Watch this law professor try to convince a physicist that Greenland’s melt will cause seas to fall
Last week, the Republican-controlled House Committee on Science held a hearing to discuss a contentious move it made during the summer — sending out subpoenas to state attorneys general who are conducting an investigation of ExxonMobil in relation to climate change. Eight environmental groups also received subpoenas.
The hearing involved bringing in legal experts to support the subpoenas — including Ronald Rotunda of Chapman University’s Fowler School of Law (written testimony here), who argued that by investigating Exxon, the attorneys general could be quashing free scientific inquiry among those who might be inclined to raise doubts about mainstream climate science.
But during the hearing, Rotunda picked an odd example of such a dissenter — Jerry Mitrovica, a Harvard geoscientist whose work has shown that when, in a warming world, you lose massive amounts of ice from Greenland or Antarctica, sea level actually plunges near these great ice sheets, but rises farther away from them. The reason is gravity: Ice sheets are so massive that they pull the ocean towards them, but as they lose mass, some of the ocean surges back across the globe.
We have covered this idea extensively in the past, including by interviewing Mitrovica. He has found, for instance, that if the West Antarctic ice sheet collapses, the United States would experience much worse sea level rise than many other parts of the world, simply because it is so distant from West Antarctica. “The peak areas are 30 to 35 percent higher,” Mitrovica told me last year.
But if Greenland melts, pretty much the opposite happens — the Southern hemisphere gets worse sea level rise. And if both melt together, they might partially offset one another.
Rotunda appears to have misinterpreted Mitrovica’s important insight as reflecting a contrarian perspective on climate change. Drawing on a Harvard magazine story about Mitrovica, in which the researcher stated that he likes studying the ancient Earth in part because it helps stay out of politicized modern climate debates, Rotunda put it like this at the hearing:
He’s shown, by his mathematical models, that if Greenland’s ice sheet melted entirely, sea level would fall, 20 to 50 meters off the adjacent coast of Greenland, with sea levels dropping as far as 2000 kilometers away. This would help Holland and the Netherlands, rather than hurt it. But he says he’s concerned that there would be political repercussions. So we’ve gotten into a world in which scientists say, you know, I’d better either come up with the right answer, or go to a different answer, because I’m going to be subject to a lot of subpoenas, there’s the threat of criminal investigation, indictments, none of which of course the Congress can do, and that means we’re not getting the science for the money. You give out these grants, and you’re not getting objective science.
Note that the statement above about how this would “help” the Netherlands seems to assume that only Greenland melts. But if we’re in a world in which that has happened, there are good reasons to fear West Antarctica may have done the same thing — making it far from clear that the Netherlands would be “helped” (to say nothing of the consequences for other parts of the world).
Meanwhile, Mitrovica has told the American Institute of Physics bulletin that Rotunda’s testimony “completely misrepresents” his work — and added that when it came to political pressure, he was talking about the pressures brought to bear from “climate change skeptics who respond to rigorous scientific work with dismissiveness, insults, and hostility.”
Bill Foster, an Illinois Democrat on the committee who also happens to be Congress’s only physicist and was involved in the discovery of the top quark, decided to question Rotunda about these Greenland claims later in the hearing. “I was fascinated by what seemed to be apparent support of an argument that the Greenland ice sheet would melt, and thereby lower the sea level,” said Foster, “and I was wondering if you can expound on how exactly the physics of this works.”
Rotunda began by getting some of the points about gravity right, but then veering off: “When the ice sheet melts, all the gravity that was then part of the island of New Greenland [sic] disappears into the ocean, it just goes away. And that ice has been pushing Greenland down, and now Greenland will be moving up, because the water is all over the place.”
Here, Rotunda seems to be confusing the immediate gravitational effect of losing ice from Greenland on the oceans with another slower phenomenon, sometimes called postglacial rebound, which also occurs as you lift the weight of ice off a landmass. Scientists like Mitrovica take both of these into account when predicting future sea level rise due to ice loss from the world’s ice sheets.
Foster was also pretty confused. “There will obviously be a local effect, where the land will pop up…” he began.
“He said 2,000 kilometers away, up to 2000 kilometers away,” said Rotunda.
“But overall, the effect, just from general principles, has to be to significantly raise water levels worldwide, unless there’s new physics I’m not aware of, I think that’s sort of fundamental,” Foster countered.
“Read his article, that’s what he says,” Rotunda responded. (In the actual article, it’s clear that Harvard’s Mitrovica believes that overall, melting Greenland causes global seas to rise, despite any local gravitational and rebound effects. The article also makes clear that these are two different effects.)
“It will be a big problem for the rest of the world if the Greenland ice sheet melts,” Foster concluded.
“It’s not going to be a problem for Europe,” quipped Rotunda.
“Well, I’m now I guess past my time here,” Foster said, “and at some point, I’d like to return to science in this committee.”