The Arctic tundra is letting loose a large and unexpected burst of methane in the autumn, finds a new study out in Nature today. Unlike the oceanic methane bubbles that made headlines a few months ago, this isn’t suggested to be an effect of climate change – it’s the formerly overlooked (or rather, never-looked-for) tail of a natural seasonal cycle. But it’s important for understanding natural methane-emitting processes that may be affected by future warming. I’ve got the full story over on Nature News.
The newly discovered surge of greenhouse gas is brought to you by International Polar Year. Thanks to that research push, a team led by biogeochemist Torben Christensen of Lund University, Sweden, got a two-month extension on the usual field season at a monitoring station in northeast Greenland. Scientists have been measuring methane emissions from far-northern tundra during the growing season for decades, but it had been assumed that once methane levels taper off in late summer, they stay at next to nil over the freezing fall and winter.
Far from it. Emissions actually spike as the ground starts to frost over, the researchers found, and cumulative emissions during the freeze-in are about equal to those in summer. If all wet meadow tundras release a similar methane burst, they calculate, about 4 million tonnes may be emitted each winter. That’s not enough to affect estimates of the total annual methane emissions from tundra (30 to 100 million tonnes), but it’s just right to account for an observed autumn surge in atmospheric methane over the frozen north that had previously gone unexplained.
The mechanism behind the burst may be the freezing itself, the authors suggest, which could physically squeeze methane from the soil.
Ecologist and IPCC co-chair Chris Field says the paper fills out an expanding picture of Arctic processes: “One of the really important things we’ve learned about high-latitude processes over the last decade is that clearly a lot of stuff happens during what we had considered to be the wintertime, when everything is frozen and shut down.”
IMAGE: IStockphoto/Riverson Clark