Davin News Server

Yellowstone Lake Ice Cover Unchanged Despite Warming Climate

by University of Wyoming

Yellowstone Lake, North America's largest high-elevation lake, freezes over 
completely in late December or early January and usually thaws in late May or 
early June. The period of ice cover has not changed in the last century, 
despite warming temperatures in the region. Credit: Lusha Tronstad

The length of time that Yellowstone Lake is covered by ice each year has not 
changed in the past century, despite warming temperatures in the region, 
according to new research led by University of Wyoming scientists.

That is an unexpected finding, as most lakes around the world are experiencing 
shorter durations of ice cover, the scientists note in a new paper published in 
the journal Environmental Research Letters.

"We show that contrary to expectation, the ice phenology of Yellowstone Lake 
has been uniquely resistant to climate change," wrote the scientists, led by 
Lusha Tronstad, lead invertebrate zoologist with UW's Wyoming Natural Diversity 
Database and Department of Zoology and Physiology, and Isabella Oleksy, a 
former UW postdoctoral researcher now on the University of Colorado-Boulder 
faculty. "The unchanging ice phenology of Yellowstone Lake stands in stark 
contrast to similar lakes in the Northern Hemisphere."

Other researchers involved in the study are from Utah State University, 
Colorado State University and Colorado Mesa University.

Situated at 7,733 feet above sea level in the heart of Yellowstone National 
Park, Yellowstone Lake is North America's largest high-elevation lake, roughly 
20 miles long and 14 miles wide with a surface area of 132 square miles. It 
freezes over completely in late December or early January and usually thaws in 
late May or early June.

Records for the lake's ice-off date have been recorded each year by Lake 
Village Ranger Station staff since 1927, and the ice-on date has been recorded 
since 1931. In addition to studying those records, the scientists analyzed 
climate data for the same period, 1927-2022, including air temperatures and 
precipitation. They also compared Yellowstone Lake's data with seven similar 
lakes in northern Europe.

The lack of long-term change in the duration of Yellowstone Lake's ice cover 
was unexpected because the Yellowstone region has seen a warming climate, the 
researchers say. Since 1950, annual temperatures have increased by 1.8 degrees 
Fahrenheit throughout the greater Yellowstone ecosystem. The changes are 
particularly pronounced at the high elevation of Yellowstone Lake, where air 
temperatures increased by about 2.5 degrees Fahrenheit between 1980-2018.

"Using local weather data, we found some evidence for increased summer, fall 
and spring temperatures, primarily in the last three decades," the scientists 
wrote about air temperatures at Yellowstone Lake. "Given the key role of air 
temperatures in driving ice formation and break-up, it is noteworthy that we 
did not find evidence for corresponding shifts in ice phenology."
Why the apparent discrepancy?

While it is possible that fall minimum temperatures-which are important in 
predicting ice formation-are not rising as quickly as overall temperature 
trends in the region, a more likely explanation is that increased snowfall at 
Yellowstone Lake has served as a buffer against warmer weather, the scientists 
say.

Snow cover, particularly in spring, can delay ice break-up. Cumulative spring 
snow, which was strongly correlated with delayed ice-off dates, has nearly 
doubled over the last century at Yellowstone Lake, the research showed. In 
general, precipitation has increased in spring and fall there.

That differs from the Upper Green River Basin to the south, where snowfall has 
declined or been relatively stable at high elevations.

"Shifts in local precipitation, especially increases in fall and spring snow, 
appear to be buffering (Yellowstone Lake) ice phenology against warming 
temperatures," the researchers wrote.

But, the team is not sure how long this phenomenon will last, noting 
projections of continued warming and shifting precipitation regimes in the high 
Rocky Mountains.

"Our results, paired with recent analyses of climate projections, suggest a 
'tipping point' may be coming when ice phenology abruptly changes for 
Yellowstone Lake," they wrote. "This tipping point will largely stem from the 
ongoing shift from snow- to rain-dominated precipitation regimes in the fall 
and spring."

"Increased spring rainfall has not yet caused a detectable long-term trend 
toward earlier ice break-up, potentially because of the counteracting effects 
of increased spring snow. As temperatures warm further, and fall and spring 
snowfall decreases, ice phenology may rapidly change on Yellowstone Lake," they 
continued.

If that happens, "there may be wide-ranging consequences for nutrient cycling, 
lake productivity, fisheries and recreation," the researchers concluded. 

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