So let's imagine the US invests say a trillion dollars in combating climate change, to pick a round figure. And in a decade we discover that out efforts have removed only a tenth of a percent of the CO2 in the air that would otherwise be there.
Good investment? I'd say not. And the 0.1% figure if being quite generous. On the other hand, we could use the money to prepare for the inevitable by building dams and dikes and what not, as @badgerfan advises.