by Lindsay McCord
As a warming climate impacts Arctic and sub-Arctic regions, frozen soils, called permafrost hold the potential to release large amounts of greenhouse gases as they thaw, triggering a feedback cycle that can further accelerate climate change.
Permafrost is frozen soil that often contains large amounts of undecomposed organic matter. When permafrost thaws, microbes start to break it down, releasing carbon dioxide and methane gas, which accelerates atmospheric warming and furthers thawing of the permafrost in a positive feedback loop.
Much of the soil in the Arctic and sub-Arctic regions is permafrost, containing 1,330–1,580 billion tons of carbon. This estimate is probably low because it does not include subsea permafrost (frozen sediment at the bottom of shallow seas). It is also uncertain because current modeling does not accurately take into account variation in soil composition across the permafrost area. There also remain large, mostly remote areas where the amount of permafrost is entirely unknown.
The current literature predicts a long and gradual release of greenhouse gases over decades and centuries, accelerating warming and the thawing of additional permafrost. There are many factors that affect the rate of carbon emissions from permafrost, and improved models must be developed to take into account different types of melting, changing hydrology, subsea emissions, and the more potent effect of methane as a greenhouse gas. Most models focus on a gradual top-down melting of permafrost, however increasing evidence shows that abrupt permafrost thaw may be more common in many areas of the Arctic and is responsible for some of the highest methane emissions in permafrost regions. Abrupt permafrost thaw causes the ground to collapse as the permafrost melts. This exposes more permafrost to the air and accelerates melting. In addition, this can cause changes to the flow of water on the surface, causing increased erosion by water. Both of these factors can cause permafrost to melt much more rapidly than the gradual top-down thaw and are not represented in large-scale models.
Subsea permafrost not only stores greenhouse gases in the substrate itself, but also provide an impermeable physical barrier to large deposits of methane gas and clathrates (a solid form of methane kept stable by high pressure). Melting of the subsea permafrost due to increased ocean temperatures provides avenues for these deposits to escape.
The impact of carbon emissions from permafrost will not likely surpass fossil fuel emissions, but will probably play a significant role in the changing climate, equivalent to that of large land-use changes. Current models do not accurately account for the variation in melting pattern, permafrost deposits, subsea permafrost, and methane, and thus need to be improved upon in order to adequately project carbon emissions from permafrost. Accurate forecasts of carbon emissions have implications for developing production climate change mitigation policies.
Schuur, E. A. G., McGuire, A. D., Schädel, C., Grosse, G., Harden, J. W., Hayes, D. J., … & Natali, S. M. (2015). Climate change and the permafrost carbon feedback. Nature, 520(7546), 171-179.