In a study, researchers show that an abrupt thawing of permafrost increases emissions by 40 percent. The permafrost regions of the Arctic are often referred to as a natural freezer, where a huge amount of carbon is stored, mainly in the form of animal and plant remains accumulated over millennia. However, these are decomposed by microorganisms as soon as the soil, which has been frozen until now, thaws. This produces climate-damaging greenhouse gases such as methane and carbon dioxide.
An international team of researchers has now found that the rate of thawing has a decisive influence on the type and amount of greenhouse gases released. As the researchers report in the journal Nature Geoscience, abrupt thawing processes, such as those possible in about five percent of Arctic permafrost landscapes, could increase total emissions by 40 percent – an increase that current climate models have not yet taken into account.
Rapid thawing processes are already changing the landscape and ecosystems of the Arctic. This means, for example, the rapid thawing and sinking of large areas of permafrost. However, this also includes so-called thaw slipping in hillsides and the formation of sinks in which rain water and meltwater accumulate, so that pools and lakes form. These so-called thermokarst lakes absorb much more solar energy on their surface than the surrounding land area. The heat stored in the water is then released to the frozen subsoil in a particularly effective way – at the bottom of the water as well as at the shore edges, which is why the permafrost in the vicinity of the lake quickly thaws. Often the shore area disintegrates and under certain circumstances the lake even runs out. Microorganisms then have the best starting conditions to decompose the animal and plant residues that were once trapped in permafrost, thereby producing greenhouse gases such as methane and carbon dioxide.
“A rapid thawing of the permafrost is always a dramatic ecological change. Permafrost landscapes, where you could just walk with hiking boots and were dry enough for trees to grow, quickly turn into a muddy mess,” says lead author Prof. Merritt Turetsky, director of the Institute for Arctic and Alpine Research (INSTAAR) at the University of Colorado Boulder.
Fast thawing releases a lot of methane
The Arctic permafrost soils contain an estimated 1440 to 1600 billion tons of carbon in the form of organic residues – spread over a total area of 18 million square kilometers. In their new study, scientists estimate that one-fifth of these landscapes contain so much underground ice that it encourages a rapid thawing of the earth. “As we now know, this rapid thawing releases a lot of carbon in the form of methane, which is about 25 times more climate-effective than carbon dioxide as a greenhouse gas. This means that rapid thawing processes on a relatively small area have an enormous long-term effect,” says co-author Prof. Guido Grosse, head of the permafrost research section of the AWI.
For the new study, the international team of researchers in various model studies had compared the amount of greenhouse gases currently released and up to the year 2300 when permafrost gradually thaws – meaning periods of several decades – and what emissions occur when the thawing processes occur within a few days or years. “Knowing these differences is very important, because our climate models can only reflect the gradual thawing of the permafrost. They thus substantially underestimate the emission and warming potential of thawing permafrost landscapes,” explains Guido Grosse.
If rapid thawing processes were included, the estimate of the warming potential from emissions from the Arctic permafrost region would be twice as high, the authors report. While this does not mean that greenhouse gas emissions in permafrost regions could be described as a climate bomb, it is clear that they will further exacerbate man-made climate change.
The results of the new study highlight the urgency to incorporate permafrost and the various mechanisms of its thawing into all climate models. At the same time, however, humanity must step up climate protection in order to limit global warming. “If we act in this decade, the worst effects of climate change can still be averted,” says Merritt Turetsky.
Source: Prof. Guido Grosse / AWI