Permafrost is soil that has remained frozen for at least two years, but some of it is ancient — frozen for tens of thousands of years or more. Since massive amounts of organic material is trapped in permafrost worldwide, scientists fear that as it thaws it will release all of that stored carbon in the form of greenhouse gases.

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This sort of process is known as a feedback loop. As global warming thaws permafrost, more greenhouse gases get released, which speeds up global warming, which thaws even more permafrost... and so on. It's bad news, and figuring out how quickly this process is occurring is important for making accurate climate change projections.

Now researchers from the U.S. Geological Survey and key academic partners including the University of Colorado Boulder have quantified how rapidly ancient permafrost decomposes upon thawing, and in the process, how much carbon dioxide is produced, reports Science Daily. Their findings are alarming, to say the least.

Researchers looked specifically at so-called "yedoma" permafrost, ancient soil that has been frozen for about 35,000 years and which is particularly rich in organics. They found that more than half of the dissolved organic carbon in yedoma permafrost was decomposed within one week after thawing. About 50 percent of that carbon was converted to carbon dioxide. To put things in perspective, these rates are among the fastest permafrost decomposition rates that have ever been documented.

"It had previously been assumed that permafrost soil carbon this old was already degraded and not susceptible to rapid decomposition upon thaw," said Kim Wickland, the USGS scientist who led the team.

Discovering that this ancient, carbon-packed permafrost decomposes this quickly and has the potential to release such massive amounts of greenhouse gases into the atmosphere is shocking. Worldwide, the amount of carbon sequestered in permafrost is four times the carbon that has been released to the atmosphere due to human activities in modern times. In other words, a time bomb is sitting underneath all of that permafrost, and now we know there's less time on the clock than previously thought.

"Many scientists worldwide are now investigating the complicated potential end results of thawing permafrost," said Rob Striegl, USGS scientist and study co-author. "There are critical questions to consider, such as: How much of the stored permafrost carbon might thaw in a future climate? Where will it go? And, what are the consequences for our climate and our aquatic ecosystems?"