10 September 2011

That time of year again (part 3)

Good news, Ruth (at least) has accepted my wager. You'll catch at least one of us at the Barn Dance in fancy dress. Come on Bob, Jo and Claire. And the rest of you.

It's mid September and all eyes are on Arctic sea ice extent as it rolls toward its summer minimum. It's of particular interest to climate nerds because ice is shiny: polar sea ice reflects sunlight back into space, whereas melted sea ice reveals the dark water beneath which absorbs the energy and warms - contributing to Global Warming and driving changes in weather and climate. Change in the sea ice extent is a gauge of change in Earth’s Albedo. I cobbled together the average figures for April to September in my last post (and spelled kilometre wrong) specifically because those are the months of the year where the sun is in the sky, either reflecting off the ice or warming the ice-free water.

image: NASA

Spend much time in the darker recesses of the Internet though and you’ll find someone tell you that ice melt in the Arctic isn’t important because when it’s summer in one hemisphere, it is winter in the other and the sea ice there is doing the polar opposite and growing. Does growth at one pole compensate for loss at the other - are pesky climate scientists alarmists only telling half the story?

It’s a nice thought, but sadly falls foul to another simple physical property - night and day. Sea ice isn’t the only thing to change seasonally. Day length changes too. And at the Poles, it changes dramatically.

Outside the summer months in the polar circles the most you can hope to see is a few hours of weak twilight each day. The sea ice may be growing again, but there’s little effect on Earth's Albedo because there's hardly any light to reflect. At the poles proper the sun doesn’t rise at all for nearly a full six months.

Meanwhile, during the polar summer when the ice is in full retreat...

Video used with kind permission of Michael Becker

p.s. while I’m waffling about a bit of ice thousands of miles away, don’t forget that we're hosting a composting class right here in Wiv at The Station Garden on Sunday Afternoon.

1 comment:

  1. If you're interested, NOAA polar night time lapse video with a full moon and the southern lights.