US trend economic growth in recent decades is about 3% a year. ... Now, if the economy is going to be a bit more than three times larger, but we are only going to emit 17% of the current level of carbon emissions, then the carbon intensity of the economy - that is the ratio of carbon emitted per dollar of goods and services created, is going to have to be only 5% of the current value.That's his response to the idea that we'll be able to wring the carbon out of our economy easily by 2050. Needless to say, while I believe that a) this is probably doable and b) it's damn important that we try, I think Staniford does a service by pointing out how difficult it will in fact be.
Basically, we'd need to have efficiency grow twice as fast as it's ever done in American history, consistently, for decades, and the fastest growth in energy efficiency came during a series of recessions known as the 1970s. To say that this is going to be easily accomplished is stretching things, to say the least.
The other point I'd make is that the enormity of the task really makes a mockery of the standard policy prescriptions. If you think that the magical market fairy will make the kinds of dramatic carbon cuts that the situation requires so long as we put a carbon tax in, well, best of luck to you. It might have been sufficient 20 years ago, if then. These days anything short of some serious national efforts (including nationalizing certain industries, massive subsidies, and draconian rationing of things like cars) will probably fail.
That said, Kevin Drum's response to Staniford is a good one to keep in mind:
Well, look: three degrees of temperature increase is still better then five degrees. Six inches of sea rise is better than 12 inches. A hundred million dead is better than a billion dead. This stuff is worth doing even if it's not perfect. After all, what is?