Andreas Späth

Antarctic meltdown

2014-05-19 14:52

Andreas Wilson-Späth

The effects our carbon-intensive way of life has on our planet are becoming harder and harder to ignore. In West Antarctica human-caused global warming is helping to push an entire continent over the edge in a dramatic, slow-motion transformation that will change the world.

I’ve previously written about the alarming rate at which sea ice is disappearing from the Arctic. While the northernmost regions of the planet are particularly sensitive to climate change, the southern continent is responding more slowly, but with even more devastating consequences in the long run.

Think of the Arctic as the global fridge. Leave the door open and you’ll see things warming up inside pretty quickly.

Think of Antarctica as the global deep freeze. Leave the door open and while things might take much longer to start melting, in the end you’re left with a much bigger mess of slush and water.

The process has already started. Two scientific papers published last week confirm that the West Antarctic Ice Sheet (WAIS) is in the early stages of collapse.

The causes of the massive meltdown are complex, but there is little doubt that the atmosphere-warming greenhouse gasses we continue to spew out of our car exhausts, factory chimneys and fossil fuel power plants have made a telling contribution to nudge the system past the point of no return.

The authors of both studies note that the process may be slow, taking anywhere from 200 to 1000 years to complete, but that it can no longer be halted, even if we stopped all carbon emissions right now.

To put the enormity of the situation into context, the WAIS, which represents only a small piece of the mass of ice that covers most of Antarctica, contains an estimated 2.2 million cubic kilometers of ice. That’s enough to cover all of South Africa in a layer of ice well over 1.5 kilometres thick.

The weight of all of this ice is so great, it pushes the bedrock on which it rests downward by up to 1000 metres, causing much of the WAIS to be located below sea level.

Constantly replenished by snow falling on its surface, the ice flows towards the coast under its own weight, where the glaciers along its edges calf icebergs or terminate in large floating ice shelves.

Studies indicate that many of the glaciers that constitute the WAIS are now losing more ice through melting than is being replaced by snowfall.

Last year, a study investigating a 364-metre-long ice core from the Antarctic Peninsula showed a steady long-term increase in the rate at which the region’s ice has been melting during the summer period, but a notable escalation of this rate since the middle of the last century. Today, the ice is melting ten times faster every summer than it did 600 years ago and the summer melt rate “is now at a level that is unprecedented over the past 1000 years”.

Rising global surface temperatures cause melting at the top while warming ocean water causes melting below where it’s in contact with the ice.

The new papers indicate that several major WAIS glaciers shrank by between 10 and 35 kilometres from 1992 to 2011 and that a process of “early-stage collapse has begun”.

In effect the WAIS sits on a bowls-shaped lower-than-sea-level depression caused by its own mass. Once the so-called grounding line of the glaciers – the line along which the ice begins to floats on sea water – has retreated beyond the lip of this bowl, warm sea water can infiltrate between the ice and the bedrock, causing the ice sheet to float and to melt more rapidly from below.

The glaciologists who conducted the studies believe that this will be followed by a near-complete loss of ice in all of West Antarctica. According to one of the lead authors, Ian Joughin, “The next stable state for the West Antarctic Ice Sheet might be no ice sheet at all.”

Sea level is estimated to rise by three to four metres as a result of the collapse of the WAIS. Since the process was not included in the estimates of the most recent report from by the UN’s Intergovernmental Panel on Climate Change (IPCC), existing forecasts of sea level rise may have to be doubled.

The time-scales involved may be slow (although not all too well constrained), but the changes we’re causing are global, enormous and already happening.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
 
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