Beaver ponds may exacerbate warming in Arctic, scientists say

Rising temperatures have spurred an influx of beavers to Alaska and northern Canada on a huge scale'

The stream through western Alaska never looked like this before. In aerial photography from the 1980s, it wove cleanly through the tundra, thin as thread. Today, in satellite images, it appears as a string of black patches: one large pond after another, dozens of metres apart.

It's a transformation that is happening across the Arctic, the result of landscape engineering on an impressive scale. But this is no human endeavour to reshape the world. It is the work of the North American beaver, and there is no sign of it stopping.