Carbon Calculating: Getting an Accurate Measure of Carbon …
Changing habits is hard when you can’t see and understand the impact of your actions. In this installment of our Carbon Calculating series, learn how to estimate your driving-related carbon footprint, including how to factor in the embodied carbon emitted during the manufacturing of your internal combustion engine (ICE) vehicle, whether it’s a car or light truck that runs on gasoline or diesel. With a reliable estimate, you can begin to track your savings as you drive less, switch to an EV, and improve your mileage by driving efficiently.
Transportation, including air travel, is responsible for 27.2% of U.S. CO2 emissions each year, according to the Center for Climate and Energy Solutions (C2ES). Driving cars and light-duty trucks accounts for 15.64% of U.S. emissions, and heavy-duty trucks used for shipping produce about 7% of the nation’s annual carbon footprint. In addition to tailpipe emissions, manufacturing a vehicle carries a substantial footprint that must be factored into daily driving impacts over the life of the vehicle. This embodied carbon results from the mining, refining, and shipping of the raw materials used to make a car or truck, as well as the manufacturing process and sending the vehicle to a dealership.
The Rocky Mountain Institute estimates that the typical car comes with embodied carbon that represents 40% of the lifetime emissions related to the vehicle. Automakers do not release lifecycle analyses or summary carbon impact reports by vehicle model, so one must estimate their car or truck’s embodied carbon amount. Based on that estimate, you can easily add a per-mile value to account for embodied carbon along with the relatively easy-to-calculate carbon footprint generated by burning fuel.
The last carbon impact related to driving comes from wear and tear on the tires and brakes, which shed 0.001 and o.002 grams of material per mile, respectively, or about 1/600th of a pound for every 10,000 miles driven. Our carbon footprint estimate will not try to factor these minute contributions into a DIY formula; they do not appear to be included in any of the carbon calculator methodologies we reviewed.
Improving MPG Takes Us Part of the Way
A newer model ICE vehicle will deliver better mileage performance than an older vehicle, which helps lower its tailpipe emissions, while switching to an EV will reduce driving emissions overall. The Department of Energy reports that the average CO2 emissions for 2021 model-year cars and light vehicles are 49% lower than in 1975, falling from 681 grams of CO2 per mile to 348 grams/mile. In order to meet the U.S. national goal of reducing emissions by between 50% and 52% compared to 2005 levels, every car on the road — not just new vehicles — would need to emit only 223.55 grams per mile. Fortunately, the rise in EVs and new emissions standards set by the U.S. Environmental Protection Agency in 2021 point to improvements, maybe even good enough to meet our national 2030.
C2ES reports that CO2 emissions in grams per mile for all types of vehicles that will be sold between 2023 and 2026 are well below 223.55 grams/mile. Removing as many gas guzzlers from the roads is critical to reducing transportation emissions by 50%.
Improved gas mileage does not justify buying a new vehicle because of the embodied carbon mentioned above. Once a car or truck is on the road, using it offsets the embodied carbon it contains because it allows you to avoid buying a new vehicle. For example, if you purchased a car that has a 17-ton (37,478 lbs.) carbon footprint when it rolls off the show floor and plan to keep it for 10 years — longer than most people retain a vehicle — each year you avoid one-tenth of the new emissions required to build your next car, or about 3,747 lbs. of CO2 annually.
Web Carbon Calculators for Cars & Trucks
As we’ve found with each round of carbon calculator reviews, the results from entering the same data in different tools produces divergent results. Vehicle calculations, however, are more straightforward than the airline and home heating formulas, and with one dramatic exception, MyClimate Calculator, the calculators tested produced results within 10% of one another and our DIY estimate.
Earth911 carbon estimates are based on driving a 2021 Ford F-150, the most popular vehicle in America, for 15,000 a year at 19 mpg,and 4,000 local miles a year in a 2016 BMW i3 with Range Extender that gets an average of 155 mpg across gas and electric usage.
For our testing, we chose two vehicles, assuming that a Ford F-150 4WD truck was driven 15,000 miles (approximately the national average miles driven per year across all age groups) and a BMW i3 electric vehicle with a gasoline backup engine used for 4,000 miles of local trips and that relied on its gas engine for approximately a quarter of the mileage.
Making Meaningful Changes
Driving less, whether in an ICE vehicle or EV, will reduce your carbon impact more than any other decision. Choosing to bike for short trips or, as we suggest, using an EV for local shopping and commuting, are important changes that will lower your footprint. Planning trips to combine stops and reduce your total mileage is another convenient way to reduce your fuel consumption and environmental impact, as well as save time. And explore public transportation and car-sharing options to reduce your need for a second or third vehicle, which will reduce the embodied carbon associated with your driving.
Because the majority of American cities still generate more electricity, 60% of the national total, by burning fossil fuels, driving electric vehicles may carry a significant carbon footprint. Find out the composition of your state’s electric generation infrastructure to understand what percentage of your power comes from oil, coal, and natural gas.
Switching to an EV can result in substantial long-term improvement in your carbon footprint. Making an EV may cause more environmental damage than building an ICE vehicle because of mining critical minerals, but an EV performs substantially better over the full lifecycle of the vehicle. You can make an even bigger difference by charging your EV at night, when electric grids are running below capacity and natural gas-powered “peaker plants” that step in to generate extra power in response to high demand are offline.
The Do-It-Yourself Estimate for Fossil-Fuel Vehicles
The most accurate way to calculate the CO2 emissions generated from driving a car or truck is to consider the vehicle’s fuel consumption rate in miles per gallon combined with the carbon content of the fuel, which varies by type. Other factors, such as the frequency of maintenance or carbon and plastic pollution from tire wear, contribute to raising or lowering the estimated emissions. But only a simple measurement is needed to begin to track and manage your driving footprint.
If you don’t know your car or truck’s mileage per gallon, this information can usually be found in the owner’s manual or on the manufacturer’s website. The U.S. Department of Energy also provides an easy way to search by year and model type. Alternatively, you can track your vehicle’s fuel usage over a known distance and divide the fuel used by the distance driven to find your mileage per gallon.
Next, find the carbon content of the fuel you use. For gasoline, the average carbon content is about 19.59 lbs. of CO2 per gallon. For diesel, the average carbon content of a gallon of fuel is about 42.21 lbs. of CO2. These values may vary slightly depending on the specific fuel blend, but you can do your calculation using these averages.
Here’s how we arrived at our cumulative DIY estimate of 16,118.9 lbs. of CO2 emissions for the two example vehicles:
Gasoline-Powered Ford F-150
To find the gasoline-powered emissions in our examples, the steps are:
[Miles driven] divided by [MPG] = [Annual Gallons Used]
Next, calculate [Annual Gallons Used] times [Carbon Content 1 Gallon of Gasoline] = [Annual Emissions]
Using the actual values, this yields a total of 15,465.71 lbs. of CO2 emissions annually:
15,000 Miles Driven divided by 19 MPG = 789.47 Gallons Used
789.47 Gallons Used times 19.59 lbs. of Carbon Content = 15,465.71 lbs. of CO2 Emitted
Clearly, driving this vehicle less will lower its impact. Cutting driving by 25%, for example, leads to a reduction of 3,866 lbs. of CO2. If your vehicle uses diesel fuel, change the carbon content value to 42.21 lbs. A diesel F-150, then, would emit 33,323.5 lbs. of carbon dioxide annually, more than twice the emission of a gasoline-powered truck.
Hybrid Electric-Gas BMW i3
The hybrid calculation involves both the gasoline and electricity-generation impacts, so we must add steps to estimate the emissions created by charging the vehicle:
4,000 Miles Driven divided by 155 MPG = 25.8 Gallons Used
25.8 Gallons Used times 19.59 lbs. of Carbon Content = 505.5 lbs. of CO2 Emitted
Based on the steps below, the gasoline burned in the BMW i3 accounts for 147.7 lbs. of CO2, only 0.09% of the total for the two vehicles. If you have multiple ICE or hybrid vehicles, it may not be worthwhile to estimate your EV electricity emissions. But, here goes …
To begin estimating, find the source of electricity used by your local utility. If your utility does not provide details about how it generates electricity, you can check the U.S. Energy Information Administration website, which provides state-level information about electric energy sourcing. The mix of fuel sources used by your utility may be complex, so we suggest picking the dominant source of energy, such as coal, oil, or natural gas, and using that as the basis for estimating your EV footprint.
Find your vehicle’s miles per kWh, which is typically reported in the dashboard of the car. If you cannot find this information, refer to the U.S. Department of Energy’s guide to EV fuel economy and find the value for your vehicle’s kWh/100 miles. Then, convert the kWh/100 miles value into miles per kilowatt-hour by dividing the kWh by 100.
For example, the Department of Energy reports that the 2016 BMW i3 is reported to be 27 kWh, which translates to 2.7 miles per kWh of electricity used by the battery. We divide 1,000 miles by 2.7, which yields a value of 370.37 kWh a year — and now we have the basis for estimating the carbon emissions based on the dominant form of fossil fuel-based electric generation in your community, using this formula:
[Total Annual kWh] times [Emissons Per kWH (in MMBtu)] times [Emissions Factor for Fuel] times [2.046 (to convert to Imperial lbs.)] = [Total Emissions]
Next, we adjust the total by the percentage of fossil fuel-source electricity to get the final estimated emissions.
[Total Emissions] times [Percentage of Fossil Fuel Electric Generation] equals [Actual Annual EV Emissions]
In our example, the utility that provides the electricity to charge the BMW i3 relies on renewable energy for 88% of the power it delivers and natural gas is the dominant non-renewable source. Many utilities burn natural gas in peaker plants, which come online during periods of high demand. But some utilities rely on natural gas around the clock, accounting for 37% of all the natural gas burned in the U.S., about 11.27 trillion cubic feet in 2021, according to the EIA. If your utility sources most electricity from natural gas, here’s the calculation you need to perform:
[370.37 kWh] times [0.0034095106405145 MMBtu/kWh] times [53.06 kg CO2/MMBtu] times [2.2046 (to convert to Imperial lbs.)] = [147.71 lbs. of CO2]
[147.71 lbs. of CO2] times [.12(Fossil Fuel Electric Generation)] equals [17.72 lbs. Actual Annual EV Emissions]
If your utility sources most electricity from mixed coal, which has an emissions factor of 95.52 kg CO2/MMBtu, here’s the calculation you need to perform:
[ kWh] * (0.0034095106405145 MMBtu/kWh) * (95.52 kg CO2/MMBtu) * 2.20462 = [Annual Emissions]
Then, we adjust the total by the percentage of fossil fuel-source electricity to get the final estimated emissions.
[Total Emissions] times [Percentage of Fossil Fuel Electric Generation] equals [Actual Annual EV Emissions]
Grading the Ground Transportation Carbon Calculators
The Cool Climate Calculator provides driving and embodied carbon results for vehicle emissions.
GradesTransportation estimate: A-Total footprint estimate: B+
Cool Climate’s carbon calculator delivers one of the most comprehensive reports across all the tools tested in this and other articles in this series. In addition to fuel-related emissions, Cool Climate accounts for the annual allocation of embodied carbon in the vehicles to their footprint estimate; however, it does not separate air and ground transportation in its results, which makes it hard to understand driving impacts separately. The calculator does not offer the ability to calculate a hybrid vehicle’s footprint but it does provide estimates of the impacts of bus, light rail, commuter rail, and intercity rail rides. Although the Cool Climate calculator does not publish its methodology, the results it provided across our home energy and transportation testing were consistent and useful.
Environmental Protection Agency
The Environmental Protection Agency carbon calculator supports easy estimates for multiple vehicles.
GradesTransportation estimate: A-Total footprint estimate: D-
The Environmental Protection Agency carbon calculator is a useful tool for estimating driving impacts because it supports entering multiple vehicles easily and asks if regular maintenance is performed — a dirty, unmaintained engine is an inefficient one. If you do not do regular maintenance, the EPA tool adds 4% more emissions to your total. The EPA tool is not suited for estimating your entire carbon footprint; it addresses only home energy, transportation (excluding air travel), and waste habits.
The MyClimate calculator requires users to convert imperial mileageand fuel efficiency to metric values.
GradesTransportation estimate: C-Total footprint estimate: B+
The MyClimate driving calculator delivered the highest estimate of all the tools tested, almost 80% more than the average across all the results. A European service, it requires metric data entry, so an American must perform conversions before entering kilometers driven and the amount of gas in liters/100 km. It also limits users to entering data about only one car, so you have to do it twice to estimate the impact of two cars. However, MyClimate offers dedicated tools for estimating the climate impact of many specific scenarios, including flight, cruise, corporate, subscriptions, and household calculators, which makes it a useful site when considering your entire carbon impact.
World Land Trust
The World Land Trust calculator rushes to sell carbon credits instead of illuminatinghow to change habits and reduce emissions.
GradesTransportation estimate: A-Total footprint estimate: C-
The World Land Trust Transport carbon calculator assesses journeys by car and on public transit, so users must enter the annual mileage for each vehicle by creating multiple journeys. We entered one journey for the truck and one for the EV to generate a cumulative emissions total. The tool asks about the type of vehicle (small, medium, and large), fuel type (petrol, diesel, and hybrid), and distance traveled in km or miles. The results from this tool were closely aligned with the majority of estimates entered across all the calculators. A carbon offset vendor, the World Land Trust presents the emissions with an offer and a price to help you buy carbon credits. The experience does not cast much light on the changes one might make to reduce their emissions.
The Terrapass carbon calculator asks the most questions about vehiclesbut ignored factors that impact EV power emissions.
GradesTransportation estimate: A-Total footprint estimate: D+
The Terrapass carbon calculator asks the most detailed questions about vehicles, including the year, make, model, and engine configuration, and it supports easily adding multiple vehicles. However, it does not factor in the emissions from energy sources for electric vehicles, which felt like a missed opportunity in light of the deep information Terrapass collects about vehicles. Although the company sells carbon offsets, the estimates were closely aligned with the average of all our manual and automated estimates. The Terrapass tool does not support reporting about food, shopping, and services purchased, so provides only a fraction of the insights needed to understand your full carbon impact.
Wren’s carbon calculator has the deepest insight into local power sourcesbut fails to help users understand how to reduce their footprint.
GradesTransportation estimate: B+Total footprint estimate: C
Wren’s carbon calculator takes local power generation into account by asking for a ZIP code, which it uses to adjust a running total estimated footprint, in our case lowering the estimate by 31.6% because of the high level of renewable energy utilized by our local utility. The driving estimate it generated was slightly higher than the average result across all the tools tested, but the individual vehicle results are not broken out for examination, which makes deciding what changes will have the greatest impact impractical. Given the depth of the questions in other categories and its apparent insight into local power sources, the brief summary results are a missed opportunity to assist users in reducing their impact. Lower emissions is always a better first step than encouraging the purchase of carbon credits. We saw inflated results in other Wren reports, and that led to a lower grade for the calculator’s full-lifestyle impact estimates.
- ^ Carbon Calculating series (earth911.com)
- ^ driving efficiently (earth911.com)
- ^ air travel (earth911.com)
- ^ Center for Climate and Energy Solutions (www.c2es.org)
- ^ Rocky Mountain Institute estimates (rmi.org)
- ^ Department of Energy reports (www.energy.gov)
- ^ C2ES reports (www.c2es.org)
- ^ C2ES.org (www.c2es.org)
- ^ national average miles driven per year (www.fhwa.dot.gov)
- ^ 60% of the national total (www.eia.gov)
- ^ composition of your state’s electric generation infrastructure (www.eia.gov)
- ^ mining critical minerals, (www.iea.org)
- ^ an EV performs substantially better (www.iea.org)
- ^ search by year and model type (www.fueleconomy.gov)
- ^ state-level information about electric energy sourcing (www.eia.gov)
- ^ guide to EV fuel economy (fueleconomy.gov)
- ^ according to the EIA (www.eia.gov)
- ^ Cool Climate’s carbon calculator (coolclimate.org)
- ^ Environmental Protection Agency carbon calculator (www3.epa.gov)
- ^ MyClimate driving calculator (co2.myclimate.org)
- ^ flight (co2.myclimate.org)
- ^ cruise (co2.myclimate.org)
- ^ corporate (co2.myclimate.org)
- ^ subscriptions (co2.myclimate.org)
- ^ household (co2.myclimate.org)
- ^ World Land Trust Transport carbon calculator (www.worldlandtrust.org)
- ^ Terrapass carbon calculator (terrapass.com)