The researchers did a comprehensive literature review for pre-1990 models; for post-1990 models, they followed the literature reviews of the Intergovernmental Panel on Climate Change (IPCC). They ended up choosing 17 models to closely analyze, dating from 1970 through 2007 — models old enough to be testable against decades of observational data.

To be clear, almost all the models chosen are no longer in use, having been superseded by more sophisticated models since. Some of the earlier ones, especially those from the 1970s and early ’80s, are fairly crude energy-in, energy-out models, with a single variable for forcing (CO2) and a crude measure of climate sensitivity (the amount temperature rises per additional ton of CO2). It wasn’t until the late ’80s that James Hansen and other scientists developed multivariable general-circulation models.

It turns out that even those crude early models were fairly accurate, which is remarkable given the sophistication of the science and the available computing power. None of the models the authors analyzed got it badly wrong.