Long-Range Ice Forecast: Things Could Get Very Grim
By Michael D. Lemonick
During the great Indian Ocean tsunami of 2004, which ultimately killed more than 200,000 people, the first breathless news reports announced: “three deaths confirmed in tidal wave.” I’m not making this up. It was pretty idiotic — they knew from eyewitness reports how huge the tsunami was, and everyone knew perfectly well that the death toll would be enormous. What, exactly, was the point of reporting the first three? It was a blatantly meaningless number, presented as though the coiffed CNN anchors were conveying actual information.
I sometimes feel the same way when I see projections about sea level rise. The best scientists can tell us today is that the ocean is likely to be 3 feet higher by 2100. That’s likely to be pretty devastating, but it could turn out to be like those first three deaths in 2004.
Sort of, anyway. I’m not suggesting the sea will rise by 200,000 feet, of course. I’m also not comparing scientists with news anchors. The latter are required to keep talking whether or not they have something meaningful to say, and if it happens to be ridiculous, nobody will remember 10 minutes later. Scientists, by contrast, generally try to keep quiet unless they have something meaningful to say, and when they finally do, to be as honest as possible about the limits of their knowledge.
Still, it’s too easy for us lay people to miss the part about limits to knowledge. When the Intergovernmental Panel on Climate Change published its last major report in 2007, scientists projected that the oceans would rise by about 2 feet under the worst-case scenario — but added in a footnote that the projections didn’t include “future rapid dynamical changes in ice flow.” In other words, nobody should take this as a real projection at all.
In plain English, the bit about dynamical changes meant that if the great glaciers on Greenland and Antarctica start flowing faster to the sea and dumping huge chunks of ice into the water, all bets are off. In the language of former defense secretary Donald Rumsfeld, that was a “known unknown.” The IPCC scientists were upfront about their ignorance.
Now we know a little better, and it isn’t especially encouraging. Research published just a couple of years after 2007 showed that even as the scientists were putting their inconclusive report together, the movement of ice on Greenland and Antarctica had already begun to speed up. There had been rapid dynamical changes in ice flow, and they’re still going on. And a flurry of studies in just the past few weeks has uncovered new areas where Antarctica’s ice is threatening to become unstable, while Greenland’s ice continues to move unabated.
The best guess now is that a worst-case rise of 2 feet is no longer in the cards. The likely increase in sea level by 2100 now stands at 3 feet, with worst-case scenarios going as high as 6 feet. Three feet would threaten many coastal cities around the world with frequent, powerful floods, as the mildest of storms could send water coursing through streets and into buildings. Six feet could make large parts of major cities — Miami, New Orleans, Shanghai, Bangkok and many more — essentially uninhabitable.
Given the choice, I’d vote for 3 feet, but I wouldn’t bet on it. I’m a reasonable person, and I have to think that if scientists have already upped their projections just since 2007, there are probably plenty of surprises left, none of them likely to be good.
The problem is that ice really doesn’t want to sit on land if it can possibly help it. It moves inexorably, toward the sea, the way lemmings do. Give it any excuse to move faster, and it will. The excuse it’s been given over the past decade or so is that while air temperatures have been rising all over the planet — the thing most people notice and think about and worry about — the ocean has been getting warmer, too.
That’s mostly why glaciers are on the move. Many of them extend some distance out into the sea before their ends crumble into icebergs, but as the sea warms, those ends are retreating, and the undersides are floating up off the sea floor. Some of the friction that keeps the uphill parts of the glacier from moving too fast is lifted, and the vast river of ice starts racing (relatively speaking), downhill.
If you assume the ice will just keep sliding at its current rate, you can probably count on a merely disastrous 3 feet of rising seas. Scientists have to make that assumption in doing their calculations, even though they know perfectly well that the assumptions they’ll be making 10 years from now could be very different.
But I’m not a scientist, so I can get away with being a little more provocative. Greenland’s glaciers only began speeding up less than a decade ago; before that, they were relatively stable. Antarctica’s glaciers — slower to respond, because the region is much colder to start with — started moving even more recently. That suggests to me that we’re very likely to be in for more surprises, as warmer oceans begin lapping at the feet of huge glaciers and ice shelves and urging the ice to move even faster.
Do I have any evidence that this will happen? Nope. But the ice wouldn’t have to move a whole lot faster to boost the mid-range estimates for sea level rise to, say, 6 feet by the end of the century. And that wouldn’t be a disaster. It would be a catastrophe.