All that says (in your second paragraph) is that if you're going to predict the actual temperature, you need an accurate CO2 prediction, which of course is true

All that says (in your second paragraph) is that if you're going to predict the actual temperature, you need an accurate CO2 prediction, which of course is true. But here is Hansen's original 1988 paper: https://pubs.giss.nasa.gov/abs/ha02700w.html https://pubs.giss.nasa.gov/abs/ha02700w.html From the abstract: "We make a 100-year control run and perform experiments for three scenarios of atmospheric composition. These experiments begin in 1958 and include measured or estimated changes in atmospheric CO2, CH4, H2O, chlorofluorocarbons (CFCs) and stratospheric aerosols for the period from 1958 to the present. Scenario A assumes continued exponential trace gas growth, scenario B assumes a reduced linear linear growth of trace gases, and scenario C assumes a rapid curtailment of trace gas emissions such that the net climate forcing ceases to increase after the year 2000." Note the word "assumes." There's no attempt to really model what humanity would choose to emit. None of these assumptions exactly match what happened with CO2 and other greenhouse gases, so of course none of them exactly match the temperature either. But adjusted for actual greenhouse emissions, they come remarkably close. Were they completely accurate in that way? Certainly not. People knew a lot less back then. It took a while to nail down things like the effect of water vapor, which is a greenhouse gas but also makes clouds that reflect sunlight away. But they were close enough to make good policy decisions, and if we'd paid attention, we'd be much better off today. Incidentally, the case for global warming doesn't depend on models. There have been warming events before, and there's enough evidence in geological history to tell us what's going to happen. Hansen's book has details.