“What’s happening here is happening on a huge scale,” says Ken Tape, an ecologist at the University of Alaska, Fairbanks, who is tracking the influx of beavers into the sparse northern landscape. “Our modelling work, which is in progress right now, shows that this entire area, the north slope of Alaska, will be colonised by beavers by 2100.”

The preponderance of beavers, which can weigh as much as 45kg, follows a collapse in trapping and the warming of a landscape that once proved too bleak for occupation. Global heating has driven the shrubification of the Arctic tundra; the harsh winter is shorter, and there is more free-running water in the coldest months. Instead of felling trees for their dams, the beavers construct them from surrounding shrubs, creating deep ponds in which to build their lodges.

Physics suggested this would happen. Beaver ponds are new bodies of water that cover bare permafrost. Because the water is warm – relatively speaking – it thaws the hard ground, which duly releases methane, one of the most potent greenhouse gases.

Scientists now have evidence this is happening. Armed with high-resolution satellite imagery, Tape and his colleagues located beaver ponds in the lower Noatak River basin area of north-western Alaska. They then analysed infrared images captured by Nasa planes flying over the region. Overlaying the two revealed a clear link between beaver ponds and methane hotspots that extended for tens of metres around the ponds.