The great aspiration of the Paris climate accord is to keep global warming from exceeding two degrees Celsius above preindustrial levels. But according to a new paper, even two degrees of warming would mean the disintegration of large sections of the polar ice sheets, boulder-spewing storms stronger than any since prehistory, and the drowning of most coastal cities by the end of the century.
“We’re in danger of handing young people a situation that’s out of their control,” the paper’s author, retired NASA climate scientist James Hansen, told the New York Times on Tuesday.
Using computer models, evidence from ancient episodes of climate change, and modern observations, Hansen and his team arrived at one essential conclusion: The melting of the Greenland and Antarctica ice sheets will set off a vicious cycle that dramatically accelerates the pace of climate change. The key concept here is ocean “stratification,” a process by which cold, fresh meltwater rises to the ocean surface while warmer salt water is pushed beneath. (The Washington Post notes that an “anomalously cold ‘blob’ of ocean water” has been detected off the southern coast of Greenland.) That warmer salt water would eventually reach the base of the ice sheets, melting them from below, thus spurring more stratification, which would then spur more melting, which would then spur more stratification, which would spur more warming, until our grandchildren are all swallowed by the sea.
But that’s not all! Hansen’s paper also projects that the influx of cold meltwater in the North Atlantic region, combined with warmer equatorial waters, would drive midlatitude cyclones so strong, the waves would be capable of thrusting gigantic boulders ashore.
Hansen’s paper took a controversial route to publication. Last year, the scientist published a “discussion paper” and shared some of his preliminary findings with the news media, sparking criticism from peers who felt he may have been counting his eggs before they hatched (into catastrophic cyclones).
“Near as I can tell, the issues that caused me concern originally still remain in the revised manuscript,” Pennsylvania State University climate scientist Michael Mann told the Post. “Namely, the projected amounts of meltwater seem unphysically large, and the ocean component of their model doesn’t resolve key wind-driven current systems (e.g. the Gulf Stream) which help transport heat poleward.”
But David Archer, a geoscientist at the University of Chicago, told the paper that the study is “another Hansen masterwork of scholarly synthesis, modeling virtuosity, and insight, with profound implications.”
Let’s hope Archer’s wrong.