A catastrophic collapse
Following the calving of one of the largest icebergs ever known - about the size of the entire city of Tshwane, and weighing about one trillion tons - Professor Nancy Bertler, of the Antarctic Research Centre at Victoria University of Wellington, New Zealand, said global warming and the hole in the ozone layer had caused the sudden break-up of “numerous ice shelves” in the region “some of which have been shown to have existed for 10000 years or more”.
While these do not add to sea levels, their removal can significantly increase the speed of land ice flowing into the sea.
And that process, Bertler warned, could have serious effects on the planet.
A sea-level rise of more than 3m would dramatically alter the coastline of many parts of the world, shows an interactive map developed by Alex Tingle.
Bertler said: “The Antarctic Peninsula is one of the fastest warming regions on Earth. Part of this warming comes from direct temperature increases in the atmosphere due to higher greenhouse gas concentrations and partly this is an indirect effect of ozone-destroying CFCs (chlorofluorocarbons).”
She said the changes had caused warmer and drier westerly winds to shift south towards Antarctica, increasing the temperature.
“This has led to a strong warming of the Antarctic Peninsula which in turn causes the catastrophic collapse of numerous ice shelves, some of which have been shown to have existed for 10000 years or more.
“As these ice shelves collapse, they don’t add to sea level rise (ice shelves are the floating tongue of an ice sheet). But with the ice shelves removed, the grounded ice sheets behind them accelerate into the ocean and that causes sea levels to rise.
“The ice sitting behind the Larsen B Ice Shelf, which collapsed in 2002, has sped up eight-fold. Most amazingly, those glaciers are still galloping towards the ocean - some 15 years after the first collapse of Larsen B.
Fortunately, the Antarctic Peninsula “doesn’t hold that much ice”.
“If all of it were to slip into the ocean, it would raise the sea level by less than 50cm (still a lot of course),” Bertler said.
But if the Ross Ice Shelf, which at about the size of France is the largest on the planet, starts to break up, that would be a bigger problem.
“If those same processes destabilise the Ross Ice Shelf, this could lead to a catastrophic collapse of west Antarctica, adding about 3.3m of sea level rise from west Antarctica alone,” said Bertler, who is leading a project to work out how long it might take for the Ross Ice Shelf to break up.
“Currently, we know little about how healthy or not the Ross Ice Shelf is but scientists are hurrying to learn more.”
She added that the Ross shelf had been found to be “very sensitive in the past and capable of rapid change”.
Previous research has shown the last time carbon dioxide levels were as high as they are now “west Antarctica, Greenland, and some parts of east Antarctica collapsed, raising the sea level by 10m to 20m”, Bertler said.
Estimates of how long it would take for such vast ice sheets to collapse run into hundreds of years. One recent study suggested the Thwaites glacier, a linchpin of the West Antarctic ice sheet, could take between 200 and 1000 years to melt.
However, Dr Natalie Robinson, a marine physicist at New Zealand’s National Institute of Water and Atmospheric Research, said the new iceberg, which removed about 12% of the ice from the Larsen C Ice Shelf, was “a normal’, if relatively large, calving event” and “very different from the collapse of its neighbouring ice shelves”.
“There appears to be no evidence that the Larsen C has been subject to the surface melt that led to the rapid and very dramatic collapse of Larsen B,” she said. “The fact that the Larsen C is able to calve such an enormous, contiguous piece of ice is more indicative of it being in pretty good health, rather than the opposite.”
And she added that the glaciers that feed into the Larsen C Ice Shelf “only have the potential to contribute one centimetre to global sea level”.
The greatest risk from the giant berg, Robinson said, was the potential danger to shipping, particularly if it splits into numerous smaller, harder-to-track ones.
“Some people are keeping an eye on a crack that will create the next iceberg from the front of the Ross Ice Shelf. But this may take 10 years or more.”
Professor Christina Hulbe, an Antarctic researcher at the University of Otago, New Zealand, also said global warming may not have played a role in the creation of the new iceberg.
“We can’t say exactly what influence climate change had on the Larsen C event,” she said. She added that the Antarctic Peninsula “used to be the fastest warming place on the planet but right now it appears to be cooling”.
“Scientists who study processes in the atmosphere and climate have determined that this is due a change in storms over the Weddell Sea, which is itself due to changes in the atmosphere further north. Put another way, the recent trend is part of the natural variation around the Peninsula.” - The Independent