The U.N.'s Intergovernmental Panel on Climate Change published its latest mammoth report last week, and the effort marks an improvement over the IPCC's last such effort in 2007. That may not be saying much, but on climate change intellectual progress of any sort is worth commending.

The IPCC's "Fifth Assessment Report," or AR5, is generating the usual alarmist headlines: "Impacts on All Continents, Worse to Come" was typical. That's partly a function of what the IPCC frontloads into the 28-page "summary...