In 1872, when Yellowstone was designated as the first national park in the United States, Congress decreed that it be “reserved and withdrawn from settlement, occupancy, and sale and … set apart as a public park or pleasuring ground for the benefit and enjoyment of the people.” Yet today, Yellowstone—which stretches 3,472 square miles across Montana, Wyoming, and Idaho—is facing a threat that no national park designation can protect against: rising temperatures.
Since 1950, the iconic park has experienced a host of changes caused by human-driven global warming, including decreased snowpack, shorter winters and longer summers, and a growing risk of wildfires. These changes, as well as projected changes as the planet continues to warm this century, are laid out in a just-released climate assessment that was years in the making. The report examines the impacts of climate change not only in the park, but also in the Greater Yellowstone Ecosystem—an area 10 times the size of the park itself.
The climate assessment says that temperatures in the park are now as high as or higher than in any period in the last 20,000 years—and are very likely the warmest in the past 800,000 years. Since 1950, Yellowstone has experienced an average temperature increase of 2.3 degrees Fahrenheit, with the most pronounced warming taking place at elevations above 5,000 feet.
Today, the report says, Yellowstone’s spring thaw starts several weeks sooner, and peak annual stream runoff is eight days earlier than in 1950. The region’s agricultural growing season is nearly two weeks longer than it was 70 years ago. Since 1950, snowfall has declined in the Greater Yellowstone Area in January and March by 53 percent and 43 percent respectively, and snowfall in September has virtually disappeared, dropping by 96 percent. Annual snowfall has declined by nearly 2 feet since 1950.
Because of steady warming, precipitation that once fell as snow now increasingly comes as rain. Annual precipitation could increase by 9 to 15 percent by the end of the century, the assessment says. But with snowpack decreasing, and temperatures and evaporation increasing, future conditions are expected to be drier, stressing vegetation and increasing the risk of wildfires. Extreme weather is already more common, and blazes like Yellowstone’s massive 1988 fires—which burned 800,000 acres—are a growing seasonal worry.
The assessment’s future projections are even bleaker. If heat-trapping emissions are not reduced, towns and cities in the Greater Yellowstone Area—including Bozeman in Montana and Jackson, Pinedale, and Cody in Wyoming—could experience 40 to 60 more days per year when temperatures exceed 90 degrees F. And under current greenhouse gas emissions scenarios, temperatures in the Greater Yellowstone Area could increase by 5 to 10 degrees by 2100, causing upheaval in the ecosystem, including shifts in forest composition.
At the heart of the issues facing the Greater Yellowstone Area is water, and the report warns that communities around the park—including ranchers, farmers, businesses, and homeowners—must devise plans to deal with the growing prospect of drought, declining snowpack, and seasonal shifts in water availability.
“Climate is going to challenge our economies and the health of all people who live here,” said Cathy Whitlock, a Montana State University paleoclimatologist and coauthor of the report. She hopes “to engage residents and political leaders about local consequences and develop lists of habitats most at-risk and the specific indicators of human health that need to be studied,” like the connection between the increase in wildfires and respiratory illness. Sounding the alarm isn’t new, but the authors of the Yellowstone report hope their approach, and the body of evidence presented, will convince those skeptical about climate change to accept that it’s real and intensifying.