News and CommentClimate Change

Thirty Kyotos Needed to Control Warming

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Science  19 Dec 1997:
Vol. 278, Issue 5346, pp. 2048
DOI: 10.1126/science.278.5346.2048

When exhausted delegates emerged from round-the-clock negotiations in Kyoto, Japan, last week with a global agreement to curb emissions of heat-trapping gases, some observers hailed the deal as a diplomatic miracle. Climate scientists say, however, that it will be miraculous indeed if the Kyoto pact—which calls for 38 industrialized nations to cut their emissions by an average of 5.2% from 1990 levels by 2012—even temporarily slows the accumulation of warming gases in the atmosphere. The cuts are too small and are likely to be overwhelmed by developing nations, they say. “It is a laudable and reasonable first step,” says Jorge Sarmiento of Princeton University, “but much deeper emissions cuts will be needed in the not too distant future if we are going to meaningfully reduce the rate of warming.”

If approved by major industrialized nations such as the United States and Japan—and that is far from certain—the new Kyoto Protocol to the 1992 Climate Change Treaty could reduce emissions of six greenhouse gases, including carbon dioxide, methane, and nitrous oxide. The United States—the world's leader in greenhouse emissions, with 25% of the total—agreed to a 7% cut from 1990 levels by 2012, while the 15 nations of the European Union committed themselves to an 8% reduction and Japan to 6%. If the cuts are achieved, industrialized nations will reduce their collective greenhouse emissions to two-thirds of what they would be in 2012 without action, according to the United Nations.

Even this significant reduction, however, won't prevent total global greenhouse emissions from rising, analysts predict. The cuts will be swamped early in the next century by increases in emissions from developing nations, such as China and India, which successfully resisted being bound by the protocol. For example, China, currently in second place, is expected to overtake the United States as the world's leading emitter of carbon dioxide within decades, as it burns more of its massive coal reserves. From 1990 to 2015, the U.S. Energy Information Administration predicts, carbon dioxide emissions from developing countries—including Russia and Eastern European nations—will nearly double, and will account for 58% of the global total even if industrial countries do not cut back.

At that rate, the 1992 treaty will not achieve its major objective—stabilizing atmospheric concentrations of carbon dioxide—says Tom Wigley, a climate researcher at the National Center for Atmospheric Research in Boulder, Colorado. Currently, carbon dioxide levels stand at about 360 parts per million (ppm), up from preindustrial levels of 280 ppm. Computerized climate models created by Wigley and others suggest that concentrations will at least double by 2100 unless developing nations hold their emissions steady and industrial nations progressively reduce emissions.

“A short-term target and timetable, like that adopted at Kyoto, avoids the issue of stabilizing concentrations entirely,” Wigley says. As a result, it will at best delay the predicted warming trend by just a few decades. Jerry Mahlman, director of the Geophysical Fluid Dynamics Laboratory at Princeton, adds that “it might take another 30 Kyotos over the next century” to cut global warming down to size.

Still, says Sarmiento, “you have to start somewhere, and the protocol at least provides a framework for revisiting the issue as our understanding improves.”


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