Unexpected future boost of methane possible from Arctic Permafrost

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Arctic landscape stores one of the largest natural reservoirs of organic carbon

ABOVE VIDEO: New NASA-funded research has discovered that the expected gradual thawing of the Arctic permafrost and the associated greenhouse gas emissions in the atmosphere may be accelerated by cases of a relatively little known process called abrupt defrosting. Abrupt defrosting takes place under a certain type of pool lake, known as a thermo-karstic lake that forms as the permafrost thaws.

(NASA) – The impact on the climate can mean an influx of permafrost-derived methane into the atmosphere in the middle of the 21st century, which is currently not the case in climate projections.

The arctic landscape preserves one of the largest natural reservoirs of organic carbon in the world in its frozen soil. But once thawed, soil bacteria in the permafrost can change that carbon in the greenhouse gases into carbon dioxide and methane, which then enter the atmosphere and contribute to global warming.

"The mechanism of abrupt defrosting and thermocracking of the lake is of great importance for the permafrost carbon feedback of this century," said Katey Walter Anthony, first author of the University of Alaska, Fairbanks, who led the project that was part of the vulnerability of Arctic-Boreal at NASA. Experiment (ABoVE), a ten-year program to understand the effects of climate change in the Arctic.

"We do not have to wait 200 or 300 years to get these large quantities of permafrost carbon." In my life, the life of my children, it would have to be pushed up. "It's happening, but it's not happening really fast now, but within a few decades must reach the peak. "

The results have been published in Nature Communications.

Using a combination of computer models and field measurements, Walter Anthony and an international team of American and German researchers discovered that abrupt defrosting more than double doubled previous estimates of permafrost-derived greenhouse effect.

They discovered that the abrupt thawing process increases the release of old carbon stored in the soil by 125 to 190 percent compared to gradually thawing alone.

Moreover, they discovered that in future scenarios for global warming as defined by the Intergovernmental Panel on Climate Change, abrupt defrosting was just as important in the modest scenario for emission reductions as in the extreme business-as-usual scenario.

This means that even in the scenario where people reduced their global carbon emissions, there will still be large methane release by abrupt defrosting.

Permafrost is ground that is frozen all year round. In the Arctic, ice-rich permafrost soils can be up to 80 meters (80 meters) thick. Due to the man-made warming of the atmosphere due to the emission of greenhouse gases, a gradual thawing of the permafrost is currently taking place, with the top layer of the seasonally thawed soil gradually becoming thicker and reaching deeper into the ground.

This process awakens microbes in the soil that break down organic matter from the soil and, as a result, release carbon dioxide and methane back into the atmosphere. This gradual defrosting process is justified in climate models and is assumed to have minimal effect since thawed soil also stimulates plant growth, which neutralises the carbon released into the atmosphere by consuming it during photosynthesis.

However, permafrost dips deeper and faster in the presence of thermo-contamination. Thermo-wrinkles form when substantial amounts of ice melt into liquid water in the deep soil.

Methane bubbles up from the thawed permafrost on the underside of the thermo squeeze through the ice at the surface. (NASA image)

Because the same amount of ice takes up more volume than water, the land surface collapses and sinks away, creating a small depression that fills with water from rain, molten snow and molten earth. The water in the lakes accelerates the thawing of the frozen soil along their shores and increases the size and depth of the lake at a much faster rate than gradually thawing.

"You can get very deep deadly holes within decades, meters to dozens of meters of vertical thaw," said Walter Anthony.

"So you are thawing the permafrost under these lakes and we have very easily measured old greenhouse gases that are coming out of it."

These old greenhouse gases, produced from microbes that chew through old carbon stored in the soil, range from 2,000 to 43,000 years old. Walter Anthony and her colleagues have extracted methane from 72 locations in 11 thermal lakes in Alaska and Siberia to measure the amount of gas released from the permafrost beneath the lakes, as well as used radiocarbon coatings on captured samples to determine their age.

They compared emissions from lakes with five locations where gradual defrosting takes place. In addition, they used the field measurements to evaluate how well their model simulated the natural field conditions.

Team members with the Alfred Wegener Institute (AWI) for polar and marine research in Germany then used VS Geological Survey-NASA Landsat satellite images from 1999 to 2014 to determine the speed of the expansion of the lake in a large region of Alaska. On the basis of this data they were able to estimate the amount of permafrost in thawed soil in the soils of lakes.

"Although change of the lake has been studied for many regions, the insight that loss of lakes and increase of the lake have a completely different result for carbon fluxes is new", says co-author Guido Grosse of AWI. "In a few decades thermokarst growth of the lake releases considerably more carbon than loss of the lake can block permafrost again [when the lake bottoms refreeze]. "

Because the thermal lakes are relatively small and spread through the Arctic landscapes, computer models of their behavior are currently not included in global climate models. However, Walter Anthony believes that including them in future models is important for understanding the role of permafrost in the global carbon budget.

Emissions from human fossil fuels are the main source of greenhouse gases in the atmosphere and in comparison therewith methane emissions of thawing permafrost constitute only one percent of the global methane budget, said Walter Anthony.

"But by the middle and the end of the century, permafrost carbon feedback should be about equivalent to the second strongest anthropogenic source of greenhouse gases, which is a change in land use," she said.


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