CO2 (carbon dioxide) is a greenhouse gas that is a by-product of most forms of energy production. Combustion of organic compounds (gasoline, ethanol, bio diesel, broccoli, cheese crackers) releases energy and CO2.
As I was riding tonight I got to thinking about how much CO2 my pickup truck emits, and how much CO2 I could avoid putting into the atmosphere by riding my bike instead of driving my truck. This caused a great deal of thought, and in order to calculate a number that I feel is reasonably accurate, I would need to consider many things.
Some of the things to include in that calculation should be not only the amount of CO2 my truck emits, but also the amount of CO2 emitted by the pumping of crude oil, its transportation to the refinery, the refinery process, and the transportation of the gas to the gas station. Also I need to include, as a constant, the amount of CO2 emitted by the original manufacturing of my truck and all of its components. I should also consider the CO2 emitted for the production of the consumables such as tires, wiper blades, brake pads, motor oil, etc.
I need to consider as well the amount of CO2 I produce while riding my bike, and the CO2 emitted to plant, produce the fertilizer, cultivate, harvest, process, and transport food to my table which I ate for energy to ride my bike. I would also need to consider the amount of CO2 emitted by the production of my bike and all of its consumables (tires, tubes, cork tape, brake pads, etc.).
Then by subtracting the net amount of extra CO2 I emitted by riding my bike (and its production and consumables) for a set distance from the amount of CO2 emitted by driving my truck (and its production and consumables) for the same distance , I can come up with a relatively accurate amount of CO2 I saved. And I am assuming there would be a substantial savings since I am pushing a very small amount of weight on my bike compared to the weight of my truck.
Whether I actually get around to producing the number is another consideration. In a very brief web search to identify numbers associated with some of the variables above it is apparent that the variation in the reported amounts of CO2 for producing various products, the varying gas mileage my truck gets in different conditions, the varying CO2 amounts emitted in my food production and by the food itself, etc. is quite overwhelming.
It may be simpler and more reasonable to narrow the considerations and use presumed numbers for the major items and let it go at that. Maybe producing a number that is within a range would be better, although determining the range parameters is a separate exercise in itself.
What I just wrote above is probably drivel. The main point I am learning from news I read and hear on the radio (NPR only!) is that excess CO2 is bad. I need to reduce the amount of CO2 my life style creates. The exact amount doesn't matter, I just need to make decisions that I think are wise, and continue to learn and adjust as time goes on.
Here is my wife's mixte that we bought used in Wisconsin about 18 or 19 years ago. It was in excellent condition when we bought it. We just didn't ride together as much as we thought we would (kids have a way of changing priorities - but in a good way). It's a Raleigh Record - a really nice bike. Since we moved back to Indiana 13 years ago, it hasn't gotten much use, and spent much of that time in the barn.
A rusty old crank. A little TLC, some extra fine steel wool and oil will hopefully bring back the shine.
It even has a Brooks saddle. I think the saddle is the single component that is in the best condition.
Really cool logo on the seat tube and the head tube also. The paint is in good condition - I'm just going to clean really well and leave as is. This bike looks like a classic and I'm not going to screw with those good looks. I may replace the rims - the existing ones are steel. 
