|Carbon dioxide-induced warming under two scenarios simulated by an ensemble of simple climate models. (Left) CO2 levels are stabilized in 2100 at 450 ppm; (right) the stabilization target is recomputed in 2050. Shading denotes the likelihood of a particular simulation based on goodness-of-fit to observations of recent surface and subsurface-ocean temperature trends (7, 8). Simulations are plotted in order of increasing likelihood, so worse-fitting models are obscured. The bar labeled "EQM" shows the models' likelihood against their long-term equilibrium warming at 450 ppm. How these likelihoods are translated into forecast probabilities is controversial, and the more asymmetric the likelihood function, the greater the scope for controversy.