Jamais at WC just put up a long and fascinating post, but I warn you number-phobes — it’s got numbers. If you just want the short, sweet point, here it is:

An aggressive focus on improvements to efficiency amounting to an average of 3-4% annually over the century could mean a world where everyone can live well without risk to the climate. To say that the effect of improving the efficiency of use is dramatic is perhaps an understatement. Without it, avoiding disastrous greenhouse effects will be nearly impossible; with it, avoiding the worst-case scenarios is almost over-determined.