There’s nothing quite like historical photos of glaciers to show what a dynamic planet we live on. Hardangerjøkulen, like many Norwegian glaciers, has retreated and thinned dramatically since the 19th century.

Satellites are giving us a better understanding of how Earth’s ice cover has changed in the more recent past. The satellite era, beginning in the 1970s, has given us a picture of accelerating ice changes in places like Alaska, Greenland, Scandinavia and Antarctica, where the loss of land-based ice is contributing to global sea level rise. In Norway our glaciers are melting. We can see it. Warmer summers, warmer winters. We must do something now.

Himalayan glaciers would mostly disappear by 2035, and the importance of mountain water to more than a billion people, have brought increased scrutiny to glacier changes and the importance of the meltwater.