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It's not another ice age, but at least it's cooler

As countries gear up for battles over ratifying the 1997 Kyoto Protocol, a recent study suggests that the world already has stepped along the path to a future cooler than it might have been.

Researchers at NASA's Goddard Institute for Space Studies (GISS) in New York report that declining greenhouse-gas emissions since the late 1980s have slowed the growth rate of the atmosphere's ability to retain heat.

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The researchers link the slower rate to implementation of the 1987 Montreal Protocol, in which countries agreed to phase out production of gases that erode the Earth's protective ozone layer. Known collectively as chlorofluorocarbons, these gases also trap heat thousands of times as effectively as carbon dioxide - the main focus of Kyoto.

If the rate of increase in greenhouse gases had been maintained at the peak reached in 1980, the climate by 2050 would have reached temperatures not currently anticipated until 2100, when CO 2 concentrations in the atmosphere are expected to have doubled, the researchers calculate.

The slowdown also "is due in part to the slower growth of methane and carbon dioxide, for reasons that aren't well understood and need more study," notes James Hansen, the NASA researcher who conducted the study with Makiko Sato, also with the GISS. The slower growth in carbon-dioxide concentrations could be due to increased CO 2 uptake by land-based plants and marine organisms, he suggests.

The work grows out of a longer-term effort by the two scientists to explore paths to adjusting the globe's thermostat other than the politically charged effort embodied in the Kyoto Protocol. By focusing on carbon dioxide, the pact sets its sights on curbing the greenhouse gas held most responsible for contributing to the climate's warming during the past century. But curbs on CO 2 mean curbs on burning coal, oil, and natural gas - the fuels of booming economies.

Drs. Hansen and Sato argue that policymakers can make significant headway by attacking other pollutants such as black carbon soot, ozone (smog) in the lower atmosphere, and methane from landfills, mining, and oil and gas production. The duo calculates that by reducing methane emissions by 30 percent, for example, the effect on climate would be comparable to the effect from cuts in CO 2 envisioned by the Kyoto Protocol during its first commitment period, which runs from 2008 to 2012. Their study appeared in the Dec. 18, 2001, issue of the Proceedings of the National Academy of Science.