But what would it take to entirely melt Antarctica, a sheet of miles-thick ice that’s larger than the United States?
Now, a blockbuster new study has produced an answer: If we burned all the fossil fuel on Earth, we would, in fact, eliminate the Antarctic ice sheet. The process would likely take up to 10,000 years, but its consequences would cause nearly 200 feet of sea-level rise and irrevocably change the face of the Earth.
The Antarctica question — whether there’s actually enough fossil fuel in the world to raise global temperatures enough to melt the entire ice sheet — surfaced at least as far back as 1979, when The New York Times published an article about the possible consequences of an Antarctic ice sheet collapse. This was the article that got climate scientist Ken Caldeira, a researcher at Stanford University’s Carnegie Institute of Science and the new study’s senior author, interested in climate change in the first place, and in the Antarctica question in particular.
“The problem has been in my head for 35 or so years, but I had never worked with people who had the tools to solve the problem,” Caldeira says. “It was a real pleasure to finally get to address this question.”
Caldeira teamed up with a group of other researchers including lead author Ricarda Winkelmann, a professor of climate system analysis at the Potsdam Institute for Climate Impact Research, to tackle the issue. The group used a state-of-the-art ice sheet model, which Winkelmann helped develop, to make projections on what would happen if humans burned various amounts of fossil fuels in the coming centuries, including what would happen if we burned all the available fuel on Earth — an amount equivalent to about 10,000 gigatons (that’s 10,000 billion tons, or 10 trillion tons) of carbon, according to previous estimates.
While “more comprehensive” models do exist, the ice and climate models used in this study are well-known, well-tested and “have been applied successfully in many ways,” said Richard Alley, a glaciologist at Pennsylvania State University, in an e-mail. The results they produced point to the possibility of a nearly unrecognizable future Earth.
It would probably only take us about 500 years to burn through all the fossil fuels, the researchers suggest. But carbon can stay in the atmosphere and cause global temperatures to remain elevated for thousands of years. So even though ice melts slowly, it’s likely to continue melting for millennia.
When it comes to destroying Antarctic ice, the biggest culprit in all this melting is the warming of the ocean, even more-so than the warming of the air, Winkelmann explains. Warming waters can melt ice sheets from the bottom up, which can destabilize them and cause large ice shelves to start breaking off into the water. In the doomsday scenario described in the paper, the entire Antarctic Ice Sheet would eventually collapse.
The result would be nearly 60 meters, or close to 200 feet, of sea-level rise, about half of which would likely occur in the first 1,000 years. “This kind of sea-level rise would be unprecedented in the history of civilization,” Winkelmann says, adding that these effects would be irreversible on human time scales. Such an enormous rate of sea-level rise would likely wipe out many of the world’s coastal cities. In the United States, alone, San Francisco would be reduced to a handful of islands, New York City would be submerged and Florida would disappear entirely.
These findings are not necessarily a surprise, says Michael Oppenheimer, Albert G. Milbank Professor of Geosciences and International Affairs in the Woodrow Wilson School at Princeton University. Previous papers have attempted to make projections about the total melting of Antarctica using much older models. “[This paper] looks a lot like what’s been done in the past, but using an advanced model rather than a model that is primitive in comparison,” he says. Caldeira adds that he believes it’s the first time anybody’s looked at the effects of continued emissions on the entire Antarctic ice sheet over such large time scales using an up-to-date model.
Still, optimists might argue that the likelihood of actually burning through so much carbon is slim. In recent years, global leaders have agreed to try and limit global warming to within 2 degrees Celsius of preindustrial temperatures, mainly by reducing carbon output and investing in renewable energy sources instead. Judgment varies on how much more carbon we can emit and still stay within the budget, but the Intergovernmental Panel on Climate Change (IPCC) estimates that to still have more than a 66 percent chance of meeting the goal, we can only burn a maximum of 300 gigatons of carbon, corresponding to about 1,000 gigatons of carbon dioxide emissions. That’s far shy of the 10,000 gigatons that would entirely take out Antarctica.
Even though many nations have already vowed to cut their carbon output by varying amounts over the coming decades, experts say the current pledges are not enough to keep us below the 2-degree threshold. “The highest carbon emissions are quite high, but I don’t think we can exclude the possibility of emissions that high,” Alley said in his e-mail. Still, burning through all the fossil fuels would represent a worst-case scenario.
That’s not to say we’re off the hook in the short term, though. “We’ve looked at this whole range of emissions scenarios,” Winkelmann says, and the team took a look at the possible effects we could see in the near future as well. If we manage to keep our carbon burning under about 600 gigatons, the researchers conclude that Antarctic melting would likely lead to less than two meters of sea-level rise. Burning through this budget could have bigger consequences, even in the short term.
Most notably, they predict that the West Antarctic ice sheet, a particularly vulnerable segment of Antarctica, could become unstable with just 600-800 gigatons of carbon burned. These projections may even be a bit conservative compared to other recent research. A high-profile study published by NASA scientists last year, for instance, claimed that a rapidly melting section of the West Antarctic Ice Sheet appeared to already be “unstoppable.”
And according to an e-mail from Eric Rignot, a principal scientist and ice expert at NASA’s Jet Propulsion Laboratory and an author of last year’s study on the West Antarctic ice sheet, all of the study’s conclusions may represent “very conservative time scales of Antarctic decay.” This is because the ice model the researchers used fails to take into account certain factors that could affect how fast the ice collapses, such as defects or fractures in the ice. These factors could cause ice to break off into the water faster than the model suggests.
Even with these issues factored in, however, the total melting of Antarctica would likely still take place on a millennial time scale. The question that remains is why even consider this finding, which makes projections for a future that neither we, nor our children or even great-grandchildren, will be around to witness.
“Really, there’s a question here of, what do we owe the Earth,” Oppenheimer says. “Putting aside all the questions of what’s going to happen in the next 50-100 years, which are really key in policymakers’ minds, there are bigger issues here which may be almost philosophical and ethical in their nature.”
And such dramatic long-term consequences could be eye-opening in a way that short-term projections sometimes aren’t, says Caldeira. “The legacy of what we’re doing over the next decades and the next centuries is really going to have a dramatic influence on this planet for many tens of thousands of years,” he says.
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