Arctic Ocean
This September, the Arctic sea ice extent has shrunk to 4.1 million square kilometres (sq km)-the second lowest in the history of satellite measurements. It is exceeded only by the all-time record low of 3.4 million sq km in 2012. "Once again, a massive loss of sea ice in the Arctic," says Prof. Lars Kaleschke from Universität Hamburg's Center for Earth System Research and Sustainability (CEN). His colleague Prof. Christian Haas from the Alfred Wegener Institute (AWI) confirms: "The trend continues." Currently, the Northeast and Northwest Passages are navigable at the same time.