Home to the world’s first national park, the Greater Yellowstone Area (GYA) is a vast ecological powerhouse that comprises 22 million acres in three states – Wyoming, Montana, and Idaho. Wildlife like grizzly and black bears, wolves, elk, moose, bison, bald eagles, and even wolverines, make the area their home – as do humans.

Residents and visitors alike savor the region’s outdoor recreation opportunities, from hiking, camping, fishing, boating, sightseeing, and wildlife watching to winter sports like skiing and snowmobiling. This summer, researchers published the Greater Yellowstone Climate Assessment, analyzing impacts of climate change on the entire ecosystem, including portions of six watersheds.

“Right now we have national assessments and some state assessments, like the Montana Climate Assessment, but we don’t really have climate assessments that focus on ecosystems,” says Cathy Whitlock, co-lead author of the Greater Yellowstone Climate Assessment. “And, of course, Greater Yellowstone is the grand ecosystem in the country,”  

Whitlock, regents professor emerita of earth sciences at Montana State University, was the first author on the 2017 Montana Climate Assessment. She explains, “I wanted to work on an effort that would look at an ecosystem that crosses state boundaries and different jurisdictions, from federal land to private land, so that we could look at that as a coherent entity.”

University of Montana Regents Professor Emeritus Steven Running says the ecosystem-level nature of the report makes it easier for people to relate to the findings, rather than trying to understand global temperature and rainfall averages in wider reports. “I think as you get down to the region, in effect the people’s backyard, then it allows them to absorb the information better because it’s familiar to what they live in every day,” Running says.

Whitlock and co-lead author Steve Hostetler, a U.S. Geological Survey climate researcher, collaborated with a team including experts from the U.S. Geological Survey, Montana State University, University of Wyoming, Greater Yellowstone Coalition, Midpeninsula Regional Open Space District, and Mountain Works, Inc.

The scientists analyzed Greater Yellowstone Area weather station data going back to 1950 and streamflow records from as long ago as 1925. Their report focuses on how climate change is already impacting the region and what the future could hold by 2100. Projections focus on two potential greenhouse gas emissions scenarios. RCP4.5 (RCP stands for Representative Concentration Pathways) is a moderate scenario “assuming significant mitigation of emissions beginning in the next few years.” RCP8.5 demonstrates a potential future with no greenhouse gas emissions mitigation, what some call a “business as usual” approach.

Warmer, more precipitation but drier summers, and less soil moisture

They found a 2.3 degree Fahrenheit rise in mean annual temperatures since 1950. During that time, annual snowfall decreased by 23 inches, and peak streamflow now occurs eight days earlier. By 2100, the researchers expect temperatures to rise 5 to 10 degrees Fahrenheit, depending on greenhouse gas emissions. Along with this warming, they found precipitation likely will increase by 9 to 15%. However, scientists do not believe this will lead to a wetter environment. Rather, the additional heat likely will boost evaporation rates, making for ever drier summers with less soil moisture.

Hotter temperatures and less moisture will create a challenge for farmers and ranchers. The warmer temperatures will lengthen the growing season (already two weeks longer than it was in the 1950s) and even allow new varieties of crops to grow, but without adequate water for irrigation, farmers and ranchers are unlikely to benefit as much as it may initially appear. The reason? Drought conditions can put stress on plants, from crops consumed by humans and animals to the natural vegetation that feeds wildlife. Hot and dry conditions can also create a hotbed for wildfires – leading to smoky skies and unhealthy air quality.

“One of the issues is, even though there’s a longer growing season, again the shift in seasonality of runoff will alter the quantity of water that’s available in the summer. For instance for irrigation, and in terms of dry land crops, the evaporation demand will be high, so again there will be a shift there in kind of the optimal season for growing those crops,” Hostetler says.

For winter recreation enthusiasts, more precipitation as rain than as snow?

Warming would also significantly affect the region’s snowpack. In winter, people flock to ski and snowboard the slopes of Jackson Hole, Big Sky, and other ski resorts in the region, and enjoy other snow-dependent outdoor sports like snowshoeing, snowmobiling, cross-country skiing, and snow biking. Warmer temperatures, less snow – and less predictable snow – could limit these recreational activities, and changing freeze-thaw cycles could make conditions subpar or even create dangerous avalanche conditions in backcountry areas.

“Winter recreation is already being affected and will be affected more in terms of snowfall as it warms up more – precipitation will fall as rain,” Hostetler says. “And just the accumulation of the snowpack will change. Also, it will melt out earlier. So, as we go further into the century, I think the snow conditions will become a little more uncertain than they are now.”

When the snowpack gradually melts in the spring and summer, it slowly drains into waterways and provides a long-lasting water source. But warming conditions will mean an earlier melt and earlier peak flow with less water left for later in the summer and beyond. Shifting seasonal patterns and longer periods with lower water levels will impact aquatic systems, and this could also lead to shortages of water for homes and businesses and for agriculture and recreation and water sources used by wildlife.

Earlier peak snowmelts mean less water to meet summer needs

“The snow melt is happening earlier, so what we see is the timing of peak runoff is happening weeks earlier and that will continue in the future,” Whitlock says. “It will occur earlier and earlier, and so that affects fish spawning and the amount of water that stays in the stream through the rest of the summer. So earlier peak runoff has ecological implications, but it also means just less water when you go into summer.”

She says this impacts activities like fishing. “Already we’re seeing a lot of our streams right now are closed to fishing because the temperatures are too warm,” Whitlock says.

Researchers also estimated just how high temperatures could soar, with Wyoming gateway communities like Jackson, Pinedale, and Cody, as well as Bozeman, Montana, expected to experience far more hot summer days than they currently do. They found that by 2100, the RCP8.5 high emissions scenario could lead to 40 to 60 additional days per year where temperatures exceed 90 degrees Fahrenheit in these areas. Smoky skies from wildfires could also make outdoor activities less appealing, and even unhealthy if the air quality is poor.

… and ‘a massive acceleration of wildfire’

Speaking from his Montana home, Running, who retired from the U. of Montana faculty in 2017, says, “We had the second hottest July on record in Missoula. It was in the mid to high 90s week after week after week through July, and it gave us a look at what the future may hold.” As he spoke on the phone while looking out a window at the smoke-filled valley, he mentioned that some fire is a natural part of the ecosystem; But severe fire seasons are not, he added. “These longer summer seasons are triggering a massive acceleration of wildfire.”

Running says the morning news in his area now features air quality updates advising people how much physical activity they can safely do given the day’s conditions. “You think ‘geez that’s the kind of thing they do in Los Angeles for air pollution,’ but we’re now doing the same thing for smoke pollution in the summer,” he says.

The implications of these patterns aren’t just ecological – they extend to the area’s economy. Yellowstone National Park alone is a huge economic driver. According to National Park Service studies, in 2018, Yellowstone visitors’ spending led to $647.1 million in cumulative economic benefit for local communities, and in 2020, despite being closed for almost two months due to the pandemic, the benefit was around $560 million.

Yellowstone National Park is just one of the attractions in the Greater Yellowstone Area, which also contains Grand Teton National Park, as well as five national forests and three wildlife refuges. Nearly two-thirds of the land area is federally owned, and much of it is available for outdoor recreation. If visitors choose not to come to the area for any number of reasons, such as rising temperatures, unhealthy air quality, fishing closures, or lack of snow for winter sports, it could have a significant economic impact.

Bringing the global issue to ‘where people are living and working’

With so much at stake for local communities, the assessment’s authors intend to perform outreach in the area to share their findings.

“The purpose of an assessment is to provide the best scientific information available and in a form that people can understand, so that we all have a common platform for understanding climate change in our region,” Whitlock says. “And that’s the goal of this Greater Yellowstone Climate Assessment. It’s to take not just a global view of climate change, but to really try to bring it down to the ground where people are living and working. So we hope that this does provide a common platform and that communities and organizations and individuals can start to plan for climate change, and also think about ways that we can reduce our emissions of greenhouse gases in the region.”

The researchers plan on conducting future climate assessments focusing on different aspects of climate change in the region, such as wildlife, aquatic systems, watershed hydrology, human health, and economic impacts. They know the implications of their findings are crucial for the region and its inhabitants.

“The worst case scenario is we could be 10-11 degrees [Fahrenheit] warmer by the end of the century,” Whitlock says. “That’s going to profoundly change this ecosystem, and I worry that my granddaughter won’t even recognize the places that I love in Yellowstone.”

However, Running notes we still have a chance to change things. “There’s a really big difference between where the climate ends up under the RCP8.5 scenario, which is basically business as usual, and the RCP4.5 scenario, which still shows temperature increase and climatic change but is nowhere near as drastic, he said. “And this, I think, should tell all of us that driving down emissions is worth doing. Because if we can avoid the 8.5-level calamity, we’re doing ourselves a significant favor and that’s what the world needs to be getting on with right now.”

Kristen Pope is an Idaho-based freelance writer who frequently covers science and conservation-related topics.