A few months ago, the question of an alternative reality occurred to me: What if our personal contribution of green house gasses from driving a car was confined to our own share of the global atmosphere? This is not how the world works, of course. Every time we burn a fossil fuel, the CO2 produced rapidly mixes with the local atmosphere, and since the atmosphere is unconfined, quickly disperses around the globe. (I couldn’t find a source for exactly how fast, but NASA’s discussion on atmospheric CO2 doesn’t discuss local concentration effects, so I conclude that our personal CO2 production becomes global relatively quickly. The effects of human additions to atmospheric CO2 are called the carbon cycle, which is complex and well described in numerous places and outside the scope of this article.)
Why ask this question? Here in the US midwest, there is a strong sense of personal responsibility, of being accountable for your actions, a human trait that I think everyone has to some degree. My intent here is to arm you with a small set of scientific facts and some basic math to answer the question above. What you do with it is of course, entirely up to you.
The US EPA provides a good explainer on CO2 from driving. This article is my source for the basic chemistry explaining the mass (weight) of CO2 from burning a gallon of gasoline. But it excludes the green house gas (GHG) output from producing that gallon of gasoline. I used the Argonne National Labs (ANL) GREET model (free registration required to download) that uses a rigorous and fully documented method and includes multiple values for various crude oil sources. As it happens, Minnesota (where I live) gets a large share of its gasoline from the Alberta tar sands and the difference is significant. Unfortunately, a new study indicates that the GREET model understates the additional burden from the Alberta tar sands by a large amount (CleanTechnica article, Inside Climate News article, The Guardian article, Nature article).
Before I get into the model, there are a few additional points to make. First, burning fossil fuels doesn’t just produce CO2. There are a number of other pollutants, such as nitrous oxides, particulates, carbon monoxide, etc. that are also produced. Nitrous Oxide for example has a global warming potential of 273 times that of CO2, but is produced in much smaller concentrations in a gasoline engine so it can be ignored for a simple analysis. CO2 is used as the measuring stick because it is the greatest mass produced when burning carbon-based fuels. (Anything made from crude oil or coal is carbon based.) Focusing only on CO2 is actually an understatement of the total impact from driving a car.
To answer the question above, we need only a few pieces of information.
- Total CO2 from consuming a gallon of gasoline, (Well to Wheels or WTW) made up of:
- CO2 produced by mining, transporting and refining crude oil to make one gallon of gasoline (Well to Pump or WTP, depends on source of crude oil)
- CO2 produced by burning one gallon of gasoline (Pump to Wheels or PTW)
- Gallons of gasoline consumed by the average driver in the US per year (personal amount depends on fuel efficiency and miles driven)
- Atmospheric pressure (weight of atmosphere per area, ~14.7 lbs/sq. in.)
- Area of earth
- Population of earth
In addition to the CO2 from the crude oil source of gasoline, gasoline consumption is highly variable from person to person. Driving 5,000 miles per year in a hybrid getting 40 MPG to driving 25,000 miles in a pickup truck getting 20 MPG covers a range of 125 to 1250 gallons (1.8 to 18 tons of CO2 / year). The source I used is the US average from a post from 2022 on the American Petroleum Institute’s website. (This seemed appropriate because API is an organization that would prefer you don’t think about the environmental impact of your gasoline consumption at all). The nice thing about using gallons of gasoline per year is that you can plug in your own number to get your personal answer to the question.
The other inputs are fundamental science and math everyone learned by the 8th grade. The inputs are combined using the following formulas to give a value for the increase in CO2 per year in parts per million (PPM) in an individual person’s share of Earth’s atmosphere from driving a passenger vehicle:
Weight of CO2 per year / Weight of individual share of atmosphere times 1 million
- Weight of CO2 per year is calculated by total CO2 from 1 gallon of gasoline times gallons of gasoline consumed in 1 year.
- Weight of individual share of atmosphere is calculated by the Individual share of Earth’s surface times atmospheric pressure in pounds / square inch.
- The Individual share of Earth’s surface is calculated by the surface area of Earth divided by the population of Earth.
The answers for the average driver and two different crude oil sources are:
Personal CO2 PPM
|Crude Oil Source
|CO2 added per year
I made a shared Google spreadsheet that contains the model inputs and calculations. You can make a copy of and change the gallons of gasoline / year or review the formulas I used.
As you have no doubt noticed, I answered a more specific question than the one posed, specifically: If all the CO2 from driving a car could be contained in an individual’s share of the atmosphere, by how much would the concentration of CO2 increase per year of driving? Since the scenario is impossible (confine your personal CO2 to your own personal share of Earth’s surface), it really isn’t possible to give a literal answer to the original question. Here are a few points that provide some context.
There is no question at this point that our collective human contribution of atmospheric CO2 is solely responsible for transforming the climate on Earth. It is inescapable that CO2 from human activity spreads around the world and heats it.
2023 was the world’s warmest year on record, by far, and this has had overwhelmingly bad effects on human society, health, economics in addition to the rest of living organisms on Earth. These effects are not evenly felt; in fact, people producing the least amount of CO2 and other pollutants are disproportionally bearing the burden.
Even if you don’t care at all about other people, we have passed the point where a rapid transition away from fossil fuels to renewable energy has a positive net effect on the economy, saving costs and increasing economic output and investment performance for all of us.
The US has about 20% of the world’s automobiles and produces about 20% of the world’s crude oil. But our population is only about 4% of world population. We make an unfair contribution to global heating. But we can also make a disproportionate positive impact by electrifying our transport (cars) and home heat (heat pumps). These are the two big changes by a wide margin, but there are other smaller ones too. Contact me if you want to know more about either of these and other changes like solar panel systems. We’re all in this together. Let’s do it.