There is an ethical issue here too: how can we expect developing countries with huge populations to make sacrifices if western countries are responsible for lion's share of emissions *already* in the atmosphere (China is now a problem, but cumulatively, it's still a very small percentage). On the other hand, you can argue about the ethics of having a population of 1.5b people and expecting the world to make the same sacrifices. A way to approach this is by assigning quotas based on land mass rathern than population, and transfer the burden to the country to control its population (or say, invade someone ;-)) .