The decision carries potential ramifications for other species affected by climate change — from Alaska's bearded seals and the Pacific walrus to dozens of species of corals — as scientists and regulators grapple with limits on computer climate models.
The Associated Press obtained the decision prior to a formal announcement expected Tuesday.
"Climate change is a reality," Ashe said. "What we don't know with reliability is what does climate change mean for denning habitat that wolverines prefer."
He added, "It's possible wolverines are adapting and continuing to adapt."
Federal wildlife officials last year had said future temperature increases could melt snowfields in high elevation mountain ranges in the Lower 48 states where wolverines are found. They called for increased protections to keep the species from going extinct.
The first indication that stance had changed came last month, in leaked memo from a Fish and Wildlife regional director in Denver who overturned her staff's recommendations for more wolverine protections.
Wildlife advocates blamed the reversal on pressure from state wildlife agencies. They said they intend to sue Ashe's agency in federal court to force it to adopt protections.
Officials from western states including Montana, Wyoming, Utah and Idaho had opposed federal protections, and said the animal's population has increased in some areas in recent decades.
That's similar to what happened to the bearded seal. It received protections from the National Marine Fisheries Service in 2012 only to lose them last month, when a federal judge sided with Alaska officials who said 100-year projections of sea ice losses were based on speculation.
At least two other species, the American pika and black-footed albatross, were denied protections in recent years after the government concluded some of the animals might die off because of climate change, but enough would survive to keep the populations viable.
But Ashe said when the evidence is clear his agency will act, such as the 2008 decision to list the polar bear as a threatened species because of sea ice losses in arctic from global warming.
For wolverines, the withdrawal also means an end to the federal government's proposal to re-introduce the species to the southern Rocky Mountains of Colorado, Wyoming and New Mexico. Ashe said he intends to encourage the state's governors to pursue reintroductions on their own.
Once found throughout the Rocky Mountains and in California's Sierra Nevada mountain range, wolverines were wiped out across most of the U.S. by the 1930s due to unregulated trapping and poisoning campaigns, said Bob Inman, a wolverine researcher with the Wildlife Conservation Society.
In the decades since, they have largely recovered in the Northern Rockies, where 250 to 300 of the animals live, but not in other parts of their historical range.
Steve Running, a University of Montana ecology professor and member of the Nobel Peace Prize-winning Intergovernmental Panel on Climate Change, said computer models used to predict future temperatures and precipitation amounts become less accurate as they go further out in time. That makes it hard to localize potential impacts.
But Running added that climate trajectories over recent decades give an accurate depiction of what's in store and should be used by wildlife managers now to make long-term decisions. Over the past 50 years, he said, the snow melt in the Northern Rockies has shifted two weeks earlier in the spring.
"If you take 50 more years and think of it as two more weeks earlier, wolverines are probably one of the classic poster children of a highly temperature-sensitive animal," he said.