Frozen carbon stores pose big warming danger


Climate change


Frozen soil sediments, like those above, contain significantly more carbon than previously thought. Released as carbon dioxide and methane, these stores could help warm our planet much faster than expected.

Credit: Edward A.G.Schuur, University of Florida

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There is double the amount of carbon stored in frozen soils than previously thought, new research has found, which could significantly increase global temperatures by the end of this century if released.

"Massive amounts of carbon stored in frozen soils at high latitudes are increasingly vulnerable to exposure to the atmosphere," said Pep Canadell, from the CSIRO's Global Carbon Project.

"The [newest] research shows that the amount of carbon stored in soils surrounding the North Pole has been hugely underestimated."

In a paper published in the latest edition of the journal Global Biogeochemical Cycles, Canadell and colleagues have revealed that frozen high-latitude soils have the potential to release vast quantities of carbon dioxide and methane into the atmosphere, and subsequently influence carbon-climate feedbacks.

"Warmer temperatures at high latitudes are already resulting in unprecedented permafrost [frozen ground] degradation...Projections show that almost all near-surface permafrost will disappear by the end of this century, exposing large carbon stores to decomposition and release of greenhouse gases," he said.

Models developed have shown that global warming could trigger an irreversible process of thawing, leaving the soils vulnerable to a range of effects.

For example, increased microbial activity in the soil would generate heat that could lead to "sustained and long-term chronic emissions of carbon dioxide and methane," Canadell said.

In addition, 'thermokast lakes' - formed as permafrost thaws - would draw heat to deeper layers and bring methane to the surface.

Increased fire frequency in a warmer world would also trigger permafrost degradation and thermokast collapse.

"Using the new carbon pool estimates from this research, permafrost degradation could account for the entire upper range of carbon-climate feedbacks currently estimated by climate models," Canadell said.

And effects could be realised with only a small fraction of the currently frozen carbon being released into the atmosphere, he added.

"For example if only 10 per cent of the permafrost melts, the resultant feedback could result in an additional 80 ppm carbon dioxide equivalent released into the atmosphere, equating to about 0.7 degrees Celcius of global warming."