James Hansen says paleoclimate data and models point to ~3°C sensitivity; urges moratorium on new coal plants without CO2 capture

Dr. James Hansen, director of NASA's Goddard Institute for Space Studies and a scientist at Columbia University's Earth Institute, told a campus audience that multiple lines of evidence—rom climate models and the planet's paleoclimate record—onverge on an equilibrium climate sensitivity near 3 degrees Celsius for a doubling of atmospheric carbon dioxide.

Hansen said the estimate from the 1979 Charney-led National Academy of Sciences review produced a central value of about 3°C with a large uncertainty, and that paleoclimate comparisons between the last ice age and the current interglacial give independent support for a similar sensitivity. "I think the Earth's history provides a much better way... and actually it gives us a higher accuracy," Hansen said during the talk.

Why it matters: Hansen stressed that climate sensitivity underpins long-term warming projections and near-term policy choices. He warned that, absent major changes in emissions trajectories, continued use of fossil fuels would push global temperatures into ranges not experienced by modern human societies, with consequential sea-level rise and other impacts.

Evidence…