New Haven, Connecticut, USA, 18 February 2019: About a fifth of the Northern Hemisphere landmass is permafrost, ground that has been mostly frozen for half-a-million years or more; however, there are signs of thaw appearing in many places across this vast landscape circling the Arctic, and at accelerated rates, said Yale Climate Connections, an initiative of the Yale Center for Environmental Communication, Connecticut, United States, in a Press communiqué.

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, the communiqué said. The major side effect of the thawing permafrost is that it will further enhance global warming with the release of large quantities of methane, a potent greenhouse gas, the communiqué further said. The permafrost contains organic matter and thawing will enable bacterial decomposition that will release methane as a by-product of anaerobic respiration, the communiqué added.

According to Yale Climate Connections, the permafrost is not the only climatic system that is susceptible to abrupt regime shifts – the Greenland Ice Sheet, the West Antarctic Ice sheet and numerous ice shelves in both hemispheres have the potential to undergo abrupt and irreversible change in their state. However, the permafrost is likely one of the fastest to respond, given its southward extent and the existence of positive feedback loops – vicious circles that can amplify the thawing initiated by human-caused warming, the communiqué said.

The principal goal of the Paris Agreement is to limit global warming to 2 degrees C above pre-industrial levels by the end of the century, the communiqué said. In part, the value of 2 degrees C derives from evidence that predicts tipping points at or beyond that threshold, the communiqué further said. 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, the communiqué also said. Crucially, the higher the rate of global warming, the sooner the tipping point could take place, the communiqué added.

According to Yale Climate Connections, while it is difficult to quantitatively pinpoint when a system is about to undergo tipping, it is likely that the permafrost, and indeed the Arctic as a whole, is already at or very near a tipping point. The communiqué said 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. The communiqué said it’s time we start accepting that climate change is here, not something waiting to happen in some hypothetical future. The communiqué added that by acting now we have some chance of disarming the ticking permafrost bomb.