New study shows Arctic has potential to alter Earth’s climate

Submitted by Marie Gilbert
Phone: 907-474-7412
10/15/09

Arctic change could alter Earth’s climate, according to a new study led by ecologists at the University of Alaska Fairbanks.

Ecologists estimate that arctic lands and oceans hold up to 25 percent of the world’s atmospheric carbon dioxide. Climate change could diminish or reverse this phenomenon, potentially accelerating predicted rates of climate change. The study is published in the November edition of Ecological Monographs.

In their review paper, David McGuire of the Institute of Arctic Biology and Alaska Cooperative Fish and Wildlife Research and his colleagues show that the Arctic has been a carbon sink since the end of the last Ice Age. Over time, it has absorbed up to 25 percent, or up to about 800 million metric tons, of global carbon. On average, says McGuire, the Arctic accounts for 10 to 15 percent of the Earth’s carbon sink. But the rapid rate of climate change in the Arctic--about twice that of lower latitudes--could make the Arctic a source of carbon dioxide instead.

Carbon generally enters arctic oceans and land from the atmosphere. This organic material accumulates in permafrost, the frozen layer of soil underneath the land’s surface. Unlike in active soils, organic material frozen in permafrost does not decompose, thus, the carbon becomes trapped in the frozen soil. Cold surface conditions have also slowed the rate of organic matter decomposition, McGuire says, allowing the Arctic to accumulate more carbon than it releases.

But recent warming trends could change this balance. Warmer temperatures can accelerate the rate of surface decomposition, releasing more carbon into the atmosphere. More concerning, says McGuire, is that the permafrost has begun to thaw, exposing previously frozen soil to decomposition and erosion. These changes could reverse the historical role of the Arctic as a sink for carbon.

"In the short term, warming temperatures could expose more Arctic carbon to decomposition," McGuire said. "And with permafrost melting, there will be more available carbon to decompose."

On the scale of a few decades, the thawing permafrost could also result in a more waterlogged Arctic, says McGuire, a situation that could encourage the activity of methane-producing organisms. Currently, the Arctic contributes as much as 50 million metric tons of methane to the atmosphere each year. In comparison, the Arctic sequesters 400 million metric tons of carbon dioxide yearly. Methane is a very potent greenhouse gas--about 23 times more effective at trapping heat than carbon dioxide on a 100-year time scale. If the release of Arctic methane accelerates, global warming could increase at much faster rates.

"We don’t understand methane very well, and its releases to the atmosphere are more episodic than the exchanges of carbon dioxide with the atmosphere," says McGuire. "It’s important to pay attention to methane dynamics because of methane’s substantial potential to accelerate global warming."

But uncertainties still abound about the response of the arctic system to climate change. For example, the authors write, global warming may produce longer growing seasons that promote plant photosynthesis, which removes carbon dioxide from the atmosphere. However, increasingly dry conditions may might counteract and overcome this effect. Similarly, dry conditions can lead to increased fire prevalence, releasing even more carbon.

McGuire contends that only specific regional studies can determine which areas are likely to experience changes in response to climate change.

"If the response of the arctic carbon cycle to climate change results in substantial net releases of greenhouse gases, this could compromise mitigation efforts that we have in mind for controlling the carbon cycle," he says.

The study was sponsored by the Arctic Monitoring and Assessment Program, Climate in the Cryosphere Program, and the International Arctic Science Committee.

CONTACT: A. David McGuire, professor of ecology, at 907-474-6242 or ffadm@uaf.edu. Daniel Hayes, postdoctoral fellow, at 907-474-2414 or djhayes@alaska.edu. Marie Gilbert, IAB information officer, at 907-474-7412 or megilbert@alaska.edu.

MEG/10-15-09/059-10