A first-rate post in Real Climate by Gavin Schmidt with a great graph makes clear an important point that is, I think, little understood. Climate models are not speculative; they’re checked against observations. No one doubts the complexity of the challenge, but what is not generally understood is how remarkably accurate the biggest and best General Circulation Models have proven to be on the big questions. (Regional climate changes are not as reliably shown, at least not yet.)
Here’s an example of the accuracy of the big picture, based on an important and almost-ignored study published last year in Science by James Hansen and his associates at GISS.
Notice how well these numerous different models track the observations of rising levels of thermal energy (heat) in oceans around the world. Note the internal consistency of the models’ results, as well as the overall match between the model and the observations.