Collaborative study shows climate change impacts on Greater Yellowstone Area


WYOMING – A first-of-its-kind recently published study indicates the Greater Yellowstone Area will see major environmental shifts within the next 80 years if there is little to no action taken to mitigate climate change.

By the end of the century the region could see annual precipitation increase by 9 to 15 percent, but the combination of higher temperatures and evaporation rates will likely make future summer conditions drier. Further reduced soil moisture in the summer months will add stress and could make drought and wildfires more common. And, based upon data collected over the past 70 years, the area could see 40 to 60 more days per year of temperatures exceeding 90 degrees – that includes Pinedale, Jackson and Cody – if there is little to no mitigation of future greenhouse gas emissions.

These were the findings of the first Greater Yellowstone Climate Assessment Report, published following a three-year collaborative study by the U.S. Geological Survey, Montana State University and the University of Wyoming. The Greater Yellowstone Coalition aided efforts by interviewing people who live and work throughout the region in order to gain better insight into local concerns on environmental action and policy.

According to the coalition, no other report has taken an ecosystem-wide look into the impacts of climate change.

“(Greater Yellowstone Coalition) plans to tackle the complex challenges facing the region by working with people to address changes in temperature, snowpack, disease, wildfires and other issues impacted by climate,” Charles Drimal, waters conservation coordinator at the Greater Yellowstone Coalition, wrote. “This report will help guide our work well into the future.”

Over the course of the three-year study, researchers gathered information on climate change in the Greater Yellowstone Area (GYA) from 1950 to 2018 and focused on six adjacent watersheds – Snake Headwaters, Upper Green, Big Horn, Upper Snake, Upper Yellowstone and Missouri headwaters.

Researchers determined that since 1950, temperatures significantly increased and snowfall decreased in the area as a result of climate change. The assessment showed temperatures in the GYA have increased by .35 degrees every decade since 1950 and are projected to increase at a higher rate in the future. Those warmer temperatures have already led to: Decreased snowpack at elevations from 5000 to 7000 feet; drier conditions conducive to fire; widespread die-offs of mature whitebark pine trees; invasive species outbreaks; and changes in the timing and rate of snowmelt, which affect fish spawning and the health of aquatic systems. These rises also directly affect grassland habitats by altering bison migratory patterns and food availability for songbirds.

Cam Sholly, current superintendent of Yellowstone National Park and sitting chair of the Greater Yellowstone Coordinating Committee, said climate change impacts aren’t limited to simply the environment.

“Every year, millions of visitors from across the world come to Yellowstone to see the park’s awe-inspiring landscapes and wildlife and spend hundreds of millions in local economies. The communities within the GYA are experiencing rapid growth as people move to the region to enjoy the amenities,” Sholly said. “Climate impacts throughout the GYA, if not addressed, will directly affect the strength of local and regional economies as resource values and use change across the region.”

Yellowstone National Park and its partners have started developing response strategies better incorporating climate data and projections into planning, operations and program management efforts in order to mitigate climate impacts, Sholly said.

The report incorporated historical data in order to better understand the GYA’s current situation. It showed the average temperature over the past two decades is as high or higher than at any period in the past 20,000 years – and likely higher than previous glacial and interglacial periods in the past 800,000 years. The current level of carbon dioxide in the atmosphere is at its highest levels in 3.3 million years.

Mean annual temperatures and precipitation fluctuated greatly in the area over the past 120 years. There was an extended dry period from 1905 to 1945, followed by a near long-term average in precipitation in the area. Temperatures over that time remained near a mean average before increasing substantially since the late 1970s. Rising temperatures, with unusually dry conditions, came together in 1988 and contributed to the extensive forest fires throughout Yellowstone National Park.

Weather stations and streamgages have also registered rising temperatures, declining snowfall and shifting peak streamflow in area watersheds since 1950. Statistics in the report show the annual temperature in the area has increased by 2.3 degrees. Average precipitation has remained near 15.9 inches but with increases in the spring and fall, while summer precipitation has dropped. Meteorological records show an increase of 17 to 23 percent in April and May, and a 42-percent increase in October. Meanwhile, there has been a 17-percent drop in June and 11-percent drop in July. Data also shows mean annual snowfall in the area has decreased by 3.5 inches per decade. Annual streamflow currently is similar to that of nearly 70 years ago but the average timing of peak flow has shifted earlier in the year by eight days, thereby extending the length of the water-limited warm season.

The report used only the most complete monthly and annual data sets from 1950 through 2018, specifically those with fewer than five days of missing observation, in its calculations. This constraint reduced the number of records but ensured all trends would be well documented and not influenced by changes in the number of stations used.

Forty-three weather stations in the Greater Yellowstone Area were analyzed – 11 in the Big Horn, eight each in the Upper Yellowstone and Snake headwaters, seven in the Upper Green, five in the Upper Snake and four in the Missouri headwaters. Statistics among those analyzed showed at least a consistent, if not rise, in mean annual temperatures throughout elevations studied. Precipitation also rose throughout all elevation levels. On average, snowfall has also risen from the start of the study except in areas of 6,000 to 7,000 feet, which have dropped significantly (about 25 inches on average) from 1950.

Historical data showed weather stations below 6,000 feet rarely received more than 75 inches of annual snowfall, but twice that amount has fallen annually when averaged across stations above 6,000. In addition, the greatest snowpack accumulation recorded by the weather stations examined occurred between 7,000 and 8,000 feet, where snowfall exceeded 150 inches six different times within the past 70 years.

“Temperatures in the Upper Green and Snake headwaters watersheds, which include high-elevation areas in the Wind River Range, are typically the coolest,” the report said. “Since 1950, total precipitation has often been highest in western watersheds, which are maximally exposed to winter storms derived from the Pacific Ocean.”

On a whole, however, temperatures in the GYA have risen 2 to 5 degrees since 1950 across all elevations below 8,000 feet, where weather station data has been available. The GYA has experienced year-to-year precipitation variability of 2.2 inches based on standard deviation of the meteorological record average while maintaining near annual average precipitation of 15.9 inches.

For context, those changing temperatures above 7,000 feet now approach those commonly recorded between 6,000 and 7,000 feet in the mid-20th century. Also, mean annual temperatures in the Missouri Headwaters and Upper Snake watersheds are now similar to those in the Big Horn watersheds, which, historically, has been the warmest sub-region of the GYA.

The report also noted that snowfall is highest above 7,000 feet, where total precipitation has increased by approximately 5 inches since the 1990s even though the mean temperatures at these elevations have also risen by 2.5 degrees since the 1980s. That snowfall, however, has leveled despite precipitation rising because of the rising temperatures above freezing.

“Temperature increases within the months have not yet equaled the historical differences between months,” the report said. “More simply, even with warming temperatures the coolest days in November are, on average, cooler than the coolest days in October, both in 1950 and today.”

As far as precipitation, the study concluded April is now as wet as May was in the mid-20th century and May precipitation has increased to a new average monthly high of 2.5 inches a month. That, coupled with a substantial drop in June, indicates that most precipitation now falls earlier in the year than in the mid-to-late 20th century.

January snowfall has declined by an average of 7.5 inches since the 1950s and March snowfall has substantially declined by about 7.0 inches compared to amounts before 1980.

“Overall, the snow-free season has lengthened with snow accumulation in June and September declining to near zero,” the report stated.

The study developed climate scenarios (read: projections) for plausible pathways for future climate change and mitigating that change. Those scenarios were largely based upon two interconnected parts: societal choices and land-use changes.

Through comprehensive studies involving downscaling and various climate models, came to a significant conclusion when developing projections for future conditions. The report stated humans are contributing to global warming through greenhouse gas and aerosol emissions, and those projections were used to understand, plan for and mitigate the potential impacts of climate change from present and future emissions.

The study acknowledged these projections could change as the area between the GYA and a town shrinks. If more people move into the GYA, it could increase emissions and hasten the documented changes.

Under the current conditions, however, one projection (RCP4.5) concluded that the number of days with the high above 90 degrees is projected to increase and exceed a week in Pinedale and a month in Cody. Based on a different projection (RCP8.5), the number of days exceeding 90 degrees would increase to nearly two months in Pinedale and Jackson, and exceed two months in Cody and Bozeman, Montana, by the end of the century. Also, by the end of the century, the number of days with the low below 32 degrees experienced by towns in the major watersheds is projected to decrease by about a month and a half under RCP4.5 and up to two and a half months under RCP8.5.

Projected annual mean precipitation in the RCP4.5 is projected to increase by 7 percent in the mid century and 8 percent by the end of the century, relative to the base period of 1986-2005. Under the RCP8.5 projection, forecasted increases are 9 and 15 percent, respectively, for the same periods.

In terms of snowmelt, RCP4.5 showed a decrease of snow-dominant area from 59 percent during the base period to 27 percent at the middle of this century and 11 percent by the end of it. Under the RCP8.5 projection, areas decreased to 17 percent and to 1 percent over the same time frames, respectively. The seaonality of the runoff is projected to change as snowfall declines and snowpack melts earlier, as both projections indicated to varying degrees.

The largest changes of snowmelt come at middle and high elevations where runoff from snowmelt increases in the spring and decreases in the summer. Timing of peak runoff is projected to shift by a month or two earlier in the year in the later part of the century under RCP8.5.

These factors led researchers to consider the potential wildfire implications of climate change.

In the future, earlier snowmelt and loss of snowpack during the warmer winters, followed by warmer summers and longer growing seasons will increase fire potential at all elevations in the GYA.

“This condition, combined with increased tree mortality, potentially will alter future fire regimes and lead to rapid changes in forest ecosystems. Sustained changes in climate and fire disturbance will also affect post-fire recovery of species, thereby changing forest composition and converting forest to grassland at lower elevations,” the report concluded. “Increased fire activity portends large ecological changes and threatens human health and the communities living in fire-prone areas.”

The report also considered the energy ramifications of these changes. Projected conditions will reduce energy demands for heating in the winters and increase energy demands for cooling in the summers. It’s estimated that the energy reduction for heating could be as much as five times greater than the increase for cooling.

Winter activities, and associated economies built upon winter recreation, will be threatened by the loss of snowpack as the Greater Yellowstone Area snow season becomes shorter and more uncertain. According to projections under RCP8.5 over the 30-year period hinged on 2050, the number of ski days during the core of the season will be reduced anywhere from six days to 29 within the GYA.

Communications with locals and stakeholders yielded varying thoughts on environmental regulations, policies and laws. The Greater Yellowstone Coalition summarized takeaways with 44 different individuals and learned most are concerned about water – specifically with impacts including drought, spring runoff and declining native fisheries. Water supply has also been determined to be a major concern for those in the area. To this end, the report emphasized local involvement, consultation and communication in terms of climate change mitigation.

“In the face of climate change, the fate of communities and environments depends on people. For the GYA, climate change mitigation and adaptation will ultimately be defined by the views and actions of its people,” the report said. “Overall, GYA communities are clearly aware of the loom threats from climate change. The findings can help us better inform and prepare to face those threats.”

In closing, the report stressed that work with local communities and tribes. Development of a list of at-risk habitats and specific indicators of ecological and human health was stressed for studying purposes. It was also emphasized to evaluate the effects of projected climate change on the most potent economies of the GYA: tourism and recreation; hunting and fishing; agriculture and forestry; and mineral and energy resource extraction.