By: Marina Kobasiuk
Snow has a varied life span across North America. In some regions after the first few snowfalls, the sight of it will be consistent through much of the winter, or the time period between snow melts will be larger. While other locations, especially coastal regions and cities, can see many melts and fresh covers of snow through the entire season. Long term climate certainly plays a part; average temperature and humidity affect how snow melts or sublimates, as does geography. These factors are important due to how easily snow can resist melting by reflecting the sun’s energy back into the atmosphere.
But what also affects how snow melts is the quality of the air that was involved when the precipitation formed. This is called snow darkening and it reduces the ability of snow to reflect radiation. Aerosols particles can be brought to the surface after snow has formed around them due to wet deposition, and then are part of the snowpack on the ground. If those particles can absorb the radiation from the sun, such as carbon rich ash for example, they encourage the melting of snow. So regions with heavy industry and pollution will see this effect more strongly from emissions much more than rural regions that are not as rich with these heavier particles, though this natural effect is not limited to pollution.
This cycle continues as once a patch of snow has melted sufficiently to reveal a much darker area of ground beneath it. Exposed to the sun this darker surface can absorb and emit radiation and also start to melt the snow around it and encourage the melting or evaporation of all the snow around such spots. So if you travel to a place with low pollution or lots of shade, you’ll likely see snow on the ground for much longer times through the winter, even as it melts away closer to larger populations!
Jacobson, Mark Zachary. Air Pollution and Global Warming: History, Science, and Solutions. 2nd ed., Cambridge University Press, 2012.