A carbon footprint (or greenhouse gas footprint) is a number or measure that shows how much greenhouse gas an activity, product, company, or country adds to the atmosphere. Carbon footprints are usually reported in tonnes of emissions (CO2-equivalent) for each unit being compared. These units might include tonnes of CO2-equivalent per year, per kilogram of protein eaten, per kilometer traveled, per piece of clothing, and others. A product’s carbon footprint includes all emissions from its entire life cycle, such as production, transportation, use, and disposal.
An organization’s carbon footprint includes both direct and indirect emissions it causes. The Greenhouse Gas Protocol, a system used to calculate emissions for organizations, divides these into three categories called Scope 1, 2, and 3 emissions. Scope 1 includes direct emissions from an organization’s operations. Scope 2 and 3 include indirect emissions, such as those from electricity use or emissions caused by customers and suppliers.
There are many ways to calculate a carbon footprint, and the methods depend on whether the focus is on a country, organization, product, or person. For example, a product’s carbon footprint can help people choose items that have a smaller climate impact. Carbon footprints also help identify which activities or products have the highest or lowest climate effects. This allows people to compare the climate impacts of individuals, products, companies, and countries and to plan ways to reduce emissions.
The carbon dioxide equivalent (CO2-eq) is a way to express a carbon footprint. It adds up all greenhouse gas emissions, including gases like methane and nitrous oxide, not just carbon dioxide. Some methods only count carbon dioxide emissions, but others include all greenhouse gases.
Different methods exist for calculating carbon footprints, and they may vary depending on what is being measured. Organizations often use the Greenhouse Gas Protocol, which includes three scopes of emissions. Countries often use consumption-based accounting to calculate their carbon footprint for a year. This method uses complex computer models to study global supply chains and includes emissions from goods and services used by residents, even if those goods and services were made in other countries.
Countries also create national greenhouse gas (GHG) inventories for the UNFCCC. These inventories only include emissions from activities within the country itself, not from imported goods or services. This method is called territorial-based or production-based accounting. In contrast, consumption-based accounting includes emissions from goods and services used by residents, even if they were produced abroad.
Consumption-based accounting is more complete because it includes emissions from all sources related to a country’s use of goods and services. It also includes Scope 3 emissions, which are not always covered in other systems. National GHG inventories for the UNFCCC do not include emissions from international transport. Comprehensive carbon footprint reporting looks at where goods and services are consumed, not just where they are made.
Definition
A carbon footprint is the total amount of carbon dioxide (CO₂) and methane (CH₄) released by a group, system, or activity. It includes all sources of these gases and how they are absorbed or stored within the area and time frame being studied. Scientists calculate this using a method called "carbon dioxide equivalent," which compares the warming effect of different gases over 100 years.
Scientists often express carbon footprints as tonnes of CO₂ equivalent. These measurements can be given for one year, one person, one kilogram of protein, or one kilometer traveled, depending on what is being studied.
Some scientists define carbon footprint only as CO₂ emissions. However, most scientists include other important greenhouse gases, such as methane and nitrous oxide. To compare these gases, scientists use CO₂ equivalents over a set time, like 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 major greenhouse gases covered by the Kyoto Protocol: 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 includes only CO₂. It describes a carbon footprint as the total amount of CO₂ released directly or indirectly by an activity or over a product's life cycle. This definition was also used in a 2007 UK report. The report said other greenhouse gases were harder to measure accurately because they have different warming effects. It also argued that including all gases might make the carbon footprint less useful. However, this approach has a problem: excluding methane can make some products or sectors, like livestock, appear less harmful to the climate than they actually are.
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, within the process of making and using products. Emissions created directly by an organization, such as from burning fuel, are called Scope 1. Emissions created indirectly by an organization, such as from using electricity or heat, are called Scope 2. Emissions from processes not directly controlled by the organization, such as transportation of materials or use of a product, are called Scope 3.
Scope 1 emissions come from sources at the location where a product is made or a service is provided. For example, in industry, this includes emissions from burning fuel on-site. For individuals, this includes emissions from personal vehicles or gas-burning stoves.
Scope 2 emissions are indirect emissions from using electricity, heat, or steam purchased by an organization. Examples of Scope 3 emissions include emissions from transporting materials before production (upstream) or emissions from using a product after it is sold (downstream). The Greenhouse Gas Protocol says it is important to track these emissions, but care must be taken to avoid counting the same emissions twice. For example, emissions from transporting materials for one company may be counted as upstream emissions for that company and downstream emissions for the company receiving the materials.
Scope 3 emissions include all indirect emissions from activities not owned or controlled by an organization. These emissions are part of the value chain, which includes suppliers, product users, and transportation of goods. 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
The current increase in Earth's average temperature is happening faster than past changes. This is mainly caused by people burning fossil fuels like coal, oil, and natural gas. More greenhouse gases in the atmosphere also come from cutting down forests and activities in farming, industry, and making cement. The two most important greenhouse gases are carbon dioxide and methane. Greenhouse gas emissions, and the total amount of carbon humans produce, have grown more during the 21st century. The Paris Agreement aims to reduce these emissions enough to keep Earth's temperature rise below 1.5 °C compared to before the industrial era.
The idea of a carbon footprint helps compare how much each person, product, company, or country affects the climate. A label showing a product's carbon footprint could help buyers choose items with lower climate impacts if they want to help reduce climate change. For example, such a label could show that beef has a larger carbon footprint than chicken.
Knowing the size of an organization's carbon footprint helps create plans to reduce it. For most businesses, most emissions are not from activities on their own property (called Scope 1) or from energy they use (called Scope 2), but from Scope 3 emissions. These are emissions from the entire supply chain, including both before and after the company's direct activities. Ignoring Scope 3 emissions makes it impossible to find all important emissions, which limits ways to reduce them. Large companies in industries like clothing or cars would need to study over 100,000 supply chain steps to fully report their carbon footprints.
Scientists have known for years about the movement of carbon emissions from one place to another. They call this carbon leakage. The idea of a carbon footprint helps address carbon leakage, which the Paris Agreement does not cover. Carbon leakage happens when rich countries move polluting industries to poorer countries. This makes it seem like the rich countries' greenhouse gas emissions are decreasing, even though emissions might be rising when looking at what people in those countries consume.
Carbon leakage and international trade have many environmental effects. These include more air pollution, less water, loss of plants and animals, more use of natural materials, and less energy available.
Experts suggest using both ways to measure emissions: one based on where goods are made (production-based) and one based on where goods are used (consumption-based). This helps share responsibility between producers and consumers. Right now, countries report their yearly greenhouse gas emissions to the UNFCCC based on emissions within their borders, called the territorial-based or production-based method. Adding consumption-based calculations to these reports would help fix problems related to 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 limits set for Annex 1 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 the goods.
Underlying concepts for calculations
Calculating the carbon footprint of a product, service, or sector needs the help of experts and a detailed review of what should be included. Carbon footprints can be measured at different levels, such as for entire countries, cities, neighborhoods, sectors, companies, or products. Some free online tools are available to help people calculate their personal carbon footprints.
Tools like the "Scope 3 Evaluator" assist companies in tracking emissions across their entire value chain. These tools also help consultants and researchers model global sustainability footprints. In every situation, several questions must be answered, such as which activities produce emissions and how much of those emissions should be assigned to a specific company. Software is important for managing companies, but new methods for planning resources are needed to improve sustainability efforts.
To cover 95% of a carbon footprint, it would be necessary to examine 12 million individual contributions from supply chains. This is based on studying 12 different sectors. Calculating Scope 3 emissions can be easier using input-output analysis, a method developed by Nobel Prize-winning economist Wassily Leontief.
Consumption-based emission accounting tracks how the demand for goods and services affects the environment along the global supply chain until they reach the end user. It is also known as consumption-based carbon accounting. In contrast, a production-based approach to calculating greenhouse gas (GHG) emissions does not focus on carbon footprints. This method, also called a territorial-based approach, only includes emissions physically produced within a specific country. Consumption-based accounting redistributes emissions from production-based accounting, considering that emissions in other countries are linked to a home country’s consumption.
Consumer-based accounting uses input-output analysis. It is used for high-level economic research on environmental or social impacts. Global supply chains can be studied using consumption-based accounting with input-output analysis supported by powerful supercomputers.
Wassily 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 and international sources like UN Comtrade and Eurostat. This method has expanded globally to multi-regional input-output analysis (MRIO), made possible by technology and data standards set by the United Nations. This analysis allows for a Structural Path Analysis, which identifies key points in supply chains that need urgent attention. Input-output analysis is popular because it helps study global value chains.
Life cycle assessment (LCA) is a method used to evaluate all environmental impacts of a product, process, or service throughout its life. It is not limited to greenhouse gas emissions but also includes water and air pollution, as well as harm to ecosystems. Recognized LCA procedures are included in the ISO 14000 series of environmental standards. A standard called ISO 14040:2006 provides guidelines for conducting LCA studies. The ISO 14060 family of standards offers more advanced tools, and the latest standard, ISO 14064:2018, includes tools to help companies reduce carbon emissions. These tools help measure, track, report, and verify GHG emissions and removals.
Greenhouse gas product life cycle assessments can follow guidelines like Publicly Available Specification (PAS) 2050 and the GHG Protocol Life Cycle Accounting and Reporting Standard.
A benefit of LCA is the detailed information it can provide on-site or through collaboration with suppliers. However, LCA has faced challenges because it sometimes stops considering impacts from upstream suppliers after a certain point, which can lead to errors. LCA has been combined with input-output analysis, allowing detailed on-site knowledge to be included. Input-output analysis connects to global economic databases, covering the entire supply chain.
Problems
Critics say the original goal of promoting the personal carbon footprint idea was to move responsibility from companies and organizations to individuals' lifestyle choices. In 2004, BP, a fossil fuel company, launched a large advertising campaign to spread awareness of the personal carbon footprint. This strategy, used by many major fossil fuel companies, has been criticized for trying to place the blame for the harmful effects of their industries on individuals' choices.
Geoffrey Supran and Naomi Oreskes from Harvard University argue that ideas like carbon footprints can limit our understanding of the climate crisis and make it harder to see the need for group actions to solve the problem.
While focusing on individual behavior has influenced public discussions, scientific studies show that this approach alone is not enough. The IPCC, in its Sixth Assessment Report (2023), stated that individual changes in behavior cannot achieve major reductions in emissions. The report noted that changes in how people use energy and services could reduce global greenhouse gas emissions by 40–70% by 2050 compared to current plans. This shows the importance of combining personal changes with large-scale solutions, such as clean energy systems, electric transportation, and shared infrastructure, to effectively address climate change. Changing personal habits helps, but completely eliminating the use of fossil fuels through large-scale changes is essential for long-term climate goals.
Focusing on carbon footprints might cause people to overlook or worsen other environmental problems, such as loss of wildlife, harm to ecosystems, and destruction of habitats. These issues are hard to measure with a single indicator like the carbon footprint. Some people may think the carbon footprint represents all environmental impacts, but this is not always true. There can be trade-offs between reducing carbon footprints and protecting the environment. For example, biofuel, a renewable energy source, can lower carbon emissions but may cause ecological problems during its production, such as the use of large-scale farming and chemical fertilizers. Another example is offshore wind farms, which might harm marine life in unexpected ways.
The carbon footprint analysis only looks at greenhouse gas emissions, unlike a life-cycle assessment, which considers all environmental effects. It is important to explain that the carbon footprint is one of several indicators, such as ecological footprint, water footprint, land footprint, and material footprint, and should not be viewed alone. In fact, the carbon footprint is part of the larger ecological footprint.
The "Sustainable Consumption and Production Hotspot Analysis Tool" (SCP-HAT) is a method to examine carbon footprints in a broader context. It includes many social, economic, and environmental factors. It provides calculations based on either consumption (like the carbon footprint approach) or production. The SCP-HAT uses data from national accounts and international trade, following UN standards, making it usable worldwide.
The term "carbon footprint" is sometimes used in limited ways that do not include all emissions from a product's full supply chain. This can lead to misleading claims about the actual carbon footprints 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. China has the highest annual emissions. The United States follows, with higher emissions per person. Large oil and gas companies are the main producers of emissions globally. Human activities have increased atmospheric carbon dioxide by about 50% compared to pre-industrial levels. Emissions have varied but been consistent across all greenhouse gases. Over 60 billion tons were emitted in 2025, more than any year before. 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 over 1870–2022. Coal caused 32%, oil 24%, and gas 10% of emissions.
Carbon dioxide is the main greenhouse gas from human activities. It causes more than half of the warming. Methane (CH₄) emissions have almost the same short-term impact. Nitrous oxide (N₂O) and fluorinated gases (F-gases) have a smaller role. In 2023, emissions of carbon dioxide, methane, and nitrous oxide were all higher than ever before.
The Carbon Trust has worked with UK manufacturers to create "thousands of carbon footprint assessments." By 2014, the Carbon Trust had measured 28,000 certifiable product carbon footprints. This organization also created a labeling system to help consumers and businesses make informed choices.
Plant-based foods usually have a lower carbon footprint than meat and dairy. This is true when comparing 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 kg CO₂ eq. Most of a food’s carbon footprint comes from farming or land use change, 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 it is packaged.
The IPCC Sixth Assessment Report found that global GHG emissions have risen in all sectors. Global consumption was 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 people contribute between one-third to one-half (36%–45%) of global GHG emissions. Wealth has a bigger impact on emissions than population growth. It also reduces the effects of technological improvements. Economic growth has led to more material extraction and higher GHG emissions. "Industrial emissions have grown faster since 2000 than in any other sector, driven by increased basic materials extraction and production," the IPCC said.
Transport emissions vary widely based on factors like trip length, electricity sources, 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. Cycling one kilometer typically emits 16 to 50 grams of CO₂ eq per kilometer. For longer distances, trains usually have a lower carbon footprint than other options.
Carbon accounting, also called greenhouse gas accounting or GHG accounting, is a system of methods to measure and track how much greenhouse gas an organization emits. It can also track projects 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 an emissions baseline, create reduction targets, and track progress. These methods help do this consistently and transparently.
The main reasons for GHG accounting are to address social responsibility concerns or meet legal requirements. Other reasons include public company rankings, financial due diligence, and potential cost savings. GHG accounting helps investors understand climate risks for companies they invest in. It also helps achieve net zero emission goals for corporations or communities. Many governments require reporting on emissions. Programs that require GHG accounting can lower emissions. Markets for buying and selling carbon credits depend on accurate emission measurements. 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. This method is called territorial emissions. Countries use it when reporting emissions and setting domestic and international targets, such as Nationally Determined Contributions. Consumption-based emissions adjust 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 on a production basis. 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 USA’s average was about 20 metric tonnes CO₂ eq per person, one of the highest in the world.
The per capita carbon footprints of countries in Africa and India were much lower than average. To stay within a 2°C target
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 is a way to reduce the amount of greenhouse gases in the air that cause climate change. This includes 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 atmosphere. Reports from 2022 say that global greenhouse gas emissions must reach their highest level 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 means the company’s carbon dioxide emissions are matched by an equal amount of carbon dioxide removed from the atmosphere. An example of carbon offsetting is reforestation, which means planting trees in areas where forests once grew.
A carbon footprint study can find specific areas that need improvement. It looks at how products are made and where materials come from. This analysis can help identify and eliminate supply chains that produce the most greenhouse gas emissions.
History
The term "carbon footprint" was first used in a BBC vegetarian food magazine in 1999. However, the broader concept of "ecological footprint," which includes the carbon footprint, was mentioned earlier, as noted by journalist William Safire in the New York Times in 1992.
In 2005, the fossil fuel company BP hired the advertising firm Ogilvy to help people understand the idea of a carbon footprint. The campaign taught individuals how to calculate their own carbon footprints and suggested ways to reduce their impact, such as "going on a low-carbon diet."
The carbon footprint is based on the ecological footprint, which measures the use of natural resources linked to activities like producing goods, living in a city, or using energy. While the ecological footprint converts carbon emissions into the area of land needed to absorb them, the carbon footprint is measured by the weight of carbon emissions over a specific time period. In 1992, William Rees published the first academic paper about ecological footprints. 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, worldwide rules for reporting carbon footprints. It was created from the International Financial Reporting Standards. The ISSB will require companies to report their Scope 3 emissions. The ISSB has considered criticisms of other programs to ensure its rules apply to everyone. It combines the Carbon Disclosure Standards Board, the Sustainability Accounting Standards Board, and the Value Reporting Foundation. It works with the Global Reporting Initiative. The ISSB is guided by the Task Force on Climate-Related Financial Disclosures. In early 2023, Great Britain and Nigeria were preparing to use these standards.
The total equivalent warming impact (TEWI) is the most commonly used measure for calculating carbon dioxide equivalent (CO2) emissions in air conditioning and refrigeration systems. It includes both direct and indirect emissions because it evaluates the emissions caused by the lifetime of these systems. The Expanded Total Equivalent Warming Impact method has been used to accurately assess emissions from refrigerators.