Digging Under CO2 Numbers
By Enrico Uva | July 9th 2012 02:00 AM | 17 comments | Print | E-mail | Track Comments

I majored in chemistry, worked briefly in the food industry and at Fisheries and Oceans. I then obtained a degree in education. Since then I have...

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Numerical results are not gospel. After crunching them again, even if they turn out to be valid, time is not lost. Investigating will often teach one something. So to learn a little more, I wondered how the EPA arrived at the figure of   8.92*10-3 metric tons CO2/gallon of gasoline.

First, since I'm a middle-aged Canadian half-raised on imperial gallons and half on liters, I'll begin with a more trivial matter---a conversion:

8.92X10-3 metric tons  CO2/gallon of gasoline * (1000 kg/metric ton)(U.S. gallon/ 3.7854 L) =
2.36 kg CO/ L of gasoline burnt.

Gasoline is a liquid mixture consisting mostly of heptane (C7H16), isooctane (C8H18), cyclopentane (C5H10) and ethyl benzene (C8H10). A heptane molecule has 7 carbons with 12.0 units of mass apiece and 16 hydrogens at 1.01 units apiece. The fraction of carbon in heptane is 7*12/(7*12+16*1.01) = 0.839. Similarly, for the other compounds mentioned, the fractions are 0.840, 0.856 and 0.904, respectively. The proportion of each of the substances in gasoline varies from about 20 to 30%, but a weighted average translates into an approximation of 86% carbon (C) content.

If each carbon atom was oxidized into carbon dioxide( CO2 ), then every gram of carbon would yield 44.0/12.0 grams of carbon dioxide, the ratio being equal to the molar mass of CO2 divided by that of C.

In reality, although some of the carbon in gasoline becomes carbon monoxide(CO), most of it is eventually further oxidized to carbon dioxide. But a bit of the carbon gets trapped in a soup of particulate matter. According to this source, only 0.015 or 1.5 % of the carbon in gasoline remains unoxidized.

Since the composition of gasoline varies, so will its density, but we'll use the vehicle-value from the engineering toolbox of 0.737 kg/L.

Now let's combine all of the above and compare it to the EPA's figure:

1.00 L of gasoline *0.737 kg gasoline/L *0.86 C/gasoline * 44.0 CO2/12.0 C *(1-0.015) = 2.3 kg CO2, quite close to the EPA value of 2.36 kg/L.  However, I'm wondering how the second decimal place and third significant figure is justified, given that the carbon percentage is known with less precision.

The unfiltered carbon dioxide emitted by gasoline combustion mixes with whatever is produced by other fossil fuel combustion, cement production, along with respiration, fermentation, volcano emissions and and organic decomposition. Much of this input is removed from the atmosphere by rain, ocean water, and photosynthesis.

The geological record indicates that the steady state gets has been disrupted continuously. At times the input rate of carbon dioxide into the atmosphere is greater, which contributes to an overall warming trend because the gas acts as an invisible blanket. (Water vapor is a stronger greenhouse gas, but whatever is added by man or the rest of nature is trivial because of the much larger original quantities involved.) When carbon dioxide levels decrease, cooling occurs.

The combustion of fossil fuels is the main reason that carbon dioxide in the atmosphere have increased from year to year. What's not mentioned too often is the role that the increase in population has played in boosting carbon dioxide emissions. From 1962 to 2011, the world population has increased by a factor of 2.23. If you consider the additional amount of cellular respiration per person and the extra animal domestication associated with a bigger population, those two alone account for 11% of the total amount of human emissions in 2011. In the same time span, consumption of fossil fuels has gone up faster (by a factor of about 3) than the population growth, up by a factor of 2.2 in half a century. (In the United States fossil fuel combustion has increased by a factor of 3.1, while population has gone up only by a factor of 1.7) But if the extra population born in the last half century was only burning as much fuel as we did in 1962, the increase in population would still account for 34% of all 2011 emissions. As it stands, in conjunction with the increased combustion rates, the 50 year-jump in population now accounts for 55% of all current anthropogenic contributions of CO2.

Notice in the table below, based on Mauna Loa measurements, that the average annual rate of CO2 increase has gone up from one decade to the next, as pointed out by CO2now.org. But I've added a new column to reveal that that the acceleration over the previous decade has been erratic.

The warming trend in the atmosphere has also been difficult to pin down---almost negligent in some areas, but pronounced in the Arctic in the last few decades. At some point, with a continuous increase in greenhouse gas emissions, there probably will be a significant increase in global temperatures, but there is no way to know when that will occur.  The problem is that, on one hand, from studying isotope ratios in ice cores, we have non-detailed patterns over long periods of time, versus what we have in the present: meticulous data over a very short time span.

 Decade Total Increase Annual Rate of increase Acceleration over previous  decade 2002 – 2011 20.72 ppm 2.07 ppm per year 0.47 ppm/year2 1992 –  2001 16.00 ppm 1.60 ppm per year 0.09 ppm/year2 1982 –  1991 15.10 ppm 1.51 ppm per year 0.11 ppm/year2 1972 –  1981 13.95 ppm 1.40 ppm per year 0.51 ppm/year2 1962 –  1971 8.88 ppm 0.89 ppm per year Mauna Loa only started recording in 1958

SOURCES:

http://co2now.org/Current-CO2/CO2-Trend/

http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0889.1984.tb00245.x/pdf (free article)

i dont know that you can count animal respiration in the numbers for example if you feed plants to livestock then the plants would just have decayed into co2 anyway if nithing had eaten them. im not sure that more animals can increase the steady state co2 in the atmosphere
Thor Russell
if you feed plants to livestock then the plants would just have decayed into co2 anyway if nothing had eaten them
Whatever plant material is not foraged does not all decompose within a year.

more animals can increase the steady state CO2 in the atmosphere.
You mean "increase the input rate". Steady state occurs when the input rate equals the output rate in an open system.

OK plant material not foraged does not decompose within a year, but how long does it take? If it just takes 3 years instead of 1, then grazing animals would just put 2 years worth in the atmosphere, and that wouldn't increase with time.
Consider two different situations, one with plants and little to no grazing animals compared to the other with grazing animals and let them be for thousands of years. They will both approach steady state unless you are assuming that the situation with no grazing animals becomes a permanent carbon sink storing carbon underground. Of course that can be the case because thats how we got fossil fuels, but that is not the normal situation.

So going back to those two situations, in this article you are doing the equivalent of counting the carbon emitted by the grazing animals as somehow different to that resulting from the decay of vegetation. That was my point about asking you to calculate the steady state of the two situations. With a fixed but large population of humans and grazing animals (without using fossil fuels and with land usage constant) you will not get continually increasing CO2 levels, you cannot. You will get the CO2 cycling faster if you are right about the decay times, but the final steady state level may little higher. I expect land use change such as cutting down a rain forest will have a much larger effect, and of course fossil fuels the greatest.
Thor Russell
I expect land use change such as cutting down a rain forest will have a much larger effect, and of course fossil fuels the greatest.
There's no doubt, but don't completely count out grasslands, which could act as a sink for carbon dioxide. See http://www.sciencedaily.com/releases/2001/01/010111073831.htm

Not sure why you spend so much time testing the EPA's CO2 calculation. We already have evidence that atmospheric temperature increases precede CO2 increases. We already know that there is no solid correlation between changes in CO2 levels and temperature. And finally we know from CERN's CLOUD experiment and Svenmark's earlier Danish experiments that cosmic rays emanating from the Sun drive our weather patterns. We skeptics just have to keep trying to tell pseudoscience warmists and wreckers of the world economy that "It's the Sun, Stupid!

... that there is no solid correlation between changes in CO2 levels and temperature.
There is a correlation but not on the very small time scale that some imagine.
We skeptics just have to keep trying to tell pseudoscience warmists and wreckers of the world economy that "It's the Sun, Stupid!
The world economy has been damaged more by mathematical models that pretended to predict the stock market than by inaccurate and oversimplistic computer models of the atmosphere.
Good idea this - people may like to follow such calculations for the first time if it is about their beloved cars and the gas they guzzle.
EPA value of 2.36 kg/L.  However, I'm wondering how the second decimal place and third significant figure is justified
Perhaps they converted units - its a well used method. See, divide 6.5 by 4 and get 1.625, an immediate improvement in accuracy by two digits!
Just testing the time recorded for my comments. It never coincides with real time, even after choosing appropriate time zone in preferences.
Wouldn't the increase in humans and domestic animals be offset by the decrease in wild populations?
But what about the accompanying increase in rats(~500 for every mile of sewer), suburban raccoons, deer and starlings, all of which are considered wild?
If you haven't figured out your C footprint: http://www.carbonfootprint.com/calculator.aspx Thanks to hydroelectric power and to the fact that I walk/cycle/ski to work, mine is only 33% as big as that of the average Canadian.
Sorry Enrico but this is all a joke, but 10 out of 10 for effort. Do you really think that individuals reducing their carbon footprints will make the slightest difference to anything other than how well they sleep at night, absolved of personal guilt while the massive global problem still remains?

Only high impact, whole population government initiatives and disincentives combined with international cooperation between countries and nations and disincentives for those that won't comply, is ever going to significantly reduce the 7 billion carbon footprints on this planet to a safe level. Its ironic that the Chinese used to value tiny feet so much that they bandaged and crippled their women to make them attractive to men and now China's average carbon footprint is turning them into a Bigfoot nation like the rest of us.

My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
Wow a hippie that doesn't think individual action is going to save the day?Fossil fuels need to be pretty much replaced the world over then everyone's footprint is little to zero.
Thor Russell
Maybe I have to face the awful reality that I'm not a hippy any more? I've spent too long at Science20, I even find myself arguing with hippies here at Byron Bay because they only seem to care about themselves and their own little hippy communities! Don't get me wrong, I think individual effort is important for that individual's conscience but it doesn't achieve much globally if a small minority of the world's population, including well educated hippies, live small carbon footprint existences. We need these people not to feel complacent and happy with themselves because they are the ones who should not be at all complacent and instead be fighting peacefully but politically effectively for more stringent global carbon footprint reductions nationally as well as globally. I'm still anti real military wars though :)
My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
It's a good point. I just wrote an article for Wired on water issues and one of the biggest jokes is those campaigns saying to use low-flow toilets and not to run water while brushing teeth, etc.  Unless you have a private well it is meaningless because the worldwide consumption of water by people directly is negligible.  But it makes people feel better to think they are doing something while ignoring the really big issues as being the problem of someone else.
Do you really think that individuals reducing their carbon footprints will make the slightest difference to anything other than how well they sleep at night, absolved of personal guilt while the massive global problem still remains?

You're right Helen--it is a lot about sleeping better at night and less about solving the problem. That's why I pointed out that much of my lower footprint is the result of luck: happening to get a job close to work and living in a province rich in hydroelectricity. Most people are not as fortunate.

Also keep in mind that I do not put much faith on individual consumer actions as revealed in my article, Global Warming Quiz: Science, Economics And Non-Hippie Solutions
Sorry if I came across a bit strong Enrico, its just that this is one of my pet hates, the way many people around here seem so environmentally pleased with themselves, as for example they pull out their green, virtually indestructible, long term, environmental hazard bags at the supermarket checkout. My husband nearly divorced me because I refuse to use these indestructible, green bags that he still uses. Instead I prefer to make a scene at every supermarket checkout that doesn't supply biodegradable plastic bags that turn into compost within 6 months. I see this as a much more generally effective strategy, as we all have to use plastic bags for our garbage and recycled, biodegradable supermarket plastic bags make ideal kitchen garbage bags. If every supermarket supplied biodegradable plastic bags then that would be a huge improvement upon the current situation where a minority of self-satisfied people use these indestructible 'green' bags while the majority of people can and are still using the non biodegradable, indestructible, plastic bags that are still being supplied in many supermarkets. I think its the same with the carbon footprint, a few self-righteous small carbon footprints amongst billions of large carbon footprints have little impact, so why should these people feel so pleased with themselves? They still live on the same planet that is still being environmentally damaged with or without them.
My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine