Melting permafrost is still an enigma in terms of its impact on the climate. What comes from underneath and how much CO2 and methane are released? Researchers report this week Nature somewhat worrying findings.
CO2 emissions from the ground are more sensitive to warming in areas where permafrost has collapsed than where it has not. There have been concerns about permafrost for a long time. Higher temperatures lead to rapid thaw in Siberia and North America, where most permafrost is found. Something called thermokarst is at play in about 20 percent of northern permafrost areas. This is a very abrupt, super-fast thaw that more or less collapses the permafrost. Unfortunately, about half of all underground carbon is stored in the northern permafrost. The sudden thaw can have all kinds of consequences for the land surface and lead to abrupt changes in the soil and the associated carbon cycle of the ecosystem.
5.5 times more CO2
Thermokarst and non-thermokarst are of course simultaneously and equally exposed to global warming. However, what has never been examined is whether there is a difference in the consequences for the CO2 storage of these two landforms. That is why Chinese scientists have investigated what happens to the CO2 in thermokarst. To this end, they simultaneously conducted experiments in thermokarst and non-thermokarst. The conclusion is worrying: warming releases 5.5 times as much CO2 from the ground in thermokarst than in adjacent normal permafrost.
What is thermokarst?
Thermokarst or cryokarst is the land that forms when permafrost in the Arctic thaws rapidly. This creates a very irregular landscape with small hills, swamps and holes (see photo above). Thaw lakes are also formed that thaw the surrounding frozen ground even faster, releasing methane and CO2. It leads to a so-called negative feedback loop, which causes the earth to warm even faster.
The researchers then looked at thirty possible causes of the effects on CO2 emissions. They found that the greater response to warming is mainly due to the lower quality of the soil substrate (the part that plants grow in) and the greater amount of soil microbes that break down organic matter in thermokarst-affected soil.
By conducting research at six other locations, the soil researchers also discovered that the formation of thermokarst significantly increases the sensitivity of CO2 emissions to a temperature increase, which is additional evidence for the stronger CO2 response of the soil to warming .
Worse than expected
Professor Yang Yuanhe calculates that if you extrapolate the response of CO2 emissions to all thermokarst in the Northern Hemisphere, an additional 0.4 gigatons of carbon will be released per year. “That is a quarter of the predicted loss of carbon in permafrost by the end of the 21st century,” Yang said.
This study therefore provides clear evidence that warming is releasing much more carbon from the permafrost than previously calculated, which is the result of the formation of thermokarst. The findings can therefore help to better understand the impact of permafrost loss on global warming.
Everything about the permafrost
Permafrost, literally frozen ground, covers no less than 20 percent of the Earth’s surface. In winter the ground is frozen several meters deep, in summer only the top layer thaws, where some plants can still grow. This layer is at most 60 to 360 centimeters thick. The permafrost itself can be tens of meters thick. More than 400 meters were once measured in Alaska.
Scientists are keeping a close eye on the permafrost because it stores four times as much carbon as humans have emitted so far. Because accurate data has only been collected since 1970 about what happens when things thaw, it is still not entirely clear how great the effect is on warming and exactly how much methane and CO2 is released from the ground. There are studies that indicate that the impact may be much greater than thought, for example because too little account has been taken of the role of soil microbes, which wake up in response to rising temperatures and break down organic material that has been lying in the permafrost for years. stored. This releases CO2 and methane, as we wrote earlier.
