Actually, we can measure CO2 in the atmosphere quite easily and down to low ppm levels as well. There are enough measurement positions around the world now to have pretty good coverage. So unlike Greeny, I would very much hesitate to be dismissive of global warming theory. But there's no headway to be made, and there's lots of economic power to be lost, in signing international energy agreements that except major players like China and India and Brazil. Brazil won't pass the USA in emissions anytime soon, but China and India will likely do so this century. Any agreement has to take that into account.