In wake of latest climate report, calls mount for global response

On Thursday, however, the House Committee on Science and Technology is set to hold Capitol Hill's first formal hearings on the report. Some analysts suggest that the evidence in the IPCC report could make it difficult for Mr. Bush to justify a veto if any bills come to his desk before his term ends.

Among the report's projections:

• Temperatures are "likely" to rise 2 degrees to 4.5 degrees Celsius by the end of the century, if CO2 concentrations reach twice their preindustrial level. Within that range, the most likely result is 3 degrees C (5.4 degrees Fahrenheit). That additional warmth will distribute itself unevenly, with the highest increases in the Arctic and progressively smaller increases farther south.

• Sea levels could rise by century's end from 28 to 58 centimeters (11 to 23 inches) above 1999 levels globally. That's a narrower range than the IPCC offered in 2001, when it projected a range of 9 to 88 centimeters. Even if CO2 concentrations could be stabilized at twice preindustrial levels by 2100, thermal expansion of the oceans alone could raise sea levels an additional 1 to 3 feet by 2300. But recent research also suggests that the Greenland ice sheet is losing mass faster than expected, leaving open the possibility that sea-level increases will be higher if the melting trend continues to accelerate. If Greenland's ice cap continues to lose mass over the next 1,000 years, the entire ice cap would vanish, raising sea levels by some 23 feet.

Overall, because carbon dioxide remains in the atmosphere for hundreds of years and a substantial part of the heating is "banked" in the oceans, the report holds that between past and future CO2 emissions, the climate will warm and sea level will rise for more than 1,000 years.

Policymakers face several challenges in trying to deal with the issue, beyond its longer-than-an-election-cycle time frame. The first is its sheer magnitude. Many climate scientists agree that emissions already are on track to double by century's end, perhaps sooner.

Under a "business as usual" approach, which in part assumes today's rate of innovation, the world would have to slash emissions by 70 to 80 percent this century to reach an often-talked-about CO2 concentration target of 450 parts per million by 2100. Over the long term, stabilizing CO2 concentrations in the atmosphere means reducing emissions close to zero.

While current legislative efforts at the state and local level represent a start, they merely "sandpaper the edge off of a catastrophe," Dr. Mahlman says.

A crucial step forward would be to agree on a clear target for stabilizing CO2 concentrations, notes Gerald Stokes, a vice president with Battelle Memorial Laboratories and a former chief scientist for the US Department of Energy's Atmospheric Radiation Measurement program.

Setting emissions targets isn't enough, he says. With a firm target that means something from the atmosphere's perspective, policymakers are in a better position to determine the technological path countries will need to follow, as well as put a firm economic value on carbon dioxide so the costs and benefits of mitigation – and of delay – can be more accurately assessed.

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