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Carbon in Polar permafrost 'behind ancient global warming'

By Linden Volsun - 07 Apr 2012 11:30:0 GMT
Carbon in Polar permafrost 'behind ancient global warming'

Permafrost image via Shutterstock

Global warming 55 million years ago may have been caused by carbon in thawed Polar permafrost, scientists say. Up until now, the most common theory was that the carbon that led the warming came from frozen methane in seabed sediment.

But climate expert Rob DeConto from the University of Massachusetts Amherst and other researchers say Paleocene-Eocene Thermal Maximum (PETM) have an alternative explanation.

"We are instead ascribing the carbon source to the continents, in polar latitudes where permafrost can store massive amounts of carbon that can be released as CO2 when the permafrost thaws."

The new theory is backed by estimates of the levels of greenhouse gas and vegetation, the way the Earth's orbit and tilt altered and the amount of carbon in rocks and freezing soil.

It is likely that the level of carbon causing PETM may have been much higher than that of today, but even so, the research could point to serious long-term issues as carbon in permafrost in the North Pole region has already started thawing because of fossil fuel burning.

Climate Scientist Rob DeConto explains, "Similar dynamics are at play today. Global warming is degrading permafrost in the north Polar Regions, thawing frozen organic matter, which will decay to release CO2 and methane into the atmosphere. This will only exacerbate future warming in a positive feedback loop."

Rob DeConto, along with other researchers from Yale, Penn State and the University of Colorado, all in the USA, the University of Sheffield, in Britain and Italy's University of Urbino, created a precise model. They investigated the source, power and timing of the carbon discharge during PETM and subsequent hot periods that seem to have been activated by alternations in the orbit of the Earth.

The high temperature of the atmosphere was created by the sun's energy, less the amount that is lost into space. CO2 gathers heat that would go back to space in other circumstances.

Through the oceans becoming more acidic during the PETM, there was a huge around of carbon going into the atmosphere, which created a rise in temperature around the world of some 5 degrees Celsius over 1,000 years, say the team.

As there would have been a huge amount of carbon needed to cause the rise, it has not been easy to explain what happened.

The team used a precise new record taken from Italian rocks to demonstrate how the PETM took place during times when the orbit of the Earth around the sun was titled and was not fully circular.

The Earth's orbit has an influence on the size, area and period of the sun's radiation and that impacts upon the seasons, especially in the Polar Regions in which collected carbon can build up.

The researchers then produced a simulation of the interplay between the climate, soil and ecosystem and took into account increasing levels of greenhouse gases and rising polar temperatures, as well as the differences in the orbit.

The study suggests that the extent and timing of the PETM, plus resulting hyperthermals, is accounted for by the orbital changes that started the decomposition of the organic carbon in the soil in the Arctic and Antarctic regions.

The huge amount of carbon stored at the poles could potentially release thousands of petagrams of carbon once the temperature threshold was achieved, prior to the PETM.

This is the first time that Antarctica has been seen as playing a vital part in the process.

The team's modelling also assists in explaining why there was a relatively quick improvement from hyperthermals connected with orbital highs that happen around every 1.2million years.

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Topics: Climate / Carbon Dioxide