The Science and Politics of Global Climate Change: A Guide to the Debate by Andrew E. Dessler, Andrew E. Dessler, Edward A. Parson, Edward A. Parson

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Climate variability has become the primary environmental concern of the 21st Century. Yet, despite the scientific community's warnings of the imminent dangers of global warming, politicians world-wide have failed to agree on what to do about this potentially devastating environmental problem. This introductory primer informs scientists, policy makers and the general public by clarifying the conflicting claims of the debate.

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1

Global climate change: a new type of environmental problem

Of all the environmental issues that have emerged in the past few decades, global climate change is the most serious, and the most difficult to manage. It is the most serious because of the severity of harms that it might bring. Many aspects of human society and well being - where we live, how we build, how we move around, how we earn our livings, and what we do for recreation - still depend on a relatively benign range of climatic conditions, even though this dependence has been reduced and obscured in modern industrial societies by their wealth and technology. We can see this dependence on climate in the economic harms and human suffering caused by the climate variations of the past century, such as the "El Niño" cycle and the multi-year droughts that occur in western North America every few decades. Climate changes projected for the twentyfirst century are much larger than these twentieth-century variations, and their human impacts are likely to be correspondingly greater.

Projections of twentyfirst-century climate change are uncertain, of course. We will have much to say about scientific uncertainty and its use in policy debates, but one central fact about uncertainty is that it cuts both ways. If projected twentyfirst-century climate change is uncertain, then the actual changes might turn out to be smaller than we now project, or larger. Uncertainty about how the climate will actually change consequently makes the issue more serious, not less. Present projections of twentyfirst-century climate change include, at the upper end of the range of uncertainty, sustained rapid changes that appear to have few precedents in the history of the Earth, and whose impacts on human well-being and society could be of catastrophic proportions.

Climate does not just affect people directly: it also affects all other environmental and ecological processes, including many that we might not recognize as related to climate. Consequently, large or rapid climate change will represent an added threat to other environmental issues such as air and water quality, endangered ecosystems and biodiversity, and threats to coastal zones, wetlands, and the stratospheric ozone layer.

In addition to being the most serious environmental problem we have yet faced, climate change will also be the most difficult to manage. Environmental issues often carry difficult tradeoffs and political conflicts, because solving them requires limiting some economically productive activity or technology that is causing unintended environmental harm. Such changes are costly and generate opposition. But for the issues we have faced previously, technological advances and intelligent policies have allowed great reductions in environmental harms at modest cost and disruption, so these tradeoffs and conflicts have turned out to be quite manageable. Controlling the sulfur emissions that contribute to acid rain in the United States of America provides a good example. When coal containing high levels of sulfur is burned, sulfur dioxide (SO₂) in the smoke makes the rain that falls downwind of the smokestack acidic, harming lakes, soils, and forests. Over the past 20 years, a combination of advances in technologies to remove sulfur from smokestack gases, and well-designed policies that give incentives to adopt these technologies, burn lower-sulfur coal, or switch to other fuels, have brought large reductions in sulfur emissions at a relatively small cost and with no disruption to electrical supply.

Climate change will be harder to address because the activities causing it - mainly burning fossil fuels for energy - are a more essential foundation of world economies, and are less amenable to any simple technological corrective, than the causes of other environmental problems. Fossil fuels provide nearly 80 percent of world energy supply, and no technological alternatives are presently available that could replace this huge energy source quickly or cheaply. Consequently, climate change carries higher stakes than other environmental issues, both in the severity of potential harms if the changes go unchecked, and in the apparent cost and difficulty of reducing the changes. In this sense, climate change is the first of a new generation of harder environmental problems that human society will face over this century, as the increasing scale of our activities puts pressure on ever more basic planetary-scale processes.

When policy issues have high stakes, it is typical for policy debates to be contentious. Because the potential risks of climate change are so serious, and the fossil fuels that contribute to it are so important to the world economy, we would expect to hear strong opposing views over what to do about climate change - and we do. But even given the issue's high stakes, the number and intensity of contradictory claims advanced about climate change is extreme. The following published statements give a sense of the range of views about climate change.

From former US Vice-President Al Gore:

[T]he vast majority of the most respected environmental scientists from all over the world have sounded a clear and urgent alarm ... [T]hese scientists are telling the people of every nation that global warming caused by human activities is becoming a serious threat to our common future ... I don't think there is any longer a credible basis for doubting that the earth's atmosphere is heating up because of global warming ... So the evidence is overwhelming and undeniable. Global warming is real. It is happening already and the anticipated consequences are unacceptable.¹

From former US Secretary of Defense and of Energy James Schlesinger:

What we know for sure is quite limited ... We know that the theory that increasing concentrations of greenhouse gases like carbon dioxide will lead to further warming is at least an oversimplification. It is inconsistent with the fact that satellite measurements over 24 years show no significant warming in the lower atmosphere, which is an essential part of the global-warming theory.²

From US Senator James Inhofe:

[A]nyone who pays even cursory attention to the issue understands that scientists vigorously disagree over whether human activities are responsible for global warming, or whether those activities will precipitate natural disasters ... So what have we learned from the scientists and economists I've talked about today?

1. The claim that global warming is caused by man-made emissions is simply untrue and not based on sound science.

2. CO₂ does not cause catastrophic disasters - actually it would be beneficial to our environment and our economy ...

With all of the hysteria, all of the fear, all of the phony science, could it be that man-made global warming is the greatest hoax ever perpetrated on the American people? It sure sounds like it.³

From the Wall Street Journal:

... the science on which Kyoto is based has never been able to explain basic questions. Most glaring is why the Earth warmed so much in the early part of the 20th century, before the boom in carbon dioxide emissions. Another is why the near-earth atmosphere (measured by satellites) isn't warming as much as the Earth's surface. There's also the nagging problem that temperatures more than 1,000 years ago appear to have been as warm, if not warmer, than today's.⁴

From the National Post of Canada:

Global warming, as increasing numbers of actual scientists will tell you, is not happening.⁵

From the well-known scientific skeptic, S. Fred Singer:

[T]he Earth's climate has not warmed appreciably in the past two decades, and probably not since about 1940.⁶

That the climate is currently warming rests solely on surface thermometer data. It is contradicted by superior observations from weather satellites and independent radiosonde data from weather balloons. Proxy (non-thermometer) data from tree rings, ice cores, etc., all confirm that there is no current warming. That the 20^th century was the warmest in the past 1,000 years derives entirely from misuse of such proxy data. . . . The claim that climate models ... accurately reproduce the temperature record of the past 100 years, is spurious.⁷

From Nobel laureate F. Sherwood Rowland, of the University of California at Irvine:

The earth's climate is changing, in large part because of the activities of humankind. The simplest measure of this change is the average temperature of the Earth's surface, which has risen approximately 0.7 degrees Celsius over the past century, with most of this increase occurring in the past two decades. In other words, the Earth is undergoing global warming ... The possibility exists for notable deterioration of the climate in the United States even on a decadal time scale ... [T]he climate change problem will be much more serious by the year 2050 and even more so by 2100.⁸

And from Jerry Mahlman, former director of the US Geophysical Fluid Dynamics Laboratory at Princeton:

... we know that the earth's climate has been heating up over the past century. This is happening in the atmosphere, ocean and on land . . . [I]f the climate model projections on the level of warming are right, sea level will be rising for the next thousand years, the glaciers will be melting faster and dramatic increases in the intensity in rainfall rates and hurricanes are expected ... Unfortunately, these projections are based on strong science that refuses to go away. Oh sure, there are people insisting that warming is just a part of natural weather cycles, but their claims are not close to being scientifically credible ... These people remind me of the folks who kept trying to cast doubt on the science linking cancer to tobacco use. In both situations, the underlying scientific knowledge was quite well established, while the uncertainties were never enough to render the problem inconsequential. Yet, this offered misguided incentives to dismiss a danger ... Global warming is unpleasant news. The costs of doing something substantial to arrest it are daunting, but the consequences of not doing anything are staggering.⁹

One of the most striking aspects of this debate is the intensity of disagreements expressed over what we might expect to be simple matters of scientific knowledge, such as whether the Earth is warming or not. Such heated public confrontation over the state of scientific knowledge and uncertainty - not just between political figures and policy commentators, but also between scientists - understandably leaves most concerned citizens confused. The state of public and political debate on the issue makes it hard for non-specialists to understand what the advocates are arguing about, or to judge the strength of competing arguments.

Our goal in this book is to clarify the climate-change debate. We seek to help the concerned, non-expert citizen to understand what is known about climate change, and how confidently it is known, in order to develop an informed opinion of what should be done about the issue. We will summarize the state of knowledge and uncertainty on key points of climate science, and examine how some of the prominent claims being advanced in the policy debate - including some in the quotes above - stand up in light of present knowledge. Can we confidently state that some of these claims are simply right and others simply wrong, or are these points of genuine uncertainty or legitimate differences of interpretation? We will also summarize present understanding and debate over the likely impacts of climate change and the responses available to deal with the issue - matters that go beyond purely scientific questions, but which can be informed by scientific knowledge.

We will also examine how scientific argument and political controversy interact. This will help to illuminate why seemingly scientific arguments play such a conspicuous role in the climate-change policy debate, and in particular how such extreme disagreements can arise on points that would appear to be matters of scientific knowledge. What do policy advocates hope to achieve by arguing in public over scientific points, when most of them - like most citizens - lack the knowledge and training to evaluate these claims? Why do senior political figures appear to disagree on basic scientific questions when they have ready access to scientific experts and advisors to clarify these for them? And finally, what are the effects of such blended scientific and political arguments on the policy-making process?

While there is plenty of room for honest, well-informed disagreement over what should be done about global climate change, it is our view that the issue is made vastly more confused and contentious than it need be by misrepresentations of the state of scientific knowledge in policy debate - in particular, by exaggeration of the extent and significance of scientific uncertainty on key points about the global climate and how it might respond to further human influences.

Before we can engage these questions, the next two sections of this chapter provide some necessary background. Section provides a brief background on the Earth's climate and the basic mechanisms that control it and can change it. Section provides a brief history of existing policy and institutions concerned with global climate change, to provide the policy context for the present debate.

1.1 Background on climate and climate change

The climate of a place, a region, or the Earth as a whole, is the average over time of the meteorological conditions that occur there - in other words, its average weather. For example, in the month of November between 1971 and 2000 in Washington D.C., the average daily high temperature was 14 °C, the average daily low was 1 °C, and 0.3 cm of precipitation fell.¹⁰ These average values, along with averages of other meteorological quantities such as humidity, wind speed, cloudiness, and snow and ice coverage, define the November climate of Washington over this period. While climate refers to average meteorological conditions, weather refers to meteorological conditions at a particular time. For example, on November 29, 1999, in Washington, D.C., the high temperature was 5 °C, the low was -3 °C, and no precipitation fell. The weather on this particular November day in Washington was somewhat colder and drier than Washington's average November climate.

Weather matters for short-term, day-to-day decisions. Should you take an umbrella when you go out tomorrow? Will freezing temperatures kill plants left outdoors tonight? Is this a good weekend to go skiing in the mountains? Should you move your outdoor party scheduled for this weekend indoors? In each of these cases, you do not care about long-term average conditions, but about conditions at a specific time - not the climate, but the weather.

Climate matters for longer-term decisions. If you run an electric utility, you care about the climate because if average summer temperatures increase, people will run their air conditioners longer each day and consume more electricity. In this case, you may need to build more generating plants to meet this increased demand. If you are a city official, you care about the climate because urban water supplies usually come from reservoirs fed by rain or snow. Changes in the average temperature or in the timing or amount of precipitation could change both the supply and the demand for water. Consequently, if the climate changes, the city may need to expand capacity to store or transport water, find new supplies, or develop policies to limit water use in times of scarcity.

To understand the processes that are changing the climate, we must first consider why the climate is the way it is, in particular places and for the Earth as a whole. Scientists have been studying these questions since the early nineteenth century, beginning with the largest question of all: why is the Earth the temperature that it is? The Earth is warmed by the Sun and cooled by emitting radiation to space. The Earth's temperature is determined by the relationship between the incoming radiation the Earth absorbs from sunlight and the radiation it emits back to space. Not all the sunlight that strikes the Earth is absorbed, however. About 30 percent is reflected back into space - which is why the Earth looks bright when viewed from space - while the other 70 percent is absorbed and warms the surface and lower atmosphere. For the Earth to stay at a constant temperature, the total energy of the incoming and outgoing radiation must be equal. Because the Sun is so hot (about 5400 °C), sunlight is strongest in the visible and near-infrared region of the electromagnetic spectrum (with wavelengths from about 0.4 to 1 micron). The Earth is much cooler, so the radiation it emits is of longer wavelengths, lying in the infrared region (with wavelengths from about 5 to 20 microns). This is the region of the electromagnetic spectrum that certain types of night-vision goggles use to give clear images in total darkness, detecting minor temperature differences among objects and people by the infrared radiation they emit. A simple calculation can determine what the average temperature of the Earth should be for the outgoing radiation just to balance the energy of the absorbed sunlight. This calculation indicates that the average temperature of the Earth's surface should be about -20 °C.

This is awfully cold. Fortunately, it is also wrong. The Earth's surface is much warmer than this, a pleasant 15 °C on average. The error in the calculation comes from assuming that the infrared radiation emitted from the Earth passes directly to space. It does not, because it must pass through the atmosphere. And while the air in a clear sky is nearly transparent to the visible wavelengths coming in from sunlight, air absorbs the infrared radiation emitted by the Earth fairly strongly. This absorption is not caused by the main components of the atmosphere, molecular nitrogen and oxygen: these gases are as transparent to infrared radiation as they are to visible light. Rather, the absorption comes from several minor atmospheric constituents, principally water vapor and carbon dioxide (CO₂). By absorbing and re-emitting infrared radiation throughout the atmosphere, these gases impede the passage of radiation from the Earth's surface to space. This process warms the Earth's surface and lowest ten kilometers of the atmosphere, while cooling the atmosphere at higher altitudes. Ever since this natural warming mechanism was first described in the nineteenth century, it has been widely called the "greenhouse effect." More recently, it has been compared to wrapping a blanket around the Earth. Neither of these analogies is really accurate, however, since both blankets and greenhouses mainly work by slowing the physical escape of warm air rather than by disrupting the passage of radiation.

The power of these "greenhouse gases" to warm the Earth's surface is awesome. Although these gases are present in the atmosphere at only minute concentrations, they warm the surface by nearly 35 °C. Their power becomes even clearer if we compare the climate of the Earth to that of the neighboring planets, Mars and Venus. Mars has a thin atmosphere that is almost completely transparent to infrared radiation, giving it an average surface temperature below -50 °C. Venus has a dense, CO₂-rich atmosphere that produces an intense greenhouse effect, raising its average surface temperature above 450 °C - hot enough to melt lead.

But if greenhouse gases in the atmosphere warm the Earth to its present habitable state, increasing the concentration of these gases could make the Earth warmer still. This possibility was proposed by the Swedish chemist Svante Arrhenius in 1906, and again with more supporting evidence by the British engineer Guy Callendar in 1938. These proposals were not initially taken seriously, because with the crude tools then available to observe infrared radiation, it looked like the levels of CO₂ and water vapor already in the atmosphere were absorbing enough radiation to create the maximum possible greenhouse effect. By the 1950s, however, more precise measurements of infrared spectra showed this belief to be

Figure 1.1. Global average concentration of CO₂ in the atmosphere over the past 1000 years, in parts per million (p.p.m.). Source: Figure SPM-2, IPCC (2001a).

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wrong, so increasing CO₂ could increase infrared absorption in the atmosphere and raise the surface temperature.

CO₂ is not the only greenhouse gas, nor is it the only one emitted by human activities. Other greenhouse gases that are increasing due to human activities include: methane (CH₄), which is emitted from rice cultivation, livestock, biomass burning, and landfills; nitrous oxide (N₂O), which is emitted from various agricultural and industrial processes; and the halocarbons, a group of synthetic chemicals of which the most important are the chlorofluorocarbons (CFCs), which are used as refrigerants, solvents, and in various other industrial applications. Human activities do not control all greenhouse gases, however. The most powerful greenhouse gas in the atmosphere is water vapor. Human activities have little direct control over its atmospheric abundance, which is controlled instead by the worldwide balance between evaporation from the oceans and precipitation.

By the 1950s and early 1960s, it was also becoming clear that human activities were releasing CO₂ fast enough to significantly increase its atmospheric abundance. Figure 1.1 shows how the abundance of CO₂ in the atmosphere has varied over the past 1000 years - remaining nearly constant for most of the millennium, then beginning a rapid increase around 1800. This rapid increase closely tracked the sharp rise in fossil-fuel use that began with the industrial revolution.

Despite clear evidence of increasing atmospheric CO₂, during the 1960s and 1970s scientific views about likely future climate trends were divided. Some scientists expected the Earth to warm from rising concentrations of CO₂ and other greenhouse gases. Others expected the Earth to cool, based partly on the record of past climate oscillations between ice ages and warm interglacial periods. The present warm period has lasted about 10 000 years, roughly the same length as previous interglacial warm periods, suggesting that we might be due for a gradual, long-term cooling as we head into another ice age. Moreover, global temperature records between about 1945 and 1975 showed a slight cooling trend. It was also clear that smoke and dust emitted by human activities could shade the Earth's surface from incoming sunlight and so magnify any natural cooling trend. By the early 1980s, however, global temperatures had resumed warming and many new pieces of evidence indicated that greenhouse gases were the predominant human influence and that warming was the predominant direction of concern.

As we will discuss in Chapter 3, the best present projections are that if emissions of CO₂ and other greenhouse gases keep growing more or less as they have been, by the end of the twentyfirst century the Earth's average temperature will rise by a few degrees Celsius. This increase might not sound like much, since many places on Earth experience much larger temperature swings. The difference between a hot summer day and a cold winter one can be as large as 50 °C, and changes half that large can occur from day to night or from one day to the next. Therefore, you might reasonably guess that an increase of a few degrees in the global temperature is not likely to matter much. But there is a serious error in this line of reasoning. While the temperature of any single place on the Earth can vary greatly, the average temperature of the whole Earth is quite constant, throughout the year and from year to year. In the Earth's past, changes of only a few degrees in global-average temperature have been associated with extreme changes in climate. For example, at the peak of the last ice age 20 000 years ago - when glaciers thousands of feet thick covered most of North America - the average temperature of the Earth was only about 5 °C cooler than it is today. Thus, the prospect of a few degrees Celsius rise in global temperature over just 100 years - and perhaps more beyond - must be considered with the utmost seriousness. In Chapter 3 we will summarize what has been learned since climate change emerged as a serious scientific question nearly 50 years ago, about the evidence for present changes, likely future changes, and their impacts.

Aside: climate change and ozone depletion People frequently confuse global climate change with depletion of the stratospheric ozone layer, but these are two distinct environmental problems. Ozone is a molecule made up of three oxygen atoms, which occurs naturally in the stratosphere (the atmospheric region from about 15 to 40 kilometers above the surface). Ozone in the stratosphere protects life on Earth by absorbing most of the highest-energy ultraviolet (UV) radiation in sunlight. To make things more confusing, ozone in the lower atmosphere (the troposphere) is a health hazard and a major component of smog, which human activities are increasing. To keep "good ozone" (up there) and "bad ozone" (down here) straight, simply remember that you want ozone between you and the Sun, but do not want to breathe it. Beginning in the 1970s, scientists realized that a group of manmade chemicals, of which the most important were the chlorofluorocarbons or CFCs, could destroy ozone in the stratosphere. The result would be more intense UV radiation reaching the surface, causing an increase in skin cancer, cataracts, and other harms to human health and ecosystems. Concern mounted further in the 1980s, when extreme ozone losses were observed over Antarctica every spring (October and November) - the "ozone hole" - and CFCs were identified as the cause. After ten years of unsuccessful attempts to solve the problem, nations agreed in the late 1980s and 1990s to a series of strict regulatory controls that have now nearly eliminated most ozone-depleting chemicals in the industrialized countries. Developing countries are now moving toward phasing out the same chemicals. Because of these controls, the concentration of CFCs in the atmosphere has already begun to decline, and stratospheric ozone is projected to recover gradually over the next 30 to 50 years. There are a few ways that climate change and ozone depletion are linked. One connection is that CFCs are strong absorbers of infrared radiation, so they contribute to climate change as well as destroying ozone. Another connection is that while climate change warms the Earth's surface and lower atmosphere, it will also make the stratosphere colder and wetter. Colder and wetter conditions are more favorable for ozone destruction, and so are likely to delay the recovery of the ozone layer even if worldwide reductions of ozone-depleting chemicals stay on course. But despite these linkages, ozone depletion and climate change are fundamentally different environmental problems. They have different causes: CFCs and certain other chemicals containing chlorine or bromine, versus CO2 and other greenhouse gases. And they have different effects: more intense UV radiation reaching the Earth's surface, harming health and ecosystems, versus changes in climate and weather worldwide. Although there are important differences between the two issues, many aspects of how nations responded to ozone provide useful analogies or lessons for how to respond to global climate change. Consequently, we will refer to specific relevant aspects of the ozone issue at several points throughout this book.