Bremerhaven, 9 April 2015. Permafrost in the Arctic and in subarctic regions will most likely continually release substantial quantities of greenhouse gases over the coming decades: that’s the verdict of an international research team, which recently compiled and analysed the latest permafrost studies. As such, they have determined that the recurring thesis that there will be a sudden and widespread release of billions of tonnes of carbon dioxide and methane is highly unlikely. The study was released today in the journal Nature.
The permafrost in the Northern Hemisphere holds nearly twice as much carbon dioxide as is currently contained in the atmosphere. “When the soil thaws, microorganisms start breaking down the organic matter that has been locked inside the earth for millennia, producing carbon dioxide and methane in the process. Therefore, if the global mean temperature continues to rise, permafrost could release more greenhouse gases,” explains Dr Guido Grosse, a permafrost researcher at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) and co-author of the current study. Accordingly, how rapidly soils in the Arctic will thaw and release greenhouse gases is an essential question – one which to date has produced a number of different answers.
In an attempt to answer that question, an international team of researchers from the United States, Europe, Canada and Russia compiled the current state of knowledge on permafrost. In the process, they came to the conclusion that over the decades to come the frozen soil will most likely gradually but steadily release large quantities of carbon dioxide and methane; they believe the thesis that rising temperatures will cause the permafrost to suddenly release huge quantities of carbon dioxide and methane is highly unlikely. “For the most part, permafrost only responds slowly to climate changes. However, once the thawing process has begun, it’s not terribly easy to stop: even if we managed to dramatically reduce anthropogenic emissions today, the permafrost would continue to thaw over the next several centuries,” says Grosse.
How much carbon is hidden in the permafrost?
In the course of their work, the researchers above all gained new insights with regard to the amount of carbon believed to be “hidden” in the permafrost regions. Whereas initial studies put the number at between 1,600 and 1,700 billion tonnes, the team used historical and current data to narrow it down to between 1,330 and 1,580 billion tonnes for those permafrost regions investigated in more detail. That amount is supplemented by up to 400 billion tonnes of additional carbon in those regions where the comparative lack of regional data makes it impossible so far to more precisely gauge the amount.
The researchers expect the majority (ca. 70 percent) to come from the uppermost three metres of the permafrost; nevertheless, considerable carbon deposits can be found as far down as 40 metres below the surface. “We believe that even the deepest frozen deposits are still climate-relevant for us humans, since these layers contain a great deal of ice, which will melt as temperatures rise and will make the permafrost, despite the depth, susceptible to rapid and extensive thawing within the next 100 to 300 years – which can of course lead to the release of greenhouse gases,” relates the AWI permafrost researcher.
Further, there is a considerable and still unmeasured amount of carbon hidden underwater in the shelf seas of northern Siberia and Alaska. The permafrost that formed here on land during the last ice age was covered with water when that age came to an end and the shelves were flooded. As a result, part of the permafrost remains today and has been dubbed submarine permafrost.
Abrupt, regional permafrost thawing
Although the researchers believe the depletion of this carbon reservoir will be gradual, in the study they also draw attention to certain regions of Siberia, Alaska and Canada, where the thawing may progress more rapidly. The reason: the soil in these areas has a high percentage of ice content near the surface. When temperatures rise quickly, these subterranean ice deposits start to melt, causing the ground above them to sink. In turn, water starts to collect in the resulting depressions, producing what are known as thermokarst lakes, under which the soil continues to thaw at an accelerated rate.
“The thawing under the lakes occurs in just a few decades and can reach to extremely deep layers. As such, we consider these thermokarst processes to be a clear sign that the thawing isn’t always gradual, but instead that under certain conditions – like intense warming or altered precipitation levels – can be quite sudden at the regional level,” explains Dr Guido Grosse.
Not all carbon is created equal
That being said, the researchers are also careful to note that the thawing of permafrost doesn’t automatically mean all of the carbon it contains will be released into the atmosphere as carbon dioxide and methane. “Even microbes have their favourite foods. There are some types of carbon they can easily digest, some that take a bit more work – and a few types that they can only break down extremely slowly,” says Grosse.
Further, initial long-term experiments indicate that the carbon loss rate is highest at the beginning, when the soil first begins to thaw out; over time, that rate declines. Nevertheless, 15 percent of the readily transformable carbon could be released as greenhouse gases by the year 2100. According to the team’s findings, this would produce a further global warming of up to 0.27 degrees Celsius by the end of this century.
Thawing permafrost in climate models
The permafrost researchers’ goal is now to integrate their findings into climate models; to date, permafrost-related processes have received little attention when it comes to making prognoses on future climate changes. Summing up, Grosse adds, “If you consider that permafrost regions, which make up nearly a quarter of the land surface area in the Northern Hemisphere, will likely release just as much greenhouse gas as the historically much touted man-made changes in land use, you begin to realise just how important these processes are for our climate.”
The international collaboration was financed by the US-based National Science Foundation (NSF). Dr Guido Grosse received funding from the European Research Council (ERC) project PETA-CARB and the Helmholtz Association’s Initiative and Networking Fund.
Notes for Editors:
The original paper was published under the following title : “Climate Change and the Permafrost Carbon Feedback“ in Nature. DOI: 10.1038/nature14338 . Link to the study: http://www.nature.com/nature/journal/v520/n7546/full/nature14338.html
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The Alfred Wegener Institute conducts research in the Arctic, Antarctic and oceans of the high and mid-latitudes. It coordinates polar research in Germany and provides major infrastructure to the international scientific community, such as the research icebreaker Polarstern and stations in the Arctic and Antarctica. The Alfred Wegener Institute is one of the 18 research centres of the Helmholtz Association, the largest scientific organisation in Germany.