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The big melt

  • Written by  Geordie Torr
  • Published in Climate
The big melt Shutterstock
01 Mar
2014
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

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.’

Changing patterns of precipitation are also a problem. ‘Glaciers will shrink if you don’t give them enough snowfall while there’s a predominantly warming trend,’ says Stokes. ‘There are one or two places where we’re seeing glaciers shrink and perhaps there hasn’t been an obvious change in air temperature, but they’ve had less snowfall, so they’re not being replenished. The glaciers on Kilimanjaro for example, might be shrinking because they aren’t receiving enough precipitation or as much precipitation as they used to get.’

 

MINORITY REPORTS

While the overall trend is for glaciers to shrink, there are some that are managing to hold their own, or even grow, but they’re well and truly in the minority. ‘The latest estimate is that there are about 300,000 glaciers around the world and you’re probably looking at only a few hundred that are actually advancing,’ says Stokes. 

‘If you warm up the atmosphere, you’re going to get more precipitation, because a warmer atmosphere can hold more moisture,’ he continues. ‘So there will be certain areas where the temperature may have been warming or may even have been staying the same, but because the glaciers were getting more snowfall, they’re growing. So there might some glaciers around the world in certain settings – close to coastlines, close to a warm ocean – where they’re getting more snowfall, but they’re very much in the minority.’

A case in point is the glaciers in Scandinavia. ‘During the 1990s, glaciers in Scandinavia were advancing, many of them were quite healthy, and that was due to a change in the amount of precipitation they were receiving,’ says Dr Stephan Harrison of the University of Exeter. ‘So, regionally, you’re always going to get glaciers that buck the trend, but globally, that isn’t the case.’

 

AN ICE CUBE’S CHANCE...

And while most glaciers are melting, the rate at which they’re melting is far from uniform. Part of this is simply down to the size of the glaciers themselves. ‘Globally, the smaller glaciers are the most vulnerable – it’s just like if I put an ice cube on the table versus a big block of ice, the ice cube’s going to disappear first, so that’s where we’ve seen glaciers disappear first,’ says Stokes. ‘The very smallest type of glacier is always going to be the most vulnerable. So that’s where we’re seeing quite dramatic change. A small glacier might lose 50 per cent of its area over a couple of decades, where the larger glacier might only lose ten per cent.’

However, local climatic conditions will also have a significant effect. One region that’s being particularly badly affected is Patagonia. ‘The Patagonian ice fields only represent about two per cent of the world’s mountain glaciers, but they represent ten per cent or so of the ice lost from the world’s mountain glaciers,’ Harrison explains. ‘They’re melting more than any other glaciated mountain region on Earth.

‘We’ve looked at all 270 major glaciers in Patagonia and out of those, I think that something like two were showing any major signs of advance,’ he continues. ‘The enormous overwhelming majority were undergoing recession.’

The Patagonian ice fields are at relatively low latitudes – around 45°S – and they come down to sea level, which, Harrison explains, is the equivalent of coming down into the Mediterranean. The glaciers exist because there’s an enormous amount of snowfall on the Andes. ‘But because they come down to near or at sea level, and because it’s relatively warm at that latitude in the Southern Hemisphere, they’re melting very quickly,’ he says. ‘The winters are cold, but the summers are warm, and changes in the southern westerlies are having a big impact on glaciers in this location.’

 

DECIDEDLY UNHEALTHY

Iceland, too, is something of a hotspot for glacier retreat. The country’s 300-odd glaciers, which cover more than ten per cent of its area, are losing about 11 billion tonnes of ice a year – hardly surprising given that Iceland is currently warming by as much as four times the Northern Hemisphere average.

The BGS’s Everest has been studying the Virkisjökull glacier in southeast Iceland for more than 15 years. The glacier drains from Iceland’s highest point down almost to sea level over a steep gradient – dropping about 2,000 metres over its nine-kilometre length. ‘That means that it’s very sensitive to climate change, so any changes that occur in the wider environment should be picked up in the glacier’s behaviour very soon after those changes occur,’ Everest says.

And that sensitivity is reflected in the glacier’s health. ‘It’s not very well, in fact, it’s decidedly unhealthy,’ Everest says. ‘In the time that we’ve been studying it, the traditional way of measuring glacier health has been lateral retreat – how much the glacier has retreated back from its former position. And since 1990, the front has retreated by about 700 metres, which doesn’t sound a lot when you’re looking at the Antarctic scale, or the Greenland scale, but for a small glacier that’s only nine kilometres long, you’re talking about nearly ten per cent of its length.’

The glacier is also thinning. ‘We’re getting an average figure of about seven or eight metres of surface loss across the whole of the lower portion of the glacier every year,’ Everest says. ‘That equates to 72 million cubic metres of ice lost every year – the equivalent of 23,000 swimming pools – just in the lower portion of the glacier.’

 

OVER THE EDGE

By studying Virkisjökull’s moraine – the debris picked up as it scours the ground below it and left behind as the ice melts – BGS scientists have determined that the glacier also retreated during the 1930s and ’40s, but then started to advance again. ‘Now, it’s starting from a point of ill-health, so the current warming is just pushing it over the edge just that little bit more,’ Everest says.

‘We picked up a change in 2007,’ he continues. ‘Prior to then, the glacier was still advancing in the winter; now it melts the whole year round. It doesn’t replenish itself – there’s no mass increase during the winter any more.’ 

That year-round melting is having a devastating effect on the glacier. ‘We’ve seen an almost doubling of the rate of retreat since 2007,’ Everest says. ‘We think its largely because the temperature has risen just enough to push the ELA that little bit higher, so the vast majority of the precipitation falling on the glacier is rainwater rather than snowfall.’

According to Everest, Virkisjökull’s behaviour is fairly typical of the southern Icelandic glaciers. ‘They’re all pretty much suffering the same way,’ he says. ‘A few are behaving a little bit slower, but in general, that trend is reflected across the whole of Iceland – and indeed, the Alps and the Rockies and New Zealand, and anywhere that there are these terrestrial Alpine-style or plateau-style glaciers. It isn’t a happy story.

‘The glacier we’re looking at is probably in a more advanced state,’ he continues. ‘It’s more sensitive, being a little bit smaller, but we would expect to see the bigger ones doing exactly the same thing as time goes by.’

 

MAJOR ISSUE

The consequences of all this melting are stark. In many arid mountain regions, communities have come to reply upon the seasonal glacier melt for their water supplies. ‘In terms of economic impact, glacier melt in places such as Central Asia and in parts of Bolivia and Peru is really significant,’ Harrison says. ‘Much of La Paz’s water comes from glaciated mountain catchments and with ice loss, that has a big impact on water supply and the regulation of water supply.

‘In Patagonia, there aren’t many people there, so it isn’t a big cultural or economic issue,’ he continues. ‘But in the arid Andes and Central Asia, where mountain communities rely on glaciers as a water source, glacier melt is a major issue.’

This story was published in the March 2014 edition of Geographical Magazine

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