PARIS — The Alps are the birthplace of downhill skiing and a crucible for mountain climbing – but now the French government is trying to help their winter tourist towns adapt to a warming world. French Prime Minister Manuel Valls visited the Mer de Glace (the Sea of Ice) Friday on Mont Blanc, where the retreating glacier has been documented for more than a century.

“The Mer de Glace reveals the extent of climate change, and, to the naked eye,” said Valls. “The time has come to mobilize.”

Researchers say the Sea of Ice is only the most accessible example of a problem the region faces as warming mountainsides become more unstable and snowfall more inconsistent, threatening jobs and lives in a region dependent on adventure tourism.

Scientists have drilled the Mont Blanc region with sensor-equipped boreholes in recent years, hoping that measuring temperatures in the permafrost will give a sense of how quickly the problem is accelerating.

The town of Lanslevillard already knows firsthand, said Xavier Bodin, a researcher for France’s elite CNRS research center who specializes in Alpine permafrost. A debris flow touched off by an unstable rock glacier swept down the slope, crushing snow equipment.

In another part of the southeast French region, pylons for a ski lift had to be re-planted because the foundation grounds were melting. Elsewhere, retreating glaciers have exposed climbers to new, untested and potentially risky routes, he said.

“The rising temperatures in the mountains strongly modify the way people approach the high altitudes,” Bodin said.