Cape Town - Antarctica is the highest, windiest, driest, wildest and coldest continent on Earth. Now, one of its massive ice sheets is melting.
Although the full environmental consequences of this profound change will only manifest globally over the coming centuries – from 200 years to 1 000 years (still extremely rapid in geological time) – many people alive today are likely to experience the first, early impacts.
The changing face of the Frozen Continent has been documented in a number of scientific studies published in recent weeks.
Two papers in particular drew a lot of attention and both came to a similar conclusion: that massive glaciers in West Antarctica have “passed the point of no return”.
This is likely to lead to the broader collapse of the vast West Antarctic Ice Sheet, causing a global sea-level rise of several metres – enough to swamp vast parts of the coastal zone where about half the world’s population lives.
One of these studies, reported in Geophysical Research Letters, looked at six huge glaciers in the Amundsen Sea sector that already contribute significantly to sea level rise and that collectively contain enough ice to boost the global sea level by 1.2m. The researchers found the glaciers were melting faster than most scientists had expected and reported that this rapidly melting section of the West Antarctic Ice Sheet appeared to be in irreversible decline, with nothing to stop the entire glacial basin from disappearing into the sea.
“This sector will be a major contributor to sea level rise in the decades and centuries to come,” said lead author Eric Rignot, a glaciologist and University of California professor, but added that at a conservative estimate it could take several centuries for all the ice to flow into the sea.
“The collapse of this sector of West Antarctica appears to be unstoppable... At this point, the end appears to be inevitable.”
In the second study, reported in Science, researchers at the University of Washington used airborne radar data, detailed topography maps and computer modelling to conclude that one of the six glaciers – the fast-moving Thwaites Glacier – was likely to disappear in a matter of centuries, potentially raising global sea level by more than half a metre.
They pointed out that this glacier acts as an “ice dam”, stabilising and regulating movement towards the sea of the West Antarctic Ice Sheet that contains enough ice to cause another three-to-four metres of global sea level rise.
“There’s been a lot of speculation about the stability of marine ice sheets, and many scientists suspect that this kind of behaviour is under way,” said glaciologist and lead author Ian Joughin. “This study provides a more quantitative idea of the rates at which the (ice sheet) collapse could take place.”
The word “collapse” implies a sudden change, but the fastest scenario based on their data is 200 years and the longest is more than 1 000 years, the authors pointed out.
A third study, by a team of British researchers, was also reported in Geophysical Research Letters.
Their three years of observations, using measurements collected by the European Space Agency’s CryoSat-2 satellite mission that carries an altimeter specially designed for this task, shows that the Western Antarctic Ice Sheet is now losing 159 billion tons of ice each year – twice as much as when it was last surveyed.
Study leader Professor Andrew Shepherd of the University of Leeds said: “The increased thinning we have detected in West Antarctica is a worrying development. It adds concrete evidence that dramatic changes are under way in this part of our planet, which has enough ice to raise global sea levels by more than a metre. The challenge is to use this evidence to test and improve the predictive skill of climate models.”
Another study in Nature, by an international team of geologists and climate scientists, found that the Antarctic ice sheet was historically less stable than previously assumed and – at one point – had caused a huge global sea-level rise in just a single century.
It reported that this ice sheet had begun melting about 5 000 years earlier than previously thought, coming out of the last ice age, and that shrinkage had accelerated during eight distinct episodes, causing rapid sea-level rise.
Meanwhile, profound change is also occurring at the opposite end of the world where – for the first time in about two million years – melting Arctic sea ice is connecting the north Pacific and north Atlantic oceans.
Two new shipping routes have opened in the Arctic: the Northwest Passage through Canada, and the Northern Sea Route, a 5 000km stretch along the coasts of Russia and Norway connecting the Barents and Bering seas.
While the melted Arctic holds huge economic potential but equally huge environmental risks, the newly opened passages leave both coasts and Arctic waters vulnerable to a large wave of invasive alien species, biologists from the Smithsonian Environmental Research Centre warned in a commentary published in Nature Climate Change. - Sunday Argus