Apparently a coal based power station is opening once every two days in China - at this rate, within 2 years, the amount of CO2 extra will equal that of the UK (pop. c. 60 million) - so 10 years for America. China has a population of about 1.5 billion - but it's the pollution as much as the population. You can't just say the population of America will increase dramatically from illegal immigrants etc. - the people don't come Mars (more like Mexico) so it doesn't matter where they leave, unless the government has some really, really effective policy.