SOURCE: Yale Climate Connections
DATE: February 12, 2019
SNIP: About a fifth of the Northern Hemisphere landmass is permafrost, ground that has been mostly frozen for half a million years or more. Now there are signs of thaw appearing in many places across this vast landscape circling the Arctic, and at accelerated rates.
It is only a matter of time until the incremental thawing of the permafrost reaches a tipping point of no return, a state of accelerated and irreversible change, the side effects of which might well push other parts of the Arctic beyond their own tipping points. Quite possibly, we are poised to witness such a transformation within our lifetimes – ice sheet loss, increased frequencies of fires in the tundra and boreal forests, and complete habitat loss for marine mammals, to name just a few examples of the changes that could occur.
The major side effect of a thawing permafrost is that it will further enhance global warming with the release of large quantities of methane, a potent greenhouse gas. The permafrost contains organic matter, and thawing will enable bacterial decomposition that will release methane as a byproduct of anaerobic respiration.
The last time there was a large-scale thaw of the permafrost was four interglacials ago. Evidence of this thawing event can be found in Siberian caves where stalactites and stalagmites growth last occurred at that time. Such deposits can only form when there is liquid water flowing. At the time of the thaw, about 450,000 years ago, the climate was about 1.5°C warmer than pre-industrial temperatures. Today, the temperature is nearly as warm – 1°C hotter than in pre-industrial times. Even more worrisome is the rate of the current warming, unprecedented in over 50 million years of geological history.
However, it is possible that a tipping of the permafrost may not happen at a specific temperature threshold, but would rather depend on the rate of human-caused warming.
[T]he “Compost Bomb instability” model proposed in 2010 by a team led by mathematician Sebastian Wieczorek predicted that decomposition of that organic matter, once initiated, would become a source of heat itself, causing an explosive increase in soil temperatures, additional decomposition, and methane release. Crucially, the higher the rate of global warming, the sooner the tipping point could take place.
There are good reasons to suspect that this would also be true for the permafrost, which like the peatlands would have the same capacity to generate internal heat due to bacterial decomposition of organic matter. If so, we might expect a tipping before reaching the 1.5°C limit as was the case for the last thaw 450,000 years ago.
Thermokarst lakes, formed from the collapse of thawing ground, are appearing at accelerated rates in Alaska and in the Canadian Arctic. Large number of gas emission craters are appearing in Siberia. Methane emissions measured from degrading permafrost on land and subsea continental shelves are increasing.
The picture emerging is that the Arctic is full of positive feedback mechanisms that can work together to amplify warming.
While it is difficult to quantitatively pinpoint when a system is about to undergo tipping (though some studies have outlined definite criteria), it is likely a decent guess to speculate that the permafrost, and indeed the Arctic as a whole, is already at or very near a tipping point. The basis for such a claim is the simultaneous shift towards tipping points in a number of interconnected systems, many of which are positive reinforcing feedback mechanisms.