There is twice as much carbon in Arctic soils and permafrost than there is in the atmosphere. As a warmer world causes permafrost like this to thaw, carbon decomposes and is released to the atmosphere. Click on image for full size (864 Kb) Courtesy of Ted Schuur

A study published in the May 28 issue of the journal Nature has helped define the potentially significant contribution of permafrost thaw to atmospheric concentrations of carbon, which have already reached unprecedented levels.

"In earlier work we estimated that widespread permafrost thaw could potentially release 0.8-1.1 gigatons of carbon per year," said Ted Schuur an ecologist at the University of Florida and the lead author of the study. "Before this study, we didn't know how fast that carbon could potentially be released from permafrost, and how this feedback to climate would change over time."

A large amount of organic carbon in the tundra is stored in the soil and permafrost. This pool of carbon, deposited over thousands of years, remains locked in the perennially frozen ground. In recent years this area began to thaw, providing increased access to plants and microbes that could shift the carbon from the land to the atmosphere.

An understanding of the rate of carbon release is necessary to estimate the strength of  positive feedback to climate change, a likely consequence of permafrost thaw. Scientists use the term positive feedback to describe the snowball effect described here: a warmer climate permits permafrost thaw, releasing more carbon into the atmosphere, which will further increase global surface temperature.

From 2004 to 2006, Schuur and his team used radiocarbon dating, a technique typically used to determine the age of artifacts, to track the movement of "old" organic carbon accumulated within the soils and permafrost at an Alaskan site. The ability to distinguish old carbon from newer carbon allowed the researchers to track current metabolism of old carbon in an area where permafrost thaw is increasing.

Surprisingly, this research revealed that during the initial stages of permafrost thaw, plant growth and photosynthesis, which remove carbon from the atmosphere, increase. This increase offsets the release of old carbon from thawing. However, sustained thaw eventually releases more carbon than plants can uptake, overwhelming their compensatory capacities. To put this in a global context, if the average global temperature continues to rise, current calculations predict that positive feedback from permafrost thaw could annually add as much carbon to the atmosphere as another significant source, land use change.

The Alaskan site where Schuur and colleagues carried out their research was monitored over the past two decades, with permafrost temperature measurements beginning before the permafrost began to thaw. This detailed record coupled with Schuur's study of ecosystem carbon exchange and old carbon release provide a comprehensive picture of the dynamics of carbon exchange in response to permafrost thaw.

"Records from this site exist on a decadal time scale, meaning we are able to more accurately account for the slow pace of change within the system. Overall, this research documents the long-term plant and soil changes that occur as permafrost thaws, thus providing a basis for making long term predictions about ecosystem carbon balance with increased confidence," Schuur reported.

Text above is courtesy of the National Science Foundation

There is twice as much carbon in Arctic soils and permafrost than there is in the atmosphere. As a warmer world causes permafrost like this to thaw, carbon decomposes and is released to the atmosphere. Click on image for full size (864 Kb) Courtesy of Ted Schuur

In 20 years of studying the Alaskan tundra, scientist Ted Schuur and his team have seen the frozen soil in their study area thaw, turning from hard ground to soft mud.

All over the Arctic, frozen soil, called permafrost, is thawing because of global warming. The team studied how the plants and soil change as permafrost thaws. Recently they have been developing new ways to monitor how thawing soil affects greenhouse gases in the atmosphere.

There is a large amount of carbon stored in the permafrost. The carbon built up in the soil over thousands of years from the remains of dead plants and animals which couldn’t decompose in frozen conditions. Today, as the soil thaws, carbon can be released into the atmosphere, increasing the amount of greenhouse gases.

A positive feedback to climate change happens when global warming causes something that, in turn, causes more warming. The process of a warmer climate causing permafrost thaw, which releases carbon to the atmosphere, which warms climate even more is an example of a positive feedback to climate change.

Carbon moves through different living and non-living parts of ecosystems in the carbon cycle, one of the biogeochemical cycles. The researchers wondered how carbon that has been in the frozen soils for hundreds to thousands of years, moved around the carbon cycle differently than carbon that was recently taken in by a plant. They used radiocarbon dating to figure out where old carbon moves in the carbon cycle as permafrost thaws.

Their results showed that when permafrost first begins to thaw, more plants are able to grow. The plants remove carbon from the atmosphere through the process of photosynthesis. This makes the amount of carbon taken out of the atmosphere greater than the amount added to the atmosphere from the soil. But the pattern does not continue this way. With more thawing, more carbon is added to the atmosphere than is taken out by plants.

This information is helping scientists make predictions about how much carbon will be released to the atmosphere from Arctic tundra in the future.

There is twice as much carbon in Arctic soils and permafrost than there is in the atmosphere. As a warmer world causes permafrost like this to thaw, carbon decomposes and is released to the atmosphere. Click on image for full size (864 Kb) Courtesy of Ted Schuur

Global warming is causing frozen soil to thaw in the Arctic. A team of scientists has been looking at how this is changing the tundra and how thawing soils are affecting greenhouse gases in the atmosphere.

There is a large amount of carbon in the frozen soil. As the soil thaws, carbon can be released into the atmosphere, increasing the amount of greenhouse gases, which causes more warming.

Carbon moves around the Earth in the carbon cycle. The researchers wondered how carbon that has been in the frozen soils for hundreds to thousands of years, moved through the carbon cycle. They used radiocarbon dating to figure out where the carbon goes as the soil thaws.

Their results showed that when soil first begins to thaw, more plants are able to grow. The plants remove carbon from the atmosphere through the process of photosynthesis. This makes the amount of carbon taken out of the atmosphere greater than the amount added to the atmosphere from the soil. But the pattern does not continue this way. With more thawing, more carbon is added to the atmosphere than is taken out by plants.

This information is helping scientists make predictions about how much carbon will be released to the atmosphere from Arctic tundra in the future.