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This blog is expressly directed to readers who do not have strong training or backgrounds in science, with the intent of helping them grasp the underpinnings of this important issue. I'm going to present an ongoing series of posts that will develop various aspects of the science of global warming, its causes and possible methods for minimizing its advance and overcoming at least partially its detrimental effects.

Each post will begin with a capsule summary. It will then proceed with captioned sections to amplify and justify the statements and conclusions of the summary. I'll present images and tables where helpful to develop a point, since "a picture is worth a thousand words".

Saturday, September 11, 2010

Invisible Energy

Summary: Since CO2 is odorless and colorless, we cannot grasp how much of this greenhouse gas we generate in our daily activities. Here, I present some graphics and descriptions that easily permit such an understanding. An inevitable conclusion is that we must all strive to minimize our activities that contribute to the accumulation of CO2 and other greenhouse gases.

Why does a large fraction of the American public deny the truth of global warming? Well, for one thing, what is out of sight is out of mind. We heat our homes with gas or oil that we do not see. Once in a while, if we look inside the furnace, we’ll marvel at the beauty of the cool blue flame. But we have no sense of how much gas is actually flowing, or how much oil we’re actually consuming. So we, the warmed citizens of this country, can’t appreciate how much of that fossil fuel is actually being burned to CO2 gas and released into the atmosphere.

Likewise, we consume electricity in our homes for lighting, powering appliances, for air conditioning in the summer, and in some cases for space heating instead of gas or oil heating mentioned above. Here too, even more so, we as consumers are fully and effectively shielded from the vast amount of carbon based fuels burned to produce the electricity we use. Almost all electric power in the US is produced from coal and natural gas. Who among us has any sense of the vast tonnage of coal, or the millions of cu. ft. of gas, that are burned (with relatively poor efficiency) to generate that power? Electricity is delivered to us through wires hidden from view inside the walls of our houses, and of course we can’t count the electrons coursing through those wires to our homes as we go about our daily routines.

Third, gasoline- or diesel-fueled transportation effectively conceals any sense of consumption of liquid. We pump an invisible liquid through an opaque hose into an unseen gas tank, that mystical internal storage compartment in our cars, trucks and buses. But we really can’t grasp how much we’re pumping in, or how much it weighs. Gas stations aren’t equipped with auto scales so that we could actually measure the weight of gasoline added by filling up. Further, we have no sense of how much CO2 is actually produced when that weighty liquid is burned to CO2 and released into the atmosphere. So there’s no sense of the CO2 burden we’re imposing on the atmosphere with every fill-up at the gas station. And of course, that CO2 vapor is colorless and odorless, so we don’t sense the final product of our transportation consumption either.

Here’s a simple illustration intended to help us grasp how much CO2 we actually release when driving a car. Suppose your car is representative, and takes about 15 gallons of gasoline to fill up the tank. When you do so, you’ve added about 84 pounds of gasoline liquid (see the first figure, below).
Weighing a tankful gas in your car on a fulcrum balance.

When burned in your engine (and after the exhaust passes through the catalytic converter of the car) you’ve produced about 260 pounds of CO2. (You’ve also produced some water vapor, but that’s not significant for our discussion about the greenhouse gas effect.) CO2 can be liquefied by applying extra pressure and cooling it; as a liquid these 260 pounds would measure about 69 gal. If that were kept in an on-board pressurized tank, it would have to be much larger than the gas tank that you filled at the pump.

But in reality, without compression and cooling CO2 is a gas. These 69 gal. of liquid CO2 would actually occupy about 16,400 gal. of gaseous volume, if that volume contained the pure CO2 and no other components of air (see the second figure, further below). But in today’s atmosphere, the distributed concentration of CO2 in the air is about 360 parts per million (ppm), meaning that in 1 million gallons, for example, of air volume, 360 gallons would be CO2 (thus, 360 ppm) and the remainder would be the other components of our atmosphere, such as nitrogen, oxygen and water vapor. So if we now equilibrate the 16,400 gallons of CO2 vapor from burning our tankful of gas into the atmosphere, and considering a cubic volume, this CO2 would be distributed into a cube about 180 feet on a side. For comparison, most mature trees are about 60-80 feet tall (see the second figure); and a building this tall would have 12-18 stories.

Virtual cube 180 feet on a side showing the volume that would be occupied by liquid CO2,
by the same amount of pure CO2 gas, and by distributed skunk-odor-linked CO2
produced by burning one tankful of gasoline.  A mature tree is shown for comparison.
Now, suppose we could attach the smelly molecule that skunks emit to every CO2 molecule. The result of burning 15 gallons of gasoline from one fill-up at the gas station would produce a cube of skunk-smelling gas that is 180 feet on side. In fact the smelly odor of skunks is a very strong odorant; usually we can detect a few ppm in the air. So if you entered this virtual cube, with skunk odor at the 360 ppm concentration that characterizes atmospheric CO2, you would be overwhelmed, and might even start feeling sick!

If you fill up your tank once a week for 1 year, you could envision lining up these cubes end-to-end. In that 1 year period, you’d be making a rectangular volume that is 180 feet wide, 180 feet tall, and almost 9,500 feet long. Thus, with our imaginary skunk-smelling CO2, you’d create a strongly skunk-smelling rectangular volume that is almost 2 miles long at the end of 1 year of driving.

This detailed illustration covers only our transportation usage of fossil fuels. But our other energy needs mentioned at the beginning of this article obviously also contribute to producing atmospheric CO2, so comparable volumes of gas, and in our illustration, skunk-smelling gas, would be produced by each one of those sources over the course of a year. The numbers will differ, but the general effect for each contributing source will be the same. Enormous volumes of equilibrated carbon dioxide are produced by each one of us as we go about our daily activities.

Global production of atmospheric CO2.  This illustration needs to be multiplied by the number of people in the U.S., or rather, since global warming is indeed a world-wide phenomenon, multiplied by the total contributions from all the people in the world. In general, our fossil fuel consumption is increasing with time, both because the population in general is increasing, and because in developing countries the per capita consumption of fossil fuels is increasing dramatically. So it’s useful to imagine our skunk-smelling CO2 gas covering this virtual earth, and growing stronger in odor every year. Indeed, we, the global population of humans, are currently adding 2 ppm of CO2 to the atmosphere every year.

The world’s CO2 burden is like a bathtub with a drain and a faucet. If we add water to this bathtub with a strong stream but open the drain only a little, it’s evident that the level of water in the tub will keep on rising. It’s the same with the CO2 in the atmosphere. There’s not much place for the added CO2 to go to in order to exit the atmosphere (except the oceans), and by our activities we keep adding CO2 to it, more than the oceans can absorb.

Conclusion. From this illustration, it’s clear that each one of us is contributing to the worsening of global warming with each energy-dependent activity that we undertake. We all have to go about our daily routines thinking of ways to reduce the burning of fossil fuels in the maintenance of our life styles. There really is no other answer to the problem that increasing atmospheric CO2 exacerbates global warming.


  1. Wow, this is really a useful way of looking at things. Thanks for taking the time to illustrate this invisible problem. However, I'm not clear on how burning 84 pounds of gasoline produced 269 pounds of CO2. Could you clarify for those of us science-challenged people?

  2. Thanks for your perceptive question! At the risk of growing too long, I did not justify this in the post. But here goes:

    Gasoline is a compound composed mainly of carbon and hydrogen. Each carbon atoms weighs 12 "units". When gasoline burns, it adds two atoms of oxygen to make carbon dioxide, CO2. Each of those oxygens weighs 16 "units". So the carbon of the gasoline (12 "units" ends up being CO2 (total of 44 "units").

    In the post, the weight ratio of 84:269 includes the hydrogen on the gasoline side of the ratio because that's what in your gas tank, but ignores the weight of the water, H20, produced by burning the hydrogen, on the CO2 side of the ratio, since that's released to the air. So 12:44 is almost the same as 84:269.

    Hope this helps!