In order to arrive at an effective policy we can project two different scenarios concerning climate change. In the business-as-usual scenario, annual emissions of CO2 continue to increase at the current rate for at least fifty years, as do non-CO2 warming agents including methane, ozone, and black soot. In the alternative scenario, CO2 emissions level off this decade, slowly decline for a few decades, and by mid-century decrease rapidly, aided by new technologies.
The business-as-usual scenario yields an increase of about five degrees Fahrenheit of global warming during this century, while the alternative scenario yields an increase of less than two degrees Fahrenheit during the same period. ...
The business-as-usual scenario, with five degrees Fahrenheit global warming and ten degrees Fahrenheit at the ice sheets, certainly would cause the disintegration of ice sheets. The only question is when the collapse of these sheets would begin. The business-as-usual scenario, which could lead to an eventual sea level rise of eighty feet, with twenty feet or more per century, could produce global chaos, leaving fewer resources with which to mitigate the change in climate. The alternative scenario, with global warming under two degrees Fahrenheit, still produces a significant rise in the sea level, but its slower rate, probably less than a few feet per century, would allow time to develop strategies that would adapt to, and mitigate, the rise in the sea level.
The alternative scenario I have been referring to has been designed to be consistent with the Kyoto Protocol, i.e., with a world in which emissions from developed countries would decrease slowly early in this century and the developing countries would get help to adopt "clean" energy technologies that would limit the growth of their emissions. Delays in that approach—especially US refusal both to participate in Kyoto and to improve vehicle and power plant efficiencies—and the rapid growth in the use of dirty technologies have resulted in an increase of 2 percent per year in global CO2 emissions during the past ten years. If such growth continues for another decade, emissions in 2015 will be 35 percent greater than they were in 2000, making it impractical to achieve results close to the alternative scenario.
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