It's not the Warming of the planet that worries me, because that's just a symptom of how we've been changing the composition of our atmosphere. On a drive to a meeting a while back, I did a little armchair math to guess how much tonnage of CO2 we contribute to the warming effect.
The USA burns a daily habit of 360 million gallons of gasoline every day on average. That's about 6.3 pounds per gallon, so that's about 2.268 billion pounds burned per day.
The hydrocarbons in gas are roughly at 1:1 ratio of H:C (of three types in the mix, some chains are 2 carbons extra, others are two carbon short, but most are equal.) That means the ratios of atomic mass are roughly 1 part Hydrogen by weight to every 12 parts Carbon.
Being generous, we might guesstimate that for every 13 parts Hydrocarbon there are two parts other additives. (e.g. Regulations in California require 2% Oxygen by weight in order to reduce carbon monoxide.) So each 12 out of 15 parts is carbon burning with external oxygen, which will add weight to the CO2 from out of the air intake. Even counting just 11 of those 15 parts by weight as burning into CO2 (and probably failing tailpipe emissions tests), that's still 4.62 pounds of carbon burning into CO2 per each gallon.
If carbon's atomic weight is 12, and is combined with 2 oxygen at a weight of 16 each, that means CO2 has an atomic weight of roughly 44, expelling roughly 17 pounds of CO2 per gallon, on a bad day. (Later reading reveals the government isn't as generous and claims 20 pounds CO2 per gallon gasoline burned. http://www.fueleconomy.gov/feg/co2.shtml )
*So* our gas burning contribution to greenhouse gases amounts to more than 6 billion pounds CO2 per day, or 3 Million TONS of CO2 daily, just from our gasoline habit alone, just in the USA.
That doesn't include other countries, nor the USA contribution by the coal and natural gas which fuel our heat and electrical plants. It's not even the deisel and related fuels used by our airliner fleets and trucking fleets. 3 million tons CO2, just from gasoline, just from the USA, every freakin' day.