A new global study has revealed that permafrost is degrading across the globe at an unprecedented rate, with some mountain regions experiencing active layer thickening at more than 36cm per year.
While permafrost is, by definition, a permanently frozen layer of ice, on top of this sits the active layer, which thaws and refreezes each year according to the seasons. The thickening of this layer comes at the expense of the permafrost.
The research, led by Professor Dmitry Streletskiy of George Washington University, compiled data from 156 monitoring sites across the Arctic, Antarctic and mountain regions across the world. The findings confirm that permafrost degradation is occurring on a global scale, extending beyond previously documented regional studies.
The active layer has increased significantly at 55% of Arctic sites and 38% of Antarctic sites between 2000 and 2024.
In European mountains and high-elevation Asian, more than 90% of monitoring sites showed significant deepening.
Streletskiy said: ‘One of Earth’s most important indicators of climate change is permafrost as it directly reacts to rising temperatures. The significance of this study lies in the fact that we’re not just looking at isolated hotspots anymore. The collaborative efforts of the involved sites show a pattern that spans continents and climate zones, telling us that global permafrost degradation is already well underway.’
The largest changes were observed in mountain regions where active layer doubled at a number of sites. In the Swiss Alps, one site at Schilthorn recorded an active layer exceeding 1,300cm in 2022, the highest on record. European mountain sites saw average increases of 10.3cm per year, though in some locations this reached 36.2cm.
The primary driver is rising summer temperatures. The study found that increased ‘thawing degree days’ (a measure of accumulated summer warmth) is the main climatic factor behind active layer thickening in Arctic lowland permafrost. Interestingly, increased rainfall also contributes, though to a lesser extent.
The effect of each additional centimetre of rainfall deepens the active layer by approximately 0.16cm, suggesting that wetter summers actually increase thawing.
Problematically, permafrost contains vast quantities of organic carbon, roughly twice as much as is currently in the atmosphere. As it thaws, this becomes vulnerable to decomposition, potentially releasing greenhouse gases, creating a worrying feedback loop.
The study also highlights significant regional variations. Sites with thick organic layers and high ground ice content showed smaller changes, acting as natural buffers against warming. On the other hand, bedrock sites with low ice content, particularly in mountain regions, experienced the most dramatic changes, as they lack the insulating properties of organic soils and the heat buffering effect of ground ice.
Continuous permafrost zones (where permafrost underlies more than 90% of the area) showed smaller increases compared to discontinuous permafrost zones, which are already closer to the thaw threshold.
Continuous permafrost, which covers more than 90% of the landscape, thawed more slowly than discontinuous permafrost, where the frozen ground is patchier and already closer to the temperature at which it thaws.
The researchers conclude: ‘More monitoring sites and longer time series in underrepresented geographic locations are needed to better understand global permafrost degradation under changing climatic conditions.’
The full research can be read here.
Photo: Himmel S