I first came across a video of this on Max Kieslers site and thought it was quite fascinating. I'm not sure how accurate it is but it's interesting to watch the amount of CO2 rocketing up in the left hand corner. Whilst watching it the USA emitted 1000 tonnes of CO2 every 5.4 seconds! It is also quite interesting to see the relationship between births and deaths. In a time period of 5 minutes while I had it running in the background there appeared to be nearly three times the amount of births than there were deaths.