Decisions made in the next decade regarding cuts in greenhouse gas emissions could determine the fate of future generations by either ensuring the ultimate demise of more than 80% of the floating ice in Antarctica, or maintaining enough of it to prevent a catastrophic amount of sea level rise.
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It showed that if greenhouse gas emissions continued at their present rate, the Antarctic ice shelves would be in danger of collapse by the century’s end.
“The long reaction time of the Antarctic ice-sheet – which can take thousands of years to fully manifest its response to changes in environmental conditions – coupled with the fact that CO2 [carbon dioxide] lingers in the atmosphere for a very long time means that the warming we generate now will affect the ice-sheet in ways that will be incredibly hard to undo”, Golledge said in a statement.
While melting ice shelves don’t contribute directly to rising sea levels because they float on the surface of the ocean, they play a crucial role in keeping the polar ice cap in place by acting as a break on the ice sheet.
The team used a state-of-the-art model to simulate Antarctica’s ice sheets under different scenarios, from a business-as-usual situation of unchecked emissions to an ambitious effort to start reducing emissions from 2020 onwards.
The world will be locked into thousands of years of unstoppable sea level rise from melting Antarctic ice if it doesn’t cut emissions and prevent another two degrees of global warming, scientists have warned.
That would expose the massive Antarctic ice sheet and trigger centuries, and even millennia, of runaway sea level rise from its melting that would be nearly impossible to stop.
But in 2013 there was insufficient knowledge about how the ice sheet might respond to future warming.
This finding, presented in a new study published Wednesday in the journal Nature, is the latest research to predict how global warming may transform global coastlines by setting in motion potentially irreversible melting of the world’s largest ice sheet. They then combined their data with climate model simulations based on varying levels of greenhouse gas emissions. “Under the most extreme scenario we considered [in the model] we lose the entire ice shelf within the next century and that has pretty dire consequences for the ice sheet”. Only a little of this has so far been caused by melting ice; most comes from the expansion of oceans as they warm.
But the IPCC only included a five centimetre contribution from melting Antarctic ice because of uncertainty over how the Antarctic ice sheet would respond to future warming.
The friction of floating ice shelves against the deeply buried rock of the coast slows the flow of ice from the interior. Warmer colours indicate relatively faster flowing ice. Graph shows the Antarctic contribution to global sea-level. “I find it disheartening that we are still talking about 2C above pre-industrial as a “reasonable” target when we already passed the threshold for a large share of the ice sheets”, he said.
Dr Golledge said atmosphere warming would need to be kept under 2C to avoid the loss of the ice shelves. But because carbon dioxide remains in the atmosphere for a very long time, ongoing emissions will continue the warming effect.
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“Our model projections show that similar levels of melt may occur across coastal Antarctica near the end of this century, raising concerns about future ice shelf stability”. “Beyond that we’re going to be in a territory of propagating changes that we can’t really reverse”.
