After last week’s monster storm that left Eastern USA snow white, the snowbanks slowly melted into pools and streams. But what if snow were black? The Bard liked nature the way he saw it, but he loved to mock our conventional sense of color.
Casting back to Physics 101, I remember learning how experience tidily lines up alongside theory. Dark surfaces feel hotter than light ones as they don’t release energy so efficiently, and dark roofs and asphalt are heat sinks making urban centers several degrees warmer than outlying countryside. There is little advantage in a black roof for absorbing heat when it is snow-covered, but a white roof in summer can significantly reduce AC bills by reflecting the sun’s rays.
Standard white paint reflects 80% of solar radiation, whereas standard black has only 5% reflectivity. The thermal emissivity of asphalt and snow are similar, but the solar reflectance index from combining reflectivity and emissivity is theoretically 100 for white versus 0 for black. Some difference!
Instead of sprinkling salt to lower the freezing point of your icy path, test whether powdered black carbon (soot) melts ice faster by absorbing heat than leaving it untreated. Almost unnoticeable traces of black carbon can have noticeable effects. Consider the melting of glaciers, which started accelerating in the Alps in the second half of the 19th Century. This was originally blamed on climate change (temperature and precipitation), but a recent model from measuring ice cores predicts a better fit to the fallout of black carbon in the Industrial Age. The Alps are encircled by cities that industrialized early and depended on burning dirty coal.
Weathermen who speak of ‘black ice’ know that it is, strictly speaking, science fiction. It’s very hard to imagine how atomic bonds would be bent to abolish the reflective properties of ice, at least in the universe we know. But who knows? Nature looks stranger every day we look closer. Black holes look black because gravity captures light from escaping. Both black coal and transparent diamonds are from carbon, not paradoxical but a discovery that would have humored Shakespeare.
If snow was not white, our world would be hotter, have higher sea levels, different fauna and flora, and no snowmen on Christmas cards. According to that incurable optimist, Dr. Pangloss, “It is demonstrable that things cannot be otherwise than as they are; for as all things have been created for some end, they must necessarily be created for the best end (Trans. Candide). But Tom Torrance, a theologian famous for embracing Carl Barth and Niels Bohr, once reminded me that we live a contingent universe, and ought to be thankful for this one and not to be born somewhere much stranger in the multiverse. Yes, let snow be white.
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