NASA scientists expressed surprise and alarm on Tuesday in announcing the discovery of a widespread thaw in Greenland unprecedented in recorded history. An estimated 97 percent of Greenland’s ice sheet has undergone thawing, jumping from 40 percent in only a five-day period in July. Typically, about half of the ice sheet sees melting, but the proportion has doubled this year due to a dome of warm air that moved over Greenland. The ice melt is unmatched in the 30 years that satellites have been monitoring Greenland, and ice core data indicates that such a thaw has not taken place since 1889. "This was so extraordinary that at first I questioned the result: was this real or was it due to a data error?" Son Nghiem of NASA's Jet Propulsion Laboratory in Pasadena said in a press release. Scientists expect such events roughly every 150 years. If such melting repeats next summer, scientists say they’ll then be able to link it to global warming.