Two and a half years ago, when the Copenhagen conference on global warming was being planned, the rapid melt of sea ice in the summer Arctic convinced many scientists that global warming was advancing far more rapidly than even the gloomiest predictions had asserted. This observation, combined with others—the accelerating disappearance of high-altitude glaciers, the record intensity of both droughts and floods in many parts of the world, the rapid acidification of seawater as emissions of greenhouse gases force oceans to absorb ever-greater quantities of carbon dioxide—caused many to urge quicker and more comprehensive action than in the past.
For instance, some of the authors of the authoritative fourth report on global warming by the Intergovernmental Panel on Climate Change in the winter of 2007 soon announced that the data on which it was based were out of date. Last March they convened a meeting in Denmark that one participant dubbed the “end of the world conference” to review new papers on a wide variety of natural systems, and concluded that “the climate system is already moving beyond the patterns of natural variability within which our society and economy have developed and thrived.” A NASA team headed by James Hansen, one of the world’s foremost climatologists, put a number on this new apprehension: if we wished “to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted,” we would need to reduce the level of CO2 in the atmosphere from its current 390 parts per million to no more than 350, and do it as soon as possible. That figure still exceeds the pre–industrial revolution concentration of 275 parts per million, but Hansen’s team calculated that it might be sufficient to stave off a number of catastrophic changes including the final melt of glaciers, further seawater acidification, and shifts in monsoon and other rain patterns.
Before long, Rajendra Pachauri, the UN’s chief climate scientist, endorsed the goal of reducing carbon levels to 350 parts per million, even though it went far beyond what his IPCC colleagues had concluded just two years earlier. “What is happening, and what is likely to happen, convinces me that the world must be really ambitious and very determined at moving toward a 350 target,” he said.1
Faced with this alarming new data, the long-planned Copenhagen conference in December seemed providentially timed. Originally seen as a venue for modest adjustments of existing policies—a place to update the 1997 Kyoto accords to include more countries and tougher emissions targets—it assumed greater import in many minds, especially once the election of Barack Obama seemed…
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