In this paper we update our earlier estimates of the cost of the Kyoto Protocol using the G-Cubed model, taking into account the new sink allowances from recent negotiations as well as allowing for multiple gases and new land clearing estimates. Rather than comparing this to the original Kyoto Protocol as other studies have done, we compare the estimates from the current Kyoto Protocol to a realistic alternative to the Kyoto Protocol outlined by McKibbin and Wilcoxen ( 1197a, 1997b, 2002). A key part of the comparison between the two alternatives is not to predict exactly what the outcome for emissions reduction might be at a future date under each approach. What we want to focus on is the importance of the inherent uncertainty about the future that should be at the heart of the design of a suatainable climate policy. To show how important uncertainty is to the design of the climate policies, we take two alternative plausible assumptions about a single aspect of the future predictions and compare the two regimes under these alternative assumptions. Since climate change is all about policy making under uncertainty it is important in comparing regimes to explore how the regimes handle aspects of uncertainty as well as the average performance of the regimes. This comparison illustrates a fundamental difference between the Kyoto Protocol and the Blueprint.