Carbon footprint

A carbon footprint is a way to measure how much different activities, products, companies, or even whole countries add to the amount of greenhouse gases in the air. These footprints are usually shown in tonnes of CO₂-equivalent for something like a year, a kilogram of food, a kilometer traveled, or a piece of clothing. This helps us compare how much each thing affects the climate.

For a product, its carbon footprint includes all the gases released from the very beginning — when it is made and shipped — all the way to when people use it and throw it away. Big groups or companies also have carbon footprints that include gases they release directly and others that come from things they use or buy. Knowing these footprints helps people make better choices, like picking products that hurt the climate less. It also helps us understand which parts of our economy cause the most problems for the climate, so we can work on fixing them.

We can measure footprints in different ways. For companies, the Greenhouse Gas Protocol splits emissions into three groups: things they directly control, things they get from the power grid, and everything else linked to what they do. For whole countries, there are two main ways to count. One looks only at what happens inside that country’s borders, while the other also counts what happens somewhere else to make the things people in the country use. This second way gives a fuller picture of how our choices affect the world.

Definition

A carbon footprint is a way to measure how much carbon dioxide (CO₂) and methane (CH₄) a person, activity, or product adds to the air. Scientists add up all the greenhouse gases and turn them into the same unit: tonnes of CO₂-equivalent.

Some scientists look only at carbon dioxide when they talk about a carbon footprint. But often, they include many greenhouse gases. They turn all these gases into CO₂-equivalent so they can be compared easily. This helps show which activities or products are more harmful to the climate.

Types of greenhouse gas emissions

See also: Carbon accounting

The greenhouse gas protocol helps count the greenhouse gases put into the air. It separates these gases into three groups, called scopes, in the value chain.

Scope 1 emissions come right from a place making something or giving a service, like burning fuel at a factory. For people, this could be gases from cars or gas stoves at home.

Scope 2 emissions are indirect. They come from buying things like electricity or heat for a place. This includes energy used away from the factory and waste made far from the factory.

Scope 3 emissions are all other indirect emissions from things the group cannot control, like gases from suppliers or people using the product. These are part of the value chain, such as moving goods. The International Sustainability Standards Board is working on a plan to include Scope 3 emissions in reports about greenhouse gases.

Purpose and strengths

See also: Carbon accounting

The world is warming up because humans burn things like coal and oil. This also happens when we cut down forests and use some farming and factory methods. These actions put extra gases into the air that trap heat. Two big gases are carbon dioxide and methane. Because of these gases, Earth’s temperature is going up. International agreements like the Paris Agreement want to stop the temperature from rising too much.

The idea of a carbon footprint helps us compare how much heat-trapping gas different things — like people, products, companies, or whole countries — add to the air. If a product has a carbon footprint label, it can show which items cause less warming, helping people choose them. For example, a label might show that beef causes more warming than chicken.

Companies can use carbon footprints to find ways to cut down on the gases they add to the air. Often, the biggest amounts come from faraway places where they get materials or sell products, not just from their own buildings or factories. This makes it important to look at all the steps that go into making and selling things.

Underlying concepts for calculations

To find out the carbon footprint of something like a product, service, or even a whole country, experts need to look at what to include. Carbon footprints can be calculated for many things — from big countries down to single products. There are free online tools that help people see their own personal carbon footprints.

Special software can help companies understand all the emissions they create, even from things they don’t directly control. This helps companies and researchers study how different parts of the world affect each other in terms of pollution. But there are many questions to answer, like which activities cause emissions and how much each part is responsible for.

Consumption-based emission accounting looks at how the things we buy affect the environment all around the world. This is different from just looking at what is made inside one country. Instead, it looks at all the emissions that happen because of what we consume, even if those emissions happen in other countries.

This type of accounting uses special methods to study how different parts of the world are connected through buying and selling goods. It can help us understand the big picture of how our choices affect the environment globally.

Life cycle assessment (LCA) is a way to study all the environmental effects of a product or service from start to finish. This includes things like water and air pollution, not just greenhouse gases. There are standard rules to follow for LCA, which help make sure the studies are done right. Combining LCA with other methods helps get a fuller picture of all the impacts, including those from faraway places that help make the product.

Problems

Some people think talking about personal carbon footprints takes attention away from big companies and groups. They say it makes it seem like it’s only people’s fault, not the industries that pollute a lot.

Only looking at carbon footprints might make us forget other big environmental problems, like losing animal homes or hurting water and soil. For example, some fuels that are better for the carbon footprint can still hurt nature when they are made. It’s important to know that the carbon footprint is just one way to see how we affect the environment, and other things matter too.

Reported values

See also: Greenhouse gas emissions

The Carbon Trust has helped many companies learn how much carbon they add to the air. By 2014, they had measured the carbon footprints of over 28,000 products.

Food

Eating plant-based foods, like vegetables and beans, usually adds less carbon than eating meat or dairy. For example, making 100 grams of protein from peas adds only 0.4 kilograms of carbon. But making the same amount of protein from beef adds almost 90 times more—about 35 kilograms of carbon. Most of this comes from farming and land changes.

By sector

The world’s carbon footprints keep growing in every area, mostly because of how much we buy and use. Transport and industry have grown very fast. Richer people tend to use more carbon.

Transport

How much carbon we add when we travel depends on many things, like how far we go and what we use to get there. For short trips, walking or biking adds the least carbon. For longer trips, trains usually add less carbon than cars or planes.

By country

Countries measure their carbon footprints in different ways. Some count only what happens inside their borders, while others also count the carbon from goods they import. On average, each person adds about 5 tonnes of carbon each year. But in places like the USA, it’s much higher—about 20 tonnes per person. In Africa and India, it’s much lower. To keep our planet safe, experts say each person should add no more than about 2–2.5 tonnes of carbon per year by 2050.

Reducing the carbon footprint

Main articles: Climate change mitigation and Greenhouse gas emissions § Reducing greenhouse gas emissions

Climate change mitigation

Working to lower the carbon footprint of products, services, and groups helps slow down climate change. These efforts are called climate change mitigation.

Reducing industry's carbon footprint

Main article: Climate change mitigation § Industry

Carbon offsetting can help a company lower its carbon footprint. This is done by giving the company a carbon credit. This credit rewards the company for reducing carbon dioxide in the air. Reforestation, which means planting new trees where forests have been lost, is one way to do carbon offsetting.

Studying a carbon footprint can show a company where it can improve. This study looks at all the steps needed to make a product, from start to finish, to find ways to cut down on greenhouse gases.

History

The idea of a carbon footprint started in 1999 in a BBC magazine. Before that, since 1992, people talked about the bigger idea of an ecological footprint, which includes carbon footprints.

In 2005, a big company called BP worked with Ogilvy to help people learn about their carbon footprints. They encouraged people to figure out their footprints and find ways to use less energy, like going on a low-carbon diet. The carbon footprint idea comes from the ecological footprint, which looks at all the resources we use. While the ecological footprint shows how much land is needed, the carbon footprint just measures the amount of carbon released over time. William Rees wrote the first academic paper about ecological footprints in 1992. Other similar ideas from the 1990s include the "ecological backpack" and material input per unit of service (MIPS).

Trends and similar concepts

The International Sustainability Standards Board (ISSB) helps companies around the world report their carbon footprints clearly. It brings together several groups to help make these rules. In early 2023, places like Great Britain and Nigeria were getting ready to use these new standards.

There is a way to measure how much warming a product or system causes, called total equivalent warming impact (TEWI). This method is often used for air conditioning and refrigeration to include all the emissions from how long the systems work. Another method, called Expanded Total Equivalent Warming Impact, helps get even more accurate numbers for refrigerators.