For the last 35 years, the snowpack in the West鈥檚 mountains has resisted the impacts of global warming. But that could soon change, according to a new study out of Oregon State University.
The study, , found that although climate change should have caused a steep decrease in snowpack, naturally occurring, decades-long weather variations shielded the Cascades, Sierras and Rockies from some of the effects. Although snow stations have recorded some decline, it hasn鈥檛 been statistically significant. But according to the study, without this natural weather variation, snowpack in Oregon could have declined between 18 percent and 54 percent over the last 35 years.
The West has a wet season and a dry season and relies on wintertime snowpack for summertime water, so this could have drastic impacts on the region. Nick Siler, a climate scientist at Oregon State University and an author on the study, says that Oregon could be hit particularly hard when this trend reverses because it tends to snow in Oregon when temperatures are close to freezing, not far below freezing. It wouldn鈥檛 take much warming to tip that snow to rain.
It鈥檚 important to note that this study looked at snowpack on April 1. Siler and his team also broke down snow seasonally, and as many skiers and snowboarders have noted, the snow seems to be coming later and later. But the snowpack present on April 1 is the snow that will get the West through the summer. April 1 snowpack declined in Oregon by an average of 14 percent across the study period 鈥� but Siler cautions the margin of error is so large, the decline isn鈥檛 statistically significant.
To figure out why the West鈥檚 snowpack stayed strong, Siler and his colleagues looked at how April 1 snowpack has changed since 1983, the first year for which there is good data. In the 35 years covered in the study, the western U.S. warmed by more than 1 degree Celsius, so it鈥檚 not as though climate change just passed the West by.
Siler and his colleagues then looked at sea surface temperatures in the Pacific, which can drive air currents and precipitation across the Western U.S. The pattern that they saw, a warmer Western Pacific and a cooler Eastern Pacific, is associated with La Ni帽a-like conditions. La Ni帽a generally means a cooler, wetter winter for the Pacific Northwest.
鈥淭emperatures have been slightly cooler than they would have been, in the absence of these circulation trends,鈥� says Siler, 鈥渂ut the bigger signal is in precipitation.鈥�
Put simply, even if it鈥檚 a little bit warmer, as long as it stays below freezing wetter years can bring more snow.
Siler says that when that masking effect goes away, 鈥渨e could experience substantial declines in April 1 snowpack.鈥�
Siler says it鈥檚 hard to know what it鈥檒l look like when this weather trend ends, but it鈥檚 possible that total snowpack could decline very, very rapidly. Though, notes Siler, there will always be a lot of year-to-year variability.
鈥淚 don鈥檛 want to give the impression that we鈥檙e predicting an immediate shift into a regime where snowpack is going to become quite scarce. But my strong feeling is that in the last 35 years, the trends that we鈥檝e seen are not a good predictor of the trends we鈥檙e likely to see over the next 35,鈥� says Siler. 鈥淲hen exactly these significant declines will appear is impossible to say.鈥�
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/A snow-machine rider takes a snowpack reading as part of Community Snow Observations, a NASA-sponsored citizen science project.