Albedo And The Dark Snow Problem
Snow is a word that conjures up many images in the mind and is associated with purity and clean environments. The expression â€śas pure as the driven snowâ€ť is a classic example. This picture of snow as a symbol derives from its color, pure, clean and white. But from the worldâ€™s highest glaciers falling down the slopes of Everest to the vast frozen wastes of the polar regions, white snow is becoming an increasingly rare thing and â€śdark snowâ€ť is taking its place. Pollution is the problem. Acceleration of climate change and global warming are the inevitable consequences. We darken our snow at our peril.
To understand the connections and interactions we need to consider something called albedo, the process by which snow and ice surfaces reflect sunlight. Albedo can be measured fairly accurately and scientists working in many different regions of the planet are reporting falling albedo levels everywhere. The cause is a steady accumulation of pollutant dust falling onto the whiteness. Tiny particles of dark dust fill the air. It may be soot from a small cooking fire in one of the worldâ€™s remote places, from a summer barbecue, a forest fire. It could be from industrial smoke and emissions. Dry or eroded soil is drawn into the air by high winds along with desert dust storms. A massive contributor to the dark snow blanket is diesel fuel, which produces super-fine micro particles known as â€śblack carbon.â€ť Once in the air they can be carried high into the atmosphere and finish up anywhere on earth.
Not only do the darker snow and ice reflect less sunlight, therefore increasing the underlying temperature, the blanket of dark material also absorbs heat from the sunâ€™s rays and compounds the problem. As so often in climate change triggers this is a cyclical phenomenon â€“ dark snow increases global temperatures and causes more rapid melting of sea and glacial ice. The increased erosion exposes more land that is free of snow and ice so that less sunlight is reflected. The length of the annual â€śmelting seasonâ€ť is extended and the whole cycle starts again creating a kind of feedback loop of warming and melting. Also, surface melting actually concentrates the pollutants which leads to more darkening and in some cases allows previously unknown microbial growth. In a beautiful example of natural adaptation in process, observers are seeing these ice-field organisms produce their own â€śsun screenâ€ť in the form of darker pigmentation to protect themselves against the powerful UV rays.
Scientists have already estimated that over 12 billion tons of the Arctic ice cap are lost every year. But new calculations, like those published in the journal Nature Geoscience, suggest that far more, perhaps even twice as much, is being lost due to decreasing albedo.
In his fascinating blog, the Danish glacial scientist Jason Box describes his work on the Dark Snow project that monitors the progress of plummeting albedo levels on the gigantic Greenland ice sheet. Jason has worked in Greenland for around 20 years and he is now reporting albedo numbers that are at record lows indicating a clear acceleration of the feedback loop that should have us all concerned.
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