The melting north.

The Arctic is one of the world’s least explored and last wild places. Even the names of its seas and rivers are unfamiliar, though many are vast. Siberia’s Yenisey and Lena each carries more water to the sea than the Mississippi or the Nile. Greenland, the world’s biggest island, is six times the size of Germany.

A heat map of the world, colour-coded for temperature change, shows the Arctic in sizzling maroon. Since 1951 it has warmed roughly twice as much as the global average. In that period the temperature in Greenland has gone up by 1.5°C, compared with around 0.7°C globally. This disparity is expected to continue. A 2°C increase in global temperatures—which appears inevitable as greenhouse-gas emissions soar—would mean Arctic warming of 3-6°C.

Almost all Arctic glaciers have receded. The area of Arctic land covered by snow in early summer has shrunk by almost a fifth since 1966. But it is the Arctic Ocean that is most changed. In the 1970s, 80s and 90s the minimum extent of polar pack ice fell by around 8% per decade. Then, in 2007, the sea ice crashed, melting to a summer minimum of 4.3m sq km (1.7m square miles), close to half the average for the 1960s and 24% below the previous minimum, set in 2005. This left the north-west passage, a sea lane through Canada’s 36,000-island Arctic Archipelago, ice-free for the first time in memory.