This Worst-Case Scenario Sea-Level Rise Study Will Give Miami Nightmares

Picture this: In less than a century, ice in Greenland and Antarctica has melted far more rapidly than even the most dire predictions have forecast. The seas worldwide have risen by meters, swamping coastal cities like Miami. Even worse, the rapid melt has led Atlantic currents such as the Gulf Stream to collapse, creating new, unstable temperature systems that spark megahurricanes across the tropics.

That's roughly the scenario in a paper recently unveiled by James Hansen, a former NASA scientist and current climate-change Cassandra. The 52-page work, available online at Atmospheric Chemistry and Physics, makes perfect nightmare fuel for Miamians. 

But unlike most sea-level rise work, Hansen's has drawn unusual criticism from colleagues in the field, who say his root assumptions are wrong and his decision to hype the piece before full peer review crosses the line between advocacy and science. 

“It is far from certain that the results contended shall match what will happen in the real world,” Peter Thorne, a climate researcher with the National University of Ireland Maynooth, tells the Washington Post.

Hansen's work actually went online last month, but it received a renewed public airing this past weekend when the New York Times devoted a lengthy column to considering its implications for Miami.  

Hansen is already famed in climate-change circles; he's widely credited with being among the first to warn of the global crisis during congressional testimony in 1988, and he now runs a climate science program at Columbia University.

His latest paper looks at a period in Earth's distant past called the Eemian interglacial period, which occurred roughly 130,000 years ago. At that point, the Earth was about one degree Celsius warmer than today, and the oceans were between 20 and 30 feet higher.

Drawing on historic research about that era, Hansen and 19 other authors who contributed to the paper consider what such a temperature rise might mean today. And they came up with a doozy of a worst-case scenario. 

Basically, the authors suggest that as the oceans warm, hot water will get trapped beneath ice sheets on both poles. That would help melt them from below as well as above, speeding up the process but also disrupting the powerful currents that govern the ocean today.

The result: potentially, inconceivably powerful "superstorms." Hansen points to huge boulders perched atop cliffs in the Bahamas dating from the Eemian period as evidence of massive storms during that period that could deposit the rocks through massive waves and ultrahigh windspeed.

Hansen's ideas are startling, but even he admits they're based on an assumption he can't prove: that warming will increase exponentially rather than linearly.

And he has come under heavy fire for the paper, to the point that the Associated Press elected not to cover its release last month. The AP's climate-change writer, Seth Borenstein, tells UnDark that he heard too much skepticism from other researchers to take the paper seriously.

"When I get this much warning or caution, it tells me that, at least for the AP, the study doesn’t quite merit coverage,” he told the site. 

Still, Miamians will find if difficult to look away from the paper. As other scientists told the New York Times this weekend, it's probably a matter of when — not if — the Magic City returns to its underwater roots from the Eemian period.