The long-term warming trend was temporary interrupted in scree slopes and rock glaciers with year-round snow cover, said Swiss permafrost monitoring service Permos.
The temporary interruption was the result of very cold ground temperatures resulting from long-lasting snow cover in spring 2016 and the late arrival of snow in winter 2016/17, Permos said in a statement.
The monitoring service noted that this marked cooling propagated down to deeps of 10 metres and even 20 metres at cold sites such as Stockhorn (3400 metres above sea level) near the resort of Zermatt in the canton of Valais.
But Permos stressed the time-out on permafrost cooling had not affected areas where snow didn’t play a cooling role, such as rock faces.
And the Swiss Academy of Sciences warned that unusual weather conditions had played a role, given snowfall had been particularly low in 2016/17.
The academy also noted that the full impact of the hot summer of 2017 could not be seen in the results.
A permanently frozen part of the ground, permafrost covers around five percent of Swiss territory, typically above 2,500 meters in altitude. It is affected by sunlight and snow cover, particularly the date snow arrives and melts away.
In 2015/16, the temperature of permafrost at a depth of 10-20 metres reached a record high in several parts of the country, Permos reported in February 2017.
Since it began monitoring the situation in 2000 the temperature of the deeper permafrost has risen faster than the surface ground temperature, the service noted at that time.
The exceptionally high permafrost temperatures in the Swiss Alps are a consequence of the planet heating up over the past decades, said Permos last year.