Observations from three satellites showed that between July 8 and July 12 of this year the proportion of the Greenland ice sheet with melting surface ice shot up from 40 percent to 97 percent. After making sure that these astonishing data were correct, scientists attributed the melt, which continued for about two weeks, to a ridge of warm air or “heat dome” that passed over Greenland for the seventh summer in a row.

Then on July 15 or 16 –no one noticed exactly when it happened –a chunk of ice 130 km² (50 square miles) in area toppled off the Petermann glacier in Greenland’s far north-west into the Nares Strait. Less than two years had passed since August 2010, when the same glacier lost another chunk, twice as large in area.