This story has been updated.
Last month, a scientific paper appeared that kicked off what is, by any stretch, the most interesting climate science debate of the year.
In the paper, former NASA climate expert James Hansen, who is widely credited with putting the climate issue itself on the map, collaborated with 16 other researchers to outline a pretty dire climate scenario. Their vast paper contemplated alarming new climate feedback loops involving the Southern Ocean, which could lead to rapid Antarctic ice sheet destabilization and dramatic sea level rise, potentially in this century.
In 2013, the consensus body of climate science, the U.N.’s Intergovernmental Panel on Climate Change, stated that sea level rise by 2100 could, at the high end, be about a meter. But here in this paper were Hansen and colleagues suggesting it could be “several meters” within 50, 100, or 200 years, depending on how fast the rate of ice loss from Greenland and Antarctica is able double.
The Hansen study, however, had not yet been peer reviewed. It appeared in a “discussion journal,” Atmospheric Chemistry and Physics Discussions, where peer review happens in the form of public, published comments. After that, reviewers and the journal decide on whether to formally publish the work (in Atmospheric Chemistry and Physics), and with what revisions.
Hansen told a press call he took this route because he wanted to contribute to the discussion before the end-of-year Paris conference of the United Nations Framework Convention on Climate Change. Hansen is a scientific luminary, but at the same time, has become an activist as well in recent years, protesting the Keystone XL pipeline and even getting arrested at protests.
And the story grew still more complicated, because the concept of peer review is in some ways less simple to apply to this research than it is to more typical scientific work.
In a sense, the work that was being released was more comparable to an academic book than a scientific article. Hansen and his fellow researchers were not publishing one new finding, based upon one new experiment or series of related experiments. Rather, they were delivering a gigantic synthesis of multiple lines of evidence to draw a connection between what appears to have happened on Earth back in the Eemian interglacial period some 120,000 years ago, when the seas rose 5 to 9 meters, and the world we could be moving into now.
And then, on top of that, they also conducted new climate modeling experiments. The result of their inquiry is 66 pages long, more than 30,000 words, and with some three hundred references.
In other words, right or wrong, this was, in many ways, blue sky territory for the climate debate.
In the past several weeks, press coverage has died down and public peer review has indeed proceed on the work — a process that some have decried, but others have celebrated. And it’s nothing if not fascinating to watch. The work has garnered 37 comments so far — including one by a formally assigned reviewer (one out of two or three), and one response to criticism by the authors.
That means that after only about a month, the work is already the most commented paper ever at Atmospheric Chemistry and Physics Discussions. The paper has also, according to statistics provided by the journal, been downloaded an impressive 24,000 times so far. The journal confirmed to the Post Monday that that is also a record — the paper is “indeed the most downloaded paper from Atmospheric Chemistry and Physics Discussions,” says Barbara Ferreira, media and communications manager for the European Geosciences Union, which publishes the journal, by email.
When you read through the comments, there are essentially two takeaways: 1) Hansen et al are definitely not backing down; and 2) while there are many critical points made by experts whose comments should be heeded, the overall discussion also gives ample reason for concern that sea level rise may be considerably underestimated by the IPCC (even if it may also be overestimated by Hansen and the other scientists publishing along with him).
So let’s go through a few comments to show you what’s going on:
A stellar review by the first assigned peer reviewer. The single most important comment to read on the paper is the first of two to three officially solicited peer reviews. This one is by geoscientist David Archer at the University of Chicago. It effusively praises the new paper, calling it “another Hansen masterwork of scholarly synthesis, modeling virtuosity, and insight, with profound implications,” “breathtakingly rich and panoramic,” and referring to Hansen as “a creative and intellectual volcano.”
Granted, Archer suggests that some parts of the paper may not belong—remarking that the work is very long and some sections are more tangential than others—but emphasizes its “important conclusions, primarily about the ice sheet melting climate feedback.” Above all, Archer makes a very important statement. He says recent discoveries about the vulnerability of West Antarctica, which are at the center of the Hansen paper, “make the IPCC prediction for year-2100 sea level rise clearly obsolete.”
A strong defense of their arguments on Eemian mega-storms by Hansen et al. Perhaps the most controversial part of the paper so far involves its suggestion that Eemian superstorms, far more powerful than anything we see today, might have thrown gigantic boulders atop islands in the Bahamas, and created other distinct geological features. The implication is that melting the planet’s ice sheets will have many profound reverberations, including changing the temperature dynamics that power the gigantic winter storms or so-called extratropical cyclones.
There have been several criticisms of this section of the paper, including by longtime New York Times climate and energy blogger and reporter Andrew Revkin, who submitted, as a formal comment, a comment he himself had solicited from another scientist about the geology involved, along with some contradicting scientific references. Hansen’s group responded by standing by their interpretation of the boulders and other features as evidence for powerful superstorms. The authors insist that of all possible explanations (including tsunamis), the most likely is indeed megawaves generated by gigantic Atlantic storms, long, long ago.
An odd digression about thermodynamics. Perhaps because the Hansen paper drew so much press attention, it has also drawn some unexpected comments. Like this one, claiming that climate change models are wrong because they “[violate] the laws of thermodynamics.” The comment led to a long comment thread, and many rebuttals. Suffice it to say that climate researchers are not going around worrying that thermodynamics violations render their entire enterprise moot. But in the brave new world of public peer review, maybe you never know what you might have to debate.
Some reasons to worry a little bit less about ice sheets. And then come the critical scientific comments. Matthew Whipple of the University of Bristol in the UK questions whether sea level did indeed rise as much in the Eemian as the paper assumes, and questions whether we know for sure that the West Antarctic ice sheet collapsed then. Mauri Pelto, a glaciologist at Nichols College in Massachusetts, questions whether ice sheets can really double their losses, and then double them again, and again — a fearsome scenario that Hansen et al put forward.
One really tough takedown. A very recent comment, by four researchers with the Canadian Centre for Climate Modelling and Analysis, Environment Canada, provides a particularly powerful critique of the Hansen paper. It focuses on one of the mechanisms that is at the center of the feedbacks described in the paper—freshwater input from ice sheets into the ocean, which, Hansen’s group says, will stratify the seas by capping warmer deeper water layers with cold, fresh layers on top of them.
“The authors provide no assessment of the likelihood of any of their scenarios, and do not cite most of the previous studies that have explored the response of the climate system to much less dramatic freshwater input,” complain the Environment Canada researchers. They further note that the Hansen climate model adds so much cold freshwater that in at least some scenarios the result is actually a global cooling trend. Therefore, the authors say, Hansen et al face a towering burden of proof to overcome:
…this paper’s projection of rapid, near-term global cooling is at odds with essentially all peer-reviewed literature on future climate projections and would suggest to most readers that the state of climate science is such that even the sign of future climate change is uncertain (let alone the magnitude). The suggestion of such fundamental uncertainty demands extraordinarily compelling evidence and a careful evaluation of plausibility and likelihood.
This criticism is actually quite similar to one levied by Kevin Trenberth of the National Center for Atmospheric Research, who remarked of the paper, “These experiments introduce a lot of very cold fresh water in various places, and then they see what happens. The question is: how relevant are these to the real world and what is happening as global warming progresses? They do not seem at all realistic to me.”
Taking all of this in, we can’t really know yet if Hansen and his fellow researchers are right—and therefore if global sea level rise could be a much bigger problem this century than forecast. We do know, though, that the researchers who produced this paper are a group of top thinkers in the field, who are unlikely to change their minds or stances; that some other top thinkers are praising them; and that still others are gravely doubting them.
What do you do in such a situation? You wait and see—at least one more official peer review is coming—and you do your best to look for the middle ground. And it does seem safe to say that in part because of this new paper, and related scientific developments, the question of just how fast the seas will rise—and by how much—has become one of the most important ones on the planet.