For 20 years, the levels of methane in the lowest layer of our atmosphere soared. But recent data indicate that the growth rate of the greenhouse gas, which is less abundant than carbon dioxide but traps 23 times more heat per molecule, began slowing in 1998. Researchers agree that the pause results from decreasing emissions of methane, but they have not pinpointed which sources have decreased and by how much. Leading hypotheses include the collapse of the Soviet Union, which resulted in a decline in energy use in the region; decreasing emissions from coal mining; and a decline in rice production. The data reported in the November 23 issue of Geophysical Research Letters also do not predict whether the trend will continue. Regardless, methane stabilization is good news, because it allows for more time to address the main culprit behind climate change: carbon dioxide.
This article was originally published with the title "Methane Flatline" in Scientific American 296, 2, 26 (February 2007)