In a contretemps indicative of the political struggle over global climate change, a recent study suggested that humans may not be warming the earth. Greenhouse skeptics, pro-industry groups and political conservatives have seized on the results, proclaiming that the science of climate change is inconclusive and that agreements such as the Kyoto Protocol, which set limits on the output of industrial heat-trapping gases, are unnecessary. But mainstream climatologists, as represented by the Intergovernmental Panel on Climate Change (IPCC), are perturbed that the report has received so much attention; they say the study's conclusions are scientifically dubious and colored by politics.

Sallie Baliunas and Willie Soon of the Harvard-Smithsonian Center for Astrophysics reviewed more than 200 studies that examined climate "proxy" records--data from such phenomena as the growth of tree rings or coral, which are sensitive to climatic conditions. They concluded in the January Climate Research that "across the world, many records reveal that the 20th century is probably not the warmest nor a uniquely extreme climate period of the last millennium." They said that two extreme climate periods--the Medieval Warming Period between 800 and 1300 and the Little Ice Age of 1300 to 1900--occurred worldwide, at a time before industrial emissions of greenhouse gases became abundant. (A longer version subsequently appeared in the May Energy and Environment.)

This article was originally published with the title Hot Words.

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