Thawing of arctic permafrost burst global warming mostly via increase in carbon dioxide emissions
Global warming causes thawing of arctic permafrost which increases decomposition of organic matter stored in arctic soils. Carbon storage in arctic soils is huge, two times of that in the atmosphere.
Two important greenhouse gas, carbon dioxide and methane, are produced during decomposition of organic matter. There is a risk that thawing of permafrost stimulates global warming resulting from increased decomposition of soil organic matter and associated greenhouse gas emissions to the atmosphere. An important question related to the development of the global climate is the ratio of carbon dioxide to methane released to the atmosphere. Methane is as a greenhouse gas 35 times stronger than carbon dioxide.
A recent study published in Nature Climate Change journal provides new knowledge on the importance of carbon dioxide and methane in climate warming. In this study an international group of scientists, led by Assistant Research Professor Christina Schädel from Northern Arizona University (USA), conduct a meta-analysis of laboratory experiments where the effects of warming on the production of carbon dioxide and methane in permafrost soils were studied. From Finland Research Director Christina Biasi and Emeritus Professor Pertti Martikainen at the University of Eastern Finland (Biogeochemistry research group, Department of Environmental and Biological Sciences) participated in the meta-analysis.
It has been predicted that maximum increase in temperature in the northern regions could be about 10oC. The study published in Nature Climate Change suggests that this increase in temperature would double the release of carbon as greenhouse gases to the atmosphere both from aerobic (oxygen present) and anaerobic (water logged soils, e.g. peatlands) soils. However, the amount of carbon loss as gases from aerobic soils is three times of that from anaerobic soils. In anaerobic soils microbes decomposing organic matter produce both carbon dioxide and methane whereas in aerobic soils mainly carbon dioxide is produced.
Although the release of greenhouse gases is higher from aerobic soils, an important question is if the anaerobic soils supporting production of the efficient greenhouse gas methane would warm the climate more than the aerobic soils. This is not true because methane contributes only to 5% to the total greenhouse gas emission. Aerobic soils with high carbon dioxide emissions thus dominate the warming.
Global warming and associated thawing of permafrost increases soil temperature but also alters soil moisture (water content) conditions in the arctic regions. An increase in temperature always enhances microbial decomposition of organic matter and production of greenhouse gases but soil moisture affects the emissions. As mentioned above soil moisture affecting amount of oxygen in soil, highly determines how much and in which ratio carbon dioxide and methane are produced in soil. In the arctic regions warming can either increase or decrease soil moisture.In the case of reduction in soil water content, oxygen from the atmosphere penetrates better into the soil. This increases decomposition and production of carbon dioxide which favors climate warming.
With the present knowledge we cannot estimate the extent of the areas in the Arcticwhich will be drier and how much new wet areas (peatlands, lakes) are formed with warming. This study stresses the importance of knowledge on changes in soil moisture so that the role of the Arctic in climate change can be better predicted.
Further information is available from following persons:
University of Eastern Finland
Research Director, Dr Christina Biasi, tel: +358 40 355 3810, firstname.lastname@example.org (English)
Emeritus professor Pertti Martikainen, tel: +358 50 357 0545, email@example.com (English, Finnish)
Shädel et al. Potential carbon emissions dominated by carbon dioxide from thawed permafrost soils. Nature Climate Change 6 (2016); DOI: 10.1038/nclimate3054