The last decade was the greater Yellowstone region’s hottest on record, according to a study released Tuesday by a pair of environment-oriented nonprofits.

The study’s findings show that temperatures over the past 10 years were 1.4 degrees above the region’s 20th century average. Summers, in particular, averaged 2.3 degrees higher than summers in the past century.

And if worldwide emissions of heat-trapping gases are not reduced, the warming will continue with disastrous effects, Stephen Saunders, president of the Rocky Mountain Climate Organization, said Tuesday.

Saunders, a former deputy assistant secretary with the U.S. Department of the Interior, announced the climate data Tuesday in Bozeman. The study was produced by Saunders’ climate organization in conjunction with the Greater Yellowstone Coalition.

The 55-page study predicts that if we do nothing to stem greenhouse gases, within 60 to 90 years, summers in Yellowstone National Park could average 9.7 degrees higher than today’s temperatures.

A temperature increase of that magnitude would “totally transform the ecosystem and the experience for people visiting Yellowstone National Park in the summer,” Saunders said.

The study is the first of its kind demonstrating global warming’s impacts on the Yellowstone region, including Yellowstone National Park, Grand Teton National Park and several designated national wildlife areas, its authors said.

Though the authors did not design new climate models for their study, they drew “the best of what’s already known” from a variety of larger studies, Saunders said.

The effects of climate change will be felt particularly by the region’s world-renowned wildlife, said Scott Christensen, GYC’s climate change program director and one of the study’s authors. Grizzly bears, pronghorn, big horn sheep and four native species of cutthroat trout are vulnerable to warming effects, he said.

Another concern is the loss of forests, which cover about 83 percent of the region, Saunders said, noting that the effects of climate change are already visible in the large-scale die-off of white bark pines due to an infestation of pine bark beetles. The beetles thrive in warmer weather and favor older trees that take 60 to 80 years to mature.

Fewer trees means fewer pinecones — a mainstay of grizzly diets, and some climate models in the report also indicate conditions for aspen growth will deteriorate.

GYC hopes the study will provide science to guide the organization’s future decisions regarding its resources and conservation efforts, Christensen said. GYC plans to look into reducing stressors for wildlife, attending to water quality and quantity, protecting wildlife migration corridors and developing academic resources.

Federal agencies can also play a role. The National Park Service has “a unique opportunity to capture the attention of American people” by adopting more sustainable practices and showcasing them to educate the throngs of park visitors each year, Saunders said.

And, the authors noted, the report’s predictions do not take into account any legislation designed to reduce emissions.

“Hopefully, we’ll be able to avoid the worst scenarios,” Christensen said. But it will take collaboration between wildlife services, nonprofits and private landowners, particularly as conditions change.

“We should not let our future unfold in this way,” Saunders said. “The threads are already being pulled from this glorious tapestry of the Yellowstone ecosystem.”

Jodi Hausen can be reached at jhausen@dailychronicle.com or 582-2630.

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