current economic woes, it is likely that it will still be an economic powerhouse when the big one eventually strikes. In order to rebuild and regenerate it is highly likely that the Japanese will have to disinvest from abroad on a massive scale, dumping government bonds in Europe and the States, selling foreign assets, and shutting down overseas factories.

It is well within the realms of possibility that as country after country finds itself fighting to cope with the swift unravelling of the global economy, a recession deeper than anything since 1929 – when the Wall Street Crash closed 100,000 businesses in the USA alone – would soon set in. Neither would it be any great surprise to find unemployment reaching staggering proportions and the political and social fabric of many states starting to pull apart. No one knows how long a post-Tokyo quake depression would last – it could be years or even decades – nor just how bad it would be.

Equally importantly, how long do we have to wait until such a speculative scenario is played out for real? Perhaps only decades, perhaps another hundred years or more, but it would be no real surprise if this great city was brought once again to its knees before the next century dawns.

Despite occasionally being depicted in the media as ‘Disasterman’, I would hate you to regard me purely as a harbinger of doom, and close the book at this point with a feeling of hopelessness about the future. Yes, the Earth is geologically very dangerous, and the more we study our planet the more potentially serious the tectonic threat to the survival of our civilisation appears to be. On the other hand, we are learning all the time; collecting data that can be utilised to counter or at least mitigate the impact of the next super-eruption or gigantic tsunami. Eventually, it probably will be possible to predict earthquakes with some accuracy and precision, and certainly, within a century, it is likely that nowhere on the planet will a volcanic island become unstable or a huge new batch of magma swell the surface without our satellites spotting them well in advance of catastrophe. On an almost daily basis Earth scientists are tackling some of the greatest threats to our society and incrementally they are getting to grips with them. At the very least, the next time our planet shudders on a grand scale we will be far better prepared than our distant ancestors, who faced the might of Toba with incomprehension and sheer terror.

Facts to fret over

• On average there are two volcanic super-eruptions every 100 millennia.

• Following the Toba super-eruption 74,000 years ago, the world would have been held in the grip of volcanic winter for at least six years.

• In the aftermath of Toba, the human population may have been reduced to just a few thousand individuals.

• In 1949 a gigantic landslide on the western flank of the Cumbre Vieja volcano on La Palma (Canary Islands) dropped 4 metres overnight.

• When the Cumbre Vieja collapses into the sea, the coastal cities of the eastern USA could be battered by tsunamis up to 50 metres high.

• The next great Tokyo earthquake is expected to cause damage totalling more than US$3.3 trillion and may trigger a global economic collapse.

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(8) Global Catastrophes

Tsunami - Earthquake Japan 2011

Pacific Tsunami Museum


The Enemy within Super-Eruptions, Giant Tsunamis, and the Coming Great Quake

Hell on Earth

Imagine the worst possible vision of hell. The vile stench of sulphurous gas pervading a world of darkness broken only by a dull red glow on a distant, invisible horizon. Heavy, grey ash pours from above like gritty snow, clogging the eyes, nose, and ears as swiftly as you can remove it. Choking and retching you ram your fingers into your mouth to try and gouge out the ashy slime those forces its way in with every struggling breath, but to no avail. Suddenly a blinding flash reveals the nightmare landscape of Tolkien’s Mordor – all familiar features blotted out and buried by ash accumulating at half a meter an hour. A titanic crash of thunder heralds the return of the darkness and the onset of a truly biblical deluge. Within seconds the ashy drifts are transformed into rushing torrents of mud that almost sweep your feet from under you. As the falling rain and ash combine, you are battered by pellets of mud that begin to weigh you down under a sticky, ever-thickening carapace of Vulcan’s ordure.

There is no sign that the Sun ever bathed the landscape in its warming rays, but it is far from cold. In fact, your body is slowly roasting in the stifling heat of nature’s own oven, your sweat sucking you dry as it drains from every pore to mix with the muddy rivulets covering every inch of your skin.

Some of the halves a billion inhabitants of the danger zones around the world’s 500 or so historically active volcanoes don’t need to use their imagination. They have already experienced hell. Show the above description to survivors of the 1991 eruption of Pinatubo (Philippines) or the twin eruptions of Vulcan and Tavurvur at Rabaul (Papua New Guinea) three years later, and they will nod their heads and say ‘I have been there!’ However awful it might sound to those of us who live far from the slopes of an erupting volcano, there is nothing unusual about the above scene. But what if it was enacted 1,500 kilometers from the eruption? Then it really would be something very special, because it would mean that the Earth was being rent by one of nature’s greatest killers – a volcanic super-eruption. These gigantic blasts dwarf even the greatest eruptions of recent times, and in comparison the cataclysmic detonation that blew Krakatoa (Indonesia) apart in 1883, killing around 36,000 of the inhabitants of Java and Sumatra, pales into insignificance. Even the titanic blast that tore the Greek island of Thera to pieces one and a half millennia before the birth of Christ (thereby engineering the demise of the Minoan civilization and launching the enduring legend of Atlantis) would be little more than a firecracker alongside such an Earth-shattering event.

Fortunately for us, super-eruptions are far from common, and it is estimated that throughout the last two million years of Earth history, there have been perhaps two such blasts every hundred millennia. The last such cataclysm shattered the crust at Taupo in New Zealand’s North Island, 26,500 years ago. This, however, does not mean we can sit back and relax for another 24 millennia or so.

Like buses, natural phenomena display scant regard for a timetable, so another super-eruption could be with us in 10 years – or even 100,000 years down the line. The really scary thing, however, is that, unlike ‘normal’ volcanic blasts, there is no possibility of avoiding the devastating consequences of a volcanic super-eruption.

Those of us tucked away in the most geologically friendly countries will still find our cozy world turned upside down by the next super-eruption, even if it occurs in a distant land on the other side of the planet. This is because of the severe impact it will have on the climate, the ash and gas ejected high into the atmosphere dramatically reducing the solar radiation reaching the surface and triggering a freezing volcanic winter worldwide.

Before examining the truly terrifying consequences of the next volcanic winter, let me take a more detailed look at the scale of volcanic super-eruptions, compared with the common-or-garden variety of volcanic blast. A number of scales have been devised in recent years to allow the sizes of volcanic events to be compared. One of the earliest and most commonly quoted is the Volcanic Explosivity Index or VEI devised by volcanologists Chris Newhall and Steve Self in 1982, primarily to allow estimation and comparison of the magnitudes and intensities of historical eruptions. Eruption magnitude refers to the mass of material erupted, while eruption intensity is a measure of the rate at which material is expelled. The index is logarithmic (like the better-known Richter Scale for earthquakes) which means that each point on the scale represents an eruption ten times larger than the one immediately below. Thus a VEI 5 is ten times larger than a 4, a VEI 6 a hundred times larger, and a VEI 7 a thousand times larger. At the bottom of the index, the gentle effusions of lava that characterize most eruptions of Kilauea and Mauna Loa on Hawaii score a measly 0, while mildly explosive eruptions that release sufficient ash to perhaps cover London or New York in a light dusting would register at 1 or 2. To a volcanologist, however, things don’t really start to get exciting until higher values are reached. VEI 3 and 4 eruptions are described, respectively, as ‘moderate’ and ‘large’. This translates into blasts big enough to cause local devastation, sending columns of ash up to 20 kilometers into the atmosphere and burying the surrounding landscape under piles of volcanic debris a meter or more deep. In 1994, the town of Rabaul in New Britain (Papua New Guinea) was destroyed by an eruption of this size, and a few years later – in 1997 – Plymouth, the capital of the Caribbean island of Montserrat, suffered the same fate.

Eruptions that score a 5 on the scale, such as the much-televised 1980 blast of Mount St Helens (Washington State, USA) typically cause mayhem on a regional scale, while VEI 6 eruptions can be regionally devastating and the effects long-lasting. The 1991 Pinatubo eruption in the Philippines was probably the largest eruption of the twentieth century, ejecting sufficient ash and debris to bury central London to the depth of a kilometer and making hundreds of thousands homeless. For years afterwards, ash-fed mudflows continued to pour down the flanks of the once-again dormant volcano, clogging rivers, burying farmland, and flooding towns and cities. For the last VEI 7 eruption we have to go back almost two centuries to 1815 – the year of the battle of Waterloo. As the armies of Wellington and Napoleon jockeyed for position across Europe, on the distant Indonesian island of Sumbawa, the long-dormant volcano Tambora ripped itself apart in a gargantuan eruption that may have been the largest since the end of the Ice Age 10,000 years ago. Sir Stamford Raffles, the then British Lieutenant Governor of Java, reported a series of titanic detonations loud enough to be heard in Sumatra 1,600 kilometers away. When the eruption ended, after 34 days, it left 12,000 dead.

In the ensuing months, however, a further 80,000 Indonesians succumbed to famine and disease as they struggled to find food and uncontaminated water across the ash-ravaged landscape. Utterly devastating though the Tambora event no doubt was to the people of Indonesia, its direct effects were nonetheless confined to one part of South East Asia. Indirectly, however, much of the world was to suffer the consequences of this huge blast. Along with some 50 cubic kilometers of ash, the climactic explosions of the Tambora eruption also lofted around 200 million tones of sulphur-rich gases into the stratosphere, within which high-altitude winds swiftly spread them across the planet. The gases combined readily with water in the atmosphere to form 150 million tones of sulphuric acid aerosols – tiny particles of liquid that are very effective at blocking out solar radiation. Within months the northern hemisphere climate began to deteriorate and temperatures fell to such a degree that 1816 became known as the ‘Year Without a Summer’. Global temperatures are estimated to have fallen by around 0.7 degrees Celsius – perhaps a seventh of the drop required to plunge the planet into full ice age – causing summer frosts, snows, and torrential rains. The miserable weather conditions may have set just the right mood for Mary Shelley’s vivid imagination to spawn its most famous offspring, Frankenstein, while the spectacular ash and gas-laden sunsets are said to have inspired some of J. M. W. Turner’s most brilliant works. Certainly the weather conditions in Europe and North America during 1816 were awful, but could a volcanic eruption in a far-off part of the world really change the climate so much as to cause a breakdown in society and end the world as we know it? Evidence from the past suggests that there is no doubt that it can. Far back in the geological record – during the Ordovician period some 450 million years ago – an enormous volcanic explosion in what is now North America ejected sufficient ash and pyroclastic flows to obliterate everything across an area of at least a million square kilometers. This is broadly the size of Egypt or four times the area of the UK. In addition the amount of gas and debris pumped into the atmosphere must have been phenomenal. A little nearer our time, just 2 million years ago, a mighty eruption at Yellowstone in Wyoming was violent enough to leave behind a gigantic crater (or caldera) up to 80 kilometers across, and pump out ash that fell across 16 states. Another huge eruption occurred at Yellowstone around 1.2 million years ago and yet another just 640,000 years ago. If this last cataclysm occurred today it would leave the United States and its economy in tatters and the global climate in dire straits.

The eruption scoured the surrounding countryside with the hurricane-force blasts of molten magma and incandescent gases known as pyroclastic flows, whose gross volumes were sufficient – if spread across the nation – to cover the entire USA to a depth of 8 centimeters. Ash fell as far afield as sites that are now occupied by the cities of El Paso (Texas) and Los Angeles (California), and Yellowstone ash from this eruption is even picked up in deep-sea geological drill cores from the Caribbean seabed. Although no eruptions have been recorded at Yellowstone for 70,000 years, the hot springs, spectacular geysers, and bubbling mud pools provide testimony that hot magma still resides not far beneath the surface.

This is further supported by the numerous earthquakes that regularly shake the region and the periodic swelling and subsiding of the land surface. No one knows when – or even if – Yellowstone will experience another devastating super-eruption. The return periods between the three greatest Yellowstone blasts range from 660,000 to 800,000 years, so we could reasonably expect another sometime soon or have to wait well over a hundred millennia. It is also perfectly possible that Yellowstone may not ever produce another super-eruption, and that the giant volcanic system will gradually fade away into final extinction.

It would be easy to sit back and say – that’s all very well, but these horrific events took place deep within the mists of time. Surely they can’t happen today? Thinking along these lines would be a very big mistake. In 181 ad a massive eruption at New Zealand’s Lake Taupo ejected pyroclastic flows that devastated a substantial portion of the North Island, while the world’s last super-eruption did even worse damage to the island not much more than 24,000 years earlier. 74,000 years ago – considerably older but still well within the time span of modern humanity – perhaps the greatest volcanic explosion ever tore a hole 100 kilometers across at Toba in northern Sumatra. This huge caldera, which is now lake filled, is very much a tourist attraction, but there is evidence of a much more sinister legacy. The eruption of Toba may have come within a hair’s breadth of making the human race extinct. Estimates of the size of the blast vary, but there is no question that – along with the Yellowstone eruptions – Toba qualifies as a VEI 8 super-eruption. It was thought that the total amount of debris ejected during the eruption was on the order of 3,000 cubic kilometers, sufficient to cover virtually the whole of India with a layer of ash one meter thick. Recent evidence from deep-sea geological cores suggests, however, that the eruption might have lasted longer than previously thought and ejected considerably more debris, perhaps up to 6,000 cubic kilometers. Almost unbelievably, this would be enough to bury the entire United States to a depth of two-thirds of a meter.

Any of our ancestors living on Sumatra at the time would without question have been obliterated. For the human race as a whole to suffer the threat of extinction, though, the effects of the eruption would have to have been severe across the whole planet, and this seems to have been the case. Along with the huge quantities of ash, the Toba blast may have poured out enough sulphur gases to create up to 5,000 million tones of sulphuric acid aerosols in the stratosphere. This would have been sufficient to cut the amount of sunlight reaching the surface by 90 per cent, leading to global darkness and bitter cold. Temperatures in tropical regions may have rapidly fallen by up to 15 degrees Celsius, wiping out the sensitive tropical vegetation, while over the planet as a whole the temperature drop is likely to have been around 5 or 6 degrees Celsius, broadly the equivalent of plunging the planet into full ice age conditions within just a few months. Temperature records from Greenland ice cores suggest that the eruption was followed by at least six years of such volcanic winter conditions, which were in turn followed by a thousand-year cold ‘snap’. Soon afterwards the planet entered the last Ice Age, and there is some speculation that in this respect, the cooling effect of the Toba eruption may have been the final straw, tipping an already cooling Earth from an interglacial into a glacial phase from which it only fully emerged around 10,000 years ago.

What then of our unfortunate ancestors: could this period of volcanic darkness and cold really have brought them to their knees? It certainly seems possible. Studies of human DNA contained in the sub-cellular structures known as mitochondria reveal that we are all much too similar – genetically speaking – to have evolved continuously and without impediment for hundreds of thousands of years. The only way to explain this extraordinary similarity is to invoke the occurrence of periodic population bottlenecks during which time the number of human beings was, for one reason or another, slashed and the gene pool dramatically reduced in size. At the end of the bottleneck, all individuals in the rapidly expanding population carry the inherited characteristics of this limited gene pool, eventually across the entire planet. Mike Rampino, a geologist at New York University, and anthropologist Stanley Ambrose of the University of Illinois have proposed that the last human population bottleneck may have been a consequence of the Toba super eruption. They argue that conditions after the Toba blast would have been comparable to the aftermath of an all-out nuclear war, although without the radiation. As the soot from burning cities and vegetation would result in a nuclear winter following atomic Armageddon, so the billions of tones of sulphuric acid in the stratosphere following Toba would mean perpetual darkness and cold for years. Photosynthesis would slow to almost nothing, destroying the food sources of both humans and the animals they fed upon. As the volcanic winter drew on, our ancestors simply starved to death leaving fewer and fewer of their number, perhaps in areas sheltered for geographical or climatological reasons from the worst of the catastrophe. It has been suggested that for 20 millennia or so there may have been only a few thousand individuals on the entire planet. This is just about as close to extinction as a species is likely to get and still bounce back, and – if true – must have placed our ancestors in as vulnerable a position as today’s White Rhinos or Giant Pandas. Against all odds it seems that the dregs of our race managed to struggle through both the aftermath of Toba and the succeeding Ice Age, bringing our numbers up to the current 6.5 billion.

Could a future super-eruption wipe out the human race? It is highly unlikely that any eruption would be of sufficient size to completely obliterate today’s teeming billions, but it is perfectly possible that our global technological society would not survive intact. Before the fall of the Berlin Wall, many national governments were quite prepared to plan for the terrible possibility of all-out nuclear war. With the threat now largely dissipated, however, there has been little enthusiasm for maintaining civil defense plans to address the threat of a global geophysical catastrophe. In the absence of such forward thinking, the impact of a future super-eruption is likely to be appalling. With even developed countries such as the United States, the UK, Germany, and Australia having sufficient stores to feed their populations for a month or two at most, how would they cope with perhaps another six years without the possibility of replenishment? In the world’s poorer countries, where famine and starvation are never far away, the situation would be magnified a thousand times, and death would come swiftly and terribly. From London to Lagos the law of the jungle would quite likely prevail as individuals and families fought for sustenance and survival. When the skies finally cleared and the Sun’s initially feeble rays brought the first breath of warmth to the frozen Earth, maybe a quarter of the current population would have died through famine, disease, and civil strife.

It is extremely unlikely, but not impossible, that another super eruption might strike within the next hundred years. But where? Restless calderas, which are constantly swelling and shaking, are clear candidates, and both Yellowstone and Toba belong in this category. Large volumes of magma still reside beneath these sleeping giants that may well be released in future cataclysms. It is likely, however, that the warning signs of these giants’ awakening – large earthquakes and severe swelling of the surface – will continue for decades or even centuries before they finally let loose. As neither volcano is displaying such ominous behavior at the moment we need not lose too much sleep over the imminence of a super eruption at either Toba or Yellowstone. Only a tiny percentage of the Earth’s 1,500 or so active volcanoes are currently, however, being monitored. Furthermore, the next super-eruption may blast itself to the surface at a point where no volcano currently exists. Perhaps even as I write this some gigantic mass of magma that has been accumulating deep under the remote southern Andes may be priming itself to tear the crust apart – and our familiar world with it.

The super-eruptions I have talked about so far have all been cataclysmically explosive affairs. There is, however, another much less common species. One that – every few tens of millions of years – erupts even greater volumes of magma, but with relatively little violence. Flood basalt eruptions involve the effusion of gigantic volumes of low-viscosity lava that spread out over huge areas. These spectacular outpourings have been identified all over the world, including India, southern Africa, the northwest United States, and northwest Scotland, but the greatest breached the surface nearly 250 million years ago in northern Siberia. Estimates vary, but it looks as if the lavas erupted by this unprecedented event covered over 25 million square kilometers – an area three times that of the United States.

Several similar outpourings have occurred throughout the Earth’s long history and have been correlated with mass extinctions. Before the Siberian outburst, for example, the Earth of the Permian period teemed with life. During the succeeding Triassic period, however, when the great flows had cooled and solidified, fully 95 per cent of all species had vanished from the face of the planet. A similar mass extinction 65 million years ago, at the end of the Cretaceous period, has been linked to the huge Deccan Trap flood basalt eruption in northwestern India. However, there is incontrovertible evidence that the Earth was struck at this time by a comet or asteroid, and  many scientists believe that this was the primary cause of the extinction of the dinosaurs and numerous other species at the end of the Cretaceous. Nevertheless, the Deccan lavas may also have had a role to play, pumping out gigantic quantities of carbon dioxide that may have led to severe greenhouse warming and the demise of organisms that were unable to adapt quickly enough. As our polluting society continues to do the same, perhaps we should take this as a salutary warning of what the future might hold for us, our world, and life upon it.

A watery grave

Although by no means the largest volcanic event of the twentieth century, the spectacular 1980 eruption of Mount St Helens, in Washington State (USA), was certainly the most filmed. Perhaps because it occurred in the world’s most media-attuned country, the explosions as the volcano blew itself apart were almost drowned out by the whir of cameras and the scribbling of journalists’ pencils. From a scientific point of view, however, the eruption was a watershed, because it drew attention to a style of eruption that had previously attracted little interest from volcanologists. Most eruptions involve the vertical ejection of volcanic debris from a central  vent, but the climactic eruption of Mount St Helens was quite different. Lava and debris from the previous eruption – all of 120 years earlier – had blocked the central conduit ensuring that the fresh magma rising into the volcano could not easily escape.

Instead it forced its way into the volcano’s north flank, causing it to swell like a giant carbuncle. By mid-May the carbuncle was 2 kilometers across and 100 meters high, and very unstable. Just after 8.30 in the morning on 18 May, a moderate earthquake beneath the volcano caused it to shrug off the bulge, which within seconds broke up and crashed down the flank of Mount St Helens as a gigantic landslide. With this huge weight removed from the underlying magma, the  gases contained therein decompressed explosively, blasting northwards with sufficient force to flatten fully grown fir trees up to 20 kilometers away and obliterating, in all, over 600 square kilometers of forest. The landslide material rapidly mixed with river and lake water forming raging mudflows that poured down the river valleys draining the volcano, while pyroclastic flows tore down the flanks and ash fell as far afield as Montana 1,000 kilometers away.

The Mount St Helens blast killed 57 people and was a disaster for the region, but its scientific importance lies squarely in its elucidation of the mechanism known as volcano lateral collapse. Most of us view volcanoes as static sentinels: bastions of strength and rigidity that are unmoving and unmovable. In fact, they are dynamic structures that are constantly shifting and changing. Far from being strong they are often rotten to the core; little more than unstable piles of ash and lava rubble looking for an excuse to fall apart. The numerous studies that followed the Mount St  Helens eruption revealed that collapse of the flanks and the formation of giant landslides is a normal part of the lifecycle of many volcanoes, and probably occurs somewhere on the planet around half a dozen times a century. Furthermore, they showed that the Mount St Helens landslide was tiny compared to the greatest known volcano collapses – with a volume of less than a cubic kilometer compared with over 1,000 cubic kilometers for the prodigious chunks of rock that had, in prehistoric times, sloughed off the Hawaiian Island volcanoes.

At this stage you might be asking yourself, so what? Surely a hunk of rock – however large – falling off a volcano can’t have a global impact – cans it? Well it probably can, provided that the collapse occurs into the ocean. In 1792, a relatively small landslide flowed down the side of Japan’s Unzen volcano and into the sea. The water displaced formed tsunamis tens of metres high that scoured the surrounding coastline, killing over 14,000 inhabitants in the small fishing villages that lined the shore. Just over a century later, in 1888, part of the Ritter Island volcano off the island of New Britain (Papua New Guinea) fell into the sea, generating tsunamis up to 15 meters high that crashed into settlements on neighboring coastlines taking over 3,000 lives. Clearly, the combination of a volcanic landslide and a large mass of water is a lethal one, but – you are no doubt thinking – how can it affect the vast majority of the Earth’s population who live far from an active volcano? The answer lies partly in the size of the largest collapses and partly in the scale of the tsunamis they generate.

Underwater images of the seabed surrounding the Hawaiian Islands show that they are surrounded by huge aprons of debris shed from their volcanoes over tens of millions of years. Within this great jumbled mass of volcanic cast-offs, nearly 70 individual giant landslides have been identified, some with volumes in excess of 1,000 cubic kilometers. The last massive collapse in the Hawaiian Islands occurred around 120,000 years ago from the flanks of the Mauna Loa volcano on the Big Island. Giant tsunamis resulting from the entry of this huge mass of rock into the Pacific Ocean surged 400 meters up the flanks of the neighboring Kohala volcano – higher than New York’s Empire State Building. Deposits of a similar age, which may be tsunami-related, have also been recognized 15 meters above sea level and 7,000 kilometers away on the southern coast of New South Wales in Australia. While the nature and provenance of both deposits is still debated, the scale of the waves generated appears to be realistic, with computer models developed to simulate the emplacement of giant volcanic landslides into the ocean coming up with similar sized tsunamis.

It seems, then, as if major collapses at ocean island volcanoes are perfectly capable of producing waves that are locally hundreds of meters high and remain tens of meters high even when they hit land half an ocean away. The next collapse in the Hawaiian Islands is likely, therefore, to generate a series of giant tsunamis that will devastate the entire Pacific Rim, including many of the world’s great cities in the United States, Canada, Japan, and China. In deep water, tsunamis travel with velocities comparable to a Jumbo Jet, so barely 12 hours will elapse before the towering wave’s crash with the force of countless atomic bombs onto the coastlines of North America and eastern Asia.

Nor is the problem confined solely to the Pacific. Scientific cruises around the Canary Islands, together with detailed geological surveys on land, have revealed a picture very similar to that painted for Hawaii. Huge masses of jumbled rock stretching for hundreds of kilometers across the seabed, and gigantic cliff-bounded collapse scars on land, testify to enormous prehistoric collapses from the islands of Tenerife and El Hierro. Of more immediate concern, it looks as if a new giant landslide has recently become activated on the westernmost Canary Island of La Palma, and is primed and ready to go. During the eruption before last, in 1949, much of the western flank of the island’s steep and rapidly growing volcano – the Cumbre Vieja – dropped 4 meters towards the North Atlantic and then stopped. Some UK and US scientists believe that this gigantic chunk of volcanic rock – with an estimated volume of a few hundred cubic kilometers, just about double the size of the UK’s Isle of Man – is now detached from the main body of the volcano and will eventually crash en masse into the sea. The problem at the moment is that we don’t have a clue when this will happen. It will probably be soon – geologically speaking – but whether it will be next year or in 10,000 years we simply don’t know. Measurements undertaken during the late 1990s using the satellite Global Positioning System  proved somewhat inconclusive but suggested that the landslide might still be creeping slowly seawards, perhaps at only a centimeter a year or even less. Even if this is the case, however, the rock mass is unlikely to complete its journey into the North Atlantic without the trigger of a new eruption.

What is certain is that at some point in the future the west flank of the Cumbre Vieja on La Palma will collapse, and the resulting tsunamis will ravage the entire Atlantic rim. Steven Ward of the University of California at Santa Cruz and Simon Day of University College London’s Benfield Hazard Research Centre created quite a stir in 2001 when they published a scientific paper that modeled the future collapse of the Cumbre Vieja and the passage of the resulting tsunamis across the Atlantic. Within two minutes of the landslide entering the sea, Ward and Day show that – for a worst case scenario involving the collapse of 500 cubic kilometers of rock – an initial dome of water an almost unbelievable 900 meters high will be generated, although its height will rapidly diminish.

Over the next 45 minutes a series of gigantic waves up to 100 meters high will pound the shores of the Canary Islands, obliterating the densely inhabited coastal strips, before crashing onto the African mainland. As the waves head further north they will start to break down, but Spain and the UK will still be battered by tsunamis up to 7 meters high. Meanwhile, to the west of La Palma, a great train of prodigious waves will streak towards the Americas. Barely six hours after the landslide, waves tens of meters high will inundate the north coast of Brazil, and a few hours later pour across the low-lying islands of the Caribbean and impact all down the east coast of the United States. Focusing effects in bays, estuaries, and harbors’ may increase wave heights to 50 meters or more as Boston, New York, Baltimore, Washington, and Miami bear the full brunt of Vulcan and Neptune’s combined assault. The destructive power of these skyscraper-high waves cannot be underestimated. Unlike the wind driven waves that crash every day onto beaches around the world, and which have wavelengths (wave crest to wave crest) of a few tens of meters, tsunamis have wavelengths that are typically hundreds of kilometers long. This means that once a tsunami hits the coast as a towering, solid wall of water, it just keeps coming – perhaps for ten or fifteen minutes or more – before taking the same length of time to withdraw. Under such a terrible onslaught all life and all but the most sturdily built structures are obliterated.

The lessons of the Indian Ocean tsunami have taught us that without considerable forward planning it is unlikely that the nine hours it will take for the wave’s advance guard to reach the North American coastline will be sufficient to facilitate effective, large-scale evacuation, and the death toll is certain to run into many millions. Furthermore, the impact on the US economy will be close to terminal, with the insurance industry wiped out at a stroke and global economic meltdown following swiftly on its heels. In this way, a relatively minor geophysical event at a remote Atlantic volcano will affect everyone on the planet. Like volcanic super eruptions, these giant tsunamis constitute perfectly normal, albeit infrequent, natural phenomena. At some point in the future one will certainly wreak havoc in the Atlantic or Pacific Basins, but when? The frequency of collapses on the Hawaiian volcanoes has variously been estimated to be between 25,000 and 100,000 years, but if giant landslides at all volcanic islands are considered, it may be that a major collapse event occurs every ten millennia or so. On a geological timescale this is very frequent indeed and should provide us with serious cause for concern. Even more worryingly, the rate of collapse may not be constant and the current episode of global warming engendered by human activities may in fact bring forward the timing of the next collapse. My own research team has linked increased incidences of past volcano collapse with periods of changing sea level, while others have suggested that a warmer and wetter climate might result in greater numbers of large volcanic landslides. Given that sea levels are forecast to continue to rise for the foreseeable future, while studies of past climate change show that a warmer planet results in heavier rainfall on many of the world’s largest volcanic island chains, perhaps we should all be thinking of moving inland and uphill, or at least of investing in a good-quality wet suit.

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(7) Global Catastrophes

Will a volcanic eruption destroy humanity? Scientists warn that world must begin preparing for explosive global catastrophe



Charles Dickens, white Christmases, and the Little Ice Age

It seems likely that almost everyone who has read this far is familiar with the Ice Age, but what about the Little Ice Age? This is the term used by climatologists to describe a cold period that lasted from at least 1450 - and possibly 1200 - until between 1850 and the start of the twentieth century. Over this period, glaciers advanced rapidly, engulfing alpine villages, and sea ice in the North Atlantic severely disrupted the fishing industries of Iceland and Scandinavia. Eskimos are alleged to have paddled as far south as Scotland, while the once thriving Viking community in Greenland was cut off and never heard from again.

Annual mean temperatures in England during the late seventeenth century were almost one degree Celsius lower than for the period 1920-1960, leading to bitter, icy winters in which ‘frost fair’ carnivals were held regularly on a frozen River Thames and snowfall was common. The snowy winters described in many of the works of Charles Dickens may well be a reflection of this colder climatic phase, and they have certainly done much to nurture our constant expectation of - and wish for - an old-fashioned ‘white Christmas’.

Just what was the cause of the Little Ice Age remains a matter of intense debate. Clearly, however, as most of the cold snap occurred prior to the industrial revolution there can be no question of human activities having played a role. Despite this, it is vital that we understand the Little Ice Age in the context of global warming, if for no other reason than if we don’t appreciate the natural variations of our planet’s recent climate it is well nigh impossible to unravel the effects arising from human activities. In fact, the Little Ice Age was not the only significant departure from the climatic norm – if there is such a thing – in historical times. Immediately prior to this cold snap, Europe, at least, was reveling in the so-called Medieval Warm Period. This time of climate amelioration, between about 1000 and 1300 ad, saw grapes grown in north of England - as they are again in today’s warming climate – while the Norse settlers of Greenland were able to graze their livestock in areas that until recently were buried beneath ice.

The emergence of the world from the Little Ice

Age towards the end of the nineteenth century, coincident with the acceleration of industrialization on a global scale, has contributed in no small way to current arguments on the causes of contemporary warming. As I noted in the last chapter, the overwhelming scientific consensus views global warming as being anthropogenic in nature, but some still hold out for an entirely natural cause; seeing the current warming in terms of the planet coming out of the Little Ice Age and entering another warm period analogous to the Medieval Warm Period. Although the available evidence irresistibly supports a human cause rather than a purely natural warming, there can be no doubt that the impact of human activities is superimposed upon a natural variability that in the recent past has resulted in significant climate change. But what is the cause? One of the most likely culprits is the Sun, whose output continues to vary on time scales ranging from 100 to 10,000 years. For example, the two coldest phases within the Little Ice Age corresponded closely with two periods of apparently reduced solar activity; the Spörer Minimum between 1400 and 1510 ad and the Maunder Minimum from 1645 to 1715. During these times, virtually no sunspots were visible and auroras were almost non-existent, suggesting a fall in the rate of bombardment of the Earth by solar radiation. While solar physicists estimate that the Sun during the Maunder Minimum may have been just a quarter of one per cent dimmer than it is today, this might have been sufficient to cause the observed cooling. Other factors may also have made a contribution, however, and a recent theory has given elevated levels of explosive volcanic activity at the time – including the great 1815 eruption of Indonesia’s Tambora volcano - at least a supporting role in the Little Ice Age cooling. Large volcanic explosions are particularly effective at injecting substantial volumes of sulphur dioxide and other sulphur gases into the stratosphere – that part of the atmosphere above 10 kilometers or so. Here they mix with atmospheric water vapor to form a fine mist of sulphuric acid that cuts out a proportion of incoming solar radiation and leads to a cooling of the troposphere (the lower atmosphere) and surface.

A very British ice age

The more we learn about past climate change, the more it becomes apparent that dramatic variations can occur with extraordinary rapidity. The return - possibly within a few decades - from increasingly clement conditions to the bitter cold of the Younger Dryas, 12,800 years ago, demonstrates this, as does the similarly rapid transition from the Medieval Warm Period to the Little Ice Age. Equally disturbing is the tendency for the climate to flip suddenly from one extreme to another when it is under particular stress, as it is at the moment from anthropogenic warming. Is there any way that current global warming can actually bring a return to colder conditions? While this would seem to be counter-intuitive, there is increasing evidence that this may well happen - at least as far as the UK and northwest Europe, and perhaps the entire North Atlantic region, are concerned. The only reason why it is possible for tropical palms to thrive in western Ireland and southwest England is because the Gulf Stream carries northwards warm water from the Caribbean. As a result, the UK and Ireland are substantially warmer than comparable latitudes in eastern Canada, which have to put up with sub-Arctic conditions.

But what would happen if the supply of warm water from the south were shut down? It is highly likely that the British climate – and perhaps that of much of northwest Europe - would become bitterly cold, and some have suggested it could even rival that of Svalbard (formerly Spitsbergen), the ice-shrouded islands off east Greenland where the polar bear is king. In a recent study, the UK Met Office simulated just what might happen if the Gulf Stream were to shut down. In the following decade, the entire northern hemisphere would cool, with the effect strongest around the North Atlantic. In the UK, bitter winters arrive within a few years of shutdown, with temperatures plunging to -10 degrees Celsius and below. One of the ways of weakening or shutting down the Gulf Stream is by short-circuiting it through releasing huge quantities of cold fresh water into the North Atlantic, and this is just what is predicted by a number of different climate models developed to look at the impact of global warming in this century and beyond. The most recent forecasts suggest that a 2-3 degrees Celsius temperature rise, which is almost certain by 2100 if not well before, will result in a 45 per cent probability of a dramatic slowdown or shutdown of the Gulf Stream. In little more than half a century, then, the seas around the UK could be significantly cooler, altering prevailing weather patterns and bringing colder conditions to the region. While the rest of the world roasts, the North Atlantic region could conceivably start to slide into a freeze very much bitterer than the Little Ice Age. And this might be just the start. The knock-on effects of changes to the ocean circulation in the North Atlantic may spread, overwhelming the current warming and bringing a return of the ice across the northern hemisphere. In conclusion, then, let’s take a look at prospects for the return of the Ice Age and the role mankind may already be playing in its reappearance.

Out of the frying pan into the fridge

In terms of the Milankovitch Cycles, our planet is already primed for the end of the current interglacial period and a return to full Ice Age conditions. Some believe that all that is needed is a trigger; a sudden shock to the system that will knock the climate out of equilibrium and set it wobbling before it collapses into an altogether less friendly state. It is questionable whether global warming can provide a shock of the appropriate magnitude, but new research is leading to increasing concern that the legacy of warming today may be freezing tomorrow. Once again, the key seems to lie in the ocean circulation system of the North Atlantic, which appears to be closely bound up with past switches from warm to cold episodes and vice versa. The Gulf Stream that most people are familiar with is actually only one part of a system of currents known by a variety of names, of which the Atlantic Overturning Circulation is probably the most revealing. As the warm, salty waters of the Gulf Stream head northwards they cool and consequently become denser. As a result, by the time they have reached the Arctic Ocean they have sunk to form a cold, deep-ocean current that heads south once more to join the wider system of ocean currents known as the Global Conveyor.

It now looks as if the operation of the Atlantic Overturning Circulation is seriously disrupted whenever cold conditions grip the northern hemisphere. During the Younger Dryas, for example, the circulation appears to have been severely reduced, lowering north European temperatures by as much as 10 degrees Celsius. Recent evidence on ocean temperatures and salinities, gleaned from studies of the shells of tiny marine organisms known as foraminifera, also points to a much weaker Gulf Stream at the height of the last Ice Age some 20,000 years ago. Then, it seems, the Gulf Stream had only two-thirds of its current strength, suggesting that the entire circulation system was comparably weakened. The question is, did this weakening have a role to play in the triggering of the last Ice Age, or was it merely a consequence? No one really knows, but there is a general feeling that a weakening of the circulation results in much colder conditions in the northern hemisphere and that such a weakening appears to be associated with large influxes of cold water into the North Atlantic. Due to melting of Arctic sea ice and the Greenland Ice Cap, this is just what is predicted to happen in the next few centuries.

During the Younger Dryas, 12,800 years ago, the release of huge quantities of water from glacial lakes resulted only in a short-lived cold snap of a thousand years or so. Then, however, the Earth was at a point in the pattern of Milankovitch Cycles when temperatures were on the way up. Now, we are poised at the transition between the present interglacial and the next Ice Age, and without the polluting effects of human activities temperatures could be expected to be on the way down. It is not unreasonable to at least consider, then, that the influx of cold, fresh water into the Arctic Ocean may trigger not just a brief period of cold in northwest Europe, but a new Ice Age affecting the entire northern hemisphere. And we may not have too long to wait. In the 1990s, US climate modelers Ronald Stouffer and Alex Hall ran a comprehensive computer model of the Earth’s climate system for almost a decade to find out what it had in store for us in the next few millennia. What they discovered was seriously disturbing. The model predicts that, in around 3,000 years’ time, intense westerly winds over Greenland will help to push large quantities of fresh Arctic water into the North Atlantic. Because of its low density, this bitterly cold water will remain at the surface, cooling the air above, and creating a low-pressure weather system that will reinforce the westward gales through a positive feedback mechanism. The effect is forecast to cool the North Atlantic by up to 3 degrees Celsius and also to weaken the Atlantic Overturning Circulation, bringing colder conditions to northwest Europe. In the model, the chilly scenario only persists for 40 years or so, but the authors are concerned that if global warming promotes the melting of Greenland ice on a grand scale, this added input of cold water might amplify a brief regional cooling into a widespread and persistent freeze. Even more worryingly, the first signs of the coming chill may already have been detected, with recent measurements revealing that an important current running south between Scotland and the Faeroe Islands has slowed by around 20 per cent in the past 50 years. Could this be the first evidence of the breakdown of the Atlantic Overturning Circulation and the slow but steady deterioration of the climate into bitter cold?

One of the best means of illustrating just what a bad time this is for us to be experimenting with the global climate is by comparing the temperature profile of this interglacial period with that of the last. It is rather sobering to see that the natural temperature trend is already downwards, and in fact this fall has been going on for several thousand years. At the moment, it looks as if the downward trend is being reversed by anthropogenic warming, and without greenhouse gas emissions the world would be around 3 degrees colder in around 8,000 years’ time - well on its way to the next Ice Age. Although fending off the chill at the moment, however, the impact of global warming on the Atlantic Overturning Circulation might well ultimately accelerate the arrival of the next Ice Age. By now I hope to have convinced you that it is at least feasible for the current global warming to trigger colder conditions, and that this may be the result of the continued and unmitigated emission of greenhouse gases. So what happens if the world comes to its senses and we cut back significantly on the amount of carbon dioxide and other gases that we pump into the atmosphere? Well, you have seen the graphs – the ice will get us anyway. It is simply just a matter of whether we want to take the icy plunge on its own or spend some time baking in the sauna first. Whichever choice we make, there is no denying that life for our descendants will become increasingly hard, should the ice return. Life in Europe, North America, Russia, and central and eastern Asia will be pretty much impossible, engendering mass migrations southwards accompanied undoubtedly by bloody wars fought over living space and resources. The climate of Ice Age Earth is simply not suited to sustaining a population totaling 8–10 billion, or thereabouts, and widespread famine alongside civil strife is certain to lead to a severe culling of the human population. There is no question that our race will survive, as it did the last time that the ice left its polar fastnesses, but it is likely to be but a pale shadow of its former self.

Facts to fret over

• Between 800 and 600 million years ago, the Earth was a frozen snowball covered with ice a kilometer or more thick.

• Just 600 human generations have passed since the end of the last Ice Age.

• At the height of the last Ice Age, temperatures in the UK were 15-20 degrees Celsius lower than they are now, and over much of North America, more than 25 degrees Celsius lower.

• Sea levels have risen by over 120 meters since the ice started to retreat around 18,000 years ago.

• A temperature rise of just 2-3 degrees Celsius – which is virtually certain before 2100 - could result in a 45 per cent probability of a dramatic slowdown or shutdown of the Gulf Stream.

• An Atlantic current flowing between Scotland and the Faeroe Islands has weakened by 20 per cent in the last 50 years.

• Without greenhouse gas emissions, the world could be 3 degrees Celsius colder in 8,000 years.

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(6) Global Catastrophes

Will a volcanic eruption destroy humanity? Scientists warn that world must begin preparing for explosive global catastrophe

Global catastrophe losses down in 2014


The good, the bad, and the downright mad

The good, the bad, and the downright mad No one on the planet is going to escape the effects of global warming, and for billions the resulting environmental deterioration is going to make life considerably more difficult. It is too late now to put the clock back, but we can at least attempt to alleviate the worst impacts of warming. The question is, will we ever be able to achieve a worthwhile international consensus that allows us to do this with any degree of effectiveness? The Kyoto Protocol gave us some hope in 1997, with its goal of a 5.2 per cent reduction of greenhouse gas emissions (below 1990 levels) by 2008–2012. Despite Russia’s ratification in 2005, however, the failure of the USA to become a signatory means that we have not progressed far from square one.

In fact, we are even worse off than this. Without US ratification, emissions from all the industrial countries put together could rise by about 12 per cent by 2008–2012, which is even higher than many ‘business as usual’ predictions. In terms of greenhouse gas emissions, things are getting steadily worse not better. It is difficult to see how this situation can improve until the United States – the world’s greatest polluter, emitting a quarter of all greenhouse gases – together with its almost equally profligate partner in crime –Australia – can be persuaded to join the rest of the international community in trying to tackle the problem. Personally, I suspect that, in terms of national governments, the only persuasion that will stand any chance of working will be the persistent pounding of eastern and Gulf Coast US cities by increasingly powerful hurricanes or perhaps a decade-long drought in Australia. There are, however, a couple of pieces of good news from the United States. By August 2005, 177 city mayors – including those of New York, Los Angeles, Chicago, and Miami – had signed up to the mayor of Seattle’s Climate Protection Agreement, which binds participating cities to strive to meet or beat the Kyoto Protocol targets. The same month, a group of nine northeast states – including New York, New Jersey, and Massachusetts – agreed to cap greenhouse gas emissions at current levels, with a goal of reducing them by 10 per cent by 2020. A small step, certainly, but a step in the right direction.

The more global warming continues to grab the limelight, so the more we hear from what I will call the ‘technofix tendency’. Some of their proposals for mitigating warming are wild and wacky, such as placing giant reflectors in space to divert solar radiation or, even more fantastically – and heaven forbid – diverting a comet or two past the Earth, using their gravity to swing the planet out into an orbit further from the Sun. Others are seriously thought-out scientific options that we may well have to adopt at some point in the future if the situation gets really out of hand. The latter include ways of using the oceans as a dumping ground for atmospheric carbon dioxide, either by physically discarding it in the deep ocean via pipeline and tanker, or by seeding the ocean with iron to encourage the growth of marine micro-organisms that extract carbon dioxide from the atmosphere. Pilot experiments have shown that both methods can work, but to operate on a large enough scale to make any difference they would be hugely expensive and require a concerted international effort that is difficult to foresee unless the current position becomes untenable. Furthermore, convincing public opinion that we need to mess about with the oceans in order to repair the damage we have wrought in the atmosphere would be a considerable PR coup. There is no doubt that if we are to have any impact on global warming we will all have to change our lifestyles, moving away from a disposable society and towards one that promotes and rewards the most effective and efficient use of available energy and resources. Tackling global warming is inextricably linked with the widespread adoption of sustainable development. Global warming will bring to an end the world as we have known it through dramatic changes to our environment, but if the situation is not to continue to slide it must also provide the incentive and impetus for changing the way we live. In the developed world we have no choice but to cut fuel consumption, invest in renewable energy sources, recycle on an immensely greater scale, and produce locally as much as possible rather than flying fruit and vegetables halfway around the planet. Much as I can understand their resistance, governments of developing countries must not follow the wasteful route to industrialization that Europe and North America have taken, for the simple and logical reason that if they don’t, they – and their people – will be the ones who suffer most. In particular, the developing world has to embrace renewable energy sources and recycling now, and the world’s economic powers have a duty to support them on this path. Despite the gloom over the failure of the Kyoto Protocol to be all-inclusive, there is an alternative plan to reduce greenhouse gas emissions on the table that might just start things moving on the long road to stabilization and even reduction.

Called Contraction & Convergence, or simply C&C, the new way forward was thought up by London’s Global Commons Institute. This ingenious plan is based upon two principles. First, those greenhouse gas emissions must be reduced and, second, that the means by which this is accomplished must be fair to all. C&C therefore proposes reducing emissions on a per capita basis.

International agreement will determine by how much emissions must contract each year, and then permits to emit will be allocated to all countries on the basis of their populations. The emission permits would be tradable so that countries such as the USA and Australia that could not manage within their allocations could buy extra ones from populous developing countries with a surplus. This remarkably simple scheme is daily attracting increasing interest, and now has powerful supporters in the UN, Europe, and China, and even amongst developing countries and US politicians. It is now inevitable that we and our descendants are going to face a long and hard struggle as our temperate world draws to a close and we enter the time of hothouse Earth. Perhaps, however, C&C can help to make the transition a little less desperate.

Facts to fret over

• By the end of this century the Earth is predicted to be hotter than at any time in the past 150,000 years.

• By 2100, global temperatures are forecast to rise by up to 8 degrees Celsius – or even more – over land, with sea levels up to 88 centimeters higher.

• Carbon dioxide concentrations in the atmosphere may be higher than at any time in the last 20 million years.

• In the year 2000, 1 in 30 of the world’s population was affected by natural disasters.

• By 2025, 5 billion people will live in countries with inadequate water supplies.

• Within 50 years all the world’s great reefs may have been wiped out by higher sea temperatures.

• The winter sports industry is unlikely to survive to 2100 in its current form.

• The probability of the West Antarctic Ice Sheet melting in the next two hundred years is 1 in 20. If this happens, all the world’s coastal cities will be drowned, from New York to London to Sydney.

The Ice Age Cometh

Fire or ice?

One of the main reasons for a growing disillusionment with science amongst the general public is the perception that scientists are always arguing with one another and constantly changing their minds. It is no use explaining that this is how science progresses, through battles between competing theses until the accumulation of evidence ensures that one triumphs and becomes an accepted paradigm. People want scientists to agree, to present a united front, and to tell them what is true and what is not. They want this because it makes life that much easier and gives them that much less to worry about. If you are concerned about your career or your marriage you don’t want to think about whether GM crops are good or bad, or whether you have to eat your beef on the bone or off, or whether your children’s children are going to fry or freeze. Here once again, however, the scientific consensus at least appears to have done another U-turn over the last couple of decades. The most maverick of climatologists now accept that the Earth is warming up rapidly and that our polluting activities are the cause. As recently as the 1980s, however, the big question in climatologically circles was when can we expect the next Ice Age? So what has changed? Well, actually, not much. The glaciers are still due to advance once again and we should expect our planet to be plunged into bitter cold within the next 10,000 years. What has changed, however, is the recognition that anthropogenic warming and its associated climatic impact may have a role to play at a critical time of natural transition when our interglacial world is due to give itself over to ice and snow for tens of thousands of years. Problematically, though, researchers are not quite sure what this role will be, and although, intuitively, you might expect global warming to delay or even fend off entirely the next Ice Age, some scientists have suggested that the ongoing dramatic rise in temperatures may actually accelerate the onset of the next big freeze. Even if the latter is shown not to be the case, we still have a problem. Knowing that a new age of ice is on the way should we not be trying actively to keep our planet warm? Should we not welcome global warming with open arms? In other words, we are currently faced with a stark choice that is only rarely voiced during the great global warming debate. How do we wish our familiar, contemporary world to end – by fire or by ice?

How to freeze a planet

During the Earth’s early history the surface boiled with lava oceans and exploding volcanoes, and although temperatures fell dramatically as prevailing geological processes moderated, our planet has been bathed in warmth for most of its 4.6 billion year history. Occasionally, however, a fortuitous combination of circumstances has heralded the formation of enormous ice sheets that have transformed a balmy paradise into a freezing hell. Artists’ impressions and television documentaries have ensured that most of us are familiar with the last great Ice Age, when mammoths roamed the tundra and our pelt-covered ancestors struggled to eke out an existence from a frozen world. Only recently, however, have studies of ice-related rock formations around the world brought to light a far more ancient and much more terrible period of refrigeration; a time when our planet was little more than a frozen snowball hurtling through space. Long, long ago, during a geological episode that is becoming increasingly and appropriately referred to as the Cryogenian (after cryogen for freezing mixture), the Earth found itself at a critical threshold in its history. It had cooled substantially since its formation over 3.5 billion years earlier and now the problem was keeping itself warm. At this time, between about 800 and 600 million years ago, the Sun was weaker and the Earth was bathed in some 6 per cent less solar radiation than it is now. Furthermore, the concentrations of greenhouse gases that are now heating up our planet – primarily carbon dioxide and methane – were not sufficiently high to hold back the bitter cold of space. Huge ice sheets rapidly formed and pushed towards the equator from poles, encasing all or most (this remains a bone of contention) of the Earth in a carapace of ice a kilometer thick. As the blinding white shell reflected solar radiation back into space, temperatures fell to −50 degrees Celsius and prospects for an eternity of ice seemed strong. But something must have happened to break the ice, as it were, otherwise I would not be here today to tell you about it; and in fact it seems that these ‘snowball’ conditions may have developed up to six times, succumbing each time to a return of warmer climes.

Just how the Earth managed to escape the clutches of the ice no one is quite certain, but it looks as if volcanoes might have been the saviours. After millions or even tens of millions of years of bitter cold, the enormous volumes of carbon dioxide pumped out by erupting volcanoes seem to have generated a sufficiently large greenhouse effect to warm the atmosphere and melt the ice.

Extraordinarily, life came through this particularly traumatic period of Earth history bruised and battered but raring to go, and hard on the heels of Snowball Earth’s final fling came the great explosion of biodiversity that marked the start of the Cambrian period 565 million years ago. Compared to the great freezes of the Cryogenian our most recent Quaternary ice ages come across as rather small beer. Nevertheless, although they affected smaller areas of the Earth’s surface, these latest bouts of cold were crucial because they coincided with the appearance and evolution of our distant ancestors. Furthermore, they may yet have a role to play in the future of our race. During recent Earth history the Sun’s output has been significantly higher than during the Cryogenian period and the level of carbon dioxide and other greenhouse gases has also been higher. Why then, at the end of the Miocene period about 10 million years ago, did glaciers once again begin to form and advance across much of the northern hemisphere? And more importantly, why, around 3 million years ago, did the southward march of the ice intensify? This remains a particularly hot topic in the fields of Quaternary science and environmental change and a detailed analysis of competing theories is beyond the scope of this book. Suffice it to say that explanations for the twenty or so ice ages that have gripped the Earth during the last 2 million years include disruption of the planet’s atmospheric circulation due to uplift of the great Himalayan mountain belt, and the drastic modification of the global system of ocean currents by the emergence of the Panama Isthmus.

Although one or both of these spectacular geophysical events may have contributed to a picture of increasing cold, the ice was already on the move, and we need to look elsewhere for the true underlying cause. What, in other words, turns ice ages on, and – just as importantly – what turns them off? This problem has intrigued scientists for many years and the solution was first put forward by the Scottish geologist James Croll as long ago as 1864 and expanded upon by the Serbian scientist Milutin Milankovitch in the 1930s. The Croll-Milankovitch astronomical theory of the ice ages proposes that long-term variations in the geometry of the Earth’s orbit and rotation are the fundamental causes of the blooming and dying of the Quaternary ice ages. In order for an ice age to get going, the astronomical theory requires that summers at high latitudes in the northern hemisphere are sufficiently cool to allow the preservation of winter snows. As more and more snow and ice accumulates year on year, so the reflectivity or albedo of the surface is increased, causing summer sunshine to have even less impact and accelerating the growth of ice sheets and glaciers. But how are the northern hemisphere summers cooled down in the first place? This is where the astronomy comes in. Cooler summers at high latitudes result from a reduction in the amount of solar radiation falling on the surface, and this in turn depends upon both changes in the tilt of the Earth’s axis and variations in its orbit about the Sun.

If the Earth’s axis was not tilted then we would not experience the seasons. During the northern hemisphere summer, for example, the North Pole is tilted towards the Sun, allowing more direct solar radiation to reach the surface in the northern hemisphere and raising the temperatures. In contrast, during the winter, the North Pole is tilted away from the Sun and the long, balmy days of summer are replaced by the cold and dark of a northern hemisphere winter. Now the southern hemisphere receives more direct sunlight with the result that those down under bask in warmth while the north shivers beneath gloomy skies. Although the tilt of the Earth’s axis averages about 23.5 degrees, it is not constant. Like a spinning top, the Earth wobbles – or processes – about its axis of rotation over a period of between 23,000 and 26,000 years. Furthermore, this wobble causes the amount of tilt to vary between 22 and 25 degrees over a period of 41,000 years. At times of least tilt, winters are actually milder, but more importantly, high latitudes receive less direct solar radiation and become cooler, making the survival of winter snows and the growth of ice sheets easier. On top of this there is another so-called astronomical forcing mechanism that contributes to the onset of ice age conditions. Like all planetary bodies, the Earth follows an elliptical rather than a circular path around the Sun, whose shape varies according to cycles of between 100,000 and 400,000 years. At the moment the Earth’s closest approach to the Sun occurs in January, when the North Pole is pointing away from the Sun, resulting in slightly colder northern hemisphere winters. Just 11,000 years ago, however, this closest approach – or perihelion – occurred in July, giving a small temperature boost to northern hemisphere summers.

Before this gets too complicated let me try and draw things together. Regular and predictable cycles – known as Milankovitch Cycles – are recognized in the behaviour of the Earth’s tilt and its orbit over periods of thousands to hundreds of thousands of years, and these cycles control the amount of solar radiation reaching the Earth’s surface and therefore its temperature. At times, a number of cycles may coincide so as to depress summer temperatures at high latitudes to a degree sufficient to allow the accumulation of winter snows. On its own this could not result in the huge ice sheets that have dominated the northern hemisphere for much of the last few million years, but as the area covered by snow and ice grows, so more and more sunlight is reflected back into space, accelerating the cooling process. This – in essence – is how ice ages start.

Conversely, at other times, the various cycles cancel one another out, the planet warms as a result, and the ice sheets retreat to their polar fastnesses.

Although Milankovitch and later researchers who have addressed the issue have been able to explain the mechanics of the ice ages and their periodicity, they have been less successful in deciding why these icy episodes appeared on the scene around 10 million years ago, rather than being apparent throughout Earth history. An answer to this may lie, however, in the carbon dioxide level of the Earth’s atmosphere, which has been steadily falling over the last 300 million years, from about 1,600 parts per million to just 279 ppm prior to the industrial revolution. It has been suggested that perhaps only when the level of carbon dioxide in the atmosphere drops below a critical threshold level – say of 400 ppm – is astronomical forcing sufficient to initiate the cycle of warm and cold that characterizes the ice ages. This begs the question that with carbon dioxide levels expected to rise above this level in a little over 20 years, have we seen off the ice ages forever? I shall return to this later.

In the meantime, on the basis that there is at least a fair chance that we will have to face them again at some time in the future, let’s examine what conditions were like in the depths of the last Ice Age. As temperatures started to fall around 120,000 years ago, so more and more of the planet’s water found itself locked up in mountain glaciers, polar sea ice, and expanding continental ice sheets in the northern hemisphere, with the result that sea level began to fall dramatically. Ice swept southwards towards the equator on at least four occasions over this period, with the peak of ice cover being reached a mere 15,000–20,000 years ago.

At this time sea level was a good 120 meters or so below what it is now – about the height of a 40-storey building – exposing new land bridges between continents and facilitating the migration of both animals and our distant ancestors. One of these land bridges developed across the Bering Straits, allowing people from Asia to cross into North America, from which, eventually, they colonized the New World. Just 600 generations ago, then, the north of our planet was in the steely grip of full glaciations with a third of all land covered by ice and 5 per cent of the world’s oceans frozen.

Compared to today, the environment at the height of the last Ice Age was desperately hostile, with mean temperatures 4 degrees Celsius lower than today but far lower at high latitudes in the north. In the UK, temperatures were reduced by between 15 and 20 degrees Celsius, transforming the country into a frozen wasteland with great sheets of ice reaching as far south as the River Thames and beyond. Some of the most inhospitable conditions were, however, to be found in North America, where temperatures over huge areas were 25 degrees Celsius lower than today and ice fields kilometers thick ensured that life was largely impossible.

Remarkably, however, just as it seemed as if the world might be returning to the ‘snowball’ state of the Cryogenian period, a surprising change took place. The planet started to warm rapidly, melting the great ice sheets at a rate far quicker than it took them to form. Melt water poured into gigantic lakes at the margins of the ice fields, which, in turn, emptied into the oceans, raising sea level and inundating land exposed just a few thousand years earlier. By 12,000 years ago, sea level was rising far more rapidly than even the most pessimistic forecasts for the next century, possibly by as much as 10 meters or so in a couple of centuries, and all the time the climate was becoming warmer and warmer – well, almost all the time that is. The journey from the depths of ice age to the current balmy interglacial was a rather bumpy one, and on more than one occasion the ice made a concerted attempt to reclaim centre stage.

Around 12,800 years ago, for example, the rapid retreat of the ice was stopped in its tracks as a new blast of cold initiated a thousand year-long freeze, known as the Younger Dryas to distinguish it from an earlier and less severe cold phase called the Older Dryas. No one is certain what caused this sudden cold snap but one suggestion is that the culprit was a huge discharge of fresh water from long-gone Lake Agassiz, one of the gigantic glacial melt water lakes that had accumulated in North America. The catastrophic emptying of this lake into the St Lawrence, and thence into the North Atlantic, may have disrupted currents carrying warmer waters into polar regions, allowing the climate at higher latitudes to cool and ice to form once again. The Younger Dryas and similar post-Ice Age cold snaps teach us a number of important lessons that we would do well to remember as our own world undergoes dramatic climate change. First, the switch from warm to cold and vice versa can occur extraordinarily rapidly – within decades – and second, the disruption of ocean currents can have serious and far-reaching consequences for climate change. 

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(5) Global Catastrophes


Tsunami que matou 220 mil pessoas no Oceano Índico completa 10 anos


Global Warming: A Lot of Hot Air?

Debate - what debate?

Global warming is about much more than hotter summers, winter floods, and farting cows. There is absolutely no question that the Earth is warming up fast, and few climate scientists would argue with this. The dispute lies in whether or not the warming we are now experiencing simply reflects a natural turnabout in the recent global temperature trend or results from the polluting impact of human activities since the industrial revolution really began to take hold.

What I find extraordinarily irresponsible is that this dispute continues to be presented, at least in some circles, as a battle between two similarly sized and equally convincing schools of scientific thought, when in fact this is far from the case. Forecasting climate change is extremely difficult, which explains why models for future temperature rise and sea-level change are constantly undergoing revision, but the evidence is now irrefutable: human activities are driving the current period of planetary warming.

Notwithstanding a few maverick scientists, oil company apologists, and the president of the world’s greatest polluter, the overwhelming consensus amongst those who have a grasp of the facts is that without a reduction in greenhouse gas emissions things are going to get very bad indeed.

Amazingly, this prospect is still played down and intentionally hidden behind a veil of obfuscation by some, most recently by the - in my opinion - self-deluded Danish statistician, Bjorn Lomborg. In his widely savaged book, The Skeptical Environmentalist, Lomborg denigrates global warming and its future impact, while at the same time, through highly selective references to scientific research, coming to the conclusion that all is right with the world. Just in case you have come across this work and been lulled by its friendly, do-nothing message into a false sense of security, let me bring you back to reality, if I may, with a few pertinent facts.

During the past 70 years, the Earth has been hotter than at any other time in the last millennium, and the warming has accelerated dramatically in just the past few decades. No doubt everyone has at least one older relative who is constantly harking back - through a rose-tinted haze - to a time when summers were hotter and the skies bluer.

Meteorological records show, however, that this is simply a case of selective memory, and in fact 19 of the hottest years on record have occurred since 1980, with the late 1990s seeing the warmest years of all across the planet as a whole. The Earth is now warmer than it has been for over 90 per cent of its 4.6 billion year history, and by the end of the twenty-first century our planet may see higher temperatures than at any time for the last 150,000 years.

The rising temperature trend we are seeing now is not simply a climatic blip or hiccup, nor can it be explained entirely, as some would still have it, by variations in the output of the Sun, although this clearly does have a significant effect on the climate. Rather, it is a consequence of two centuries of pollution, which is now enclosing the Earth in an insulating blanket of carbon dioxide, methane, nitrous oxide, and other greenhouse gases.

Since the late eighteenth century our race has been engaged in a gigantic planetary trial, the final outcome of which we can still only guess at. Unfortunately for us the experiment has now entered a runaway phase, which, due to its inherent inertia, we cannot immediately stop but only slow down. Even if we were to stabilize greenhouse gas emissions today, both temperatures and sea levels would continue to rise for many hundreds of years. The big question of our time is – do we have the resolve to do even this or will we run from the problem and let the devil take the hindmost? Let’s head for the laboratory and see how things are progressing.

The great global warming experiment

We know from studies of polar ice cores that before the hiss of steam and grinding of metal on metal that heralded the arrival of the industrial world, the concentrations of greenhouse gases in the atmosphere had been pretty much constant since the glaciers retreated at the end of the last Ice Age. Since pre-industrial times, however, carbon dioxide levels in the atmosphere have risen by 30 per cent, alongside sharp increases in other greenhouse gases, in particular methane and nitrous oxide.

Atmospheric concentrations of carbon dioxide levels are now higher than they have been for at least 420,000 years and may not have been exceeded during the past 20 million years. The rate of increase in the gas has also been quite unprecedented, and was greater in the last hundred years than at any time in at least the previous 20,000. Being concoctions of the twentieth century, other polluting gases such as chlorofluorocarbons and hydrofluorocarbons were not even present in the atmosphere a couple of centuries ago.

As these gases have accumulated in the Earth’s atmosphere so they have, quite literally, caused it to act in the manner of a greenhouse, allowing heat from the Sun in but hindering its escape back out into space. In fact, our atmosphere has operated in this way for billions of years, moderating temperature swings and extremes, but our pollution is now strongly enhancing this greenhouse effect, with the result that the Earth has been progressively warming up for most of the last hundred years.

Because the climate machine is so complex, however, no single influence can be taken in isolation and many other factors affect global temperatures. Not least of these is the output of the Sun, which is also variable over time, and which must be taken into account before allocating a rising temperature trend purely to the accumulation of man-made greenhouse gases. The Sun follows a regular 11-year pattern of activity, known as the sunspot cycle, during which time its output varies by about 0.1 per cent. Solar output also changes over longer periods, ranging from hundreds to tens of thousands of years, and these can play a significant role in cooling or warming the planet and – in recent centuries – in modifying or masking the effect of anthropogenically derived gases.

Volcanic eruptions can also have a significant effect on the Earth’s climate. Although the detailed picture is somewhat more complex, large explosive eruptions inject massive volumes of sulphur dioxide and other sulphur gases into the stratosphere, which have a broadly cooling effect through reducing the level of solar radiation reaching the Earth’s surface. Significant, if short-lived, reductions in global temperatures followed the eruptions of both El Chichón (Mexico) in 1982 and Pinatubo (Philippines) in 1991. Sometimes volcanoes and the Sun combine to bring about longer-lasting episodes of climate change. For example, a combination of reduced solar output and elevated volcanic activity has been implicated in the medieval cold snap known by climate scientists as the Little Ice Age. This lasted from about 1450 ad to perhaps the end of the nineteenth century and saw frost fairs on the Thames and bitter winters in many parts of the world. Attempting to pin down the true variation in global temperatures over the past thousand years is difficult, not least because records prior to the last couples of hundred years are far from reliable.

A further complication arises from the fact that while one part of the world might be heating up, another might be cooling down. One argument that is still used by opponents of anthropogenic warming is that the world underwent a pronounced cooling between 1946 and 1975, thereby invalidating the idea that elevated levels of greenhouse gases must automatically result in global warming.

More detailed examination of the record for this period reveals, however, that although much of the northern hemisphere cooled noticeably, the reverse was the case in the southern hemisphere, which warmed appreciably. In reality, although there was a small overall temperature fall at this time, this is now being attributed to a masking of the warming trend by sulphur gases emitted by volcanic eruptions and by heavy industries at the time unfettered by clean air laws.

The bad news is that this masking effect, now fashionably referred to as global dimming, may mean that temperatures are set to rise further than previously forecast. In any case, notwithstanding this blip, instrumental records show that global temperatures have been following an inexorably upward path since such records began in 1861. The record also shows that the 1990s was the warmest decade since the mid-nineteenth century and 1998 the warmest year on record. In Europe, the veracity of global warming really hit home during the summer of 2003, when record-breaking temperatures across the continent claimed up to 35,000 lives due to heat stress.

If our great experiment was designed specifically to heat up the planet then based upon the results to date it seems that we can pat one another on the back at a job well done and sit back and relax as the experiment grinds away of its own accord, racking up the heat and clocking up an ever-increasing list of unexpected consequences. But of course, this was not the intention of the experiment at all. Indeed, it is only in recent decades that the polluting effect of human activities on the global environment has been thought of in these terms.

The great experiment has never been anything other than a side effect of our race’s constant thirst for more; more growth, more goods, more wealth. Now that it has become apparent that we have been messing, admittedly involuntarily, with the natural functioning of the Earth we have no choice but to close the experiment down. Continuing political procrastinations and the muddying of the scientific waters by vested interest groups antagonistic to proposals to mitigate global warming have ensured that, although now ratified, the Kyoto Protocol falls far short of achieving its goal of a 5.2 per cent reduction (below 1990 levels) in global greenhouse gas emissions by 2008-2012. This failure is primarily due to countries such as the United States and Australia refusing to sign or make even the called-for tiny cutbacks in emissions. With reductions in emissions needing to be of the order of 60 per cent if a real dent is to be made in the ever-climbing concentrations of atmospheric greenhouse gases, prospects look bleak indeed.

Rather like trying to turn around a supertanker, the enormous inertia that has already built up in the system would still mean that, even if we came to our senses and made dramatic cuts in emissions within the next few years, both temperatures and sea levels would continue to rise for centuries to come. It seems inevitable; therefore, that we are going to face dramatic changes to our environment - some for the better, but most not. What is certain is that our children and their descendants are going to find the Earth a very different place.

Hothouse Earth

The world of 2100 ad will not only be far warmer but will also be characterized by extremes of weather that will ensure, at the very least, a far more uncomfortable life for billions. Already, the wildly fluctuating weather patterns that are held by many to be a consequence of global warming, combined with increased vulnerability in the developing world, are leading to a dramatic rise in the numbers of meteorological disasters.

In its 2004 World Disasters Report, the International Federation of Red Cross and Red Crescent Societies reveals that the annual numbers of disasters due to storms, floods, landslides, and droughts have climbed from around 200 before 1996 to more than 700 in the first few years of the millennium. Few think that the situation will get better and the chances are that things will get progressively worse.

Increasingly, those occupying low-lying coastal regions will be hit by rising sea levels and heavier rainfall that will mean that lethal floods become the norm rather than the exception. In contrast, more and more people will starve as annual rains fail year after year and huge regions of Africa and Asia fall within the grip of drought and consequent famine.

The summer of 2005 provided a glimpse of what we can expect to become the norm, with record monsoon rains bringing floods to the Indian city of Mumbai that claimed more than 1,000 lives, while prolonged drought brought famine to more than 4 million people, a quarter of them children, in the west African state of Niger. It also looks as if the Earth will become a windier place, with warmer seas triggering more and bigger storms, particularly in the tropics. I will return to the manifold hazard implications of global warming later, but let’s look now at the latest predictions for temperature rise over the next hundred years. After all, this is the critical element that will drive the huge changes to our environment in this century and beyond.

In 2001, the Intergovernmental Panel on Climate Change, or IPCC, published its Third Assessment Report on global warming; three massive tomes totaling over 2,600 pages. The IPCC was established in 1988 by the UN Environmental Programme and the World Meteorological Organization, with a remit to provide an authoritative consensus of scientific opinion on climate change using the best available expertise. The important word here is consensus.

Over 1,000 scientists were involved in either the writing of the report or the reviewing of its content, leaving little doubt of its validity except in the minds of the irrationally skeptical, the eternally optimistic, or the downright Machiavellian. If the content of the third IPCC report could be summed up in a few words, they would probably be ‘Did we say in our second assessment report that things would be bad? Well, we were wrong. They are going to be much worse than that.’

Let’s look at what the panel says about rising temperatures. Over the course of the last century, global temperatures rose by 0.6 degrees Celsius. By 2100, the IPCC worst case scenario predicts that temperatures will be almost 6 degrees Celsius higher than they are now, and even the average prediction would see us roasting as a consequence of a 4-degree Celsius rise. If this does not sound much, consider that just 4 or 5 degrees Celsius mean the difference between full Ice Age conditions and our current climate. The transition between the two involved huge changes in the Earth’s environment, not only in the climate and weather but also in vegetation and animal life.

There is every reason to expect that as the post-glacial temperature rise doubles again we will experience equally dramatic changes. This time, however, there are two important differences. First, the Earth has to feed, clothe, and support 6.5 billion souls, rather than a few million, and secondly today’s comparable temperature rise is taking place over the course of just a hundred years rather than thousands.

Many of the consequences of such a dramatic rise in global temperatures are obvious, but others less so. The Polar Regions and mountainous areas with permanent snow and ice are already suffering, and warming will continue to exact a severe toll here. Over the last hundred years there has been a massive retreat of mountain glaciers all over the world, while since the 1950s the Arctic ice has started to thin dramatically with the result that the North Pole was ice free in summer 2000.

Furthermore, the extent of Arctic sea ice in spring and summer is 10-15 per cent smaller than it was 40 years ago, while ice on lakes and rivers at higher altitudes in the northern hemisphere now melts in spring two weeks earlier than a century ago. Northern hemisphere spring snow cover is already 10 per cent down on the 1966–1986 mean and IPCC predictions suggest that polar and mountainous regions of the hemisphere could be 8 degrees Celsius warmer by 2100. In 2004, the concentration of carbon dioxide in the atmosphere was 380 parts per million (ppm). Even if, at some future time, we managed to stabilize the concentration at 450 ppm, temperatures would continue to rise, albeit more slowly, beyond the year 2300.

Dramatically increasing the rate of melting of snow and ice means rising sea levels: tide gauge data indicate that global sea levels rose by between 10 and 20 centimeters during the twentieth century, and this rise is expected to escalate drastically in the coming hundred years, with sea levels predicted to be 40 centimeters and perhaps over 80 centimeters higher by 2100. Most of the recent and predicted rise comes from the thermal expansion of the oceans as they warm up or by the addition of water from the rapidly melting mountain glaciers. Failure to cut back on greenhouse emissions, however, may lead in future to catastrophic melting of the Greenland and Antarctic ice sheets, resulting in terrible consequences for coastal areas.

Worst case scenarios in the IPCC report forecast the near elimination of the Greenland Ice Sheet, generating a 6-metre rise in sea level by the year 3000. More worrying, although the great West Antarctic Ice Sheet (WAIS) appears at present to be stable, severe warming over the next few centuries could result in its permanent disintegration and loss. The probability of the collapse and melting of the WAIS in the next two hundred years has been put as high as 1 in 20. Should either the Greenland Ice Sheet or the WAIS melt fully, and then virtually all the world’s major coastal cities will find themselves under water. Even without this, however, the effects of rising sea level in the next hundred years will be devastating for low-lying countries. For example, a 1-metre rise would see the Maldives in the Indian Ocean under water, while a combination of rising sea level and sinking of the land surface are forecast to result in a 1.8-metre rise in Bangladesh in just fifty years or so. This will see the loss of a huge 16 per cent of the land surface, which supports 13 per cent of the population.

Coastal flooding will also be enhanced by storm surges, with the numbers affected predicted to rise by up to 200 million people by 2080. Because the oceans are so slow to respond to change, the problem of sea-level rise is not going to go away for a very long time. Even if we stabilized greenhouse gases in the atmosphere at current concentrations, sea level would continue to rise for a thousand years or more.

It has become fashionable to blame every weather-related natural disaster on global warming. While it is not possible to say that a specific storm or flood is due to warming, there is accumulating evidence for ever-greater numbers of extreme weather events. Extreme precipitation events have increased by up to 4 per cent at high and mid-latitudes during the second half of the twentieth century, and more rainstorms, floods, and windstorms are forecast.

Current climatic characteristics are likely to be enhanced, so regions that are already wet will get wetter and those that are dry will suffer from prolonged and sustained drought. Northern Europe and the UK will therefore face more floods, while the North African deserts begin to creep towards southern Europe, and Australia begins to bake beneath a blazing sun.

The Atlantic’s ‘hurricane alley’ is likely to get much busier in the next half-century, and a paper published in 2005 proposes that tropical cyclones have become twice as destructive over the past three decades. It also predicts that the Caribbean islands, the south-eastern and Gulf coasts of the USA, Japan, and Hong Kong – amongst other targets – can expect to take an increasing battering in years to come. So far few are prepared to stick their necks out and say that this is definitely the result of global warming.

However, as a rise in sea surface temperatures has been proposed as the primary driving mechanism for these more powerful storms, it would seem to be a reasonable link to make; global warming means warmer seas, which in turn are likely to give us more and bigger storms. As the tropical Atlantic has warmed over the past five years so the rate of hurricane formation has doubled. At the same time, the storms are getting stronger, with a 250 per cent increase in storms with sustained wind speeds exceeding 175 kilometers an hour. With increased warming of the oceans expected to continue throughout the twenty-first century, prospects for the inhabitants of hurricane alley look far from rosy.

Where wind leads, so waves often follow, and evidence is now coming to light of bigger and more powerful waves. Around the western and southern coasts of the UK, average wave heights – about 3 meters – have risen by over a meter compared to three decades ago, while the height of the largest waves has increased by an alarming 3 meters, to 10 meters. Although not yet attributed directly to global warming, the increased wave heights reflect changes in the weather patterns of the North Atlantic that in turn can be linked to the reorganization of our planet’s weather system as it continues to warm. More coastal erosion is already taking its toll along many sections of the UK’s most exposed coastlines; a situation that is likely to get much worse and that will undoubtedly be exacerbated by rising sea levels and storms.

It also looks as if global warming is leading to more frequent El Niño events; the second largest climatic ‘signal’ after the seasons. An El Niño involves a weakening of the westward-blowing trade winds and the resulting migration of warm surface waters from the west to the eastern Pacific, devastating local fisheries and seriously disrupting the world’s climate. The frequency of this particularly insidious phenomenon has risen from once every six years during the seventeenth century to once every 2.2 years since the 1970s and global warming is being held up as a possible culprit.

As the Earth continues to heat up, it looks as if it won’t only be the seas and the skies that become increasingly agitated: the planet’s crust will also join in. Already warmer temperatures in mountainous regions such as the Alps and the Pyrenees are causing the permafrost to melt at higher altitudes, threatening villages, towns, and ski resorts with more frequent and more destructive landslides. As the melting ice weakens the mountains, Switzerland is experiencing more rock falls, landslides, and mudflows, but things could get much worse. Whole mountainsides, consisting of billions of tones of rock, could collapse, burying entire communities under massive piles of rubble.

Over the last 100–150 years the tops of mountains in Western Europe have warmed by one or two degrees Celsius and this may be accelerating. In the mountains above the Swiss ski resort of St Moritz, for example, the temperature has risen by half a degree Celsius in just the last 15 years. Continued warming at this rate could destabilize mountain tops right across the planet, making life both difficult and dangerous for the inhabitants of high mountain terrain. A colleague of mine, Dr Simon Day, has even proposed that increasing rainfall on ocean island volcanoes may trigger gigantic landslides capable of sending huge tsunamis across the Pacific or Atlantic Oceans.  

Clearly then, a major consequence of global warming will be a far more hazardous world, few of whose inhabitants will escape scot-free. Already, things are getting rapidly worse, particularly along low-lying coasts and islands. In the 1990s over 40 per cent of Solomon Islanders were either killed or impinged upon by storm and flood. Other low-lying southwest Pacific island states such as Tonga and Micronesia are also faring badly.

Over the same period 1 in 12 people in Australia and 1 in 200 in the USA were hit by natural disasters, and in the UK 1 in 2,000. But this is just the start. In the first year of the new millennium, more than 200 million people were affected by natural disasters – mostly flood, storm, and drought – an amazing 1 in 30 of the planet’s population, and global warming has not really got going yet. Without doubt, all of us will be forced to embrace natural hazards as a normal, if unwelcome, part of our lives in the decades to come. Furthermore, the consequences of global warming stretch far beyond making the Earth more prone to natural catastrophes. Other dramatic and widespread changes are on the way that will have an equally drastic impact on all our lives. National economies will be knocked sideways and the fabric of our global society will begin to come apart at the seams, as agriculture, water supplies, wildlife, and human health become increasingly embattled.

A few countries will be able to adapt to some extent but the speed of change is certain to be so rapid as to make this all but impossible for the most vulnerable nations in Asia, Africa, and elsewhere in the developing world. Against a background of soaring populations, falling incomes, and increasing pollution, there is no question that the impact of global warming will be terrible. One of the greatest problems will be a desperate shortage of water.

Even today, 1.7 billion people – a third of the world’s population - live in countries where supplies of potable water are inadequate, and this figure will top 5 billion in just 25 years, triggering water conflicts across much of Asia and Africa. Alongside this, crop yields are forecast to fall in tropical, subtropical, and many mid-latitude regions, leading to the expansion of deserts, food shortages, and famine. The struggle for food and water will lead to economic migration on a biblical scale, dwarfing anything seen today, bringing instability and conflict to many parts of the world.

In Europe and Asia trees come into leaf in spring a week earlier than just 20 years ago and autumn arrives 10 days later than it did. While this may seem beneficial, it will also encourage new pests to move into temperate zones from which they have previously been absent. Termites have already established a base in the southern UK where, in places, temperatures are now high enough for malarial mosquitoes to survive and breed.

In the tropics there will be an enormous rise in the number of people at risk from insect-borne diseases, especially malaria and dengue fever, while the paucity of drinkable water will ensure that cholera continues to make huge inroads into the numbers of young, old, and infirm. In urban areas, a combination of roasting summers and increased pollution will also begin to take their toll on health, particularly - once again - in poor communities where air-conditioning is out of the question.

With land temperatures across all continents due to rise by up to 8 degrees Celsius by the end of the century, temperate and tropical forests, which currently help to absorb greenhouse gases, will start to die back, taking with them thousands of animal species unable to adapt to the new conditions. And not just the forests: grasslands, wetlands, coral reefs and atolls, mangrove swamps, and sensitive polar and alpine ecosystems will all struggle to survive and adapt, and many will fail to do so.

Even our leisure activities will be affected. Not only will southern Europe become too dry for cereal crops, but it will also be too hot - in the summer months at least - for sun seekers. Prospects for the winter sports industry also look bleak, with most mountain glaciers likely to have vanished by the end of the century, and snowfall much reduced. From a biodiversity point of view – as well as a tourist industry one – probably the worst recent forecast is that all the great reefs will be dead and gone within 50 years; some of the greatest natural wonders of the world obliterated by warmer seas just so that some of us can continue to live, or strive for, lives of conspicuous consumption.

Everything I have talked about so far is either already happening or has been predicted by powerful computer-driven climate models that are constantly being upgraded in attempts to forecast better what global warming holds in store for us.

We must always be prepared, however, to expect the unexpected; drastic consequences that so far have been regarded as possible but not likely, or others that have simply not been thought of. When sea levels were rising rapidly following the end of the last Ice Age 10,000 years ago, the weight of the water on continental margins appears to have had a dramatic effect, causing volcanoes to erupt, active faults to move, and huge landslides to collapse from continental shelf regions. The average rate of sea-level rise during post-glacial times was - at around 7 millimeters a year - just about comparable with the rise we would see should the Greenland or West Antarctic ice sheets eventually succumb to global warming.

The problem is that we don’t know how big or how fast a rise is needed to see these effects happening again, although, interestingly, the Pavlov volcano in Alaska is induced to erupt in winter when low-pressure weather systems passing over raise sea level by just a few tens of centimeters. Perhaps then, we face not just a warm but a fiery future. There are other worries too. The accumulation of gases from the decomposition of organic detritus leads to the formation of what are called gas hydrates in marine sediments. These are methane solids that look rather like water ice, whose physical state is very sensitive to changes in temperature.

A warming of just one degree Celsius may cause rapid dissociation of the solid into a gaseous state, exerting increased pressure on the enclosing sediments and potentially leading to the destabilization and collapse of huge sediment mass. This mechanism has been put forward for triggering the Storegga Slides - a pair of gigantic submarine landslides off the coast of southern Norway - as the Earth continued to warm up 8,000 years ago. The collapses sent huge tsunamis pouring across northeast Scotland, leaving sandy deposits within the thick layers of boggy peat. If global warming really gets going and continues unhindered for the next few centuries then it looks as if things may start to get very exciting indeed.

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