Thawing Permafrost: A Tipping Point for the Climate
Permafrost regions, containing three times more carbon than all living vegetation on Earth, are at risk of reaching a tipping point due to heatwaves and wildfires, leading to massive greenhouse gas emissions.
Permafrost, ground that remains frozen year-round, covers a vast area of 20m sq km, mostly in Russian Siberia, Canada, Alaska, and parts of Europe. This region stores 1,500 gigatons of carbon, a huge amount that can cause significant changes in the atmosphere with even small alterations to the system.
What is Permafrost and Why is it a Concern?
Permafrost has been frozen for thousands of years, locking in a lot of carbon in the form of old plant remains. As the climate warms due to human activities like burning gas, oil, and coal, the permafrost starts to thaw, exposing these plants to microbes that eat the organic matter and release carbon dioxide and methane into the atmosphere. This process can become self-reinforcing, leading to more warming.
The Tipping Point and its Consequences
The thawing of permafrost creates a fundamentally different landscape, with the formation of lakes, wetlands, or river gullies, known as thermokarsts. Once the permafrost's threshold is passed, and the ice has gone, the landscape changes, and it is not going to come back for hundreds of years. This means that the system has effectively tipped into one that will keep emitting carbon for decades or centuries.
Greenhouse Gas Emissions from Permafrost
The amount of greenhouse gas that could be released from permafrost this century is significant, with estimates suggesting 200 to 300 gigatons of CO2 equivalents if the world warms by between 1.8C and 3.6C by the end of the century. The release of methane, which is about 30 times more potent as a greenhouse gas than CO2, is also a concern, although it breaks down more quickly over 10 to 15 years.
The factors determining whether permafrost releases methane or CO2 depend on whether the thaw leads to a dry or wet environment. If the exposed landscape is dry, microbes will oxidize the carbon into CO2, but if it is a wetland or lake, microbes will produce methane. The research challenge is to figure out how much of the thawing permafrost will get wetter or drier.
The permafrost region is too big for the full system to go over a threshold at the same time, unless global heating reaches 6C. However, as the thaw progresses, there will be many local tipping points that happen in succession, adding to the stress on the climate system. By the end of the century, the permafrost will become a big emitter in its own right.
The economic damage of permafrost thaw will be enormously higher than the economic benefits, with half of Russia's oil and gas coming from permafrost areas that will not be working well in a couple of decades. The only way to limit the thawing of millions of square kilometers is to reduce emissions rapidly. For every degree of global warming that is limited, 4m sq km of permafrost can be saved from thawing and releasing greenhouse gases.
The scientific uncertainty surrounding permafrost thaw is significant, with the precise rate of change and whether we will enter wetter or drier pathways being less clear. However, it is virtually certain that a large magnitude of CO2 and/or methane will be released, and global warming is up to four times higher in the Arctic than the global mean.
The researcher's feelings about their work are ones of concern and frustration, with the realization that permafrost is just one of many tipping point processes that are irreversible. The damage being done now will mean the Earth keeps emitting greenhouse gases for centuries, affecting not just the current generation but many generations to come.
