Despite evidence that climate change threatens their habitat, the U.S. Fish and Wildlife Service announced Tuesday that it was withdrawing a proposal to list North American wolverines as a threatened species under the Endangered Species Act. Environmental groups decried the decision, saying it ignored “the best available science” and threatening to sue “unless the Service takes action to protect the wolverine as the Endangered Species Act requires.”

The wolverine, described by the Fish and Wildlife Service (FWS) as “a large but elusive member of the weasel family,” requires deep snow to build sheltered dens in which to raise its young. According to the Center for Biological Diversity, global warming over the next 75 years is projected to wipe out 63 percent of the snowy habitat wolverines need to survive. Experts say there are only 300 wolverines left in the lower 48 states.

But the FWS said: “While it is clear that the climate is warming, after carefully considering the best available science, the Service has determined that the effects of climate change are not likely to place the wolverine in danger of extinction now or in the foreseeable future.”

Whereas with polar bears, scientists were able to point to specific evidence of impacts from climate change, it is more difficult to collect such observations about wolverines, one FWS official said in a memo: