Monday’s new study greatly increases the potential for catastrophic near-term sea level rise. Here, Miami Beach, among the most vulnerable cities to sea level rise in the world. Photo by Joe Raedle/Getty Images
By Eric Holthaus July 20 2015 4:23 PM slate.com
In what may prove to be a turning point for political action on climate change, a breathtaking new study casts extreme doubt about the near-term stability of global sea levels. The study—written by James Hansen, NASA’s former lead climate scientist, and 16 co-authors, many of whom are considered among the top in their fields—concludes that glaciers in Greenland and Antarctica will melt 10 times faster than previous consensus estimates, resulting in sea level rise of at least 10 feet in as little as 50 years.
The study, which has not yet been peer reviewed, brings new importance to a feedback loop in the ocean near Antarctica that results in cooler freshwater from melting glaciers forcing warmer, saltier water underneath the ice sheets, speeding up the melting rate. Hansen, who is known for being alarmist and also right, acknowledges that his study implies change far beyond previous consensus estimates. In a conference call with reporters, he said he hoped the new findings would be “substantially more persuasive than anything previously published.” I certainly find them to be. To come to their findings, the authors used a mixture of paleoclimate records, computer models, and observations of current rates of sea level rise, but “the real world is moving somewhat faster than the model,” Hansen says….
Hansen’s study does not attempt to predict the precise timing of the feedback loop,only that it is “likely” to occur this century. The implications are mindboggling: In the study’s likely scenario, New York City—and every other coastal city on the planet—may only have a few more decades of habitability left. That dire prediction, in Hansen’s view, requires “emergency cooperation among nations.” ….
The village of Ilulissat is seen near icebergs that broke off from the Jakobshavn Glacier on July 24, 2013 in Ilulissat, Greenland. (Joe Raedle/Getty Images)
By Chris Mooney July 23 2015 Washington Post
It has been widely discussed — but not yet peer reviewed. Now, though, you can at least read it for yourself and see what you think. A lengthy, ambitious, and already contested paper by longtime NASA climate scientist James Hansen and 16 colleagues appeared online Thursday in Atmospheric Chemistry and Physics Discussion, an open-access journal published by the European Geosciences Union. The paper, entitled “Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 ◦C global warming is highly dangerous” is now open for comment — peer review in this journal happens in public.
And given how much attention the work has already received, it’s likely to generate plenty of comments from fellow scientists. The study raises the possibility of a more rapid rate of sea level rise in this century than forecast by the U.N.’s Intergovernmental Panel on Climate Change, whose research is widely regarded as the gold standard of climate research — but also often criticized for being too conservative. Moreover, the study postulates that this faster sea level rise, brought on by the melting of parts of Antarctica and Greenland, could lead to a number of climate change “feedbacks” that could shut down the oceans’ circulation; stratify the polar seas with warmer waters trapped below cold surface layers; increase the temperature difference between low and high latitudes; and generate stronger storms.
In reporting on the paper this week, The Post solicited comments from five noted climate scientists — as did other journalists — so in a sense, the peer review has already begun. One of them — Kevin Trenberth of the National Center for Atmospheric Research — strongly criticized the study, saying that “there are way too many assumptions and extrapolations for anything here to be taken seriously other than to promote further studies.” Other researchers also expressed skepticism about some parts of the work — particularly the suggested feedbacks — but acknowledged that they, too, have great concerns about sea level rise from the melting of ice sheets, especially if global warming exceeds 2 degrees Celsius above pre-industrial levels. So it remains to be seen what the scientific community, overall, will make of this work. Nevertheless, it is already notable that a group of prominent scientists — not just Hansen, but also his 16 co-authors, working in fields, such as glaciology, oceanography, and paleo-climatology (or the study of the climates of past planetary eras) — are worried that sea level rise of more than 1 meter is a threat this century. Now, the question becomes to what extent the broader scientific community does — or does not — agree. In the end, that process could very well lead many researchers to seek out a middle ground. In fact, some already have. “There is no doubt that the sea level rise, within the IPCC, is a very conservative number,” says Greg Holland, a climate and hurricane researcher at the National Center for Atmospheric Research, who has also reviewed the Hansen study. “So the truth lies somewhere between IPCC and Jim.”
To read the full Hansen et al study, click here. [The world’s most famous climate scientist just outlined an alarming scenario for our planet’s future]
A New Climate-Change Danger Zone?
By Elizabeth Kolbert July 23, 2015 the New Yorker
How much does the climate have to change for it to be “dangerous”? This question has vexed scientists ever since the first climate models were developed, back in the nineteen-seventies. It was provisionally answered in 2009, though by politicians rather than scientists. According to an agreement known as the Copenhagen Accord, which was brokered by President Barack Obama, to avoid danger, the world needs “to hold the increase in global temperature below 2 degrees Celsius” (3.6 degrees Fahrenheit).
Now a group of climate modellers is arguing that the danger point is, in fact, a lot lower than that. In a paper set to appear online this week in Atmospheric Chemistry and Physics, the modellers, led by James Hansen, the former director of NASA‘s Goddard Institute for Space Studies, warn that an increase of two degrees Celsius could still be enough to melt large portions of Antarctica, which, in turn, could result in several metres’ worth of sea-level rise in a matter of decades. What’s important about the paper from a layperson’s perspective—besides the fate of the world’s major coastal cities, many of which would be swamped if the oceans rose that high—is that it shows just how far from resolved, scientifically speaking, the question of danger levels remains. And this has important political implications, though it seems doubtful that politicians will heed them.
To understand the significance of the new paper, it helps to go back to a pair of earlier papers on Antarctic melt, which appeared last year. In those papers, two teams of scientists independently reached the same conclusion: the disintegration of a major portion of the West Antarctic Ice Sheet is probably already under way. “Early stage collapse has begun,” one of the teams wrote in the journal Science. The leader of the other team seconded that view, saying, “The collapse of this sector of West Antarctica appears unstoppable.”
The two papers were, to put it mildly, bad news. “This is what a holy shit moment for global warming looks like” is how Mother Jones put it. All told, the West Antarctic Ice Sheet contains enough water to raise global sea levels by more than ten feet. Still, both of last year’s papers concluded that the melt of a major portion of the ice sheet, while perhaps already irreversible, would likely take centuries to play out.
What the new paper does is look back at a previous relatively warm period, known as the Eemian, or, even less melodically, as Marine Isotope Stage 5e, which took place before the last ice age, about a hundred and twenty thousand years ago. During the Eemian, average global temperatures seem to have been only about one degree Celsius above today’s, but sea levels were several metres higher. The explanation for this, the new paper suggests, is that melt from Antarctica is a non-linear process. Its rate accelerates as fresh water spills off the ice sheet, producing a sort of “lid” that keeps heat locked in the ocean and helps to melt more ice from below. From this, the authors conclude that “rapid sea level rise may begin sooner than is generally assumed,” and also that a temperature increase of two degrees Celsius would put the world well beyond “danger.”
“We conclude that the 2°C global warming ‘guardrail,’ affirmed in the Copenhagen Accord, does not provide safety, as such warming would likely yield sea level rise of several metres along with numerous other severely disruptive consequences for human society and ecosystems ,” Hansen and his colleagues wrote.
The new paper has received a lot of attention because, as Eric Holthaus put it for Slate, Hansen is “known for being alarmist and also right.” (I wrote a Profile of Hansen for the magazine, in 2009.) The paper has not been peer-reviewed—it is being published in a “discussion” journal—and several other scientists have called its methods iffy. Kevin Trenberth, a prominent researcher at the National Center for Atmospheric Research, in Boulder, Colorado, for example, told the Washington Post that the paper was “rife with speculation and ‘what if’ scenarios,’ ” and that many of the scenarios “did not seem at all realistic.”
But whether or not Hansen is in this case right, his new paper highlights a crucial point, one that even those who question his methods would probably agree on. The two-degree goal offered in the Copenhagen Accord is more a reflection of what seemed politically feasible than what is scientifically advisable. A group of prominent climatologists put it this way a few months before the accord was drafted: “We feel compelled to note that even a ‘moderate’ warming of 2°C stands a strong chance of provoking drought and storm responses that could challenge civilized society, leading potentially to the conflict and suffering that go with failed states and mass migrations.”
Meanwhile, holding warming to two degrees would, at this point, require a herculean effort—one that the same world leaders who agreed to the Copenhagen Accord now seem unwilling or unable to make. A number of commentators have recently questioned whether, practically speaking, it is even still possible. “The goal is effectively unachievable,” David Victor, of the University of California, San Diego, and Charles Kennel, of the Scripps Institution, wrote recently in Nature. (The commentary was accompanied by a drawing of a feverish and exhausted-looking globe hooked up to a variety of life-support systems.) Thus, whether the “danger” zone lies below two degrees Celsius or above, the world seems bent on reaching it—with all the suffering and challenges to “civilized society” that go with it.