Research by Dr. James E. Hansen, a principal author of one of the first papers spelling out the links between increasing atmospheric levels of carbon dioxide and rising global temperatures, has concluded that the quickest way to slow warming would be to cut other heat-trapping greenhouse gases first.

The research Global warming in the twenty-first century: An alternative scenario argues that rapid warming in recent decades has been driven mainly by non-CO2 greenhouse gases such as chlorofluorocarbons, methane, and nitrogen oxide, and not by the products of fossil fuel burning, CO2 and aerosols.

The research says that there could even be a decline in the rate of global warming in the next 50 years if a reduction of black carbon and CO2 emissions were matched with lower sources of methane and ozone precursors.

The findings appearing in the most recent publication of the US Proceedings of the National Academy of Sciences, found that the burning of fossil fuels, although substantially raising carbon dioxide levels in the atmosphere, also produces a pall of particle haze that reflects as much of the sun’s energy back into space as the release of carbon dioxide has trapped in the air. This haze is likely to be cleaned up in coming years, removing its cooling sun-blocking effect, says the research.

In the analysis, Dr. Hansen and his colleagues compiled data and scientific papers on topics ranging from rice production, which releases methane, to urban pollution, a source of ozone and sooty particles, to obtain detailed estimates of the rate of change in different greenhouse emissions. Calculations of how different amounts of the gases in the future would affect the inflow of energy from the sun and escape of heat from the earth were then performed.

Dr. Hansen, who has pressed countries to cut emissions of carbon dioxide for the last 20 years, believes that it may be easier and less costly to slow climate change than previously thought, but that CO2 levels still need to be reduced to prevent further warming.

On a further optimistic note, in contrast to the difficulties of controlling CO2, technologies already exist to capture or eliminate many of the other kinds of emissions, for example capturing methane produced by decomposing organic material in landfills, and many non-CO2 greenhouse gas emissions are already declining.

Vice President Al Gore, who played a major role in establishing the Kyoto Protocol on reducing CO2 emissions, has frequently cited Dr. Hansen’s work and the researcher even testified before a Senate committee that human activities were changing the climate in 1988.

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