-1-Economists’ Voice www.bepress.com/ev July, 2007© The Berkeley Electronic PressFirst the uncertainties; then the cer-tainties; then the urgencies; and fi-nally, what do uncertainties imply about waiting for their resolution before acting.The uncertainties are many and great. How much carbon dioxide may join the atmosphere if nothing is done about it? That depends on projections of population, economic growth, energy technology, and possible feedbacks from warming that reduce albedo—ice and snow cover, for example.Next, how much average warming globally is to be expected from some specified increase in the concentration of carbon dioxide and other “greenhouse” gases? For a quarter century the range of uncertainty has been about a factor of three. (As more becomes known, more uncer-tainties emerge. Clouds and oceans are active participants in ways unappreciated two decades ago.)How will the average warming translate into changing climates everywhere: precipitation, evaporation, sunlight and cloud cover, tempera-ture and humidity (daytime/nighttime, summer/winter) over oceans and plains and mountains, the frequency and severity of storms, of protract-ed droughts? Will rain replace snow in moun-tains, and melting of snow cover occur before irrigation can benefit?What will be the impacts of such changes in climate on productivity, especially in agricul-ture, fisheries, and forests, and on comfort and health? Both the vectors and the pathogens of disease, especially in the tropics, will be affect-ed, almost certainly for the worst. (Here produc-tivity enters again: will malaria, river blindness, etc., have been overcome by advances in public health technology?) What will happen to eco-logical systems, to vulnerable species?How well can people, businesses, govern-ments, and communities adapt to the climate changes, especially in countries heavily depen-dent on food production, in countries with poor educational and technological attainment, poor fiscal or legal systems? And of course, what are the likely costs of various mitigation strategies, mainly shifting to Winner of the 2005 Nobel Prize in Economics, Thomas C. Schelling has published widely on military strategy and arms control, energy and environmental policy, climate change, nuclear proliferation, terrorism, organized crime, foreign aid and international trade, conflict and bargaining theory, racial segregation and integration, the military draft, health policy, tobacco and drugs policy, and ethical issues in public policy and in business.Climate Change: The Uncertainties, the Certainties, and What They Imply About ActionThomAs C. sChEllIng-2-Economists’ Voice www.bepress.com/ev July, 2007renewable energy sources and conserving ener-gy, with technologies mostly not yet ready?Finally, what will the world be like in 50, 75, or 100 years when climate change may become acute? Think back seventy-five years: what was the world like, compared with now? Will the world be as different from now in seventy-five years as it is now from seventy-five years ago? How would we, seventy-five years ago, have predicted the consequences of climate change in today’s world, and who are “we” who might have predicted those consequences? The uncertainties are immense, and I’ll draw some conclusions shortly. But what are the cer-tainties?It has been known for a century that the planet Venus is so bathed in “greenhouse gases” that its surface temperature, hundreds of degrees above Earth’s, does not allow water to exist in liq-uid form, and that Mars is so deficient in green-house gases that its temperature is too cold to allow water to exist in liquid form on its surface. Earth has been blessed with such a concentration of gases in the atmosphere that we have a climate consistent with liquid water and terrestrial life.It has been known for a century that if a glassed chamber of carbon dioxide is subjected to infrared radiation—the radiation by which earth’s heat, perpetually renewed by sunlight, is returned to space to keep our temperature even—the energy output is less than the energy input in direct proportion to the rise in tempera-ture of the gas in the chamber. The greenhouse “theory,” as it is sometimes disparagingly referred to, is established beyond responsible doubt.So the basics of global warming are not in scientific dispute. There is serious uncertainty about the quantitative parameters, and there can be doubt whether the experienced warming of recent decades is entirely due to the “green-house effect,” there being other conjectured pos-sible solar influences. But the “theory” is not in doubt. (Incidentally, actual greenhouses don’t work by the “greenhouse effect,” but it is too late to change the terminology.)If we know that the earth is ineluctably warming, with possible drastic effects on cli-mates around the world, but not how fast or how far, what are the most urgent things to do about it? One, of course, is to keep studying the phenomena; huge advances in understanding of the climate phenomena and their ecological impact are occurring. It is a happy coincidence that concern for climate-affected greenhouse gases arose just as earth-reconnaissance satel-lites became available to study glaciers, forests, sea level, atmospheric and ocean temperatures, snow and ice albedo, sunlight-reflecting aero-sols of sulfur, cloud reflectance, and all manner of things we need to understand.Under “urgencies,” I put energy research and development, especially government spon-sored research and development (R and D), and most importantly multi-government R and D. We need, urgently, to better understand what al-ternatives to fossil fuels there will be, how much energy can be conserved, how to extract carbon dioxide from the atmosphere, and if necessary how to increase the earth’s albedo, its reflectance of incoming sunlight.There are two important ways to induce or provide the necessary research and development. One is to use the price system, the “market,” let-ting private initiative finance and direct the work, through appropriate taxes, subsidies, rationing, and—most important—through convincing the private sector, firms and consumers, that fossil fu-els are going to become
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