This satellite image of the Arctic ice cap shows the extent of summer sea ice in 2012, compared with summer sea ice in 1979 (yellow outline), when satellites first observed the area. Now about half of the ice cap melts in summer due to rising global temperatures.
My latest piece for National Geographic online, posted February 2:
As scientists and much of the public differ on the causes of climate change, the planet keeps getting warmer … and the effects are adding up. (More at the link above.)