How much warming would be needed for there to be significant effects on ecosystems and for a significant amount of greenhouse gasses to be released and affect the carbon cycle?
We’re seeing significant amount of thaw already, at least in the Northern Hemisphere. The areas of thawing permafrost are increasing and the southernmost boundaries between continuous and discontinuous permafrost are moving northward as well as the southernmost boundaries of discontinuous permafrost.
As far as ecosystems are concerned, we’ve been seeing a change in hydrology, which has a significant impact on ecosystems locally. The availability of water to a given ecosystem is a major factor that determines which flora and fauna can live there. Depending on the soil, topography, and drainage conditions, the soil can either become waterlogged as the permafrost thaws, or the soil can dry out as the water above the thawing permafrost drains away. We’ve seen both situations happening already: boreal forests are either turning into bogs, swamps or wetlands when there’s too much water (for example in the Tanana Flats near Fairbanks, Alaska), or they are turning into grasslands or steppe-like ecosystems when conditions become too dry (examples can be found in Mongolia or in East Siberia).
As for effects on the carbon cycle and the release of greenhouse gasses into the atmosphere, we’re already seeing significant impacts from this. Several groups of scientists have been having a look at this (including papers by Ted Schuur et al which was published in 2009, as well as papers by Sergey Zimov and Katie Walter), and we have evidence that thawing permafrost is releasing at least carbon dioxide and possibly also methane to the atmosphere. We’re seeing this even with the very moderate degradation of permafrost that’s happening right now.
All climate models predict average temperatures to be warmer by the middle to the end of the 21st century, and permafrost projections show that by the end of the century, at least half of the recently stable permafrost area will experience some degree of degradation. So it means that the thawing of permafrost will become much more common than it is right now as the century progresses, and we’ll likely start seeing a significant and noticeable impact of thawing permafrost on the carbon cycle.
Vladimir Romanovsky on the Current State of Permafrost
HT The Cost of Energy via twitter
Lou has a post you should read
Earth: Ground zero for the permafrost bomb