Magazine article Geographical

The Big Melt: All over the World, Mountain Glaciers Are in Retreat, Providing One of the Clearest and Most Unambiguous Signals That Climate Change Is Already under Way

Magazine article Geographical

The Big Melt: All over the World, Mountain Glaciers Are in Retreat, Providing One of the Clearest and Most Unambiguous Signals That Climate Change Is Already under Way

Article excerpt

There are few more potent visual illustrations of the stark reality of climate change than a pair of before-and-after shots of a shrinking glacier--a once-mighty river of dirty ice diminished, retreating in the face of rising air temperatures. And all over the globe, from sea level to the tops of some of the world's highest mountain ranges, glaciers are doing just that.

The statistics are alarming. The number of glaciers in Glacier National Park in Montana has dropped from about 150 when the park was established in 1910 to only 25 glaciers larger than ten hectares in 2010. Between 2004 and 2011, glaciers in the Canadian high Arctic shed about 580 gigatonnes of ice, while over the past decade, Tibetan glaciers have lost about 16 gigatonnes of ice a year.

Glaciers in the French Alps have lost a quarter of their area in the past 40 years, and across the Alps as a whole, they're losing about two to three per cent of their surface area and volume each year. At this rate, there will be only a few glaciers left in the Alps at high altitude by the end of the century.

In the tropical Andes, glaciers have shrunk by between 30 per cent and 50 per cent over the past 30 years--the highest rate observed over the past three centuries. In some cases, they've disappeared altogether. At the current rate of retreat, many more of the small glaciers could disappear within the next ten to 15 years, affecting water supplies for several large populations.

'Individual glaciers respond to local conditions,' says Professor Jonathan Bamber of the University of Bristol. 'But if you look at whole mountain ranges, over a long enough time series, almost every major mountain range that has a significant number of glaciers is showing a decline in volume and area.'

And it all adds up. One recent study determined that between 2003 and 2009, the glaciers outside of the Greenland and Antarctic ice sheets lost an average of about 260 billion tonnes of ice per year, causing an annual rise in sea level of about 0.7 millimetres.

WARMING PLANET

The story that the world's glaciers is telling us is pretty unambiguous. 'It's a kind of truism that if the planet warms, well, ice melts,' says Bamber. 'Glaciers are an effective measure of the health of the planet. If glaciers, globally, are receding, it means that over the past few decades, the planet has warmed.'

Dr Chris Stokes of Durham University agrees. 'The great thing about glaciers is that nobody can argue with their data,' he says. 'They faithfully do what the climate tells them to do. If you're seeing a worldwide glacier recession, it's almost impossible to argue that that's not a result of some sort of climate change. Indeed, the vast majority of glaciologists, if not all, are in agreement that what we're seeing now is as a result of the kinds of atmospheric temperature changes and ocean warming that we're seeing recorded by meteorological stations around the world.'

And the bad news is that the situation appears to be getting worse. 'We're seeing larger areas of glaciers subject to melting and we're also seeing more intense melt in some regions,' Stokes says.

The problem is particularly acute for glaciers that are fed from plateaus. 'If you push the temperature up just a very small amount, because they're fed from plateaus, you actually push the equilibrium line altitude [ELA: the average elevation of the zone on a glacier where accumulation is equal to loss over a one-year period] just that little bit higher onto the plateau and it significantly reduces the area where the glacier accumulates snow,' explains Dr Jeremy Everest of the British Geological Survey (BGS).

'As soon as it stops doing that, then obviously the amount of mass that it receives as snow is significantly reduced and the rest of the glacier just gets rained on, which does it no good whatsoever,' he continues. 'So you get this threshold change whereby up to a point, the glacier was relatively happy even though it was retreating, and then suddenly, it goes into almost catastrophic decline. …

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