By Bobby Marsland ‘11
The past few months have seen a whirlwind of activity and controversy on the climate change front. In November, journalists[CC1] hacked into the email accounts of prominent climate scientists at the University of East Anglia in Britain, finding messages discussing different ways to hide features in the data that disagreed with the hypothesis of man-made climate change. This generated the international scandal now known as “Climategate,” which led some conservative commentators like Rush Limbaugh to conclude that the whole climate change issue had been a hoax from the very beginning. In December, however, the world leaders convened in Copenhagen[CC2] appeared completely unmoved by this development, as they proceeded to operate under the assumption that climate change was a scientifically certain and imminent threat and attempted (unsuccessfully) to reach a global consensus on plans for immediate action.
These events have further polarized what was already a point of bitter contention in American politics. On the one extreme are politicians and voters who put complete faith in the scientists who prophesy climate doom, and who tend to dominate the mainstream of political life, while on the other are the “fringe” elements who use “Climategate” as an excuse to doubt the honesty of all climate scientists and ignore them altogether. These extreme positions attract the most attention in the media and the blogosphere, yet neither of them makes any effort to get at the real science behind the issue. While a detailed scientific description of all the factors that contribute to global warming is beyond the reach of the ordinary politician or voter, a basic understanding of the problem is quite accessible, and is an essential prerequisite for a reasonable debate about the proper political attitude toward climate change.
Despite the Earth’s continuous heating from sunlight, it remains at a relatively constant average temperature due to the simultaneous release of heat to space via infrared radiation. Most objects on Earth and most atmospheric gases emit infrared radiation, with the amount of heat lost through radiation varying with the temperature of the source. This is clear to anyone who has looked through infrared goggles – living animals, car exhaust, and poorly insulated houses all look brighter than the surrounding environment because their temperatures are warmer. The simplest way of thinking about the Earth’s average temperature is to picture it getting warmer and warmer from the sun’s light, until it finally is warm enough to lose the same amount of heat per second through infrared radiation that it receives from the sun.
To understand the “greenhouse effect,” it is necessary to note that the radiation is not all emitted from a single surface at a single temperature, but rather it is emitted from every layer of the atmosphere. Since the temperature of the atmosphere decreases with altitude (until about 10 km), the radiation emitted from higher up is weaker than that emitted from lower down. “Greenhouse gases” are gases in the atmosphere that absorb certain frequencies of infrared radiation and thereby prevent it from travelling too far through the atmosphere. Radiation at frequencies that are affected by greenhouse gases will not escape to outer space unless it is emitted from a high enough altitude, where there are fewer gas molecules to block its escape. Since the radiation emitted from these higher altitudes is weaker, adding greenhouse gases reduces the amount of heat that leaves the Earth. This reduction means that the Earth no longer radiates enough heat to balance the amount it absorbs from the sun, and so it heats up until the radiation intensity returns to its original level.
The size of the reduction in the rate of heat loss that results from changing greenhouse gas concentrations (often referred to as “climate forcing”) has been calculated, and the results are widely accepted. Using these numbers, it is relatively straightforward to estimate the “climate sensitivity,” which is the temperature change that would result if human activity were to generate enough carbon dioxide to raise the concentration to twice the amount it was in 1750 (which could happen in the next decade or so). Professors Richard Lindzen and Yong-Sang Choi of MIT have calculated that this temperature change comes out to only about 1 degree Celsius, if all the other properties of the Earth’s surface and atmosphere are held constant.
This temperature change, however, produces other effects that can amplify or mitigate this baseline calculation. Clouds constitute one of the most important, but also unpredictable, effects. They block almost all the outgoing radiation from the surface and lower atmosphere, and emit weaker radiation at the lower temperature of the cloud top, thereby decreasing the amount of heat leaving Earth and tending to increase the temperature. On the other hand, they reflect much of the sunlight that hits them back into space, decreasing the amount of heat that is absorbed by Earth in the first place. It is difficult to tell which effect dominates, because the strength of the warming effect depends also on the height of the cloud tops, and the specifics of cloud formation are quite complicated.
Due to the magnitude and unpredictability of the climatic consequences of clouds, Lindzen, Choi, and many other scientists are currently focusing much of their research on the effects of surface temperature upon cloud formation. According to many climate models, the total result of clouds and all the other feedback is to amplify strongly the original 1-degree temperature rise. But some scientists, including Princeton Physics Professor William Happer, argue that the models do a poor job representing clouds, and that on average clouds serve to cool the Earth. Based on a preliminary analysis of satellite data on the rate at which heat leaves the Earth, Lindzen and Choi have estimated that this cooling effect is strong enough to reduce the warming due to a doubling of carbon dioxide from 1 degree to 0.5 degrees Celsius.
This summary has been extremely brief and has left out many details; for a more quantitative treatment, check out the link[CC3] in the Tory online edition at www.princetontory.com. Even from this simple account of the science, however, it is possible to see, first of all, that greenhouse gases such as carbon dioxide do indeed form an essential part of the atmospheric warming mechanism, and, second of all, that the complexity of the Earth’s feedback mechanisms make it extremely difficult to predict the impact of a change in greenhouse gas concentrations on global climate. Although many of the most influential climate scientists (such as the members of the Intergovernmental Panel on Climate Change) deny [CC4] the significance of these difficulties, it remains true that no one has yet been able to reach any reliable conclusions as to whether climate feedback effects amplify or diminish carbon dioxide-induced warming.
A proper solution to the issue is therefore much more elusive than either of the extreme positions would allow, for it requires an important decision in the face of uncertainty. On the one hand, it is most likely that the atmosphere’s feedback effects would tend to mitigate the effects of changes in atmospheric composition, thus stabilizing the Earth’s temperature. Most feedback systems in nature operate in such a way as to reduce the impact of small changes; this is what allows natural environment to remain so stable over such lengthy periods. On the other hand, modern technology surely grants us the ability to have an enormous impact on our environment, and therefore demands extreme care in its use. The very possibility of doubling the Earth’s carbon dioxide concentration is astounding, and it would not be surprising if such a major change were to overwhelm the natural stability of the climate.
In the face of this uncertainty, it is tempting to maintain the reduction of carbon dioxide emissions as a top priority, because by the time the science tips the scales conclusively in favor one side or the other, irreversible damage may have already occurred. The reasoning behind the recent invasion of Iraq should serve as a much-needed reminder not to let overwrought speculation scare us into an imprudent course of action, as significant damage can be done by rash action. The time, money, and resources spent on fighting the vague and elusive enemy of climate change detract from our ability to deal with more pressing problems such as the economic crisis and national defense, and any global regulations of carbon dioxide emissions could cause serious damage [CC5] to developing nations. These and other factors must be seriously considered and weighed against the likelihood of severe man-made climate change, and the likely effectiveness of proposed policies must be carefully evaluated.
None of this can happen in the current political and scientific climate, where imminent and catastrophic man-made climate change is generally accepted as an indisputable fact. Our brief outline above has indicated how complicated the question really is, and how much more work is needed to arrive at any definite conclusion. In order to reach a reasonable balance between the costs and benefits of national regulations and international agreements about carbon dioxide emissions, world leaders must take seriously the arguments advanced by those who disagree with the “consensus,” and judge them on their merits as best they can. Only a free and respectful dialogue between both sides of the climate debate can produce genuine solutions, and provide a check against rash action that could be dramatically misguided in these difficult times.