Global Warming: A Threat to Mankind
Global warming refers to increasing temperatures and consequent climate changes worldwide. Scientists believe the earth may be warming up because heat-trapping gases are building up in the atmosphere, disturbing a natural process that maintains the world’s climates. This process, called the greenhouse effect, works just as its name suggests. Gases naturally present in the earth’s lower atmosphere act like the glass in a greenhouse, allowing the sun’s radiation in and trapping the heat that would otherwise escape back into space. This natural balancing act between incoming and outgoing radiation keeps the earth from either icing up or overheating. Now human activities are upsetting the balance by dumping heat-trapping gases into the air. Excess carbon dioxide, chlorofluorocarbons, nitrous oxide, methane and possibly ozone appear to be causing a gradual increase in global temperatures. (Agrawala, 1999)
The Human Factor
Carbon dioxide is a natural greenhouse gas, a plentiful by-product of respiration and plant decay. But carbon dioxide is also given off when we burn fossil fuels to power our cars and heat our homes. Burning forests to make farmland adds still more carbon dioxide–from the fire itself, and from the loss of trees and vegetation that would otherwise be removing carbon dioxide from the air. In the last century, these human activities have caused a 25 percent increase in carbon dioxide concentrations in the air worldwide. If current trends continue, scientists predict that the amount of carbon dioxide will double by the year 2050, leading to an overall warming of between 1.5 and 4.5 degrees centigrade. That could be enough to melt polar icecaps, flooding the world’s coastal areas. Warming would affect global rainfall patterns and cause major shifts in desert and fertile regions.
Carbon dioxide, however, is not the only natural greenhouse gas whose concentrations are increasing because of human activities. Methane, ozone and nitrous oxides are also building up above natural levels. Methane gas is emitted during such activities as rice cultivation and animal husbandry. Methane is also a by-product of landfills, coal seams, natural gas exploration and the burning associated with deforestation. Nitrous oxides. found only occasionally in nature are being added in vast quantities to the earth’s atmosphere as we burn fossil fuels. Ozone, whose importance as a worldwide greenhouse gas is still being debated. is created when sunlight shines through air polluted with auto and industrial emissions. (Anderson, 2003)
Chlorofluorocarbons (CFCs) are the only greenhouse gases that are not found in nature. First manufactured in the 1930s, this group of chemicals has been widely used since in refrigerators and air conditioners and as propellants in aerosol cans (the U.S. banned CFC use in aerosol cans in 1978). Although less plentiful in the air than the other greenhouse gases, CFCs are 25,000 times more efficient at trapping heat and are so stable that they can stay in the air for up to 100 years.
Ethics and Global Warming
Potential confusion about the climate change problem begins even with the terms used to describe it: from ‘greenhouse effect’ to ‘global warming’ to the more recently favored ‘climate change’. To begin with, many people spoke of ‘the greenhouse effect’. This refers to the basic physical mechanism behind projected changes in the climate system.( Alley 2000) Some atmospheric gases (called ‘greenhouse gases’ [GHG]) have asymmetric interactions with radiation of different frequencies: just like glass in a conventional greenhouse, they allow shortwave incoming solar radiation through but reflect some of the Earth’s outgoing long-wave radiation back to the surface. This creates “a partial blanketing effect,” which causes the temperature at the surface to be higher than would otherwise be the case (Houghton 1997, pp. 11–12). Humans are increasing the atmospheric concentrations of these gases through industrialization. This would, other things being equal, be expected to result in an overall warming effect.
The basic greenhouse mechanism is both well understood and uncontroversial. Still, the term ‘greenhouse effect’ remains unsatisfactory to describe the problem at hand. There are two reasons. First, there is a purely natural greenhouse effect, without which the earth would be much colder than it is now. Hence, it is not accurate to say that “the greenhouse effect” as such is a problem; in fact, the reverse is true: without some greenhouse effect, the Earth would be much less hospitable for life as we know it. The real problem is the enhanced, human-induced, greenhouse effect. Second, it is not the greenhouse effect in isolation which causes the climate problem. Whether an increase in the concentration of greenhouse gases does in fact cause the warming we would otherwise expect depends on how the immediate effects of an increase in low frequency radiation play out in the overall climate system. But that system is complex, and its details are not very well understood.
For a while, then, the term ‘global warming’ was favored. This term captures the point that it is the effects of increased levels of greenhouse gases which are of concern. However, it also has its limitations. In particular, it highlights a specific effect, higher temperatures, and thus suggests a one-dimensional problem. But while it is true that rising temperature has been a locus for concern about increasing human emissions of greenhouse gases, it is not true that temperature as such defines either the core problem or even (arguably) its most important aspects. Consider, for example, the following.
First, a higher global temperature does not in itself constitute the most important impact of climate change. Indeed, considered in isolation, there might be no particular reason to prefer the world as it is now to one several degrees warmer. However, second, this thought is liable to be misleading. For presumably if one is imagining a warmer world and thinking that it may be appealing, one is envisioning the planet as it might be in a stable, equilibrium state at the higher level, where humans, animals, and plants have harmoniously adapted to higher temperatures. But the problem posed by current human behavior is not of this kind. The primary concern of many scientists is that an enhanced greenhouse effect puts extra energy into the earth’s climate system and so creates an imbalance. Hence, most of the concern about present climate change has been brought about because it seems that change is occurring at an unprecedented rate, that any equilibrium position is likely to be thousands, perhaps tens or hundreds of thousands, of years off, and that existing species are unlikely to be able to adapt quickly and easily under such conditions. Third, though it is at present unlikely, it is still possible that temperature might go down as a result of the increase in atmospheric greenhouse gas concentrations. But this does not cast any doubt on the serious nature of the problem. This is partly because a rapid and unprecedented lowering of temperature would have similar kinds of adverse effects on human and nonhuman life and health as a rapid warming, and partly because the effects most likely to cause cooling (such as a shutdown of the thermohaline circulation [THC] which supports the Gulf
Stream current to Northern Europe) may well be catastrophic even in relation to the other projected effects of global warming.
For all these reasons, current discussion tends to be carried out under the heading ‘climate change’. This term captures the fact that it is interference in the climate system itself which is the crucial issue, not what the particular effects of that interference turn out to be. The fundamental problem is that it is now possible for humans to alter the underlying dynamics of the planet’s climate and so the basic life-support system both for themselves and all other forms of life on Earth. Whether the alteration of these dynamics is most conveniently tracked in terms of increasing, declining, or even stable temperatures is of subsidiary interest in comparison to the actual changes in the climate itself and their consequences for human, and nonhuman, life. (Michaels and Balling 2000)
What do we know about climate change? In 1988, the Intergovernmental Panel on Climate Change (IPCC) was jointly established by the World Meteorological Association and the United Nations Environment Pro- gram to provide member governments with state of the art assessments of “the science, the impacts, and the economics of—and the options for mitigating and/or adapting to—climate change” (IPCC 2001c, p. vii). (Lomborg 2001) The IPCC has, accordingly, submitted three comprehensive reports, in 1990, 1995, and 2001. The results have remained fairly consistent across all three reports, though the level of confidence in those results has increased.
The Ocean Conveyor has been called the climate’s “Achilles Heel” (Broecker 1997), because it appears to be a major threshold phenomenon. There are two grounds for concern. First, there is strong evidence that in the past the conveyor has slowed, and slowed very quickly, with significant climatic consequences. One such event, 12,700 years ago, saw a drop in temperatures in the North Atlantic region of around 5 degrees Celsius in a single decade. This apparently caused icebergs to spread as far south as the coast of Portugal and has been linked to widespread global drought. Second, the operation of the conveyor is governed by factors that can be affected by climate change. In particular, the world’s currents are driven by the sinking of a large volume of salty water in the North Atlantic region. But this process can be disrupted by an influx of fresh water, which both dilutes the salty water and can also create a lid over it, restricting heat flow to the atmosphere. ((Dickson et al. 2002)
The possibility of dramatic climate shifts of this sort complicates the picture of a global warming world in several ways. First, it suggests that gradual warming at the global level could cause, and coexist with, dramatic cooling in some regions. (Among other things, this has serious ramifications for our ability to plan for future changes.) Second, it envisages that the major losers from climate change may not be the usual suspects, the less developed countries (LDCs).
Scientists aren’t any time soon going to give politicians some magic answer. Policy makers for a long, long time are going to have to deal with a situation where it’s not clear what the costs and benefits are, where lots of people disagree about them, and they can’t wait until everything is resolved. (Robert J. Lampert) (Revkin 2001b) Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly. Therefore, you need to continue to make the lack of scientific certainty a primary issue. (Frank Luntz, in Lee 2003) It is sometimes argued that the uncertainty of the scientist’s predictions is a reason for not acting at present, and that we should wait until some further research has been concluded. This argument is poor economics. (Broome 1992, p. 17)
Politically, the most common objection raised to action on climate change is that of scientific uncertainty. (Traxler 2002) The first thing to note is that, at least in economics, uncertainty is a technical term, to be distinguished from risk. In the technical sense, a risk involves a known, or reliably estimable, probability, whereas an uncertainty arises when such probabilities are not available. So to say that there is scientific uncertainty surrounding global warming is to claim that we do not know, and cannot reliably estimate, the probability that climate change will occur, nor its extent if it does occur.
This distinction is useful; because the first problem with the objection from scientific uncertainty is that the IPCC does not seem to view global warming as uncertain in the technical sense. As we have seen, the 2001 Scientific Assessment explicitly assigns probabilities to its main climate predictions, making the situation one of risk, rather than uncertainty. Furthermore, these probabilities are of considerable magnitude. (For example, the IPCC says that it is “very likely” that in the twenty-first century there will be “higher maximum temperatures and more hot days over nearly all land areas” [IPCC 2001c, p. 162], by which they mean a probability of 90–99 percent [IPCC 2001c, p. 152, n. 7].) Given that many of the effects assigned high probabilities are associated with significant costs, they would seem to justify some kinds of action. But perhaps the idea is that the IPCC’s probability statements are not reliable, so that we should ignore them, (Reilly et al. 2001) treat the situation as genuinely uncertain, and hence refuse to act. Still, there is a difficulty. For, to an important extent, some kind of uncertainty “is an inherent part of the problem” (Broome 1992, p. 18). Arguably, if we knew exactly what was going to happen, to whom, and whose emissions would cause it, the problem might be more easily addressed; (Dimitrov 2003) at the very least, it would have a very different shape. Hence, to refuse to act because of uncertainty is either to refuse to accept the global warming problem as it is (insisting that it be turned into a more respectable form of problem before one will address it) or else to endorse the principle that to “do nothing” is the appropriate response to uncertainty. The former is a head-in-the-sand approach and clearly unacceptable, but the latter is also dubious and does not fit our usual practice.
The third, and perhaps most crucial, point to make about the problem of uncertainty is that it is important not to overplay it. For one thing, many decisions we have to make in life, including many important decisions, are also subject to considerable uncertainties.
Now it seems clear that uncertainty in the first kind of case is worse than uncertainty in the second, and potentially more paralyzing. Furthermore, and this is the crucial point, it seems reasonably clear that scientific uncertainty about global warming is of the second kind. As Donald Brown argues: “A lot of climate change science has never been in question, . . . many of the elements of global warming are not seriously challenged even by the scientific skeptics, and . . . the issues of scientific certainty most discussed by climate skeptics usually deal with the magnitude and timing of climate change, not with whether global warming is a real threat” (Brown 2002, p. 102). To see this, let us briefly examine a number of sources of uncertainty about global warming.
The first concerns the direct empirical evidence for anthropogenic warming itself. This has two main aspects. First, systematic global temperature records, based on measurements of air temperature on land and surface-water temperature measurements at sea, exist only from 1860, and satellite-based measurements are available only from 1979. The direct evidence for recent warming comes from the former. But skeptics suggest that the satellite measurements do not match the surface readings and do not provide evidence for warming. ( Santer et al. 2003)
Second, there is no well-defined baseline from which to measure change. ( Jamieson 1991)
While it is true that the last couple of decades have been the warmest in human history, it is also true that the long-term climate record displays significant short-term variability and that, even accounting for this, climate seems to have been remarkably stable since the end of the last Ice Age 10,000 years ago, as compared with the preceding 100,000 years. ( Houghton 1997) Hence, global temperatures have fluctuated considerably over the long term record, and it is clear that these fluctuations have been naturally caused.
The skeptics are right, then, when they assert that the observational temperature record is a weak data set and that the long-term history of the climate is such that even if the data were more robust, we would be rash to conclude that humans are causing it solely on this basis. Still, it would be a mistake to infer too much from the truth of these claims. For it would be equally rash to dismiss the possibility of warming on these grounds. For, even though it might be true that the empirical evidence is consistent with there being no anthropogenic warming, it is also true that it provides just the kind of record we would expect if there were a real global warming problem.
This paradox is caused by the fact that our epistemological position with respect to climate change is intrinsically very difficult: it may simply be impossible to confirm climate change empirically from this position. This is because our basic situation may be a bit like that of a coach who is asked whether the current performance of a fifteen-year-old athlete shows that she will reach the highest level of her sport. Suppose the coach has the best evidence that she can have. It will still only be evidence for a fifteen-year-old. It will be at most consistent with reaching the highest level. It cannot be taken as a certain prediction. But that does not mean it is no prediction at all, or worthless. It is simply the best prediction she is currently in a position to make.
Fortunately, for the climate change problem, the concern with the empirical record is not the end of the matter. For the temperature record is far from our only evidence for warming. Instead, we also have strong theoretical grounds for concern. First, the basic physical and chemical mechanisms which give rise to a potential global warming effect are well understood. In particular, there is no scientific controversy over the claims (a) that in itself a higher concentration of greenhouse gas molecules in the upper atmosphere would cause more heat to be retained by the earth and less radiated out into the solar system, so that other things being equal, such an increase would cause global temperatures to rise; and (b) that human activities since the industrial revolution have significantly increased the atmospheric concentration of greenhouse gases. Hence, everyone agrees that the basic circumstances are such that a greenhouse effect is to be expected. (Gardiner 2004b)
Second, the scientific dispute, insofar as there is one, concerns the high level of complexity of the global climate system, given which there are the other mechanisms that might be in play to moderate such an effect. The contentious issue here is whether there might be negative feedbacks that either sharply reduce or negate the effects of higher levels of greenhouse gases, or even reduce the amount of them present in the atmosphere. However, current climate models suggest that most related factors will likely exhibit positive feedbacks (water vapor, snow, and ice), (United Nations
Environment Program 1999) while others have both positive and negative feedbacks whose net effect is unclear (e.g., clouds, ocean currents). Hence, there is genuine scientific uncertainty. But this does not by itself justify a skeptical position about action on climate change. For there may be no more reason to assume that we will be saved by unexpectedly large negative feedbacks than that the warming effect will be much worse than we would otherwise anticipate, due to unexpectedly large positive feedbacks.
This is the basic scientific situation. However, three further aspects of uncertainty are worth mentioning. First, the conclusions about feedback are also open to doubt because considerable uncertainties remain about the performance of the models. In particular, they are not completely reliable against past data. This is to be expected because the climate is a highly complex system which is not very well understood. Still, it clouds the overall picture. Second, as mentioned earlier, the current models tend to assume that atmospheric feedbacks scale linearly with surface warming, and they do not adequately account for possible threshold effects, such as the possible collapse of the West Antarctic Ice Sheet. Hence, they may underestimate the potential risks from global warming. Finally, there is a great deal of uncertainty about the distribution of climate change. Though global rises may seem small, they disguise considerable variation within years and across regions. Furthermore, though it is very difficult to predict which regions will suffer most, and in what ways, such evidence as there is suggests that, at least in the medium term, the impact will be heaviest in the tropical and subtropical regions (where most of the LDCs are), and lighter in the temperate regions (where most of the richer countries are).
In conclusion, there are substantial uncertainties surrounding both the direct empirical evidence for warming and our theoretical understanding of the overall climate system. But these uncertainties cut both ways. In particular, while it is certainly conceivable (though, at present, unlikely) that the climate change problem will turn out to be chimerical, it is also possible that global warming will turn out to be much worse than anyone has yet anticipated. More importantly, the really vital issue does not concern the presence of scientific uncertainty, but rather how we decide what to do under such circumstances.
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