The ability of a theory to make predictions is a hallmark of science. An especially good test of a theory is whether it can make a prediction before experiments or observations reveal the correct answer. As shown below, even the relatively primitive climate models of 20 years ago made predictions about the size of global warming which are consistent with what the climate actually did over the last 20 years.

In 1990, the IPCC's First Assessment Report (FAR) included the results of climate models in which greenhouse gases (GHG) increased over time.

The increases were based on estimates of past emissions and future "business as usual" increases. The top figure shows radiative forcing (RF), which tells us how much heat the GHG traps. In the models, RF increased at a rate of about .67 W/m²/decade.

FAR showed a range of warming rates calculated by different climate models. During the 1975-2025 period, the models exhibited Global Mean Surface Temperature warming of about .15 to .34^oC/decade.

According to the latest IPCC report (AR5), from 1990 to 2010, RF actually changed at a rate of roughly .3 W/m²/decade, or 45% as fast as the 1990 Business As Usual scenario. FAR overestimated RF because it did not account for increased reflectivity associated with pollution. If 45% of the forcing generates 45% of the response, then the climate models in FAR imply a warming of about .07 to .15^oC/decade.

From 1990 to 2010, observed Global Mean Surface Temperature increased at a rate of .12^oC/decade, within the range implied by the climate models reported in 1990.