A carbon footprint (or greenhouse gas footprint) is a number that helps compare how much greenhouse gas an activity, product, company, or country adds to the air. These footprints are usually measured in tonnes of emissions (CO₂-equivalent) for each unit being compared. Units might include tonnes of CO₂-equivalent per year, per kilogram of protein eaten, per kilometer traveled, per piece of clothing, or other examples. A product’s carbon footprint includes all emissions from its entire life cycle, starting with production, moving through the supply chain, and ending with its use and disposal.
An organization’s carbon footprint includes both direct and indirect emissions it causes. The Greenhouse Gas Protocol, a system for calculating emissions, divides these into three categories: Scope 1, 2, and 3. Scope 1 emissions are direct emissions from an organization. Scope 2 and 3 emissions are indirect emissions, with Scope 3 including emissions from activities the organization does not own or control.
There are many ways to calculate a carbon footprint, and the method depends on whether the focus is on a country, organization, product, or person. For example, a product’s carbon footprint can help people choose climate-friendly options. For reducing climate change, carbon footprints help identify which activities have high or low emissions. This concept allows people to compare the climate impacts of individuals, products, companies, and countries. It also helps create plans to reduce emissions.
The carbon dioxide equivalent (CO₂-eq) emissions per unit of comparison is a standard way to express a carbon footprint. This method adds up all greenhouse gas emissions, not just carbon dioxide. It includes emissions from activities, events, organizations, and services. Some definitions only consider carbon dioxide emissions, but others include other gases like methane and nitrous oxide.
Different methods exist for calculating carbon footprints, and they may vary depending on the entity being studied. For organizations, the Greenhouse Gas Protocol is often used. It includes three scopes of emissions. For countries, it is common to use consumption-based emissions accounting to calculate their carbon footprint for a year. This method uses input-output analysis and supercomputers to study global supply chains. Countries also prepare national greenhouse gas (GHG) inventories for the UNFCCC. These inventories only include emissions from activities within the country, using a method called territorial-based or production-based accounting. This approach does not include emissions from goods and services imported for use by residents. Consumption-based accounting, however, includes emissions from imported goods and services, making it more complete.
Comprehensive carbon footprint reporting, which includes Scope 3 emissions, helps address gaps in current systems. National GHG inventories for the UNFCCC do not include emissions from international transport. Comprehensive reporting focuses on where emissions occur due to the final use of goods and services.
Definition
A carbon footprint is a way to measure the total amount of carbon dioxide (CO₂) and methane (CH₄) released by a group of people, a system, or an activity. This includes all sources of emissions, places where carbon is stored, and other factors within the boundaries of the activity being studied. The measurement is expressed in terms of carbon dioxide equivalent, which compares different gases based on how much they contribute to global warming over 100 years.
Scientists often report carbon footprints as tonnes of CO₂-equivalent. These measurements can be given per year, per person, per kilogram of protein, per kilometer traveled, or other units. Some scientists define carbon footprints using only carbon dioxide, but most include several major greenhouse gases. To compare these gases, scientists use CO₂-equivalent values over a specific time period, such as 100 years. Some groups use the terms "greenhouse gas footprint" or "climate footprint" to show that all greenhouse gases are included, not just CO₂.
The Greenhouse Gas Protocol includes seven important greenhouse gases covered by the Kyoto Protocol. These gases are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃).
In contrast, the IPCC's 2022 definition of carbon footprint focuses only on carbon dioxide. It describes a carbon footprint as the total amount of CO₂ emissions directly or indirectly caused by an activity or accumulated over the life of a product. This definition was first proposed in the UK in 2007 and was based on the idea that other greenhouse gases are harder to measure due to their different global warming potentials. However, this approach has a drawback: it may underestimate the climate impact of activities that produce large amounts of methane, such as livestock farming.
Types of greenhouse gas emissions
The Greenhouse Gas Protocol is a set of rules for measuring greenhouse gas emissions. These rules group emissions into three categories, called scopes (Scope 1, 2, and 3), based on their position in the chain of activities involved in producing goods or services.
Scope 1 emissions are direct emissions caused by an organization, such as burning fuel on-site. For example, in industry, this includes emissions from burning fuel at a factory. For individuals, emissions from personal vehicles or gas stoves are also Scope 1.
Scope 2 emissions are indirect emissions from purchasing electricity, heat, or steam used at a location. These emissions occur outside the organization but are linked to its operations.
Scope 3 emissions are indirect emissions from activities not directly controlled by the organization, such as those from suppliers or product users. These include emissions from transporting goods, using products, or handling waste after a product is sold. Scope 3 emissions are part of the value chain, which includes all activities connected to producing and using a product.
The Greenhouse Gas Protocol explains that Scope 3 emissions can be challenging to track because they may overlap between different organizations. For example, emissions from transporting materials for one company might be counted as Scope 3 for the supplier and Scope 1 for the company receiving the materials.
In 2022, about 30% of U.S. companies reported Scope 3 emissions. The International Sustainability Standards Board is working to include Scope 3 emissions in all greenhouse gas reporting guidelines.
Purpose and strengths
Global temperatures are rising faster now than in the past. This increase is mainly caused by humans burning fossil fuels like coal, oil, and natural gas. More greenhouse gases are also added to the atmosphere because of deforestation and activities in farming, industry, and cement production. The two most important greenhouse gases are carbon dioxide and methane. Since the start of the 21st century, greenhouse gas emissions and the total carbon footprint of humans have grown. The Paris Agreement aims to reduce these emissions enough to keep global temperatures from rising more than 1.5°C above levels before the industrial era.
The carbon footprint helps compare the climate impact of people, products, companies, and countries. If products had labels showing their carbon footprint, consumers could choose items with lower emissions to help reduce climate change. For example, labels might show that beef has a larger carbon footprint than chicken.
Understanding an organization’s carbon footprint allows it to create plans to reduce emissions. For most businesses, most emissions are not from activities on-site (called Scope 1) or from energy they use (called Scope 2), but from Scope 3 emissions. These emissions come from the broader supply chain, including activities before and after the company’s direct operations. Ignoring Scope 3 emissions makes it harder to find all important emissions, which limits options to reduce them. Large companies in industries like clothing or automobiles may need to examine over 100,000 supply chain steps to fully report their carbon footprints.
Scientists have known for years about the movement of carbon emissions, called carbon leakage. This happens when countries move polluting industries to other countries. Wealthier countries often move these industries to poorer countries. This can make it seem like emissions are decreasing in the wealthier countries, even if emissions are actually higher when looking at total consumption.
Carbon leakage and international trade affect the environment in many ways, including more air pollution, less water, loss of wildlife, more use of natural resources, and less available energy.
Experts suggest using both consumption-based and production-based methods to calculate emissions. This helps share responsibility between producers and consumers. Today, countries report their greenhouse gas emissions to the UNFCCC based on emissions that happen within their borders, called the territorial or production-based approach. Adding consumption-based calculations to these reports could help solve problems caused by carbon leakage.
The Paris Agreement does not require countries to include emissions from international transport in their national totals. These emissions are reported separately and are not subject to the reduction goals of certain countries under the Climate Convention and Kyoto Protocol. The carbon footprint method includes emissions from international transport, assigning these emissions to the country that imports goods.
Underlying concepts for calculations
Calculating the carbon footprint of a product, service, or sector needs specialized knowledge and careful study of what to include. Carbon footprints can be measured at different levels, such as entire countries, cities, neighborhoods, sectors, companies, and individual products. Free online tools are available to help people calculate their personal carbon footprints.
Software programs like the "Scope 3 Evaluator" assist companies in reporting emissions across their entire value chain. These tools help consultants and researchers model global sustainability impacts. In each situation, several questions must be answered, such as which activities cause emissions and how much of those emissions should be assigned to a specific company. Software is important for company management. However, new methods for organizing business resources are needed to improve sustainability efforts.
To achieve 95% coverage of a carbon footprint, it would be necessary to evaluate 12 million individual contributions from supply chains. This is based on analyzing 12 case studies from different sectors. Calculating Scope 3 emissions can be made easier using a method called input-output analysis. This method was originally developed by economist Wassily Leontief, who won a Nobel Prize.
Consumption-based emission accounting tracks the effects of demand for goods and services through global supply chains to the final consumer. This method is also called consumption-based carbon accounting. In contrast, a production-based approach to calculating greenhouse gas (GHG) emissions does not focus on carbon footprints. This method is also called a territorial-based approach. It includes only emissions produced within a specific country. Consumption-based accounting redistributes emissions from production-based methods, considering that emissions in other countries are necessary to meet the needs of consumers in the home country.
Consumer-based accounting uses input-output analysis. It is used for important economic research related to environmental or social impacts. Global supply chains can be studied using consumption-based accounting with input-output analysis, supported by powerful supercomputers.
Leontief created input-output analysis (IO) to show how consumption and production are connected in an economy. It includes the entire supply chain and uses data from national accounts, such as input-output tables, and international sources like UN Comtrade and Eurostat. Input-output analysis has been expanded globally to multi-regional input-output analysis (MRIO). Advances in technology and global standards set by the United Nations have made this possible. This analysis allows for structural path analysis, which identifies and ranks the most important parts of supply chains for action. Input-output analysis is popular because it helps study global value chains.
Life cycle assessment (LCA) is a method for evaluating all environmental impacts of a product, process, or service throughout its life. It is not limited to greenhouse gas emissions. It is also called life cycle analysis and includes impacts like water pollution, air pollution, and harm to ecosystems. Widely accepted procedures for LCA are included in the ISO 14000 series of environmental standards. A standard called ISO 14040:2006 provides the framework for conducting an LCA study. The ISO 14060 family of standards offers more advanced tools. The latest standard, ISO 14064:2018, provides tools to help companies measure, monitor, report, and verify GHG emissions and removals.
Greenhouse gas product life cycle assessments can also follow guidelines like Publicly Available Specification (PAS) 2050 and the GHG Protocol Life Cycle Accounting and Reporting Standard.
One advantage of LCA is the detailed information it can provide through on-site studies or by working with suppliers. However, LCA has faced challenges because it sometimes stops considering impacts from suppliers beyond a certain point, which can lead to errors. LCA has been combined with input-output analysis to include more data from global economic databases, covering the entire supply chain.
Problems
Critics say the idea of tracking personal carbon footprints was created to make individuals take more responsibility for climate change, while reducing the focus on companies and industries. In 2004, the fossil fuel company BP promoted this concept through a large advertising campaign, which helped make it more widely known. This strategy, used by many major fossil fuel companies, has been criticized for trying to shift the blame for the harmful effects of their industries onto personal choices.
Geoffrey Supran and Naomi Oreskes from Harvard University argue that focusing on carbon footprints can limit our understanding of the climate crisis and make us overlook the need for collective action to solve it.
While discussions about personal behavior have influenced public conversations, scientific studies show that changing individual habits alone is not enough to significantly reduce greenhouse gas emissions. The Intergovernmental Panel on Climate Change (IPCC) states in its Sixth Assessment Report (2023) that changes in how people use energy and services can reduce global emissions by 40–70% by 2050 compared to current trends. This highlights the importance of combining personal changes with large-scale solutions, such as switching to clean energy, using electricity for transportation and heating, and building shared infrastructure, to address climate change effectively. While reducing emissions through personal choices is important, completely eliminating the use of fossil fuels through systemic changes is essential for long-term climate goals.
Focusing only on carbon footprints may cause people to ignore or worsen other environmental problems, such as loss of wildlife, harm to ecosystems, and destruction of natural habitats. These issues are difficult to measure using only a carbon footprint, which only tracks greenhouse gas emissions. Some people may believe that a carbon footprint represents all environmental impacts, but this is not always true. For example, reducing a carbon footprint by using biofuel—a renewable energy source—can sometimes lead to environmental harm during its production, such as through the use of chemicals in farming. Similarly, offshore wind farms, while helpful for reducing emissions, may affect marine life in unexpected ways.
A carbon footprint analysis only considers greenhouse gas emissions, unlike a life-cycle assessment, which looks at all environmental impacts. It is important to explain that the carbon footprint is one of several tools used to measure environmental effects, such as ecological footprint, water footprint, land footprint, and material footprint. These tools should not be used alone. In fact, the carbon footprint is a part of the broader ecological footprint.
The "Sustainable Consumption and Production Hotspot Analysis Tool" (SCP-HAT) is a method that helps place carbon footprint analysis in a larger context. It includes many social, economic, and environmental indicators. It provides calculations based on either consumption (like the carbon footprint approach) or production. The tool uses data from countries’ economic records and international trade, following United Nations standards, making it useful for global comparisons.
The term "carbon footprint" is sometimes used in limited ways that do not include all emissions from a product’s entire supply chain, such as Scope 3 emissions. This can lead to misleading information about the true environmental impact of companies or products.
Reported values
Greenhouse gas emissions (GHG emissions) from human activities make the greenhouse effect stronger, which contributes to climate change. Carbon dioxide (CO2) from burning fossil fuels (such as coal, oil, and natural gas) is the main cause of climate change. The largest annual emissions come from China, followed by the United States, which has higher emissions per person. The main producers of emissions globally are large oil and gas companies. Human activities have increased atmospheric carbon dioxide by about 50% since pre-industrial times. Emissions levels have varied but have been consistent across all greenhouse gases. Over 60 billion tons of emissions were recorded in 2025, which is the highest amount ever. Total cumulative emissions from 1870 to 2022 were 703 GtC (2575 GtCO2), of which 484±20 GtC (1773±73 GtCO2) came from fossil fuels and industry, and 219±60 GtC (802±220 GtCO2) from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions from 1870–2022, coal 32%, oil 24%, and gas 10%.
Carbon dioxide is the main greenhouse gas from human activities. It causes more than half of the warming effect. Methane (CH4) emissions have a similar short-term impact. Nitrous oxide (N2O) and fluorinated gases (F-gases) have a smaller role in comparison. In 2023, emissions of carbon dioxide, methane, and nitrous oxide were all higher than ever before.
The Carbon Trust has helped UK manufacturers create "thousands of carbon footprint assessments." By 2014, the Carbon Trust had measured 28,000 certifiable product carbon footprints. This organization has also developed a labeling system to help consumers and businesses make better choices.
Plant-based foods usually have a smaller carbon footprint than meat and dairy. This is true when comparing food by weight, protein content, or calories. For example, producing 100 grams of protein from peas emits 0.4 kilograms of carbon dioxide equivalents (CO2 eq). Producing the same amount of protein from beef emits nearly 90 times more, at 35 kgCO2 eq. Most of a food’s carbon footprint comes from farming processes or land use changes, not from transport or packaging. This means choosing what to eat can reduce a carbon footprint more than how far food travels or how much packaging it has.
The IPCC Sixth Assessment Report found that global GHG emissions have continued to rise across all sectors. Global consumption is the main cause. The fastest growth was in transport and industry. Wealth is a key driver of global carbon emissions. The IPCC noted that the wealthiest 10% of the world’s population contributes between 36% to 45% of global GHG emissions. Researchers have found that wealth has a bigger impact on emissions than population growth. It also reduces the benefits of technological improvements. Economic growth has led to more material extraction and higher GHG emissions. "Industrial emissions have grown faster since 2000 than any other sector, driven by increased basic materials extraction and production," the IPCC said.
Transport emissions can vary widely based on factors like trip length, the source of electricity in local grids, and public transport occupancy. For driving, the type of vehicle and number of passengers matter. For short to medium distances, walking or cycling usually have the lowest carbon footprint. The carbon footprint of cycling one kilometer is usually between 16 to 50 grams CO2 eq per kilometer. For moderate or long distances, trains usually have the lowest carbon footprint compared to other options.
Carbon accounting, also called greenhouse gas accounting or GHG accounting, is a system to measure and track how much greenhouse gas an organization emits. It can also track efforts to reduce emissions in areas like forestry or renewable energy. Companies, cities, and other groups use these methods to help limit climate change. Organizations often set a baseline for emissions, create goals to reduce emissions, and track progress. These methods help do this consistently and transparently.
The main reasons for GHG accounting are to address social responsibility or meet legal requirements. Other reasons include public company rankings, financial planning, and cost savings. GHG accounting helps investors understand climate risks for companies they invest in. It also helps achieve net zero emission goals for businesses or communities. Many governments require reporting on emissions. Evidence suggests that programs requiring GHG accounting can lower emissions. Markets for buying and selling carbon credits depend on accurate measurements of emissions and reductions. These methods help understand the impacts of products and services by measuring their GHG emissions throughout their lifecycle (carbon footprint).
CO2 emissions of countries are usually measured based on production, also called territorial emissions. Countries use this method when reporting emissions and setting targets like Nationally Determined Contributions. Consumption-based emissions, on the other hand, account for trade. To calculate consumption-based emissions, analysts track goods traded globally. When a product is imported, all CO2 emissions from its production are included. Consumption-based emissions reflect the lifestyle choices of a country’s citizens.
According to the World Bank, the global average carbon footprint in 2014 was about 5 tonnes of CO2 per person, measured by production. The EU average for 2007 was about 13.8 tonnes CO2 eq per person. For the USA, Luxembourg, and Australia, it was over 25 tonnes CO2 eq per person. In 2017, the average for the USA was about 20 metric tonnes CO2 eq per person, one of the highest in the world.
The carbon footprints per person in countries in Africa and India were much lower than the global average. To stay within a 2°C climate target by 2050, assuming a global population of about 9–10 billion, a carbon footprint of about 2–2.5 tonnes CO2 eq per person is needed. These calculations use a consumption-based approach with a Multi-Regional Input-Output (MRIO) database. This database tracks all greenhouse gas emissions in the global supply chain and assigns them to the final consumer of goods.
Reducing the carbon footprint
Efforts to reduce the carbon footprint of products, services, and organizations help limit climate change. These actions are called climate change mitigation.
Climate change mitigation, also known as climate change decarbonisation, refers to steps taken to reduce greenhouse gases in the atmosphere that cause climate change. These steps include saving energy and using clean energy instead of fossil fuels. Other methods involve changing how land is used and removing carbon dioxide (CO₂) from the air. Reports from 2022 state that global greenhouse gas emissions must reach their highest point before 2025 and then decrease by about 43% by 2030 to limit warming to 1.5°C. This requires quick changes in energy, transportation, and land-use systems.
Carbon offsetting helps reduce a company’s total carbon footprint by giving it a carbon credit. This credit allows the company to balance its carbon dioxide emissions by supporting activities that remove the same amount of carbon dioxide from the atmosphere. An example of carbon offsetting is reforestation, which involves replanting trees in areas where forests were previously lost.
A carbon footprint study can find specific areas that need improvement. It examines the entire supply chain and uses methods like input-output analysis to understand how different parts contribute to emissions. This analysis can help identify and eliminate supply chains with the highest levels of greenhouse gas emissions.
History
The term "carbon footprint" was first used in a BBC vegetarian food magazine in 1999. However, the larger idea of "ecological footprint," which includes the carbon footprint, was mentioned earlier. Journalist William Safire wrote about this in the New York Times as early as 1992.
In 2005, the fossil fuel company BP worked with the advertising firm Ogilvy to help people understand the concept of a carbon footprint. The campaign taught individuals how to calculate their own carbon footprints and offered ways to reduce their impact, such as choosing to "go on a low-carbon diet."
The carbon footprint comes from the ecological footprint, which tracks how much carbon is released through human activities. Both use the same method to measure resource use, whether it is for a product, person, city, or country. In the ecological footprint, carbon emissions are shown as the area of land needed to absorb them. In contrast, the carbon footprint is measured by the weight of carbon emissions over a specific time period. William Rees wrote the first academic paper about ecological footprints in 1992. Other related ideas from the 1990s include "ecological backpack" and "material input per unit of service" (MIPS).
Trends and similar concepts
The International Sustainability Standards Board (ISSB) works to create strict, global rules for reporting carbon footprints. It was created from the International Financial Reporting Standards. The ISSB requires companies to report their Scope 3 emissions. It has considered feedback about other similar efforts to ensure its standards apply to all businesses. The ISSB combines the Carbon Disclosure Standards Board, the Sustainability Accounting Standards Board, and the Value Reporting Foundation. It works with the Global Reporting Initiative. It is influenced by the Task Force on Climate-Related Financial Disclosures. In early 2023, Great Britain and Nigeria were preparing to use these standards.
The concept of total equivalent warming impact (TEWI) is the most commonly used measure for calculating carbon dioxide equivalent (CO₂) emissions in air conditioning and refrigeration sectors. It includes both direct and indirect effects by considering emissions from the entire lifetime of systems. The Expanded Total Equivalent Warming Impact method has been used to more precisely measure emissions from refrigerators.