A Climate of Catastrophe

The facts in the new U.N. report aren’t as dire as its advertising.

WSJ editorial. Excerpts:

"the report doesn’t tell us much that’s new since its last report in 2013, and some of that is less dire."

"The report says the Earth has warmed by 1.1 degree Celsius since the last half of the 19th century, which is 0.1 degree warmer than its last estimate. This is not apocalyptic. The five-alarm headlines arise from the predictions of future temperature increases if greenhouse gas emissions, especially CO2, continue to increase. 

Yet the report’s estimate of “climate sensitivity”—its response to a doubling of CO2—has moderated at the top end. The likely sensitivity range, says the report, is 2.5 to 4 degrees Celsius higher than in the late 1800s. The likely range was 1.5 to 4.5 in the 2013 report.

The new report offers five climate scenarios based on estimates of CO2 emissions. The intermediate scenario’s “best estimate” is a 1.5 degree increase by 2040 and a range of 2.1 to 3.5 by 2100. This is a highly speculative estimate on which to bet the U.S. economy.

The biggest difference is the new report’s direct linkage of warming to catastrophic weather events such as hurricanes, severe heat waves or rain events, drought and so on. The summary says this is based on “new methodology” and evidence, which means computer models. We await what independent climate experts say as they dig into these models.

But we know climate models are far from perfect, which explains the varying “confidence” levels attached to the report’s predictions. Steven Koonin, the scientist and former Obama official, devotes an illuminating chapter to “many muddled models” in his recent book about climate science, “Unsettled.”

The report also downplays some of the disaster scenarios you read about. It has “low confidence” that the Antarctic sea ice will melt. It says it is likely that tropical cyclones have increased around the world, but there is “low confidence in long-term (multi-decadal to centennial) trends in the frequency of all-category tropical cyclones.” Keep that in mind when the next hurricane becomes proof in the press of climate catastrophe."