The decline of snowpack in the Northern Hemisphere is expected to decrease due to less pollution settling into snow. Researchers at the Department of Energy’s Pacific Northwest National Laboratory predict that the reduction in snowpack will be less than half what has been predicted, which is good news for many people who rely on snowmelt in high mountains for water and food production, as well as those who depend on winter recreation. Factors affecting snowpack include warming temperatures, pollution, dust, and the shape of snow grains as they pack together on the ground.
The warmer it is, the more snow melts, which is bad news for mountain snowpacks and the people who rely on them. Estimated 2 billion people rely on spring and summer snowmelt in the mountains to provide fresh water for drinking and food production. If mountain snow melts faster or earlier than usual, it can lead to problems such as swollen rivers and flooding in the spring, and parched crops and wells in late summer.
The biggest factors affecting future snowpack are temperature and the effect of dark particles like pollution and dust. These particles absorb more sunlight than pure snow, warming faster and passing along the sun’s warmth to nearby snow. Clean snow reflects an estimated 80 to 90 percent of sunlight, while dirty snow reflects less.Researchers predict cleaner snow in the future due to reduced pollution and wood burning.
Researchers have found that cleaner snow will likely come at a time of warmer temperatures, which lower the snowpack in many ways. The simplest explanation is that less precipitation falls as snow and more as rain, and warmer temperatures also melt the snow that has fallen. The warming effect is dominant, but cleaner snow will cancel out some of the effect. Researchers studied snowpack trends in Northern Hemisphere high mountains from 1995-2014, modeling trends from 2015 to 2100 using two scenarios: one where carbon dioxide emissions continue to rise significantly and one where emissions decline.
In both scenarios, temperatures are expected to warm, the deposition of dark particles known as black carbon is expected to decrease, and dust is expected to increase. If carbon dioxide emissions rise due to continued fossil fuel use, temperatures rise significantly, and when changes in dark particles aren’t considered, the team estimates a snowpack loss of about 58%. However, cleaner snow from less pollution—even with more light-absorbing dust—reduces that loss by 8 percent. If carbon dioxide emissions are curtailed significantly (SSP 126), snowpack loss is much less, and when cleaner snow is factored in, snowpack loss is slashed by more than half—52%.
Another factor influencing the future snowpack is the loss of “biological soil crust,” where bacteria, lichens, algae, and other organisms infiltrate and stabilize the soil surface. Researchers expect this type of soil to be reduced as temperatures warm, leading to more dust in the future.
While there are many factors in play, the PNNL team found that rising temperatures and reduced dark particles are the two most powerful factors influencing the future snowpack. Determining which one is the more dominant influence is crucial to determining the fate of the snowpack in the future.