A team of scientists presented data on Tuesday suggesting that even as the state of Alaska has warmed up extremely rapidly in recent years, snowfall in the iconic Denali National Park has increased dramatically during the era of human-driven global warming.
The researchers from Dartmouth College; the University of Maine, Orono and the University of New Hampshire set up a camp at 13,000 feet atop Mount Hunter, within view of Denali. There, they drilled into the snow to extract lengthy cores of ice that provided a historical record of snowfall patterns going back more than 1,000 years – and found a marked change over the past 150 years or so.
"We were shocked, frankly, at just how much snowfall had increased," said Erich Osterberg, a Dartmouth researcher who was one of the study's authors.
The ice cores showed an enormous upswing in the rates of snowfall beginning around the Industrial Revolution in the 19th century, when humans began burning fossil fuels to produce energy in large quantities. The increase over time represented more than a doubling in the amount of snow.
"Snowfall before the Industrial Revolution averaged about eight feet of fresh snow a year at this site, and now we get over 18 feet of fresh snow," Osterberg said.
"We can say confidently that the amount of snowfall we see today has never been seen previously during that whole 1,200-year record," Osterberg said. "That we are way outside the range of what was natural conditions before the Industrial Revolution."
Climate change increases the volume of precipitation, because a warmer atmosphere holds more water vapor. But it isn't supposed to increase it this much.
The researchers attribute part of the snowfall increase to the atmosphere retaining more water vapor, but also say that the warming up of the tropical Pacific Ocean changed atmospheric patterns, leading more storms to track across Alaska – thus accounting for the one-two punch.
Yet despite all of this, Osterberg said, Alaska's glaciers are still widely retreating at lower altitudes – even though they are being fed with heavy volumes of snow at high altitudes, where there is little melt.
Two years ago, scientists reported that Alaska's glaciers were losing 75 billion tons of ice annually.
That's not surprising given that Alaska has warmed about 3 degrees Fahrenheit over the past 60 years as an average, with the most recent years even warmer.
"The Alaska glaciers are the fastest-melting in the world," Osterberg said. "That's all driven by the summertime warming, despite the fact that snowfall has doubled."
Two scientists who commented on the new study for The Washington Post highlighted its demonstration of how long-term warming can interact with other weather factors to create compounding effects.
"This appears to be a classic situation where we are seeing linkages among local, regional and hemispheric phenomena," said David Robinson, a climate scientist at Rutgers University who tracks patterns in snow cover. "All are likely at play here, and there seemingly is ample room to explain this change in terms of both natural variability and anthropogenic influences acting at all these scales."
"You've always got different things going on," added Mark Serreze, director of the National Snow and Ice Data Center in Boulder, Colorado. "Warming effects that influence how much moisture the atmosphere can hold, but also shifts in weather patterns."
Serreze said the snowfall changes documented in the new study are just part of a much larger set of changes to the Arctic's hydrological system, which include earlier spring melting of mountain glaciers and snowpack, leading to large river discharges to the sea, and more odd events – such as rain falling atop snow, turning it into ice.
The new work, published in Nature Scientific Reports, Osterberg said, highlights that even as the globe overall experiences a slow, average warming of 1 or more degrees Celsius (1.8 degrees Fahrenheit), certain areas can see drastically bigger changes.
"On a regional basis, climate changes, from increased CO2 pollution, are much bigger than what you assume from global averages," he said.