Soil that remained at or below 0°C for at least two years is called permafrost. It contains a lot of frozen organic material that has accumulated over thousands of years from dead plants and animals. This also means that this frozen ground holds a large amount of carbon. Studies have shown that there is around twice as much carbon in permafrost as there is in the Earth’s atmosphere.
Why is permafrost a tipping point?
As the climate warms, the risk of permafrost thawing increases. This wakes the microbes in the soil from their hibernation, allowing them to break down the organic carbon in the soil. This process releases CO2 and methane into the atmosphere. Since both of them are greenhouse gases, this heats up the atmosphere, which leads to more thawing of permafrost, and so on. As we can see, this is a self-reinforcing process.
Furthermore, in some areas of decomposition, so much heat can be released that a so-called “compost bomb” is triggered. In this case, the internal heat generation becomes the main driving force for further thawing and the release of carbon. However, this process depends on how wet, insulated and organic-rich the soil is and occurs locally rather than across the whole permafrost simultaneously.
Where is the tipping point of the permafrost?
In one study, a tipping point for the compost bomb was reached at a warming of about 1.2°C above pre-industrial levels. But as I mentioned earlier, this will be a very regional effect. Some studies suggest a more widespread tipping point could occur beyond 5°C above pre-industrial levels.
What would happen if we crossed the tipping point?
Permafrost thawing will be a continuous positive feedback to climate change rather than an abrupt tipping point. That is, if we stop warming, emissions from the permafrost should also stop, but pragmatically, it is not possible for the released carbon to return to the permafrost. So this process is irreversible. A large-scale thawing of permafrost would release around twice as much carbon as is already present in the atmosphere. This would lead to a significant warming of the atmosphere and certainly trigger further tipping points.
Apart from warming the atmosphere, thawing permafrost increases the risk of releasing ancient viruses that are unknown to our immune system. This could lead to several pandemics.