[I first wrote a version of this piece for the GetDowntown blog for Commuter Challenge month. I've revised and added to it a bit (see preceding entry for the first version), and I've now posted the new version on EcoGeek.

I've seen lots of "environmental footprint calculators" that will tell you something about your carbon emissions - how many tons of CO2 you are responsible for with your lifestyle and choices - but I don't think I've ever seen anything that gives you a sense of what that volume is. I don't know if this information is going to be useful or not. To some people it's probably going to seem big, but to others it may seem smaller than they had thought. I still found it an interesting exercise to go through.]

May is a good month for commuting to work by alternate methods. Bike-to-Work Day is celebrated in many communities in May. In my town, we have a month long Commuter Challenge encouraging people to discover commuting alternatives. When I saw that the coworking space I am affiliated with had avoided about a half a ton of CO2 emissions, I started to wonder about what that volume looked like. The term ‘ton’ is used to mean ‘a lot,’ but how big is that when talking about a gas? A car weighs a ton or two (a current model Ford Focus has a curb weight of about a ton and a half), but it’s made from much heavier materials. CO2 is a gas, though, so it is much harder to have an image of what it means to have a ton of CO2.

A little research and some calculation shows that a ton of CO2 will fill a volume of about 17,850 cubic feet at standard atmospheric pressure. To help visualize it, this is roughly the volume of a two story house, about 2,000 square feet in size (25 feet deep x 40 feet wide x 17.86 feet tall). Locate a house that is about that size, then imagine that volume filled with pure carbon dioxide; that’s what one ton of CO2 is.

And that’s just the carbon dioxide. If we are talking about automobile emissions, then there are all kinds of nitrogen oxides, uncombusted hydrocarbons, soot, and other pollutants that are being put into the atmosphere, as well.

To get a sense of larger volumes, the Hindenburg was about 6 million cubic feet in volume. That would be about 336 tons if it was filled with CO2. The New Orleans Superdome has a building volume of about 123.6 million cubic feet, which would hold almost 7000 tons of CO2. It would take more than 140 Superdome buildings to contain a million tons of CO2.

Another way to look at it is to think about how long it takes for you to put a ton of CO2 into the atmosphere. The EPA uses the figure of 19.4 pounds of CO2 per gallon of gas. So, roughly speaking, every 100 gallons of gas you use puts a ton of CO2 into the atmosphere. A car that is driven 12000 miles and averages 24 MPG in a year puts 5 tons of CO2 into the atmosphere.