Munich

As Europe swelters in one of its hottest summers since records began, the heat is making itself felt in the high Alps, where thawing ice is destabilizing landscapes that are normally frozen.

Researchers who study permafrost say that the patterns of disruption being seen in the Alps right now could soon be replicated on a larger scale, with global warming eroding the quarter of the Earth's land surface that is permanently frozen.

In the Alps, most ground above an altitude of 2,500 metres — including about 6% of Switzerland — remains frozen throughout the year, with only a surface layer less than 5 metres thick melting in the summer and re-freezing in winter. Above 3,000 metres, temperatures rarely exceed 0 °C for any length of time during the summer. In the past few weeks, however, ice has been thawing out steadily at altitudes of up to 4,600 metres.

Slopes containing ice-filled cracks and discontinuities have become unstable, rendering the area unsafe for climbers. On 15 July, for example, nearly 100 people were taken off the Matterhorn — Switzerland's best-known peak — by helicopter, after a rockslide had blocked their descent. At least 50 climbers have been killed this summer by Alpine rockfalls.

“Unfortunately, it is only incidents such as that at the Matterhorn that seem to raise awareness of the importance of permafrost research,” says Daniel Vonder Mühll, a geophysicist at the University of Basel in Switzerland.

Marcia Phillips, a geographer at the Swiss Federal Institute for Snow and Avalanche Research in Davos, investigates long-term permafrost changes in Switzerland, their impact on slope failure, and the stability of structures designed to hold back avalanches in Alpine valleys.

Digging deep: Swiss permafrost probes could provide clues to long-term climate change. Credit: L. KING

The institute is involved in PERMOS, a scheme to monitor permafrost temperature and slope stability at 26 drilling sites throughout the Swiss Alps. “There is a large variability, due to differences in topography. But by and large the threat of slope failure is increasing,” says Phillips.

Permafrost thawing is not restricted to the Alps. In northern Europe and Russia, for example, thawing permafrost is a growing challenge to the construction and operation of roads, bridges and oil and gas pipelines.

Climatologists see permafrost as a sensitive lead indicator of climate change. Researchers in the European Union-funded Permafrost And Climate in Europe (PACE) project have found evidence of temperature increases of between 0.5 and 2.0 °C over the past 60–80 years in permafrost soils in European mountain regions, from the Sierra Nevada in Spain to the arctic archipelago of Spitsbergen (C. Harris (ed.) Permafrost and Periglacial Processes 12 (1); 2001).

“There is clear evidence for accelerated thawing in the upper permafrost layer in many regions,” says Lorenz King, a geographer at Justus Liebig University in Giessen, Germany. If heavy snow in the winter insulates the ground from low air temperatures, permafrost can thaw even more deeply in summer, says Phillips.

Scientists have also suggested that permafrost melting can release vast amounts of carbon into the atmosphere, as the organic material that it contains is broken down by bacteria (see Nature 409, 751; 200110.1038/35057477). This raises the spectre of a vicious circle in which these increasing quantities of greenhouse gases drive climate change, melting more permafrost and accelerating global warming.