My Article on the Temperature Hiatus

I have an article on the temperature hiatus at the Yale Forum on Climate Change and the Media.

A few quotes:

Kevin Trenberth:

“One of the things emerging from several lines is that the IPCC has not paid enough attention to natural variability, on several time scales,” he says, especially El Niños and La Niñas, the Pacific Ocean phenomena that are not yet captured by climate models, and the longer term Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) which have cycle lengths of about 60 years.

From about 1975, when global warming resumed sharply, until the 1997-98 El Niño, the PDO was in its positive, warm phase, and heat did not penetrate as deeply into the ocean. The PDO has since changed to its negative, cooler phase.

“It was a time when natural variability and global warming were going in the same direction, so it was much easier to find global warming,” Trenberth says. “Now the PDO has gone in the other direction, so some counter-effects are masking some of the global warming manifestations right at the surface.”

Ben Santer:

The bottom line, Santer says, is “there are multiple, not mutually exclusive interpretations of modeled versus observed differences, and claiming that there is only one explanation is not scientifically accurate.”

“We study the signal. If others want to study the noise, let them.”

Ray Pierrehumbert:

“There’s really nothing in this that changes our estimates of climate sensitivity.” Calculation of that all-important number from the 20th century record is not possible, because the aerosol forcing is not well known, nor are the data for ocean warming up to the task.

“Any estimate of sensitivity requires all of the record and not just the last 20 years of it,” Pierrehumbert says. “The smaller the piece of it you take, the less certainty you have in your result.” Nonetheless, he agrees that earlier warming may have been deceiving.

“I think it’s true that some rather sloppy discussion of the rapid warming from the 20th century has given people unrealistic expectations about the future course of warming.”

The complete article is here.