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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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