For tens of thousands of years the Arctic permafrost regions served as an area of carbon storage. Soils in higher latitudes tend to store more carbon that in tropical latitudes due to lower metabolic activity (Related: New Study Maps Out the Global Pattern of Soil-based Carbon Storage). The intense cold in the Arctic region slows down bacterial activity, the main form of decomposition of dead vegetative matter. Permafrost, by definition, is a subsurface layer of soil in the Arctic that remains at or below freezing for at least two years at a time. These soils contain large amounts of carbon that accumulated over a thousands of years as surface vegetation dies and mixes into the soil. Permafrost covers about 25% of the land area in the Northern Hemisphere in Alaska, Canada, Siberia, and Greenland.
A look at global temperature anomalies for 2000 to 2009 shows that the Arctic is experiencing a higher rate of warming than most other places in the world. Rising temperatures means that permafrost areas are beginning to thaw and microbial activity is accelerating. This increase in bacteria-led decomposition is releasing enormous amounts of stored carbon from the Arctic soil.
A recently published study looked at winter carbon dioxide emissions in the Arctic between 2003 to 2017. The researchers found that the Arctic region has transitioned from a carbon sink to a source of carbon emissions. The study found that while 1 billion metric tons of carbon were taken up by Arctic trees and plants during the summer growing season, 1.7 billion metric tons of carbon were lost from the Arctic during the winter months.
Natali, S. M., Watts, J. D., Rogers, B. M., Potter, S., Ludwig, S. M., Selbmann, A. K., … & Björkman, M. P. (2019). Large loss of CO 2 in winter observed across the northern permafrost region. Nature Climate Change, 9(11), 852-857. doi:10.1038/s41558-019-0592-8
Permafrost Becoming a Carbon Source Instead of a Sink, NASA Earth Observatory