Oh, and one other thing.
The carbon tax can start out small, and be gradually increased so businesses can plan for the higher prices in the future and the economy can adjust to it gradually.
And if sufficient nations sign on, they can collectively punish those countries that won't cooperate by imposing sanctions on trade. So if China won't tax its coal, Exxon won't sell them oil and Wal-Mart won't buy their consumer goods and electronics.