As an ecologist at the University of Florida, Ted Schuur was initially interested in large-scale releases of carbon into the atmosphere. Unlike other well-documented carbon sources such as fossil fuel burning or deforestation, our understanding of organic carbon stored in the soil and permafrost of the Arctic tundra is poor.
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 tundra in Alaska. 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. This NSF-funded study, published in the May 28 issue of the journal Nature, revealed that rapid thaw has the potential to make a significant contribution to already unprecedented levels of carbon in the atmosphere.
Monitored over the past two decades, records from the Alaskan site where Schuur and colleagues carried out their research date back to before the permafrost began to thaw. These records, coupled with the more recent study of ecosystem carbon exchange and old carbon release provide a comprehensive picture of the movement of carbon 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.
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 ability to compensate.
To put this work in a global context, the researchers calculated that widespread permafrost thaw could potentially release 0.8-1.1 gigatons of carbon per year. This amount is smaller than the annual amount released by fossil fuel burning, but could be a significant source of carbon in the future. “What we didn’t know was how fast that carbon could potentially be released from permafrost, and how this feedback to climate would change over time,” said Schuur.
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.