(2) Global Warming & Global Society



What is the IPCC?

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 jointly by the United Nations Environmental Panel and World Meteorological Organization because of worries about the possibility of global warming. The purpose of the IPCC is the continued assessment of the state of knowledge on the various aspects of climate change, including scientific, environmental, and socio-economic impacts and response strategies. The IPCC is recognised as the most authoritative scientific and technical voice on climate change, and its assessments have had a profound influence on the negotiators of the United Nations Framework Convention on Climate Change (UNFCCC) and its Kyoto Protocol.

The meetings in The Hague in November 2000 and in Bonn in July 2001 were the second and third attempts to ratify (i.e. to make legal) the Protocols laid out in Kyoto in 1998. Unfortunately, President Bush pulled the USA out of the negotiations in March 2001. However, 186 other countries made history in July 2001 by agreeing the most far-reaching and comprehensive environmental treaty the world has ever seen. But the Kyoto Protocol has yet to be ratified.

The IPCC is organised into three working groups plus a task force to calculate a number of greenhouse gases produced by each country. Each of these four bodies has two co-chairmen (one from a developed and one from a developing country) and a technical support unit. Working Group I assesses the scientific aspects of the climate system and climate change; Working Group II addresses the vulnerability of human and natural systems to climate change, the negative and positive consequences of climate change, and options for adapting to them; and Working Group III assesses options for limiting greenhouse gas emissions and otherwise mitigating climate change, as well as economic issues. Hence the IPCC also provides governments with scientific, technical, and socio-economic information relevant to evaluating the risks and to developing a response to global climate change. The latest reports from these three working groups were published in 2001 and approximately 400 experts from some 120 countries were directly involved in drafting, revising, and finalising the IPCC reports and another 2,500 experts participated in the review process. The IPCC authors are always nominated by governments and by international organisations including Non-Governmental Organisations. These reports are essential reading for anyone interested in global warming.

The IPCC also compiles research on the main greenhouse gases: where they come from, and the current consensus concerning their warming potential (see below). The warming potential is calculated in comparison with carbon dioxide, which is allocated a warming potential of one. This way the different greenhouse gases can be compared with each other relatively instead of in absolute terms.

The Global Warming potential is calculated over a 20- and 100-year period. This is because different greenhouse gases have different residence times in the atmosphere because of how long they take to break down in the atmosphere or be absorbed in the ocean or terrestrial biosphere. Most other greenhouse gases are more effective at warming the atmosphere than carbon dioxide but are still in very low concentrations in the atmosphere. As you can know there are other greenhouse gases which are a much more dangerous mass for mass than carbon dioxide but these exist in very low concentrations in the atmosphere, and therefore most of the debate concerning global warming still centres on the role and control of atmospheric carbon dioxide.

What is climate change?

Many scientists believe that the human-induced or anthropogenically enhanced greenhouse effect will cause climate change in the near future. Even some of the global warming sceptics argue that though global warming may be a minor influence, natural climate change does occur on human timescales and we should be prepared to adapt to it. But what is climate change and how does it occur?

Climate change can manifest itself in a number of ways, for example, changes in regional and global temperatures, changing rainfall patterns, expansion and contraction of ice sheets, and sea-level variations. These regional and global climate changes are responses to external and/or internal forcing mechanisms. An example of an internal forcing mechanism is the variations in the carbon dioxide content of the atmosphere modulating the greenhouse effect, while a good example of an external forcing mechanism is the long-term variations in the Earth’s orbits around the sun, which alter the regional distribution of solar radiation to the Earth. This is thought to cause the waxing and waning of the ice ages. So in terms of looking for the evidence for global warming and predicting the future, we need to take account of all the natural external and internal forcing mechanisms. For example, until recently the cooling that occurred globally during the 1970s was unexplained until the ‘external’ and cyclic variations every 11 years in the sun’s energy output, the so-called sunspot cycle, was taken into consideration.

We can also try to abstract the way the global climate system responds to an internal or external forcing agent by examining different scenarios. In these scenarios, I am assuming that there is only one forcing mechanism which is trying to change the global climate. What is important is how the global climate system will react. For example, is the relationship like a person trying to push a car up a hill which, strangely enough, gets a very little response? Or is it more like a person pushing a car downhill, which, once the car starts to move, it is very difficult to stop. There are four possible relationships and this is the central question in the global warming debate, which is most applicable to the future.

(a) Linear and synchronous response. In this case, the forcing produces a direct response in the climate system whose magnitude is in proportion to the forcing. In terms of global warming, an extra million tonnes of carbon dioxide would cause a certain predictable temperature increase. This can be equated to pushing a car along a flat road: most of the energy put into pushing is used to move the car forward.

(b) Muted or limited response. In this case, the forcing may be strong, but the climate system is in some way buffered and therefore gives a very little response. Many global warming sceptics and politicians argue that the climate system is very insensitive to changes in atmospheric carbon dioxide so very little will happen in the future. This is the ‘pushing the car up the hill’ analogy: you can spend as much energy as you like trying to push the car but it will not move very far.

(c) Delayed or non-linear response. In this case, the climate system may have a slow response to the forcing thanks to being buffered in some way. After an initial period, the climate system responds to the forcing but in a non-linear way. This is a real possibility when it comes to global warming and why it is argued that as yet only a small amount of warming has been observed over the last 100 years. This scenario can be equated to the car on the top of a hill: it takes some effort and thus time to push the car to the edge of the hill; this is the buffering effect. Once the car has reached the edge it takes very little to push the car over, and then it accelerates down the hill with or without your help. Once it reaches the bottom, the car then continues for some time, which is the overshoot, and then slows down of its own accord and settles into a new state.

(d) Threshold response. In this case, initially, there is no or very little response in the climate system to the forcing; however, all the response takes place in a very short period of time in one large step or threshold. In many cases, the response may be much larger than one would expect from the size of the forcing and this can be referred to as a response overshoot. This is the scenario that most worries us, as thresholds are very difficult to model and thus predict.

However, thresholds have been found to be very common in the study of past climates, with rapid regional climate changes of over 5°C occurring within a few decades. This scenario equates to the bus hanging off the cliff at the end of the original film The Italian Job; as long as there are only very small changes, nothing happens at all. However, a critical point (in this case weight) is reached and the bus (and the gold) plunge off the cliff into the ravine below.

Though these are purely theoretical models of how the global climate system can respond, they are important to keep in mind when reviewing the possible scenarios for future climate change.

Moreover, they are important when we consider why different people see different global warming futures despite all having access to the same information. It depends on which of the above scenarios they believe will happen. An added complication when assessing climate change is the possibility that climate thresholds contain bifurcations. This means the forcing required to go one way through the threshold is different from the reverse. This implies that once a climate threshold has occurred, it is a lot more difficult to reverse it. The bifurcation of the climate system has been inferred from ocean models which mimic the impact of fresh water in the North Atlantic on the global deep-water circulation, and we will discuss this can of worms in great detail later.

Linking global warming to climate change

We have seen that there is clear evidence that greenhouse gas concentrations in the atmosphere have been rising since the industrial revolution in the 18th century. The current scientific consensus is that changes in greenhouse gas concentrations in the atmosphere do cause global temperature change. However, the biggest problem with the global warming hypothesis is understanding how sensitive the global climate is to increased levels of atmospheric carbon dioxide. Even if we establish this, predicting climate change is complex because it encompasses many different factors, which respond differently when the atmosphere warms up, including regional temperature changes, melting glaciers and ice sheets, relative sea-level change, precipitation changes, storm intensity and tracks, El Niño, and even ocean circulation. This linkage between global warming and climate change is further complicated by the fact that each part of the global climate system has different response times. For example, the atmosphere can respond to external or internal changes within a day, but the deep ocean may take decades to respond, while vegetation can alter its structure within a few weeks (e.g. change a number of leaves) but its composition (e.g. swapping plant types) can take up to a century to change. Then, add to this the possibility of natural forcing which may be cyclic; for example, there is good evidence that sunspot cycles can affect climate on both a decadal and a century timescale.

There is also evidence that since the beginning of our present interglacial period, the last 10,000 years, there have been climatic coolings every 1,500 ±500 years, of which the Little Ice Age was the last. The Little Ice Age began in the 17th and ended in the 18th century and was characterized by a fall of 0.5–1°C in Greenland temperatures, significant shift in the currents around Iceland, and a sea-surface temperature fall of 4°C off the coast of West Africa, 2°C off the Bermuda Rise, and of course ice fairs on the River Thames in London, all of which were due to natural climate change. So we need to disentangle natural climate variability from global warming. We need to understand how the different parts of the climate system interact, remembering that they all have different response times. We need to understand what sort of climatic change will be caused and whether it will be gradual or catastrophic. We also need to understand how different regions of the world will be affected; for example, it is suggested that additional greenhouse gases will warm up the poles more than the tropics. All these themes concerning an understanding of the climate system and the difficulty of future climate prediction are returned later.

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(1) Global Warming & Global Society


National Geographic - Global Warming


The 2000 Intergovernmental Panel on Climate Change (IPCC), amounting to 2,600 pages of detailed review and analysis of published research, declares that the scientific uncertainties of global warming are essentially resolved. This report states that there is clear evidence for a 0.6°C rise in global temperatures and 20 cm rise in sea level during the 20th century. The IPCC synthesis also predicts that global temperatures could rise by between 1.4°C and 5.8°C and sea level could rise by between 20 cm and 88 cm by the year 2100. In addition, weather patterns will become less predictable and the occurrence of extreme climate events, such as storms, floods, and droughts, will increase.

These papers try to unpick the controversies that surround the global warming hypothesis and hopefully provide an incentive to read more on the subject. It starts with an explanation of global warming and climate change and is followed by a review of how the global warming hypothesis was developed. The papers will also investigate why people have such extreme views about global warming, views which reflect both how people view nature and their own political agenda.

The papers examine the evidence showing that global warming has already occurred and the science of predicting climate change in the future. The potentially devastating effects of global warming on human society are examined, including drastic changes in health, agriculture, the economy, water resources, coastal regions, storms and other extreme climate events, and biodiversity. For each of these areas scientists and social scientists have made estimates of the potential direct impacts; for example, it is predicted that by 2025 five billion people will experience water stress. The most important impacts are discussed in our papers, along with plans to mitigate the worst of them.

There are also potential surprises that the global climate system might have in store for us, exacerbating future climate change. These include the very real possibility that global deep-ocean circulation could alter, plunging Europe into a succession of extremely cold winters or causing unprecedented global rise in sea level. There are predictions that global warming may cause vast areas of the Amazon rainforest to burn, adding extra carbon to the atmosphere and thus accelerating global warming. Finally, there is a deadly threat lurking underneath the oceans: huge reserves of methane which could be released if the oceans warm up sufficiently – again accelerating global warming. The final papers look at global politics and potential adaptations to global warming. It should be realized that the cost of significantly cutting fossil-fuel emissions may be too expensive in the short term and hence the global economy will have to become more flexible and thus adapt to climate change. We will also have to prioritize which parts of our global environment to protect. The theory of global warming thus challenges our current concepts of the nation-state versus global responsibility, and the short-term vision of our political leaders, both of which must be overcome if global warming is to be dealt with effectively. Be under no illusion: if global warming is not taken seriously, it will be the poorest people in our global community, as usual, that suffer most.

What is global warming?

The Earth’s natural greenhouse

The temperature of the Earth is controlled by the balance between the input from energy of the sun and the loss of this back into space. Certain atmospheric gases are critical to this temperature balance and are known as greenhouse gases. The energy received from the sun is in the form of short-wave radiation, i.e. in the visible spectrum and ultraviolet radiation. On average, about one-third of this solar radiation that hits the Earth is reflected back to space.

Of the remainder, some is absorbed by the atmosphere, but most is absorbed by the land and oceans. The Earth’s surface becomes warm and as a result emits long-wave ‘infrared’ radiation. The greenhouse gases trap and re-emit some of this long-wave radiation, and warm the atmosphere. Naturally occurring greenhouse gases include water vapor, carbon dioxide, ozone, methane, and nitrous oxide, and together they create a natural greenhouse or blanket effect, warming the Earth by 35°C. Despite the greenhouse gases often being depicted in diagrams as one layer, this is only to demonstrate their ‘blanket effect’, as they are in fact mixed throughout the atmosphere.

Another way to understand the Earth’s natural ‘greenhouse’ is by comparing it to its two nearest neighbours. A planet’s climate is decided by several factors: its mass, its distance from the sun, and of course the composition of its atmosphere and in particular the amount of greenhouse gases. For example, the planet Mars is very small, and therefore its gravity is too small to retain a dense atmosphere; its atmosphere is about a hundred times thinner than Earth’s and consists mainly of carbon dioxide. Mars’s average surface temperature is about −50°C, so what little carbon dioxide exists is frozen in the ground. In comparison, Venus has almost the same mass as the Earth but a much denser atmosphere, which is composed of 96% carbon dioxide. This high percentage of carbon dioxide produces intense global warming and so Venus has a surface temperature of over + 460°C.

The Earth’s atmosphere is composed of 78% nitrogen, 21% oxygen, and 1% other gases. It is these other gases that we are interested in, as they include the so-called greenhouse gases. The two most important greenhouse gases are carbon dioxide and water vapour. Currently, carbon dioxide accounts for just 0.03–0.04% of the atmosphere, while water vapour varies from 0 to 2%. Without the natural greenhouse effect that these two gases produce, the Earth’s average temperature would be roughly −20°C. The comparison with the climates on Mars and Venus is very stark because of the different thicknesses of their atmospheres and the relative amounts of greenhouse gases. However, because the amount of carbon dioxide and water vapour can vary on Earth, we know that this natural greenhouse effect has produced a climate system which is naturally unstable and rather unpredictable in comparison to those of Mars and Venus.

Past climate and the role of carbon dioxide

One of the ways in which we know that atmospheric carbon dioxide is important in controlling global climate is through the study of our past climate. Over the last two and half million years the Earth’s climate has cycled between the great ice ages, with ice sheets over 3 km thick over North America and Europe, to conditions that were even milder than they are today. These changes are extremely rapid if compared to other geological variations, such as the movement of continents around the globe, where we are looking at a time period of millions of years. But how do we know about these massive ice ages and the role of carbon dioxide? The evidence mainly comes from ice cores drilled in both Antarctica and Greenland. As snow falls, it is light and fluffy and contains a lot of air. When this is slowly compacted to form ice, some of this air is trapped. By extracting these air bubbles trapped in the ancient ice, scientists can measure the percentage of greenhouse gases that were present in the past atmosphere. Scientists have drilled over two miles down into both the Greenland and Antarctic ice sheets, which has enabled them to reconstruct the amount of greenhouse gases that occurred in the atmosphere over the last half a million years. By examining the oxygen and hydrogen isotopes in the ice core, it is possible to estimate the temperature at which the ice was formed. The results are striking, as greenhouse gases such as atmospheric carbon dioxide (CO2) and methane (CH4) co-vary with temperatures over the last 400,000 years. This strongly supports the idea that the carbon dioxide content in the atmosphere and global temperature are closely linked, i.e. when CO2 and CH4 increase, the temperature is found to increase and vice versa. This is our greatest concern for future climate: if levels of greenhouse gases continue to rise, so wills the temperature of our atmosphere. The study of past climate, as we will see throughout this book, provides many clues about what could happen in the future. One of the most worrying results from the study of ice cores, and lake and deep-sea sediments, is that past climate has varied regionally by at least 5°C in a few decades, suggesting that climate follows a non-linear path. Hence we should expect sudden and dramatic surprises when greenhouse gas levels reach an as yet unknown trigger point in the future.

The rise in atmospheric carbon dioxide during the industrial period

One of the few areas of the global warming debate which seems to be universally accepted is that there is clear proof that levels of atmospheric carbon dioxide have been rising ever since the beginning of the industrial revolution. The first measurements of CO2 concentrations in the atmosphere started in 1958 at an altitude of about 4,000 metres on the summit of Mauna Loa mountain in Hawaii. The measurements were made here to be remote from local sources of pollution. What they have clearly shown is that atmospheric concentrations of CO2 have increased every single year since 1958. The mean concentration of approximately 316 parts per million by volume (ppmv) in 1958 rose to approximately 369 ppmv in 1998. The annual variations in the Mauna Loa observatory are mostly due to CO2 uptake by growing plants.

The uptake is highest in the northern hemisphere springtime; hence every spring there is a drop in atmospheric carbon dioxide which unfortunately does nothing to the overall trend towards ever higher values. This carbon dioxide data from the Mauna Loa observatory can be combined with the detailed work on ice cores to produce a complete record of atmospheric carbon dioxide since the beginning of the industrial revolution. What this shows is that atmospheric CO2 has increased from a pre-industrial concentration of about 280 ppmv to over 370 ppmv at present, which is an increase of 160 billion tonnes, representing an overall 30% increase. To put this increase into context, we can look at the changes between the last ice age, when temperatures were much lower, and the pre-industrial period. According to evidence from ice cores, atmospheric CO2 levels during the ice age were about 200 ppmv compared to pre-industrial levels of 280 ppmv – an increase of over 160 billion tonnes – almost the same CO2 pollution that we have put into the atmosphere over the last 100 years. This carbon dioxide increase was accompanied by a global warming of 6°C as the world freed itself from the grips of the last ice age. Though the ultimate cause of the end of the last ice age was changes in the Earth’s orbit around the sun, scientists studying past climates have realized the central role atmospheric carbon dioxide has as a climate feedback translating these external variations into the waxing and waning of ice ages. It demonstrates that the level of pollution that we have already caused in one century is comparable to the natural variations which took thousands of years.

The enhanced greenhouse effect

The debate surrounding the global warming hypothesis is whether the additional greenhouse gases being added to the atmosphere will enhance the natural greenhouse effect. Global warming skeptics argue that though levels of carbon dioxide in the atmosphere are rising, this will not cause global warming, as either the effects are too small or there are other natural feedbacks which will counter major warming. Even if one takes the view of the majority of scientists and accepts that burning fossil fuels will cause warming, there is a different debate over exactly how much temperatures will increase. Then there is the discussion about whether global climate will respond in a linear manner to the extra greenhouse gases or whether there is a climate threshold waiting for us.

Who produces the pollution?

The United Nations Framework Convention on Climate Change was created to produce the first international agreement on reducing global greenhouse gas emissions. However, this task is not as simple as it first appears, as carbon dioxide emissions are not evenly produced by countries. The first major source of carbon dioxide is the burning of fossil fuels, since a significant part of carbon dioxide emissions comes from energy production, industrial processes, and transport. These are not evenly distributed around the world because of the unequal distribution of industry; hence, any agreement would affect certain countries’ economies more than others. Consequently, at the moment, the industrialized countries must bear the main responsibility for reducing emissions of carbon dioxide to about 22 billion tons of carbon per year. North America, Europe, and Asia emit over 90% of the global industrially produced carbon dioxide. Moreover, historically they have emitted much more than less-developed countries.

The second major source of carbon dioxide emissions is as a result of land-use changes. These emissions come primarily from the cutting down of forests for the purposes of agriculture, urbanization, or roads. When large areas of rainforests are cut down, the land often turns into less productive grasslands with considerably less capacity for storing CO2. Here the pattern of carbon dioxide emissions is different, with South America, Asia, and Africa being responsible for over 90% of present-day land-use change emissions, about 4 billion tons of carbon per year. This, though, should be viewed against the historical fact that North America and Europe had already changed their own landscape by the beginning of the 20th century. In terms of the amount of carbon dioxide released, industrial processes still significantly outweigh land-use changes.

So who are the bad guys in causing this increase in atmospheric carbon dioxide? Of course, it is the developed countries that historically have emitted most of the anthropogenic (man-made) greenhouse gases, as they have been emitting since the start of the industrial revolution in the latter half of the 1700s. Moreover, a mature industrialized economy is energy-hungry and burns vast quantities of fossil fuels. A major issue in the continuing debate is the sharing of responsibility. Non-industrialized countries are striving to increase their population’s standard of living, thereby also increasing their emissions of greenhouse gases, since economic development is closely associated with energy production. The volume of carbon dioxide thus will probably increase, despite the efforts to reduce emissions in industrialized countries. For example, China has the second biggest emissions of carbon dioxide in the world. However, per capita the Chinese emissions are ten times lower than those of the USA, who are top of the list. So this means that in the USA every person is responsible for producing ten times more carbon dioxide pollution than in China. So all the draft international agreements concerning cutting emissions since the Rio Earth Summit in 1992 have for moral reasons not included the developing world, as this is seen as an unfair brake on its economic development. However, this is a significant issue because, for example, both China and India are rapidly industrializing, and with a combined population of over 2.3 billion people they will produce a huge amount of pollution.

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