How Worried Should You Be About Antarctica's 'Collapsing' Ice Sheet?

The use of the term "collapse," which connotes an imminent calamity, rather than a long, relatively slow process (glaciers melting at, literally, a glacial pace) generated quite a bit of chatter in the climate journalism community, but in interviews, scientists defended the word as apt for this situation.

"Indeed, it is possible that the [word] 'collapse' brings the wrong thought to some people. On the other hand, it is clear that Joughin et al. did not simulate the worst case, so care is required in more than one direction," Richard Alley, one of the foremost experts on the fate of the world's ice sheets, said in an email conversation. Alley was not involved in the new research on the West Antarctic Ice Sheet.

"The uncertainties in sea-level rise projections have always been strongly on the 'bad' side — there is a central or best estimate, and the rise might be a little less than that, or a little more, or a lot more," Alley said. "Over the last couple of decades, the sea-level rise from the ice sheets has been about 0.6 mm/yr, from a reservoir of more than 60 meters, which is about the same as me going on a diet and losing 1/3 of one potato chip over a year.

Obviously, if I were serious about dieting, I could lose weight much faster than that. We are rather confident that too much warming will cause ice-sheet shrinkage, and the possibility that the ice sheets will diet seriously has been weighing on us for a long time."

Projected sea level rise through 2100, based on different emissions scenarios, or "pathways."

Image: U.N. Intergovernmental Panel on Climate Change

How is sea level rise, including from melting Antarctic ice, already affecting us?

Sea level rise is not just a concern for the future, it is already heightening coastal flood risks worldwide. For example, because the sea level in the New York City area rose by about a foot between 1900 and 2012, when Hurricane Sandy struck, about 80,000 more people were affected by flooding in New York and New Jersey than would have been without that increase.

Sea level rise is already escalating the risk of severe coastal flooding in states like Florida, Virginia and New York, and is expected to ratchet up flooding risks in the coming years.

Research by Climate Central, a nonprofit climate science and journalism organization, found that $71 billion of Florida property sits on land less than two feet above the high tide line. "Within less than the term of a 30-year mortgage, sea level rise could cause floods this high to occur once every five years, or even every year, depending on the location," a Climate Central report found.

Virtually all of South Florida would be inundated if sea levels were to rise by 10 feet.

The Thwaites Glacier alone is contributing about 10% to the current globally averaged rate of sea level rise, which is about 0.13 inches per year, Joughin says. That may sound minimal, but added up over the course of a century, that would yield one foot of sea level rise. Because of expected increases in the loss of land-based glaciers in Greenland, Antarctica and other areas, Joughin says the end-of-century figure may be closer to three feet.

"It shouldn't be forgotten that real problems are happening to real people now," as a result of sea level rise and coastal storms, Joughin says.

Do these findings mean New York, Singapore, and Dhaka will be underwater during the next 50 years?

No, but they do mean that these cities, and other coastal locations, need to prepare for increased impacts from the combination of sea level rise and the surge associated with coastal storms.

"Sea level rise is gradual, but over the long term the effects add up," says Joughin. Nobody is going to wake up and find themselves suddenly flooded. That said, rising seas do increase the likelihood of storm surges reaching farther inland. And if you happen to live in Bangladesh or other low lying regions, even the current rate [of sea level rise] is important."

Are we totally screwed already, making it pointless to try to cut emissions, since the collapse of this region of the ice sheet is viewed as inevitable? What could emissions cuts do to lessen the severity of Antarctic ice melt and sea level rise?

The studies on the collapse of parts of the West Antarctic Ice Sheet actually reinforce the need to address the emissions of greenhouse gases, such as carbon dioxide, that are helping to increase global temperatures. We've already destabilized part of Antarctica, the studies showed, but we have a choice about what else we want to set into motion.

The decisions made now and during the next few decades will determine how much more of the ice sheet we destabilize, and how quickly.

Here's how Eric Rignot, a senior research scientist at NASA and co-author of one of the new studies, thinks about the energy options before us.

"Sustained climate warming will not make things any better in Antarctica," he told Mashable. "It is difficult to say, but broadly speaking, by slashing emissions now we will avoid hitting major surprises down the line, and extreme scenarios of rapid change which we have no idea about."

When it comes to melting glaciers, no one likes a surprise party.

Topics: Antarctica, Climate, Florida, Hurricane Sandy, ice sheet, ice sheet collapse, sea level rise, U.S., US & World, World