There has been a tremendous amount of information put out about various green and energy-related items. But a lot of the time, people have difficulty comprehending what all of this means. A car emits 6000 lbs. of CO2 a year. … A well-insulated home can save 400,000 Btus a month. … Normal use of electricity amounts to 700 kilowatt-hours of electricity a month. … What does that mean? Such an overload of numbers may seem too distant to be meaningful.

Automobile Carbon Emissions

To put these numbers in perspective, some standard units need to be defined in understandable terms, beginning with carbon emissions. A gallon of gasoline weighs about 6.3 pounds. It contains quite a bit of carbon in it, as gasoline is a hydrocarbon. When it burns, each molecule of carbon in the gasoline links up with two molecules of oxygen. Without getting too much into the chemistry of this, the 6.3-pounds gallon of gasoline produces about three times as much carbon dioxide by weight. That is, 1 carbon unit plus 2 oxygen units. Therefore, burning a gallon of gasoline produces about 19 pounds of CO2.

Now, think about a 20-pound bag of charcoal for a backyard grill. That is a good comparison to the carbon dioxide output from burning one gallon of gasoline. Imagine periodically tossing charcoal briquettes out the window of your car as you are going down the road. That is what it is like.

So, a 16-gallon tank of gasoline produces more than 300 hundred pounds of CO2. That is like loading 15 large bags of charcoal into a car trunk. In a year, a car that actually gets 25 mpg and drives 12,000 miles will use 480 gallons of gas and will produce 9,120 pounds of CO2. This is about twice as heavy as the weight of the car itself. And double that emissions weight for a vehicle that gets only 12 to 13 actual mpg.

It is often heard that trees can absorb some of this human-generated CO2. While there is no simple formula to tell us how much CO2 any given tree will absorb – it depends on many different variables – one reasonable estimate is that a moderately fast-growing hardwood tree will sequester about 135 lbs of CO2 per year. The car that gets 25 mpg would need 68 trees to cover its annual CO2 output.

Carbon Statistics

The average daily U.S. CO2 emissions per person is 122 lbs or more than 22 tons of CO2 annually. That would be the equivalent of 2,250 twenty-pound bags of charcoal a year! The average daily output per person for the world is only 24 lbs, nearly five times less than the U.S. average, while the amount that could be emitted per person without raising CO2 levels in the atmosphere would be 9 pounds.

The per capita daily usage in Ireland is just about half of that in the United States at 63 lbs. Italy is 46.5 lbs., Switzerland 33 lbs., and in Brazil only 10.9 lbs per person per day. Some of these countries have very high standards of living but do so in a much less wasteful way. It would be wise to study how they are doing this and incorporate their methods and techniques into everyday lives in this country.


Because buildings produce the vast majority of CO2, a basic understanding of what a typical US home emits in a year is needed. According to the EPA’s personal emissions calculator, the average U.S. household produces over 27,000 lbs. of CO2 annually, and that is for a two-person home. Evanston homes are typically larger than the US average. Using the charcoal bag analogy, that would be 1,350 of the 20-pound bags of charcoal. Good luck storing that in the garage.

Most people do not think twice about leaving a light bulb on. However, a 40-watt bulb burning for 24 hours requires one kilowatt of electricity, which produces about 1 lb. of CO2 (here in northern Illinois). To put that in perspective, an average person can generate maybe 100 watts during an hour on a bicycle – and be dead tired doing it. Stationary bikes can be connected to various types of lights. It is very instructive to try to illuminate a 100-watt incandescent bulb even for a relatively short period of time. When the light source is switched over to an equivalent fluorescent bulb, the effort is many times easier.


With more and more news about global warming, there are many new forms of abstract numbers that we are being exposed to. Figuring out a way to relate those numbers to understandable experiences can help one see the light.