There are huge quantities of methane locked in ice sheets around the world, threatening to speed up climate change as they get released in melting ice. But determining which methane is the ancient kind and which is much younger and hails from, say, plant life that has decayed in lakes hasn't been easy—until now. The BBC reports that researchers have been able to ID the former by logging the ratio of different isotopes of carbon found in the methane molecules. Scientists were then able to test some of the 150,000 sites in Alaska and Greenland where methane is seeping into the atmosphere, and found that some are indeed releasing ancient methane.
"We observed most of these cryosphere-cap seeps in lakes along the boundaries of permafrost thaw and in moraines and fjords of retreating glaciers," wrote the researchers. "If this relationship holds true for other regions where sedimentary basins are at present capped by permafrost, glaciers, and ice sheets ... by 2100, a very strong increase in methane carbon cycling will result, with potential implications for climate warming feedbacks." (Read more climate change stories.)