October 17, 2019

In Greenland, a Disturbing Loss of Ice

“During the past week, temperatures at the highest reaches of the Greenland ice sheet rose above freezing, melting snow at the Summit Station (10,550 feet above sea level) for the first time since July 2012 and perhaps only the third time in the last seven centuries.

Across lower elevations around the margins of the ice sheet, bare glacial ice melted at an unprecedented rate, losing 12.5 billion tons of water on Thursday alone, with daily losses likely exceeding any point in at least the past 70 years.

The Greenland ice sheet covers an area the size of Alaska with enough ice to raise global sea level by more than 20 feet. Greenland gains ice each winter from compacting snow accumulation and loses ice from melt water and icebergs discharged to the ocean. A dry, warm spring this year left a thin snow cover over bare glacial ice. Spring warming followed by a large melt event in June led scientist Jason Box of the Geological Survey of Greenland to predict record ice losses this year. The peak of the melt season passed in mid-July with more typical summer conditions, but the past week again saw a large increase in the area and intensity of melt across the Northern Hemisphere’s remaining ice sheet.

This latest heat wave was particularly unusual as a dome of warm air arrived from the east, associated with the remnants of the record-setting European heat wave last month. Most large melt events on Greenland involve warm, humid air masses arriving from North America and the western Atlantic Ocean. This surge of warm air started in North Africa, traveled north across Europe and then westward across the North Atlantic Ocean toward and across Greenland. Air masses originating over North Africa are known to reach Greenland — Saharan dust has been traced to the ice sheet — but this recent air mass was exceptionally warm. By following the path of the heat wave, scientists predicted the extensive melt several days in advance. Air temperatures at Summit hovered near or above freezing for more than 11 hours on Wednesday, which is nearly twice as long as the last melt event there in 2012.”

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