Among scientists there is wide concern that carbon dioxide (C02) and methane gases being spewed into the air will lead to global climate change because of the greenhouse effect. But that outlook stems from certain assumptions. One is that the amount of methane in the atmosphere will continue to soar. That's worrisome because methane causes more than 10 times as much warming as C02.

Now comes evidence that this assumption may be wrong. After examining samples of air collected from 37 sites around the world from 1983 to 1990, climatologists led by Edward J. Dlugokencky of the University of Colorado have discovered that the increase in methane levels seems to be slowing. In fact, observes Dlugokencky in the journal Nature, if the trend continues, methane should peak by the year 2006. The result: less global warming than predicted. Dlugokencky suggests the ebb in growth results from better methods of capturing the methane escaping from oil wells plus a downward shift in two historical trends: ever-rising numbers of cattle and rice paddies, both major producers of methane.

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