Wolverines won’t get protection as a threatened species, federal authorities announced Tuesday — citing scientific uncertainty about precise impacts of climate change.

This U.S. Fish and Wildlife Service decision reverses a proposal last year to protect wolverines and encourage voluntary efforts to help them in western states, including Colorado.

Fewer than 300 wolverines have survived in the lower 48 states. The only one confirmed in Colorado, solo wanderer M56, hasn’t emitted a signal since October 2012.

Fish and Wildlife director Dan Ashe acknowledged disagreement among federal biologists and, speaking from Aspen in a teleconference with journalists, called his decision complex and challenging.

“This isn’t about whether we believe the climate is changing. We do,” Ashe said.

“We know too little about the ecology of wolverines. … We can’t make a reasonable prediction that wolverines will likely be endangered in the immediate future.”

The federal proposal to protect wolverines was based on beliefs that species needs heavy late-season snow to form dens and that snow may decrease across suitable habitat.

“We found we had to question this assumption,” Ashe said.

Beyond climate change, federal biologists who conducted the analysis on wolverines “really didn’t see any other significant threats,” he said.

While the wolverine population is estimated at fewer than 300, that number probably has increased since the mid-19th century and appears at least stable, Ashe said.

The decision not to list surprised Colorado Parks and Wildlife officials, who were evaluating the new federal posture, state spokesman Matt Robbins said.

Colorado high country offers suitable habitat, and the state has been seen as potentially useful for possible efforts to protect wolverines. Federal officials say they will continue to encourage states to reintroduce wolverines.

Colorado wildlife commissioners a few years ago asked staffers to launch stakeholder discussions for a state project to help wolverines.

Wolverines remain on the state’s list of endangered species, which means they can’t be hunted here.

A lone male wolverine, M56, trekked from Wyoming into Colorado in 2009 with a cigar-size transmitter in his belly. For years, M56 seemed to thrive, roving as far as 100 miles from forests west of Fort Collins across Interstate 70 to the Mosquito Range mountains southeast of Leadville.

But Colorado’s discussions, which included the ski resort industry, fizzled.

Wildlife conservation groups decried the federal decision not to protect wolverines as wrong and on Tuesday began building a lawsuit against the Fish and Wildlife Service.

“They’re insisting on a level of certainty that won’t exist until wolverines are extinct,” Earthjustice attorney Tim Preso said.

The Endangered Species Act “requires this agency to follow the best available science, and in this case the science points in one direction,” Center for Biological Diversity endangered species director Noah Greenwald argued. “The agency went against its own biologists.”

Bruce Finley: 303-954-1700, bfinley@denverpost.com or twitter.com/finleybruce