From: Roger Greenway, ENN
Published July 19, 2014 07:14 AM

Update: Melting permafrost and Global Warming

You have probably heard that melting permafrost is a big contributor to increasing the levels of greenhouse gases in our atmosphere, and that melting permafrost may even cause an unstoppable acceleration of global warming.

New research, however, supported by the National Science Foundation (NSF), counters this widely-held scientific view that thawing permafrost uniformly accelerates atmospheric warming, indicating instead that certain arctic lakes store more greenhouse gases than they emit into the atmosphere.

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The study, published this week in the journal Nature, focuses on thermokarst lakes, which occur as permafrost thaws and creates surface depressions that fill with melted fresh water, converting what was previously frozen land into lakes.

The research suggests that arctic thermokarst lakes are "net climate coolers" when observed over longer, millennial, time scales.

"Until now, we've only thought of thermokarst lakes as positive contributors to climate warming," said lead researcher Katey Walter Anthony, associate research professor at the University of Alaska Fairbanks Institute of Northern Engineering. "It is true that they do warm climate by strong methane emissions when they first form, but on a longer-term scale, they switch to become climate coolers because they ultimately soak up more carbon from the atmosphere than they ever release."

The researchers observed that roughly 5,000 years ago, thermokarst lakes in ice-rich regions of North Siberia and Alaska began cooling, instead of warming the atmosphere.

"While methane and carbon dioxide emissions following thaw lead to immediate radiative warming," the authors write, "carbon uptake in peat-rich sediments occurs over millennial time scales."

Using published data from the circumpolar arctic, their own new field observations of Siberian permafrost and thermokarsts, radiocarbon dating, atmospheric modeling and spatial analyses, the research team studied how thawing permafrost is affecting climate change and greenhouse gas emissions.

Researchers found that "thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago," according to their article, published online today. They found that high rates of carbon accumulation in lake sediments were stimulated by several factors, including "thermokarst erosion and deposition of terrestrial organic matter, nutrient release from thawing permafrost that stimulated lake productivity, and by slow decomposition in cold, anoxic lake bottoms."

Image shows Ice melting in the frozen peat creating these shallow ponds and lakes in the Hudson Bay Lowlands in Manitoba, Canada. The lakes are up to several hundred meters across.
Credit: Geological Survey of Canada (via National Snow & Ice Data Center)

Read more at Research.gov.

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