The ground that thaws each summer above Earth's permafrost is getting deeper almost everywhere scientists measure it, and the fastest changes are happening in high mountains. At some high-elevation bedrock sites in the Swiss Alps, the thawed layer deepened by as much as 36 centimeters (14 inches) per year.

The findings come from the first global assessment of long-term active layer monitoring, published in Communications Earth & Environment. The study was released in late August and has drawn renewed attention this week. It draws on measurements from 156 monitoring sites across the Arctic, Antarctica and mountain regions from 2000 to 2024.

The Ground Layer That Thaws Every Summer

Permafrost is ground, soil, or rock that stays frozen for at least two consecutive years. It underlies nearly 15% of the Northern Hemisphere's land. Above it sits the active layer, a band of ground that thaws each summer and refreezes each winter.

In a stable climate, that layer stays about the same depth from decade to decade. When it gets thicker year after year, it means summer heat is reaching deeper and the permafrost beneath is shrinking from the top down.

Scientists measure it in a simple way. Anna Klene, a University of Montana geographer and study co-author, has spent about three decades in Alaska's Brooks Range driving a metal probe into the ground until it hits frozen earth. "It's not super sophisticated," she told Earth.com. Repeated over many years at hundreds of sites, those measurements become a powerful climate record.

Mountains Are Thawing Fastest

Across the network, active layer thickness increased significantly at 55% of Arctic sites and 38% of Antarctic sites, George Washington University reported. More than 90% of monitored mountain sites in Europe and high Asia showed increases, as did sites in South America, and several mountain sites saw the active layer double.

The paper reports that at high-elevation bedrock sites in the Swiss Alps, the active layer increased by 0.9 to 36.2 centimeters per year, while one site showed a slight decrease. In 2022, the active layer at Switzerland's Schilthorn site exceeded 1,300 centimeters (about 43 feet), the deepest on record and confirmed by multiple boreholes.

European mountain sites averaged about 10.3 centimeters per year, more than ten times the Arctic average of about 0.8 centimeters. On the Tibetan Plateau and nearby high Asia, often called the Third Pole, the average was about 3.2 centimeters per year.

Mountain permafrost is often bedrock with relatively little ice and sits close to the melting point, so added heat goes quickly into thawing. Arctic lowlands with thick peat and organic soils changed far less. In the Arctic, warmer summers were the main driver, and wetter summers added to the thaw.

Wildfire, Roads and Unstable Slopes

Fire also leaves a mark — sites previously burned by wildfire showed larger increases, because fire strips away the insulating layer of vegetation and moss that shields frozen ground from summer heat, Earth.com reported. As wildfire seasons lengthen across Alaska, Canada and Siberia, that link could matter more.

The practical stakes are large. Roads, railways, airports, pipelines and buildings across northern Alaska, Canada, Siberia and the Tibetan Plateau sit on frozen ground. When it thaws, foundations shift, pavement buckles and repairs mount. Earlier work by Streletskiy and colleagues estimated that as much as 50% of Arctic infrastructure could face a high risk of damage by 2050.

Russia's gas-producing north shows how this plays out. On the Yamal Peninsula, the active layer deepened by about 0.4 to 0.7 centimeters per year, and near Urengoy by about 2.7 centimeters at sites where pockets of permanently unfrozen ground called taliks have appeared, according to data reported by IntelliNews.

In steep mountains, ice in rock cracks acts like cement. As thaw reaches deeper, slopes can lose that support, raising concern about rockfall and landslides around Alpine towns, cable cars and mountain huts. The study itself focuses on thaw depth rather than slope failures.

Carbon is the global concern — scientists estimate the top three meters of permafrost hold about 70% of the organic carbon stored in permafrost soils. As it thaws, microbes can release that carbon as carbon dioxide and methane, adding to warming.

Limits of the Measurements

The study is a synthesis of field measurements, not a model, which gives it strength. But it has limits. Mountain sites vary greatly from one slope to the next, and high-elevation climate data are often too coarse to explain every local change.

In ice-rich Arctic ground, the surface can also sink as ice melts, so a probe measured from the surface may understate how much permafrost has actually been lost. And the study does not estimate how much carbon has been released.

"The significance of this study lies in the fact that we're not just looking at isolated hotspots anymore," said lead author Dmitry Streletskiy of George Washington University.

Planning on Thawing Ground

For most readers, the effects arrive indirectly, through infrastructure repair costs in Alaska and other cold regions, through travel and safety advisories in mountain areas, and through the long-term climate effect of released carbon.

Alaskans can follow state and borough guidance on building and road conditions on permafrost. Hikers and climbers in the Alps and other high ranges should check local hazard warnings, since rockfall risk can rise during warm spells.

The researchers call for more monitoring, especially in Antarctica and mountain regions where sites are sparse. Each new season of probe measurements will show whether the deepening continues at the same pace.

What Readers Want to Know

What is the active layer? It is the top layer of ground above permafrost that thaws each summer and refreezes each winter.

What did the study find? The active layer deepened at most of 156 monitoring sites worldwide from 2000 to 2024, fastest in mountain regions.

How fast is it thawing in the Swiss Alps? At some high-elevation bedrock sites, the active layer deepened by up to about 36 centimeters per year.

Why does a thicker active layer matter? It signals permafrost loss, which can damage roads and buildings, destabilize slopes, and release carbon.

How does wildfire affect permafrost? Fire removes insulating vegetation, so burned sites showed larger increases in thaw depth.

Is this a new study? It was published in late August 2026 and has drawn renewed attention since.