A national fair share is not a domestic reduction target. National fair shares are by definition shares in the common international effort to stabilize the global climate system.Some countries have fair shares that are greater than anything they could ever do domestically – and in order to meet their full fair share, they must support additional action beyond their borders. Given its great wealth and historical responsibility, the US is one such country. Any reasonable understanding of its fair share in the global climate effort must include not only domestic action, but also meaningful support for action in poorer countries.