It’s almost April. Ah, April in Cape Breton. The snow finally begins to melt, bare patches of ground appear on sunny slopes and … Wait! Didn’t that happen in January? Yes, it’s been a weird winter all right. By the end of January it looked like May, with the snow all but melted. Winter finally showed up in February. Then March roared in like a lion. Or maybe more like a polar-vortex bear? March felt like January, with windchills that could peel the skin right off your face. Until, suddenly, March switched from January to July.
What’s with the weather yo-yo? Well, I am not now, nor have I ever been, a climate scientist. But as I understand it, a wobbly jet stream is leading to wonky weather (excuse the technical terms). Here’s the gist of it: the jet stream is formed by the temperature contrast between the arctic and the mid-latitudes. The arctic is warming faster than mid-latitudes, reducing the temperature contrast between the two regions. As this temperature contrast decreases, the jet stream slows. As the jet stream slows, it meanders more, forms kinks, tends to stall. Next thing you know Texans are freezing while Cape Bretoners are sunbathing.
I was one of those Cape Bretoners sunbathing last week, which brings me to the albedo effect. Albedo (not to be confused with libido, which also relates to heat, but in a different sense) is defined in my Encyclopedic Dictionary of Exploration Geophysics as: ‘reflectivity of a free surface for electromagnetic radiation.’ Whether or not we know the word we all know what it is: I felt it personally during our unseasonable heat wave, sweltering under the sun in a black shirt. Dark colours have low albedo and absorb more radiation in the form of sunlight. Time to change! We wear white when we want to feel cooler because light colours have high albedo and reflect the sun’s rays.
Snow has high albedo, which in snowy climes we know all too well. No matter how cold it is, sunlight reflecting off snow can give us a bad sunburn or even cause snow blindness. So the arctic, with all that ice and snow, has high albedo, reflecting much of the sun’s energy back into space. But as noted above, it is warming faster than the rest of the planet. The reasons are complex and still under study, but the albedo effect is considered a contributing factor. Ice has high albedo, but rising temperatures are melting summer sea ice, exposing low-albedo dark water. Dark water absorbs more heat, melting more ice, exposing yet more water to absorb more heat and melt yet more ice. It’s a positive feedback loop.
The same positive feedback process is accelerating glacial retreat. Exposed rock at the foot of a glacier absorbs heat and melts ice, exposing more rock, melting more ice. During ice ages the albedo effect does the opposite. Growing glaciers reflect more and more of the sun’s rays, speeding up global cooling and accelerating ice-sheet advance.
The albedo effect is also underway right here in the Holler. The snow will melt anyhow as temperatures rise, but the albedo effect kickstarts the annual melt and then revs it into high gear. Sunlight reflects off high-albedo snow but is absorbed by low-albedo dark surfaces. Surfaces like tree trunks. The bark absorbs more of the sun’s radiation and soon a melt ring, or well, forms around the trunk. This exposes more of the trunk, which absorbs more heat, which melts more snow, until the sun’s rays touch the ground at the base of the tree. Now things really take off. The circle of bare ground absorbs more heat than the surrounding snow and expands ever outward. Eventually circles from nearby trees join up and the snow is in full retreat, skulking around in dark and shady places.
Any dark object illustrates the power of the albedo effect. A pile of frozen moose poop sets off a ring of snowmelt. Twigs, spruce needles, old leaves; all absorb the sun’s heat and sink into the snow as it melts beneath them. When you see a speck of stump or boulder or wood pile emerge, watch the albedo effect in action as the snow melts more rapidly from that spot, exposing more dark surface, absorbing yet more sunlight, melting yet more snow. The positive feedback loop is underway. The rate of melt is accelerating.
So there you have it. The albedo effect influences our climate on a global scale. It can accelerate global warming, like now, or global cooling during ice ages. But it is also a local phenomenon, one that we welcome every spring. It hastens the snow melt, warms the soil and sets the stage for the surging renewal of life. And before you know it, albedo leads to libido and the cycle of life continues. Happy spring!
Sue McKay Miller
March 26, 2021
It’s a “spring” flower!