Data from three satellites show the massive ice sheet covering the Arctic territory of Greenland underwent an unusual melting earlier this month.
The U.S. space agency NASA says the data shows 40 percent of the ice sheet, stretching from Greenland's coastal edges to its 3.2-kilometer-thick center, had experienced some thawing by July 8, and accelerated to 97 percent four days later. The ice melt was the largest detected in more than 30 years of satellite observations.
A scientist at Dartmouth College says such pronounced melting has not occurred since 1889.
NASA says the melting coincided with an unusually strong ridge of warm air, known as a heat dome, that parked itself over the ice sheet on July 11 and remained for about five days.
Scientists say they cannot determine whether the recent melting is a natural event or the result of man-made climate change.
Last week, a NASA satellite captured images of a huge iceberg measuring twice the size of New York City's Manhattan island breaking off from the Petermann Glacier, one of the largest in Greenland.
Some information for this report was provided by AP, AFP and Reuters.