Blowing Hot and ColdA. Climate change may be slow and uncertain, but that is no excuse for inaction. One reason why uncertainty over climate change looks to be with us for a long time is that the oceans, which absorb carbon from the atmosphere, act as a time-delay mechanism. Their massive thermal inertia means that the climate system responds only very slowly to changes in the composition of the atmosphere. Another complication arises from the relationship between carbon dioxide (CO2), the principal greenhouse gas (GHG), and sulphur dioxide (SO2), and a common pollutant. Efforts to reduce man-made emissions of GHGs by cutting down on fossil-fuel use will reduce emissions of both the gases. The reduction in CO2will cut warming, but the concurrent SO2cut may mask that effect by contributing to the warming.B. There are so many such fuzzy factors—ranging from aerosol particles to clouds to cosmic radiation—that we are likely to see disruptions of familiar climate patterns for many years without knowing why they are happening or what to do about them. Tom Wigley, a leading climate scientist and member of the UN"s Intergovernmental Panel on Climate Change (IPCC), goes further. He argues in an excellent book published by the Aspen Institute, "US Policies on Climate Change: What Next", that whatever policy changes governments pursue, scientific uncertainties will "make it difficult to detect the effects of such changes, probably for many decades."C. As evidence, he points to the negligible short-to medium-term difference in temperature resulting from an array of emission "pathways" on which the world could choose to embark if it decided to tackle climate change. He plots various strategies for reducing GHGs that will lead in the next century to the stabilization of atmospheric concentrations of CO2at 550 parts per million (ppm). That is roughly double the level which prevailed in preindustrial times, and is often suggested by climate scientists as a reasonable target. But even by 2040, the temperature differences between the various options will still be tiny—and certainly within the magnitude of natural climatic variance. In short, in another four decades we will probably still not know if we have over-or under-shot.D. However, that does not mean we know nothing. We do know, for a start, that the "greenhouse effect" is real: without the heat-trapping effect of water vapor, CO2, methane and other naturally occurring GHGs, our planet would be a lifeless 30℃ or so colder. Some of these GHG emissions are captured and stored by "sinks", such as the oceans, forests and agricultural land, as part of nature"s carbon cycle.E. We also know that since the industrial revolution began, mankind"s actions have contributed significantly to that greenhouse effect. Atmospheric concentrations of GHGs have risen from around 280ppm two centuries ago to around 370ppm today, thanks chiefly to mankind"s use of fossil fuels and, to a lesser degree, to deforestation and other land-use changes. Both surface temperatures and sea levels have been rising for some time.F. There are good reasons to think temperatures will continue rising. The IPCC has estimated a likely range for that increase of 1.4℃-5.8℃ over the next century, although the lower end of that range is more likely. Since what matters is not just the absolute temperature level but the rate of change as well, it makes sense to try to slow down the increase.G. The worry is that a rapid rise in temperatures would lead to climate changes that could be devastating for many (though not all) parts of the world. Central America, most of Africa, much of south Asia and northern China could all be hit by droughts, storms and floods and otherwise made miserable.H. The colder parts of the world may benefit from warming, but they too face danger. One is the conceivable collapse of the Atlantic "conveyor belt", a system of currents that gives much of Europe its relatively mild climate; if temperatures climb too high, say scientists, the system may undergo radical changes that damage both Europe and America. That points to the biggest fear: warming may trigger irreversible changes that transform the earth into a largely uninhabitable environment.I. Given that possibility, extremely remote though it is, it is no comfort to know that any attempts to stabilize atmospheric concentrations of GHGs at a particular level will take a very long time. Because of the oceans" thermal inertia, explains Mr. Wigley, even once atmospheric concentrations of GHGs are stabilized, it will take decades or centuries for the climate to follow suit. And even then the sea level will continue to rise. This is a vast challenge, and it is worth bearing in mind that mankind"s contribution to warming is the only factor that can be controlled. So the sooner we start drawing up a long-term strategy for climate change, the better.J. That is why the long-term objective for climate policy must be a transition to a low-carbon energy system. Such a transition can be very gradual and need not necessarily lead to a world powered only by bicycles and windmills, for two reasons that are often overlooked.K. One involves the precise form in which the carbon in the ground is distributed. According to Michael Grubb of the Carbon Trust, a British quasi-governmental body, the long-term problem is coal. In theory, we can burn all of the conventional oil and natural gas in the ground and still meet the most ambitious goals for tackling climate change. If we do that, we must ensure that the far greater amounts of carbon trapped as coal (and unconventional resources like tar sands) never enter the atmosphere. The other reason, as scientists took care to point out, is that it is net emissions of CO2that need to peak and decline. That leaves scope for the continued use of fossil fuels as the main source of modern energy if only some magical way can be found to capture and dispose of the associated CO2. Happily, scientists already have some magic in the works.L. Two decades ago, the world faced a similar dilemma: evidence of a hole in the ozone layer. Some inconclusive signs suggested that it was man-made, caused by the use of chlorofluorocarbons (CFCs). There was the distant threat of disaster, and the knowledge that a concerted global response was required. Industry was reluctant at first, yet with leadership from Britain and America the Montreal Protocol was signed in 1987. That deal has proved surprisingly successful. The manufacture of CFCs is nearly phased out, and there are already signs that the ozone layer is on the way to recovery.M. This story holds several lessons for the admittedly far more complex climate problem. First, it is the rich world which has caused the problem and which must lead the way in solving it. Second, the poor world must agree to help, but is right to insist on being given time—as well as money and technology—to help it adjust. Third, industry holds the key: in the ozone-depletion story, it was only after DuPont and ICI broke ranks with the rest of the CFC manufacturers that a deal became possible.N. The final lesson is the most important: that the uncertainty surrounding a threat such as climate change is no excuse for inaction. New scientific evidence shows that the threat from ozone depletion had been much deadlier than was thought at the time when the world decided to act.
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