Horstman Glacier September 2006 (Photo: Hans Roemer)
By: Kristina Swerhun
Date: July 2008
After a great winter we’re slowly seeing the melting of our winter snowpack. How fast it will melt will be mostly dependant on temperature. Snow that finds itself next to exposed rock will be the first to go since rock absorbs more energy from the sun and warms, melting the surrounding snow. The term used to describe how much of the sun’s energy will be reflected by a surface is albedo. Albedo is dependant on colour and texture. For example, fresh asphalt has an albedo of 4%, the percentage of solar radiation of all wavelengths reflected by it to the amount incident upon it. Snow on the other hand has an albedo of 90% and gives you an idea of why we’re especially prone to sunburns on a sunny day on the glacier; the sun’s rays are effectively coming at us from the top and bottom.
When you hear that the north will be most impacted by climate change, it is an example of the albedo effect resulting in a snow-temperature feedback. If a snow covered area warms and the snow melts, the albedo decreases, more sunlight is absorbed, and the temperature tends to increase. The converse is true: if snow forms, a cooling cycle happens. The intensity of the albedo effect depends on the size of the change in albedo and the amount of solar radiation.
I was recently at a mountain climate conference in southwest Colorado and in that area the rate of snowmelt is significantly increased by dust that is blown onto the snow from the nearby Colorado Plateau, mostly as a result of grazing. The snow was definitely visibly brown, even high on mountain peaks. As you’ve probably figured out, the reason for increased melting is that the dust on the snow (and bigger particles as well) lowers the albedo of the surface, which absorbs more energy from the sun and melts the underlying snow. In the spring, water from the melting snow trickles through the dust, which accumulates at the surface continually decreasing albedo until all the snow is melted, or until snow falls again.
I was happy to report at the conference that in southwest BC we didn’t have this phenomenon to the same extent, but I also started thinking about what else could change our snowmelt patterns besides temperature alone. I know our snow doesn’t stay snowy white during the summer, and that energy absorbing particles that find their way onto our snow come in the form of fungus spores, conifer needles, lichens, maybe a little dust, and possibly ash from regional forest fires to name a few. Another factor that would decrease albedo would be red snow algae (Chlamydomonas nivalis) a unicellular, photosynthetic plant. So if you’re on the snow this summer, keep an eye out for any snow that is uncharacteristically discoloured. These observations could provide clues to changes in our snowmelt patterns, which could affect the quality and quantity of our water and the health of our streams.