Scientists have long known that the amount of ice in the Antarctic is steadily decreasing. They were surprised, however, to discover recently that up to a quarter of the melting occurs in the depth of winter, when the average temperature is 15C below freezing. The melting is caused by a phenomenon called the föhn effect.

The föhn or foehn wind was first noted in the Alps, and occurs when a wind blowing over mountains descends on the far side. The increase in pressure at lower altitude causes the mass of air to warm up by about one degree per hundred metres. Such a wind blowing down from a high mountain range can easily rise above freezing. The Chinook wind in the Rocky Mountains is sometimes called “snow eater” for its capacity to strip snow from the slopes.

The winter Antarctic ice melt was discovered by a team led by Peter Kuipers Munneke of Utrecht University, using data from satellites and unmanned weather stations. It was presented to the European Geosciences Union in Vienna in April. The Antarctic has the highest elevation of any continent, and consequently fierce föhn winds. The new results show that these hot winds are making a significant contribution to ice melt.