Joe Nocera is having an important debate with James Hansen. Â Nocera celebrates Hansen as a pioneer climate scientist and as a good economist. Â Hansen demands a carbon tax now. Â All economists agree with adopting this efficient policy. Â As I write in Climatopolis, I’m a supporter of $10 gasoline now. Â Â Where Nocera and Hansen part company is on Hansen’s doomsday rhetoric about the consequences of the President giving the green light to the Keystone Pipeline. Â Below the fold, I discuss some nuanced issues.