MIT's Integrated Global System Model makes probabilistic projections of climate change. The computer simulation has been continuously improved since its inception in 2003, and improvements made in the estimate of input parameters. Hence, the model makes warmer projections for Earth's surface warming over the 2003 estimates: median surface warming at the end of this century is computed to 5.1C (middle red line above) compared to 2.4C in 2003 (blue lines). Is Waxman-Markey enough? Not by a long shot.
[chart courtesy Kevin Drum, Mother Jones]