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our planet home – arctic sea ice is diminishing

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Records of Arctic sea ice have been regularly kept since 1980 or so, and there’s been some satellite mapping since the late seventies. The sea ice starts its growth in autumn, reaching its greatest extent at the end of the northern winter. This year has been unusual – after a more rapid freeze-up than usual in September, the growth of ice has slowed substantially, and by the end of October the sea ice extent had reached a new record low for this thirty-five year period. Two principal causes of this slow growth were the high surface temperatures in open waters of the arctic region, as well as high air temperatures. The USA’s National Snow and Ice Data Center (NSIDC) provides lots of useful information on the issue and does its best to explain the complex local and general factors driving arctic ice formation and melting.

Arctic sea ice is ice that forms and deforms in the ocean rather than on land, so it doesn’t include icebergs or glaciers. It’s covered in snow most of the year, and its bright surface reflects 80% of sunlight back into space, whereas melted ocean water absorbs 90% of sunlight, causing a positive feedback loop, an acceleration of global warming effects. The term used to describe the whiteness or reflectivity of a surface is albedo. For our planet, albedo is affected primarily by ice and cloud cover.

While it may be that we’ll record the lowest ice maximum ‘on record’ by the end of this winter, we should recall that thirty-odd years isn’t much of a period in geological terms. Nor does melting sea ice substantially affect sea level rise, unlike melting ice sheets and glaciers. The main concern is this change in albedo, and its effect on ocean temperatures, which will not only effect ocean life in the region but also the melting of frozen coastal regions, and weather conditions, in largely unforeseeable ways.

Another issue is that ‘old sea ice’, the type that survives the annual freeze and melt cycle, has reduced substantially since records have been kept. This old ice stretched over a distance of 1.9 million square kilometres back in 1984, but this year that has reduced to about 110,000 square kilometres, according to a report from episode 592 of the SGU. This is a measure of sea ice extent, rather than volume, which would be much more difficult to measure. In any case, it’s a massive reduction in just a generation or so, but again we don’t have long-term data to tell us whether or not the planet has experienced these sorts of rapid changes before. It’s reasonable to suspect not, and that the great volumes of greenhouse gases we’ve been emitting into our atmosphere are having unprecedented effects, but we can’t be sure. In any case, our activities are certainly affecting our planet home, and theatening island and coastal populations around the globe. As mentioned, the warming of the oceans, and of the atmosphere above them, affects the polar jet stream and can have knock-on effects world-wide. The rise in sea level is generally the effect most human populations are concerned with, though the most wealthy residents of low-lying areas seem breezily unconcerned, as this podcast episode from climate one, discussing the response of residents in the San Francisco Bay area, clearly shows.

Arguably though, it’s not so much complacency as bewilderment that’s hampering responses. Projections of sea-level rise are notoriously varied, in keeping with the enormous complexity of the interacting effects of warming. We’re on much safer ground when making observations of past effects than when predicting future ones, and even then it’s tricky, because we don’t have direct measurements beyond a fairly recent time period. It’s generally agreed that the oceans have risen by about 15-20 cm in the last century, but predictions of the rise over the next thirty-odd years to mid-century vary wildly, with climate scientists bickering over the damage such varied estimates is wreaking on their profession.

So what is to be done? Allowing our bewilderment to inhibit all action is obviously counter-productive. We should continue to monitor, model and project, and to speed up the process of reducing greenhouse gas emissions, with smart solutions to our energy needs as well as ways of minimising those needs, while considering matters of equity and opportunity re developing and developed regions. And we should continue to pressure and push our politicians towards promoting these reductions and solutions.

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Written by stewart henderson

November 24, 2016 at 7:12 am

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