For years now, scientists have been investigating how the gradual thawing of near-surface permafrost, which takes place in the uppermost layers of Arctic soils and in the course of decades, will affect the release of previously frozen carbon to the atmosphere. Now an international team of researchers, including AWI researcher Prof Guido Grosse, has underscored the urgent nature of another phenomenon, which has only been sporadically investigated: the abrupt thawing of ice-rich permafrost, which can transform entire landscapes in only months of years through subsidence, the formation of meltwater ponds, and massive landslides – and release the carbon buried even further below in the process. The team’s commentary was recently released in the journal Nature.
In this context the report’s first author, Prof Merritt Turetskyfrom the University of Guelph, Canada, describes the permafrost carbon stockpile as a “sleeping giant” that is now rousing. The abrupt thawing of these soils and subsequent carbon mobilisation is likely to have serious impacts on global warming.
“To date, the various rapid thawing processes have only been observed at the local or regional scale. There hadn’t been any efforts to compile the studies and data so as to estimate the total amount of mobilised carbon, as has been done for the gradual, near-surface thawing,” explains Guido Grosse, a permafrost expert at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI).
Permafrost influences roughly one-quarter of the Earth’s surface. These frozen soils lock up carbon in biomass from dead plants, animals and microbes over millennia, preventing its breakdown and keeping it out of the atmosphere. As a result, permafrost region soils now hold twice as much carbon – about 1600 billion tonnes (gigatonnes) – as the atmosphere (ca. 830 gigatonnes).
In their commentary, the team discusses the importance of abrupt thaw for carbon release estimates, northern ways of living and climate policy. The researchers put together results from abrupt thaw studies from a range of environments across the permafrost zone to estimate the overall effect.
According to Guido Grosse: “Thanks to rapid processes like thermokarst and thermo-erosion, even permafrost buried several metres below the surface can thaw in just a handful of years – or in extreme cases, like thaw slides, large volumes of soil can thaw in a matter of weeks. Whereas in the past, these processes were assumed to be local in nature, more and more studies indicate how widespread they are, and how they are occurring more and more frequently, even in the coldest regions of the High Arctic.”
Unlike gradual thawing, which chiefly affects the surface and penetrates the lower layers only very slowly, abrupt permafrost thawing disrupts deeper carbon stockpiles more rapidly. In addition, abrupt thawing releases more methane – a more potent greenhouse gas than carbon dioxide – than does gradual thawing.
Although initial estimates show that only 20% of the permafrost region is vulnerable to abrupt thawing, the additional emissions produced could potentially double the climate feedback associated with permafrost thawing by the end of the century.
In addition, the team calls for more measurement and monitoring of Arctic permafrost, as well as improved modelling and reporting of effects of thaw on climate– above all, the effects of rapid thawing have to be taken into account, because they will manifest in politically relevant timescales: according to the researchers, the abrupt thawing will have substantial consequences, ranging from costly infrastructure damage to roads and rail lines, to making it even more difficult to meet emission targets intended to limit global warming– and neither gradual, near-surface thawing nor abrupt, deep thawing and the accompanying carbon release have been reflected in the climate models employed by the IPCC.