Dramatic ice melt seen in Greenland
An unusual ridge of warm air causes over half the surface sheet to melt in four days.
During a four-day period this month, 57% of the surface of the Greenland ice sheet melted, bringing the total melted area to 97% of the surface, according to NASA.
The melting is the most severe that has been observed since researchers have been monitoring the ice sheet, the agency said in a statement. According to records from ice cores, it is the worst melt since 1889.
But what particularly surprised scientists was the speed with which the melt occurred. When SonNghiem of the Jet Propulsion Laboratory in La Cañada Flintridge first observed the data from the Oceansat-2 satellite on July 12, he was taken aback.
“This was so extraordinary that at first I questioned the result: Was this real or was it due to a data error?” he said.
It was only when researchers combined the Oceansat-2 results with data from two other satellites that they became convinced it was accurate.
The data showed that, on July 8, about 40% of the surface of the ice sheet had melted. By July 12, 97% had melted.
The extreme melt coincided with an unusually strong ridge of warm air, or a heat dome, over Greenland. The ridge was one of a series that has dominated Greenland’s weather since the end of May.
“Each successive ridge has been stronger than the previous one,” said climatologist Thomas Mote of the University of Georgia in Athens.
The most recent one reached Greenland on July 8, then remained stationary beginning three days later. By June 16, it had begun to dissipate.
On average, about half of the surface of the ice sheet melts every summer. The high altitudes refreeze relatively quickly, while liquid from lower elevations runs off into the ocean, to be replenished in winter.
It is not yet clear whether enough water from the current melt entered the ocean to affect sea levels.