Humans have a hard time conceiving of the incredible scale of an ice sheet, so the consequences of such a change can be lost upon us. But in a new paper in the Proceedings of the Institution of Civil Engineers — Forensic Engineering, researchers Ted Scambos of the National Snow and Ice Data Center in Boulder, Colo., and John Abraham of the University of St. Thomas in St. Paul, Minn. — summarize what we now know about West Antarctica. That includes a finding that may serve as a wake-up call for Americans in particular.
Namely: If West Antarctica collapses entirely — a process that would likely play out over centuries, but that could substantially begin in this one — the expected 11 feet of sea level rise won’t just spread out evenly across the ocean. The United States will actually get a lot more sea level rise than many other parts of the world — possibly over 14 feet. Call it geophysical karma — we’re the nation most responsible for global warming and, at least in this particular case, we’ll get more of the consequences.
So what source of cosmic equity will mete out just deserts in this case? As it turns out — and the mechanisms will be explained in much more detail below — the answer is none other than Isaac Newton’s law of universal gravitation — which states that all objects in the universe attract one another in relation to their masses (and the distance between them).
The U.S. has caused more global warming than any other country
Let’s first consider who’s responsible for the global warming that the world is currently experiencing and will continue to experience in the future.
You may have heard that China has recently surpassed the United States in annual greenhouse gas emissions — becoming the largest emitter. That’s true, but it’s a relatively recent occurrence (within the last decade). Looking back over time, the United States is far and away the number one emitter.
This analysis from the World Resources Institute shows that from 1850 to the year 2011, the United States, a single country, produced 27 percent of the total carbon dioxide emissions of the world. No other single country was close — indeed, the U.S. even outdistanced all the nations of the European Union combined:
And the thing about carbon dioxide is, it stays up in the atmosphere for a very, very long time. A recent study by geoscientist Raymond Pierrehumbert of the University of Chicago found that, for a sudden pulse of carbon dioxide in the atmosphere that raises the concentration to 1,250 parts per million over pre-industrial levels (which were about 280 parts per million), about 900 parts per million of carbon dioxide will still be up there after 100 years. Indeed, concentrations will only decline to 675 parts per million over another 900 years.
Thus, much of the carbon pollution emitted over the last 150 or 160 years is very much still with us. It’s still determining our future even today. Which means that for the global warming that the world is currently experiencing and will experience, the United States remains more responsible than any other single country.
And now the comeuppance: In the event of a collapse of the West Antarctic ice sheet, scientists have determined that the United States will receive more sea level rise than almost any other part of the world. (Granted, so will other countries in North America, like Canada and Mexico, which have considerably less global warming responsibility.)
Here’s how it works: The ice sitting atop West Antarctica is incredibly massive. Basically, we are talking about nearly 500,000 cubic miles of ice, because the vast ice sheet is well over a mile thick in many places. This is why West Antarctica can lose the equivalent of a Mount Everest worth of ice every two years, and seem to barely even change.
And because West Antarctica is so massive, it has a dramatic gravitational pull on the objects around it. This is Newton 101. “It’s really fundamental. What you might almost call high school physics,” explains Jonathan Bamber, a professor of physical geography at the University of Bristol in the United Kingdom.
In this case, West Antarctica is so large that it pulls the global ocean toward it, which slopes upward toward the ice sheet and the Antarctic continent in general. But if West Antarctica were to lose a substantial part of its ice, then the gravitational pull would relax, and sea level would actually decrease near the ice sheet even as it spreads and increases across the global ocean.
But not evenly. Instead, areas farther from West Antarctica would get more sea level rise, and North America and the United States might get more than any other inhabited place on Earth. “The water that had been held close to West Antarctica spreads out across the ocean,” explains Penn State glaciologist Richard Alley, “and we’re far enough away that we weren’t in the ‘pile’ that was held close to West Antarctica when the ice sheet was there and its gravity attracted the water to make the pile, but we get our share of the water from that pile when it spreads out.”
Here’s a figure from Bamber’s research, showing the distribution of sea level rise after a full loss of West Antarctica, equivalent to 3.3 meters or about 11 feet of sea level rise, globally averaged:
In the figure above, to determine how much sea level rise various regions get, you multiply the globally averaged sea level rise, 11 feet, by an additional factor as shown in the figure. According to Bamber, at the high end, the U.S. might get about 25 to 27 percent more sea level rise than the global average. So multiply 11 by 1.27 and you get just shy of 14 feet. (Not every part of the U.S. coast gets exactly the same amount, of course, due to local factors.)
Harvard’s Mitrovica puts the number slightly higher. Here’s a figure of his own, with a different color scheme but the same punchline:
“The peak areas are 30 to 35 percent higher” for the U.S. coast, says Mitrovica. So here, you could conceivably be pushing toward 15 feet.
The consequences would be staggering. We don’t know what the United States will look like far in the future, when such an amount of sea level rise might be realized. But for the present day, Climate Central researcher Benjamin Strauss has calculated that “12.8 million Americans live on land less than 10 feet above their local high-tide line.”
Don’t mess with geophysics
So why does the United States get extra sea level rise? It turns out to be a geophysical “triple whammy,” in Mitrovica’s words.
The first and largest part of the effect is simply gravity. But that’s not the only effect.
In addition, explains Mitrovica, taking a gigantic amount of ice off of the land of West Antarctica leads the crust of the Earth to rebound and thrust upward — pushing the ocean away from it. “That Jack in the Box will be pushing water out of the Antarctic,” says Mitrovica. Some of that pushed water also comes all the way to the northern hemisphere and adds additional sea level rise.
And then, there’s the most mind-boggling effect of all — what Bamber calls “true polar wander.” Basically, moving this massive amount of ice off of West Antarctica also shifts the planet’s axis of rotation slightly. Bamber likens it to how a spinning wheel with gum stuck to it will change its spin somewhat if you stick the gum somewhere closer to the center of the wheel, where the axis of rotation is.
For this reason, says Bamber, “the water sloshes about a little bit in the east-west direction,” and North America gets more of it than Europe does. Triple whammy indeed.
There is, however, one way for the United States to get out of this special problem — albeit not a very good one. It is to cause even more global warming, so much so that we lose not only West Antarctica, but also the even bigger ice sheet of Greenland (which is generally considered the second-most-unstable major ice sheet).
Greenland has the same gravitational effect on the ocean. But in this case, its loss would send more water back toward the Southern Hemisphere, as its own “pile” of collected ocean water sloshes away.
So in some sense, if both Greenland and West Antarctica go, gravity’s scales would be more balanced. Not that this is good news for anybody. After all, on top of West Antarctica’s 11 feet of sea level rise, Greenland would contribute 20 more feet if it fully melted. So the world overall would experience truly massive sea level rise — albeit somewhat more evenly distributed between the two hemispheres.
Barring that, though, the justice meted out by gravity looks to be uncannily accurate. The United States has historically contributed 27 percent of all emissions, and according to the estimates by Bamber and Mitrovica, it will get almost exactly as much extra sea level rise (as a percentage).
What will never be equitable, though, is this: The U.S. is a rich country. It can pay a lot more to adapt to climate change and to rising sea levels. Poorer countries might get a little less sea level rise in scenarios like the one discussed here — but they’re radically less able to cope with it.
And gravity can’t do anything about that.