The Truth About: Carbon Footprint Calculators
A carbon footprint is a best guess about how much greenhouse gas my actions (and those taken on my behalf) cause to be put into the atmosphere. It’s an attempt to measure the harm I do, understand it and then reduce it by making different choices. If you’re wondering whether it matters, I recommend reading The Uninhabitable Earth. (If you can’t find it through your local library, that’s an affiliate link. My commission doesn’t raise your price and supports The Cool Effect.)
All carbon footprint calculations are incomplete because the economy is complex. A gallon of gas burned in your car directly emits CO2 and other greenhouse gasses (usually measured in CO2 equivalent). The equipment that mines petroleum also gives off pollution, as does the equipment that refines and transports it, and the equipment that makes that equipment. Add this in and the total emissions from a gallon of gas rise by a third to 27.6 lbs.
What about the emissions that occur when the road between the oilfield and the refinery is repaved? Are they divided between the footprints of all humans who drive that road, or all humans who consume the products that travel on it?
In one sense, including all these detailed calculations doesn’t matter. A best guess will be useful as long as it includes as many of these contributors as is practical. We can act on it, and our actions will definitely be righter than if we didn’t act at all.
You can make an educated guess about the carbon you personally emit in several ways. Using a calculator such as this one or this one is quick and easy, and it will give you a number to start with. Alternatively, you could read How Bad Are Bananas? The Carbon Cost of Everything by Mike Berners-Lee, and pull out your calculator. I like the second method because unlike an opaque online calculator, Berners-Lee explains his numbers and reasoning in detail. I love detail! Let's start with a table, and then for people who also love detail there's quite a bit of explanation below.
And now for the detail! By the way, my math skills aren't extraordinary. I assure you they are very ordinary. If you see a mistake or have a better source, please, please tell me!
Electricity. When people think of pollution related to energy usage they often think first about electricity, and then they go turn off the hallway light. Good job!
My household uses an average of 4.7 kWh per day (check your power bill to find your usage). This is reeaally low because we designed and built our house specifically for low electricity. Different grids emit different amounts of CO2. If you’re in the U.S., go to the EPA’s Power Profiler to learn exactly how dirty your electricity is.
4.7 kWh per day X 365 days per year X 0.805 lbs per kWh = 0.69 tons per year
In comparison, my parents live just up the road and use an average of 31.4 kWh with a high of 46 kWh on a cold day, which works out to 4.61 tons per year. This is just about average in the U.S. My family’s electricity use is inverted compared to most everyone else’s: our lowest months are the coldest (see the tiny dip in the graph below). According to Berners-Lee my electricity should probably be thought of as electricity that must be generated in addition, and therefore through the most-flexible, highest-carbon methods: another lump of coal into the generator. By using the least when everyone else is using the most, we’re driving less of the high-polluting generation than we otherwise would.
Gasoline. We own an elderly truck for farm tasks and limited outings and an efficient small car for weekday commuting. Each of these vehicles consumes about 200 gallons of gas a year for regular operation, plus about 50 gallons total for vacations. The tractor uses about 6 gallons of diesel. Our camp stove (when it’s too hot for the wood stove) uses maybe 4 gallons of gasoline.
200+200+50+6+4= 460 gallons per year X 27.6 lbs per gallon = 6.35 tons per year
Living in the country and commuting to town certainly can be a very wasteful arrangement. However, the average single American driver burns 656 gallons a year (emitting over 9 tons of carbon), compared to our 460 for two drivers.
Still room for improvement, I agree. I’m excited to switch to a more efficient car when the farm truck dies, but I’m not going to do that early because only about half the emissions of a vehicle are in the gas it burns. If you’re interested in car impacts, learn more in the last half of this post. The point is, cars get a lot of attention and they deserve it, but in the end it’s only a portion of the pollution we emit.
An online calculator gives me more like 3.76 tons per year, with the same gas usage. Looks like they’re including only the pollution from burning the gas, and leaving out the impact from manufacturing that gas. As far as I can tell, no calculator includes the impact from manufacturing the car.
Wood. We heat with a wood stove. Wood is a tricky thing to calculate because the amount we use is an estimate. Different woods emit different amounts of CO2, and we use a mix. Wood also emits other greenhouse gasses and particulates. The dryness of the wood and the operation of the wood stove affect the efficiency of the burn. We have a cook stove, which are not the most efficient. How the wood is harvested and processed affects the emissions. The best guess I can find is something like 2.5 tons per cord of hard wood (a cord is a 4ft x 4ft x 8ft stack).
1.5 cords per year X 2.5 tons per cord + a small amount of energy to process – some because we also burn less-emitting soft wood = maybe 3 tons per year
If we heated with electricity rather than wood, would we put less CO2 into the atmosphere? On the one hand, the point is moot. We didn’t choose wood for environmental reasons, we chose it for resilience. But I want to know.
If we take my parents’ house mentioned above as an example, the difference between a cold month and a shoulder season month (in which there is very little energy used for either cooling or heating) is about 10 kWh per day. We have about three cold months and two and a half cool months that require some heating. So that might be 1,275 kWh per year just for heating, which works out to 0.51 tons.
If I was using my wood stove only to heat, I’d be emitting 2.49 extra tons for the luxury of using wood. However, our wood stove also cooks two meals a day and does some of our hot water in cool months and all of it in cold months. Typical hot water users spend 800 kWh on that alone in the winter, or 0.32 of a ton. Cooking counts for something, too. It’s still dirtier to use wood over electricity, but not by that much.
Employment. All those buildings at my husband’s university have lights and air handling systems running right now. They have IT infrastructure, maintenance needs and trash haulage.
Berners-Lee discusses an unusually detailed audit by a university in England that is serendipitously comparable to ours in many characteristics. I took that number, 5.5 tons for every student and employee, and adjusted it to reflect the difference between typical UK emissions and typical American emissions (15 average tons/person/year vs. 24 for personal footprint). This can’t be accurate, but I bet it’s a closer guess than using data from American university audits which don’t seem to be very complete. At any rate, it’s a guess.
5.5 tons per year in UK X 1.6 US factor = 8.8 tons per year
Your employment footprint may be captured in the footprints of the people who buy your products, and some calculators even include services. If your workplace doesn’t do a detailed audit, perhaps you could encourage them to. It would reveal any areas of waste, which would be good for the bottom line.
Healthcare. Employer spending on healthcare is probably included in employment, so I used the portion we pay, including health insurance (8/9ths of our spending on healthcare). Berners-Lee gives an average value of 110 grams per dollar. The point here is just that the emissions of healthcare aren’t nothing, and only some of the online calculators include them.
110g per dollar spent X about 9000 dollars = something like 1.1 tons per year
Trash. Americans generate over 1200 lbs of trash per person per year, which causes air pollution in three different ways. First by organic wastes rotting anaerobically producing methane, a much more potent greenhouse gas than CO2. This stuff should really be composted, folks. Ours is eaten by the chickens. If you live in an apartment, you can utilize a worm composting bin. Second, some areas burn trash to produce electricity, which has positives and negatives.
Third, by not being recycled, plastics, aluminum and other materials that enter landfills increase the amount of new plastic and aluminum that must be mined and refined. Recycling is complicated because of the emissions and social costs of shipping trash around the world. We should strive to do it better, but the easiest way to reduce trash is to reduce the things we buy in the first place.
The four of us generate about 300 lbs of trash per year and a similar amount of recycling. This doesn’t count over ten tons of demolition material I’ve hauled to the dump and metal I’ve taken to the recycling facility in order to remediate our land. We didn’t buy that stuff, but when we bought this land we assumed responsibility for escorting it to the least-bad resting place.
300 lbs of trash X 1.54 lbs per lb = 0.23 tons per year
Food. This one is tougher to calculate for us because we grow a lot of what we eat. This makes it easier to reduce our pollution, but harder to guess how much we’re still emitting. I can use a calculator’s number for a “low-meat diet” which is 3.56 tons per year, but because the methodology isn’t accessible I’m not sure how closely that matches what we actually eat, and how we purchase that food. I’m sure it doesn’t account for homegrown sweet potatoes and local pastured meat.
Alternatively I can use Berners-Lee’s lbs/dollar for a “typical” cart of grocery purchases, which is almost certainly incorrect given that what we actually buy at the store is stuff we can’t currently produce: cheese, toilet paper, pet food, tortillas. Not typical.
$400 per month X 12 X 1.37 lbs per dollar = 3.28 tons per year
That’s only for purchased food. Most people in the developed world don’t have livestock, so the footprint of all the animals that breathe and burp on their behalf is captured in the dietary number. We keep goats, chickens and geese. Studies have been done on the carbon footprint of goats, but it’s difficult to translate that information to my little herd. If I treat the money I spend on their feed as grocery spending, I get about 0.21 of a ton.
However, only about a quarter of the CO2 equivalent a ruminant produces comes from the manufacture of their feed. For a goat, something like 57% of their impact is methane they burp. About a third of our feed goes to my milkers and the rest to the poultry, so maybe the true value is closer to 0.4 of a ton. Then again, buck goats and growing goat kids eat mainly grass, so their methane emissions aren’t well-captured in that feed-based equation. But I think I can safely say it’s not more than one ton.
Other consumer spending. Here the calculator’s number is the best guess, because there isn’t an easy way to massage Berners-Lee’s data to reflect the total miscellaneous spending in a household. He does give an interesting number for, say, shoes: 25.4 lbs for a typical new pair, of which we buy, on average, one per year.
I put into the calculator the dollar amounts we spend on clothes and shoes with three of us buying relentlessly used and all of us preferring a limited, well-curated wardrobe. On the other hand, we buy more tools and equipment than most people because of the farming (see a more detailed discussion of our consumer choices here). Also in this category is holiday, entertainment and curriculum spending.
The calculator gives me this number: 4.88 tons per year
Flights. In the last seven years I’ve taken two short flights to see family. My husband attends an annual conference that usually requires flying, but not always. I think of us as being a low-flight family, but that opinion is influenced by my experience as a child living in Alaska. To get anywhere from there you’ve got to fly, and back then we did, at least three times a year. Nevertheless, one middle-distance flight on average per year emits about 1 ton.
What’s my family’s total carbon footprint? Adding all the tons above gives 30 per year for my family of four. If I do my absolute best to give the same information to several different calculators, I get something between 13 and 24. Why, oh why the difference?
It’s partly because the closest thing the calculators can consider to my wood cook stove is a pellet stove, which puts out less pollution. However, I have yet to see a pellet stove I can bake a quiche in, and they also don’t all make hot water so it’s not comparable. If you heat with oil or gas, the calculators will be more accurate for you. The calculators also don’t appear equipped to include the carbon footprint of working or disposing of trash.
This source used a calculator on my county, and came up with the average CO2 emissions for my neighbors. The household average in my county is 48.4 tons per year, which works out to about 21 tons per person. This is opaque in a similar way to using the calculator on myself: I have no idea if they included healthcare, working, etc.
Another aspect of life in America is my family’s share of our local and national infrastructure: our portion of repaving Highway 16 and keeping the lights on in the county tax office. One study calculated this as 5 tons per year per person. Adding that to my hand-calculated number above, our household footprint works out to 50 tons, or 12.5 tons per person.
This still looks pretty good compared to our current county average (which may not even include infrastructure), but it looks terrible compared to where we need to be. In order to meet the Paris targets, household average emissions in the U.S. need to fall from about 52 to about 12 tons. No way are any of us getting there, if each of us is responsible for 5 tons of government emissions before we even get out of bed in the morning.
So what can we do? First, we can use our numbers from the calculators or our own math to improve the areas we have control over: buy less, buy used, eat kinder, reduce driving and electricity usage thereby improving our finances, our health and our overall quality of life. We can acknowledge that those numbers are incomplete and personal choices alone don’t get us to a safe atmosphere, and vote and agitate to green our government’s actions.
To buy us all time we can support projects like The Cool Effect that simultaneously protect vital habitat, make life better for some of the poorest people on Earth AND reduce humanity’s total emissions, for a ridiculously small amount of money (about $17/month, in my family’s case). We can plant trees. My family has planted over a hundred so far on our land. We have plans for many more, and we support organizations that plant trees elsewhere, too. Even if you aren’t concerned about climate change, these actions that improve our own lives and the lives of others are totally worth it for the other benefits.
Have you calculated your carbon footprint, and if so, what did you learn? What got included, and what was left out? Have you used this information to inform your choices about diet, travel, or other lifestyle conundrums? Tell us about it below.