Nature, fossil fuels, and global warming

I’m commenting ont todays column:

Particularly this statement:

*Consider two of the carbon calculators I found on the Web. Both agree that driving a medium-size car 10,000 miles a year will generate roughly four tons of carbon dioxide annually. *

Ok, I drive over 10,000 miles per year, I’m certain. I use 15 gallons of gas per week. I don’t know the specific gravity of gas, but a gallon of gas has to weigh somewhere close to a gallon of water, so lets assume it’s the same or close just to get a quick number. That’s about 8 lbs./gallon x 15 gallons per week x 52 weeks = 6240 lbs., the weight of all the fuel I use.

I might occasionally use more, but I know I drive over 10K miles, so I gotta think that number is at least in the ballpark.

So that’s a little over 3 tons.

Something much less than 100% of the fuel comes out the other end of my car as exhaust. Less than 100% of that is CO2, and another fraction of it is CO that is unstable and quickly grabs oxygen from the air and becomes CO2, but still 100% of the exhaust is not CO2.

So how can 4 tons of CO2 be produced from burning 3 tons of fuel?

Of course, I’m not foolish enough to believe Cecil is wrong, I just don’t understand. Can someone enlighten me?

A gallon of gas is about 6 pounds; however, CO2 isn’t all from your gas - the mass of the carbon-dioxide is one carbon atom, and two from the air your engine sucks in - that’s 12 parts per 20 that are from oxygen in the weight of carbon dioxide.

So 60% of the weight of exhaust doesn’t come from the octane.

You use 15 gallons a week when you drive 10K a year? I’m going to guess that’s an SUV. I do about 10 gallons every two weeks, doing about 10K a year, getting about 30 mpg.

That should read “…one carbon atom, and two oxygen atoms…”

and the twelve parts per twenty refers to atomic weights: oxygen atoms have 6 protons each, carbon 8. I’m assuming the neutrons are in the same ratio, but I didn’t bother to check.

short answer: as you burn the fuel, it becomes heavier. With hydrocarbons, you’re exchanging approximately 2 hydrogens (extremely light atoms) with 2 oxygens (heavier atoms). So, masswise, more CO2 is emitted than fuel you burn.

long answer: assume all the fuel you burn is hexanes (which are 6 carbon hydrocarbons, molecular weight of 86.2).

This is an approximation, as gasoline is made up of all sorts of hydrocarbons, but hexanes is one of them, and this is a back of the envelope calculation.

Carbon dioxide has a molecular weight of 44.0. Perfect combustion of one hexane molecule produces six molecules of carbon dioxide. So 86.2 grams of hexanes will (theoretically) produce 264 grams of CO2 (6 x 44 g).

Hexanes has a density of 0.66, meaning it is lighter than water. 4 liters of water (approximately 1 gallon) weighs 8.8 pounds. So 4 liters of hexanes weighs 5.8 pounds (8.8 x 0.66).

Let’s recalculate your numbers with the above variables plugged in:

5.8 pounds/gallon x 15 gallons/week x 52 weeks/year = 4524 pounds/year. I’ll convert this to metric: 4524 pounds/year x 1 kg/2.2 pounds = 2056 kg

Again, assuming complete combustion:
2056 kg hexanes x 264/86.2 = 6300 kg = 13860 pounds = 6.9 tons.

I would guess that given that gas is not pure hexanes, and incomplete combustion, and that your driving might or might not be atypical, is where the 4 tons comes from.

The take home lesson is that the amount of carbon dioxide produced is heavier than the amount of fuel burned.

Whoops - Oxygen has 8 protons, carbon 6.

Gas is mostly octane, but the ratios remain exactly the same as in Chibby’s post - each carbon atom takes two oxygen atoms.

One other minor point that will inflate the number of trees John White (and, no doubt, Metalhead as well) will soon be planting. The factors of carbon sequestration per tree given by those sites are averages for full-grown, mature trees. To offset this year’s carbon dioxide production, you need to plant many more sapling trees. The number will, I believe, vary by species.

I always wondered why we still use wood for houses, too. It seems like a plastic plank with some rebar in it would be just as solid as wood, probably cheaper, and would not have any problems with rot, termites, etc. It’s all inside the walls and covered with drywall and whatever exterior on the home, so the material isn’t that important…so why is it always wood?


That was truly educational. I guess it was a knee-jerk reaction to think of combustion as breaking the fuel down, but in reality it’s more of an exchange, and a lopsided one at that. Thanks folks!

Oh, and to clarify, I don’t drive an SUV, it’s actually a 6-cyl. Hyundai, but I drive a lot more than 10K miles a year, more like 15. I was just going ahead with the bigger number to prove that, in my erroneous calculation, there was no way it would be close to 4 tons.

I have a different question:

Cecil mentions that we are releasing carbon in coal and oil that has been sequestered for millions of years.

So… Does that mean the Earth was running a carbon defecit during that period? Where did all the extra carbon originally come from?

And… If we do shift the climate back to what it was in the “days of the dinosaurs”, should I look into insurance to protect my home from giant insects and other precambrian fauna?

At least one problem with plastic is the nasty stuff most plastic releases when burning.

In wouldn’t characterize it as the Earth running a carbon deficit. The Earth’s atmosphere has probably been running a carbon deficit for at least two and a half billion years. Generally a good thing for us, since we happen to not like the type of CO[sub]2[/sub] rich atmosphere planets like Venus and Mars have.

Assuming the amount of carbon on the Earth hasn’t changed much since the Earth formed (a difficult assumption to prove, but one that simplifies our thinking a lot), all the carbon currently in the biosphere (estimated at 1.5 x 10[sup]18[/sup] g = 1.5 trillion tons) has been drawn down from the atmosphere, lithosphere, and hydrosphere (air, rocks, and oceans) of the Earth. There doesn’t seem to be much of an issue with this, though, since carbon is pretty transient in the biosphere, returning quickly on geological time scales into sedimentary rock, the atmosphere, or the oceans.

I don’t know if any insurance companies offer this option: maybe this is your big break to set up your own insurance company. I suspect you’d make a killing for the first few million years after your grand opening, but after that; watch out as new pests evolve! :wink:

Lumber is still probably cheaper and easier to come by than plastics. Plus it’s easier to build with. And then there’s cultural inertia.

And to think of the years I wasted teaching chemistry as an assistant. None of it seems to stick.

Same with physics. The average college graduate does not remember that the thicker extension brings MORE electricity to the other end, not less. Sheesh.

Most plastics release water vapor and carbon dioxide when burned. What’s polyethylene? A bunch of ethylene molecules strung together.

Dont recycle that milk jug, shred it and burn it in a power plant as fuel!

“Whoa Nelly”

“Under Bush the U.S. has disavowed the Kyoto agreement”…so says Cecil.

If I’m not mistaken, in 1997 the Senate voted 95-0 not to ratify the Kyoto agreement during the Clinton administration. You’ll never hear that on you’re Nightly News. You’ll only hear that Bush “disavowed” the Kyoto Protocol.

I don’t think that the Senate was at a 95-0 elected political majority, so I am going to have to presume that there was a lot of bi-partisanship.

Could it be that our Senators saw through a treaty in 1997 that sought to sink our economy to a point equal to other economies (EU).

If someone’s political memory lasts for a day, it’s easy to put the political woes of Kyoto on Bush.


Korndog: You won’t hear it on the news because it is not actually true.

The vote you speak of was a sense of the Senate vote and reflects what the the Senate felt our negotiating position should be on Kyoto (i.e., that it should include developing countries). It was taken prior to the Kyoto accord being reached and certainly way prior to the details being spelled out. Furthermore, the science of global warming has advanced in the intervening ~5 years.

It was only under Bush that the U.S. dropped out of the negotiations that were putting all the details onto Kyoto and said that we would not ratify it.

The accord is arguably harder on the industrialized EU countries than it is on us since it mandates essentially the same fractional cuts and they are already using energy more efficiently (e.g., less per capita and they tax gasoline more to have its price better reflect all the externalized costs).

Furthermore, at least some of the E.U. countries have standard of livings that are arguably higher than ours, at least as concerns the “median” standard of living.

As for harm to the economy, here in a recent New York Times magazine article is the view of John Browne, the CEO of British Petroleum (whose company has cut emissions somewhat more dramatically than Kyoto and 8 years ahead of schedule) on that subject:

P.S.–Political winds change with time. Many, a year or two ago, were saying that Kyoto would never be ratified by enough countries to go into force…especially when Bush decided that the U.S. would not ratify it. (I think countires representing something like 55% of the world’s greenhouse gas emissions have to ratify it for it to go into force in the ratifying countries.) Now, most of the major industrialized nations—with the exception of the U.S. and maybe Australia—have ratified it and it is considered only a matter of time for Russia to ratify it and for it to go into force.

The greenhouse gasses generated by humans are being shunted out the ozone hole surrounding the southern pole. Recent reports that this hole is shrinking are somewhat concerning though. To help reverse this disturbing phenomenon, I’ve re-started using spray-on antiperspirant. As for the ‘natural’ sources of CO2, such as forrest fires and the Ann Arbor Hash Bash, for some reason, Mother Nature directs these innocuous emmissions to the equitorial regions to rejoin the natural carbon cycle.

Stay cool.


Greenhouse gases being shunted out the ozone hole? Cite.