What is a carbon footprint—and how to measure yours

As awareness of climate change grows, so does the desire to do something about it. But the scale of the problems it causes—from wildfires to melting glaciers to droughts—can seem utterly overwhelming. It can be hard to make a connection between our everyday lives and the survival of polar bears, let alone how we as individuals can help turn the situation around.

One way to gain a quantifiable understanding of the impacts of our actions, for good and bad, is through what is known as a carbon footprint. But while the concept is gaining traction—Googling “How do I reduce my carbon footprint?” yields almost 27 million responses—it is not always fully understood.

What is a carbon footprint?

So, what exactly is a carbon footprint? According to Mike Berners-Lee, a professor at Lancaster University in the UK and author of The Carbon Footprint of Everything, it is “the sum total of all the greenhouse gas emissions that had to take place in order for a product to be produced or for an activity to take place.”

For most consumers in developed countries, these products and activities tend to fall into four principal categories: household energy use, transport, food, and everything else, which is mostly the products we buy, from utensils to clothes to cars to television sets.

Each of these activities and products has its own footprint; a person’s carbon footprint is the combined total of the products they buy and use, the activities they undertake, and so on. A person who regularly consumes beef will have a  larger food footprint than his vegan neighbor, but that neighbor’s overall footprint may be larger if she drives an hour to work and back in an SUV each day while our meat-eater bicycles to his office nearby. Both their footprints may pale in comparison to the businesswoman across the street, who flies first-class cross-country twice a month.

Unsurprisingly, in general terms the size of a person’s carbon footprint tends to increase with wealth. In his book, Berners-Lee writes that the average global citizen has a carbon footprint that is equivalent to the emission of seven tons of carbon dioxide per year. However, that figure is approximately 13 tons for the average Briton and roughly 21 tons per person in the United States.; The “average American takes just a couple of days to match the annual footprint of the average Nigerian or Malian,” he writes.

How is a carbon footprint calculated?

It isn’t easy to calculate a carbon footprint; indeed, Berners-Lee calls it the “essential but impossible” measurement.

Consider, for example, the personal carbon cost of taking a commercial flight. On the one hand, the calculation is straightforward: take how much fuel a plane burns and how many greenhouse gases are emitted during the course of a flight and divide by the number of passengers. But the footprint is larger for first-and-business-class passengers, because they take up more space and because their higher cost creates an extra incentive for the flight to actually take place. Other considerations include how much cargo the plane is carrying, and the altitude at which the plane flies.

Even so, it is a relatively simple calculation compared to assessing the emissions involved in every step of, say, the manufacture of a car: the emissions that take place at the assembly plant, the generation of electricity to power that plant, the transport of all the component items, the factories at which the components were made, the creation of the machinery used at those factories and at the assembly plant and so on, all the way back to the extraction of the minerals that are the car’s building blocks.

Because of the complexity involved in such calculations, Berners-Lee concedes that in such cases it is “never possible to be completely accurate.” The good news, he argues, is that for most individuals, that doesn’t matter. “Usually, it’s good enough just to have a broad idea,” he says.

What steps a person can take to reduce their personal footprint the most of course depends on the kind of lifestyle they presently live, and the same actions are not equally effective for everyone. For example, switching to an electric car is far more impactful in Vermont, where more than half the state’s electricity is generated by hydropower, than in West Virginia, where it is almost entirely generated by coal. Berners-Lee notes that, “for some people, flying may be 10 percent of their footprint, for some people it’s zero, and for some it’s such a huge number that it should be the only thing they should be thinking about.”

A cornucopia of calculators

To that end, in recent years, a veritable cornucopia of personal carbon footprint calculators has emerged online. By entering information about your household energy use, food consumption, and travel habits, for example, these calculators aim to provide you with an approximation of the amount of greenhouse gases being emitted to support your way of life. This one from the Nature Conservancy focuses on home energy use, transportation, diet, and shopping; this, from the United States Environmental Protection Agency, also considers transportation and energy use but adds in waste—specifically, how much you recycle. It also enables you to calculate how much your footprint could be reduced by taking steps such as insulating your home, driving less, or procuring a more fuel-efficient vehicle. This one shows just how much of an idealized personal carbon budget is taken up by consuming two large cheeseburgers a month or spending two nights in a hotel.

Are carbon footprints just fossil fuel propaganda?

It has been claimed that the earliest such calculator appeared in 2004 as part of the “Beyond Petroleum” campaign of oil giant BP—a fact that causes some observers to criticize the pressure to reduce personal carbon footprints as a “sham” to “promote the slant that climate change is not the fault of an oil giant, but that of individuals.”

“A few years ago, Shell promoted a tweet into my thread that asked, ‘What are you doing to reduce your carbon footprint?’” recalls Katharine Hayhoe, chief scientist for The Nature Conservancy and a professor at Texas Tech University. “So, I replied with something along the lines of, ‘You are responsible for 2 percent of global emissions, equivalent to the entire country of Canada; when you have a plan to get rid of those, I’d be happy to talk to you about my personal carbon footprint.’ And they hid my reply.”

“It’s really important that all of us think about what we’re consuming, whether it’s fish or furniture or air conditioning: where it came from, what impact it had,” says Kert Davies, director of the Climate Investigations Center. “But industry then turned it around and made it: ‘It’s not our fault, you’re using our product. You deal with it.’”

That is all the more egregious, he argues, given that the fossil fuel industry has directly fought to limit some of the measures that are often cited as ways for people to reduce their personal carbon footprints: more fuel-efficient vehicle standards, or clean energy technology, for example.

“If not for fossil fuel companies, you would already be driving an EV, your house would be more efficient to run if industry hadn’t blocked solutions and obscured the truth about the urgency of addressing climate change,” Davies adds.

Do carbon footprint calculators have a role?

Hayhoe argues that there are other problems with the concept of personal carbon footprints, not least the fact that many of the proposed means to reduce those footprints are unavailable to those who, for example, don’t have access to public transport, or can’t afford the upfront cost of an electric car or a heat pump, or who live in food deserts, where healthier, lower-impact foods such as vegetables and grains are harder to come by.

“There’s a role for the personal carbon footprint concept in high income countries among middle-to-high income people,” she explains. “There’s a very big role for the personal carbon footprint among the very richest people in the world. But we have to realize it is a limited concept—it does not apply to everyone.”

In addition, she argues, acting by ourselves is just one small part of what is required to affect change in a system that, despite the best individual efforts, remains dominated by the production and use of fossil fuels.

“I would say personal carbon footprint calculators are a useful tool to assess the impact of your immediate actions: where you live, where you travel, what you eat,” she says. “But what’s much more important than your personal carbon footprint is your climate shadow. Where do you keep your money? How do you vote? What about the businesses you work with, or the university you’re a part of, or the Rotary Club of which you’re a member—what are they doing, and how could you advocate for change?

“So, in a nutshell, when people ask me what they should do, I say: Do something, anything, but then talk about it. The only way to bring the carbon footprint of everybody in rich countries to where it needs to be for a sustainable planet is to change the system, and to change the system we have to use our voice.”