“When you start flooding areas with permafrost you immediately trigger permafrost degradation,” said Ken Tape, an assistant professor at the University of Alaska in Fairbanks who has researched the beavers. “You start thawing the frozen ground that’s holding the soil together, and that water and soil and other things are washed away.”

What remains is a pitted landscape, with boggy depressions, that directs warmer water onto the permafrost, leading to further thawing. As permafrost thaws it releases carbon dioxide and methane, which in turn contributes to global warming and helps increase the speed that the Arctic, which is already warming faster than the rest of the planet, defrosts. Worldwide, permafrost is estimated to contain twice as much carbon as is currently in the atmosphere.

The beavers are far from primary drivers of global warming — that distinction belongs to humans, after all. And arctic permafrost is already thawing because of warmer temperatures. But the beavers’ handiwork accelerates the thawing and exacerbates climate change, Dr. Tape said.

“Whether you want to call them ecosystem engineers or keystone species, beavers have a huge impact on the landscape,” he said.