Sunday, April 29, 2012

An Impressive Fact About Carbon Dioxide

Here's an interesting statistic(*) from the conclusion of David Archer's book The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth's Climate:
"If we add up the total amount of energy trapped by CO2 from the gallon of gas over its atmospheric lifetime, we find that our gallon of gasoline ultimately traps one hundred billion (100,000,000,000) kilocalories of useless and unwanted greenhouse heat. The bad energy from burning that gallon ultimately outweighs the good energy by a factor of about 40 million."
(*) Except I think the last number should be 3.5 million, not 40 million. Archer says a gallon of gasoline "yields about 2500 kilocalories of energy," which is 2.8 MJ/L. But all the numbers I've found are about 32 MJ/L, such as here and here and here. That factor of 11.5 knocks down the final ratio to a still impressive 3.5 million.

(If I made a mistake, let me know.)


Matt C said...

The energy value of gasoline you cite is its "low heating value," or how much heat energy is produced by 1 liter of gasoline. For gasoline combusted to drive cars, the pertinent value is how much mechanical work is derived from that gallon of gasoline to move the car. This mechanical work would vary from vehicle to vehicle and in different situations, however the quoted value seems like a low average value.

george said...

"Useless and unwanted" greenhouse heat is a completely tendentious and insupportable statement. It is an opinion but a completely uninformed one as there is no data as to what temperature is best for life on earth and that temperature is likely to vary from species to species. There is no metric by which such things can be measured.

Unknown said...

George -Yes, mammoths would like it colder and dinosaurs would like it warmer- we are mainly concerned with the species, including ours, that have prospered since the last glacial period, I expect.