James Hansen
Credit: Columbia University

James Hansen, the former NASA scientist whose congressional testimony put global warming on the world’s agenda a quarter-century ago, is now warning that humanity could confront “sea level rise of several meters” before the end of the century unless greenhouse gas emissions are slashed much faster than currently contemplated.

This roughly 10 feet of sea level rise—well beyond previous estimates—would render coastal cities such as New York, London, and Shanghai uninhabitable.  “Parts of [our coastal cities] would still be sticking above the water,” Hansen says, “but you couldn’t live there.”

This apocalyptic scenario illustrates why the goal of limiting temperature rise to 2 degrees Celsius is not the safe “guardrail” most politicians and media coverage imply it is, argue Hansen and 16 colleagues in a blockbuster study they are publishing this week in the peer-reviewed journal Atmospheric Physics and Chemistry. On the contrary, a 2 C future would be “highly dangerous.”

If Hansen is right—and he has been right, sooner, about the big issues in climate science […]