A moss's tale of gassy climate burps.

A study of ancient moss in Chile suggests that the atmospheric concentration of carbon dioxide gas jumped quite dramatically 12,700 years ago - by an amount and at a speed that has astonished climate experts. The new data show that in just a few decades, levels of this greenhouse gas climbed by about 80 parts per million, an increase roughly equaling the human-caused accumulation of carbon dioxide during the last two centuries.

James White of the University of Colorado at Boulder and his colleagues discovered the evidence of a planetary burp in carbon dioxide by analyzing the ratio of two carbon isotopes in moss preserved within peat deposits. White sees similarly abrupt, but less major changes in such gas concentrations at other times in the moss record. This is the first evidence that carbon dioxide concentrations have undergone such rapid natural jumps, he says.

Because carbon dioxide traps heat in the lower atmosphere, climate researchers expect that such a major buildup of this greenhouse gas should have warmed the planet at that time. White notes that the jump in gas concentrations comes right before a major melting of northern hemisphere ice sheets left over from the last ice age.

Researchers face a difficult time explaining how levels of. carbon dioxide could change so much in just a few decades. But they do know the answer probably lies somewhere in the ocean, which holds much more carbon dioxide gas than is stored in the atmosphere. White speculates that the carbon dioxide surge may have resulted from abrupt changes in ocean circulation.