Areas of the Arctic have stored large quantities of carbon in the soil for millennia. However, a new international study published in Nature Climate Change shows that a shift is under way in these permafrost regions. Now Arctic areas emit more carbon into the atmosphere during winter than the vegetation absorbs in summer. In addition, there is a risk of significant increases in emissions of carbon dioxide into the atmosphere, of up to 41 per cent, if we do not succeed in curbing our own emissions.
"We've known that warmer temperatures and thawing permafrost have been accelerating winter CO2 emissions, but we haven't had a clear accounting of the winter carbon balance," says Sue Natali, director of the Arctic programme at the Woods Hole Research Center, which headed the study.
Four Swedish researchers from the University of Gothenburg, Lund University and Stockholm University have participated in the study. Mats P. Björkman, who participated in the study from the University of Gothenburg, says:
"The warming in the Arctic is happening faster than anywhere else in the world, and the largest increase in temperature occurs during the winter. For a long time, it has been assumed that the soil processes almost come to a halt during the winter, and for this reason measurements of greenhouse gas flows have focused on the Arctic growing season."
Net emissions of 700,000 tonnes of carbon dioxide
The international research team has compiled winter measurements from 104 different places around the Arctic. The study clearly states that winter processes definitely need to be taken into account and that these areas emit about 1.7 million tonnes of carbon into the atmosphere from October to April. This compares with the estimated 1 million tonnes that vegetation in the same area are arrumed to absorb during the summer. This means that the previously stable Arctic carbon sink is changing into a source of carbon.
Many different factors affect the decomposition of organic material during the winter, which in the final stage leads to carbon dioxide or methane emissions. The availability of liquid water, often found in thin layers or micro-accumulations around soil particles, is what generates most of the emissions. With increased temperatures, the proportion of available water will increase, resulting in a marked increase in the rate of decomposition.
"Other factors also come into play, such as the type and quantity of vegetation," says Frans-Jan Parmentier, associate professor at Lund University. "But in the final analysis, temperature matters most. Increasing winter temperatures will play a major role in these areas in the future."
Despite the bleak the research results, we can affect the trend, Mats P. Björkman maintains. "Although carbon dioxide emissions during the winter will increase with global warming, this positive feedback can be prevented if we take a stand and act quickly for a transition to a climate-neutral society."
In recent decades considerable research resources have been invested in establishing the carbon balance in the Arctic, which partly forms the basis of the UN Climate Panel's reports. "Fieldwork in the Arctic is not a bed of roses, especially during the winter when the forces of nature affect how, when and where we can take measurements, he says."
Link to the article in Nature Climate Change
Additional reading
BECC – Biodiversity and Ecosystem Services in a Changing Climate
MERGE – Modelling the Regional and Global Earth System
APE – Alpine and Polar Ecology
