Public Release: 

Thawing permafrost may have led to extreme global warming events

University of Sheffield

Scientists analysing prehistoric global warming say thawing permafrost released massive amounts of carbon stored in frozen soil of Polar Regions exacerbating climate change through increasing global temperatures and ocean acidification.

Although the amounts of carbon involved in the ancient soil-thaw scenarios was likely much greater than today, the implications of this ground-breaking study are that the long-term future of carbon deposits locked into frozen permafrost of Polar Regions are vulnerable to climate warming caused as humans emit the greenhouse gas carbon dioxide by burning fossil fuels for energy generation.

Researchers in centres across America, Italy and the University of Sheffield, analysed a series of sudden, and extreme, global warming events - called hyperthermals - that occurred about 55 million years ago, linked to rising greenhouse gas concentrations and changes in Earth's orbit, which led to a massive release of carbon into the atmosphere, ocean acidification, and a five degrees Celsius rise in global temperature within just a few thousand years.

It was previously thought that the source of carbon was in the ocean, in the form of frozen methane gas in ocean-floor sediments but now the experts believe the carbon released into the atmosphere millions of years ago came from the Polar Regions.

Professor David Beerling, of the University of Sheffield's Department of Animal and Plant Sciences, said: "For the first time, we have linked these past global warming events with a climatically sensitive terrestrial carbon reservoir rather than a marine one. It shows that global warming can be amplified by carbon release from thawing permafrost."

"The research suggests that carbon stored in permafrost stocks today in the Arctic region is vulnerable to warming. Warming causes permafrost thaw and decomposition of organic matter releasing more greenhouse gases back into the atmosphere.

"This feedback loop could accelerate future warming. It means we must arrest carbon dioxide emissions released by the combustion of fossil fuels if humanity wishes to avoid triggering these sorts of feedbacks in our modern world."

The breakthrough was made through cross-disciplinary collaborations with climate and vegetation modellers, isotope geochemists and permafrost experts led by Rob DeConto at the University of Massachusetts, in collaboration with the University of Sheffield, Yale, the University of Colorado, Penn State, and the University of Urbino, Italy.

Rob DeConto added: "Similar dynamics are at play today. Global warming is degrading permafrost in the north Polar Regions, unlocking once-frozen carbon and methane and releasing it into the atmosphere. This will only exacerbate future warming in a positive feedback loop."

The temperature of Earth's atmosphere is a result of energy input from the sun minus what escapes back into space. Carbon dioxide in the atmosphere absorbs and traps heat that would otherwise return to space.

The global warming events were accompanied by a massive input of carbon to the atmosphere plus ocean acidification, and were characterized by a global temperature rise of about five degrees Celsius within a few thousand years.

Until now, scientists have been unable to account for the massive amounts of carbon required to cause such dramatic global warming events and Antarctica, which on today's Earth is covered by kilometres of ice, has not been appreciated as an important player in such global carbon dynamics.

The research is published in the journal Nature.

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