Patrick Burkhart and his colleagues recently published a review of their research on the cryosphere, which is a collective term for all the ice on the surface of the Earth. In addition to their review of the science, the new information they add is a photographic project documenting the retreat of glaciers around the globe.

The retreat of the cryosphere is one of the many lines of evidence supporting the idea that the earth has been warming over the last half-century. There are several different ways to look at this. You can look at each pole to see the extent of ice coverage at their peak in winter and minimum in summer. You can look at specific ice sheets, like Greenland. You can look at glaciers. And you can look at total global ice, the cryosphere, which of course is the best single measure.

With regard to glaciers, the authors point out that there are many variables affecting the current size of any individual glacier. It is possible but difficult to account for all these variables and isolate one as a primary cause of melting. However, you can survey glaciers from around the world, which is a good way to control for local variables. When we do this we find there is a significant trend toward glacial retreat.

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