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 per cent, 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 per cent 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
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 B.C.
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 (
a unicellular, photosynthetic
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.
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