Scientific American headline

This month’s Yale Climate Connections “This is not cool” video provides valuable context for public understanding of ECS – equilibrium climate sensitivity.

The video opens with Patrick Brown of the Carnegie Institute for Science, Stanford University, explaining that ECS is the measure of the amount of global warming expected from a doubling of the carbon dioxide levels from pre-industrial times. Penn State’s Michael Mann says that doubling could come as early as mid-century, and he says a 3-degree C increase in warming is generally considered to be in the mid-range of estimates.

Scientists taking no comfort from #climate sensitivity estimate uncertainties. Click To TweetBut Mann points to lots of uncertainty over that 3-degree figure and says some project the increase may be “as little as” two degrees C and others lean toward an increase of 4.5 to 5 degrees C.

Pointing to research he conducted with scientist Ken Caldeira of Stanford, Brown says that the models best simulating the recent past “tend to produce more warming” than those low- or mid-range estimates. He says their research “cuts off the probability of these low estimates of warming” and instead indicates higher-end estimates “appear to be more likely.”

“Uncertainty is not our friend” in this case, Mann says, as the climate system may be “even more sensitive than we thought.”

Scientist Andrew Dessler of Texas A&M University agrees with Mann’s point that “the evidence may indeed be pointing to the problem being worse than we had anticipated, not better.”

Dessler said his “best guess” currently, based on the evidence he’s seen, calls for an increase of 3 to 4 degrees C from a doubling of CO2 concentrations over pre-industrial levels.

Author and activist Bill McKibben says a critical unknown involves not solely the sensitivity of the climate per se, but of civilizations generally – political, economic, and psychological systems. He points to the recent tragedies involving Puerto Rico as a result of Hurricane Maria as illustrative.

“The idea that climate sensitivity from observations is a lot lower than the models, that the models are ‘running hot’” and showing more warming and not less … “that idea is headed for the junkyard,” Dessler concludes.