80% of Antarctic ice sheet at risk of melting if global warming targets not met
A new study by Nature, used computer modeling to predict the long-term effects of greenhouse gases which found that all but one scenario would lead to loss of large parts of the Antarctic ice sheet. Making significant greenhouse gas emissions reductions beyond 2020 was the only scenario that could avert losing around 80% of the ice sheet. The study shows that the world would need to achieve the target of keeping global warming at or below 2°C through 2100.

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.

This finding, presented in a new study(opens in a new tab) 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.

An international team led by Nicholas Golledge, a senior research fellow at Victoria University’s Antarctic Research Center, uses computer modeling to try and predict the long-term -- meaning out to 3,000 years -- response of the entire ice sheet to global warming.

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What researchers found contains a high degree of uncertainty, but even with that caveat, it is concerning.

In all but one scenario the team simulated, huge chunks of Antarctica would slide into the sea, set into motion by the loss of floating ice shelves that buttress the inland glaciers. This melt would raise sea levels, altering global weather patterns and ocean circulation in the process.

Making significant cuts to greenhouse gas emissions soon after 2020 was the only scenario that could avert this long-term fate, the study found.

However, before panicking about an imminent increase in sea levels, consider that the Antarctic ice sheet can take thousands of years to fully respond to environmental changes. The problem is that molecules of carbon dioxide, which is the longest-lived greenhouse gas, can stay in the air for centuries. This means that emissions cuts today will not take effect for decades to centuries from now.

The climate system is like a giant ship, which takes a long time to come to a stop or change directions. At the helm are human beings, who are responsible for adding greenhouse gas emissions to background levels of such gases, and thereby heating up the air, land and sea.

“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.

Studies published since the U.N. Intergovernmental Panel on Climate Change's most recent major report in 2013, have shown that Antarctica has the potential to contribute far higher amounts of sea level rise during this century than previously thought. This is because of instabilities in the West Antarctic ice sheet in particular, where glaciers that terminate in the ocean are being undermined from above and below by warming air and ocean temperatures.

“If we lose these ice shelves, the Antarctic contribution to sea-level rise by 2100 will be nearer 40 centimeters [15.8 inches],” Golledge said in a press release.

The study pinpoints ocean warming as the instigator in long-term Antarctic ice melt, since it is warming oceans that are thought to be the key factor so far in causing some glaciers to flow faster toward the sea. Think of these ice shelves as corks in a bottle, preventing the bottle from being poured.

"In our experiments, we find that prolonged ocean warming of 0.5 degrees Celsius (0.9 degrees Fahrenheit) above present, together with atmospheric warming of 2 degrees Celsius (3.6 degrees Fahrenheit), ultimately leads to the loss of 80% to 85% of all floating ice in Antarctica," the study found.

Antarctic ice melt presents a moral quandary

Richard Alley, an expert in ice sheet dynamics at Penn State University who was not involved in this new study, said, in general, ice can respond rapidly on human timescales while also evolving over long periods of time.

Antarctic ice-sheet evolution simulated at 10 km resolution at 3,000 CE under a high emissions scenario. Warmer colors indicate relatively faster-flowing ice. Graph shows the Antarctic contribution to global sea-level. Credit:

"Ice can respond to its environment rapidly on a human time scale, but much of the response can be very slow (more than 10,000 years…). Many more studies have found similar results, so we have high confidence that the ice-sheet response to human-caused or natural forcing begins almost instantly but continues for very long times," Alley wrote in an email in response to an inquiry regarding another prominent Antarctica study published on Monday.

"The uncertainties about ice sheets remain very large and difficult to quantify, so one study is very unlikely to be the last word, and eventually the assessment activities of the National Academy of Sciences, IPCC, or similar bodies really are needed to make sense of the information," Alley wrote.

There is a psychological challenge for people to overcome in addressing long-term global warming, when most leaders and individuals tend to focus on shorter-term threats.

However, Golledge says not to focus too much on the long lag time in Antarctica's response to global warming, since many other climate impacts -- from extreme weather events to species extinction -- will occur earlier than Antarctic melt.

"We can't take the view that because the ice sheet[s] are responding more slowly then we don't need to worry about emissions, because changes in other components of the Earth system will still cause us problems in the immediate future," Golledge told Mashable in an email.

"It's a chain of events, like toppling Dominoes if you like. We need to think of the Earth system in its entirety and stop the first part of that chain reaction, and that's hard because of the myriad ways that individual components behave and interact with each other," he said.

The study shows that the world needs to meet the global warming target that world leaders have already agreed to, which is to keep warming at or below 2 degrees Celsius, or 3.6 degrees Fahrenheit, above preindustrial levels through 2100.

Currently, the world is on track to blow past this target by more than 1 degree Celsius, and possibly even more than that. To meet the 2-degree target, many experts say countries need to bring carbon emissions to zero by the end of the this century.

“Missing the 2-degree target will result in an Antarctic contribution to sea-level rise that could be up to 10 meters (33 feet) above present day,” Golledge said. “The stakes are obviously very high -- 10% of the world’s population lives within 10 meters of present sea level.”

According to Golledge, the last time carbon dioxide concentrations in the atmosphere were similar to present levels was well before humans emerged, about 3 million years ago. Back then, global average temperatures were about 3 degrees Celsius warmer than they are now, and sea levels were about 20 meters, or 66 feet, above current levels.

"We’re currently on track for a global temperature rise of a couple of degrees which will take us into that ballpark, so there may well be a few scary surprises in store for us, possibly within just a few hundred years," Golledge said in a statement.

Much as Pope Francis has done, Golledge framed the issue in moral terms in an email conversation with Mashable.

"We need to reduce emissions in the next decade because if we don't, we won't be able to undo the changes. Maybe that doesn't worry some people, but for others, maybe those with children, there's a moral obligation to do everything we can now, before the opportunity is lost," he said.

The new study comes at a time of intense interest in the climate community into the various factors controlling shifts in the Antarctic ice sheet. Most of those studies have caused researchers to increase their sea level rise projections based on higher melt scenarios.

One study, published Monday, showed the sea level rise-related effects on U.S. coastal communities of low versus high emissions scenarios.

"I see two things coming through the literature in nearly all cases," Golledge told Mashable.

"Emissions at present levels (i.e. no reduction) lead to dire consequences before the end of this century, and we're now more-or-less committed to significant sea-level rise from Antarctica, it's just a question of how much, and how quickly."