A carbon footprint (or greenhouse gas footprint) is a calculated value or index that makes it possible to compare the total amount of greenhouse gases that an activity, product, company or country adds to the atmosphere. Carbon footprints are usually reported in tonnes of emissions (CO2-equivalent) per unit of comparison. Such units can be, for example, tonnes CO2-eq per year, per kilogram of protein for consumption, per kilometer travelled, per piece of clothing and so forth. A product's carbon footprint includes the emissions for the entire life cycle. These run from the production along the supply chain to its final consumption and disposal.
Similarly, an organization's carbon footprint includes the direct as well as the indirect emissions that it causes. The Greenhouse Gas Protocol (for carbon accounting of organizations) calls these Scope 1, 2 and 3 emissions. There are several methodologies and online tools to calculate the carbon footprint. They depend on whether the focus is on a country, organization, product or individual person. For example, the carbon footprint of a product could help consumers decide which product to buy if they want to be climate aware. For climate change mitigation activities, the carbon footprint can help distinguish those economic activities with a high footprint from those with a low footprint. So the carbon footprint concept allows everyone to make comparisons between the climate impacts of individuals, products, companies and countries. It also helps people devise strategies and priorities for reducing the carbon footprint.
The carbon dioxide equivalent (CO2eq) emissions per unit of comparison is a suitable way to express a carbon footprint. This sums up all the greenhouse gas emissions. It includes all greenhouse gases, not just carbon dioxide. And it looks at emissions from economic activities, events, organizations and services. In some definitions, only the carbon dioxide emissions are taken into account. These do not include other greenhouse gases, such as methane and nitrous oxide.IPCC, 2022: Annex I: Glossary [van Diemen, R., J.B.R. Matthews, V. Möller, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, A. Reisinger, S. Semenov (eds)]. In IPCC, 2022: Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [P.R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA.
Various methods to calculate the carbon footprint exist, and these may differ somewhat for different entities. For organizations it is common practice to use the Greenhouse Gas Protocol. It includes three carbon emission scopes. Scope 1 refers to direct carbon emissions. Scope 2 and 3 refer to indirect carbon emissions. Scope 3 emissions are those indirect emissions that result from the activities of an organization but come from sources which they do not own or control.Green Element Ltd., What is the Difference Between Scope 1, 2 and 3 Emissions? , published 2 November 2018, accessed 11 November 2020
For countries it is common to use consumption-based emissions accounting to calculate their carbon footprint for a given year. Consumption-based accounting using input-output analysis backed by super-computing makes it possible to analyse global supply chains. Countries also prepare national GHG inventories for the UNFCCC. The GHG emissions listed in those national inventories are only from activities in the country itself. This approach is called territorial-based accounting or production-based accounting. It does not take into account production of goods and services imported on behalf of residents. Consumption-based accounting does reflect emissions from goods and services imported from other countries.
Consumption-based accounting is therefore more comprehensive. This comprehensive carbon footprint reporting including Scope 3 emissions deals with gaps in current systems. Countries' GHG inventories for the UNFCCC do not include international transport. Comprehensive carbon footprint reporting looks at the final demand for emissions, to where the consumption of the goods and services takes place.
Definition
A formal definition of carbon footprint is as follows: "A measure of the total amount of carbon dioxide (CO2) and methane (CH4) emissions of a defined population, system or activity, considering all relevant sources, sinks and storage within the spatial and temporal boundary of the population, system or activity of interest. Calculated as carbon dioxide equivalent using the relevant 100-year global warming potential (GWP100)."
Scientists report carbon footprints in terms of equivalents of tonnes of CO2 emissions (CO2-equivalent). They may report them per year, per person, per kilogram of protein, per kilometer travelled, and so on.
In the definition of carbon footprint, some scientists include only CO2. But more commonly they include several of the notable greenhouse gases. They can compare various greenhouse gases by using carbon dioxide equivalents over a relevant time scale, like 100 years. Some organizations use the term greenhouse gas footprint or climate footprint to emphasize that all greenhouse gases are included, not just carbon dioxide.
The Greenhouse Gas Protocol includes all of the most important greenhouse gases. "The standard covers the accounting and reporting of seven greenhouse gases covered by the Kyoto Protocol – carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PCFs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3)."
In comparison, the IPCC definition of carbon footprint in 2022 covers only carbon dioxide. It defines the carbon footprint as the "measure of the exclusive total amount of emissions of carbon dioxide (CO2) that is directly and indirectly caused by an activity or is accumulated over the lifecycle stages of a product." The IPCC report's authors adopted the same definition that had been proposed in 2007 in the UK. That publication included only carbon dioxide in the definition of carbon footprint. It justified this with the argument that other greenhouse gases were more difficult to quantify. This is because of their differing global warming potentials. They also stated that an inclusion of all greenhouse gases would make the carbon footprint indicator less practical. But there are disadvantages to this approach. One disadvantage of not including methane is that some products or sectors that have a high methane footprint such as livestock appear less harmful for the climate than they actually are.
Types of greenhouse gas emissions
The greenhouse gas protocol is a set of standards for tracking greenhouse gas emissions. The standards divide emissions into three scopes (Scope 1, 2 and 3) within the value chain. Greenhouse gas emissions caused directly by the organization such as by burning fossil fuels are referred to as Scope 1. Emissions caused indirectly by an organization, such as by purchasing secondary energy sources like electricity, heat, cooling or steam are called Scope 2. Lastly, indirect emissions associated with upstream or downstream processes are called Scope 3.
Direct carbon emissions (Scope 1) Direct or Scope 1 carbon emissions come from sources on the site that is producing a product or delivering a service. An example for industry would be the emissions from burning a fuel on site. On the individual level, emissions from personal vehicles or gas-burning stoves are Scope 1.
Indirect carbon emissions (Scope 2) Indirect carbon emissions are emissions from sources upstream or downstream from the process being studied. They are also known as Scope 2 or Scope 3 emissions.
Scope 2 emissions are the indirect emissions related to purchasing electricity, heat, or steam used on site. Examples of upstream carbon emissions include transportation of materials and fuels, any energy used outside of the production facility, and waste produced outside the production facility. Examples of downstream carbon emissions include any end-of-life process or treatments, product and waste transportation, and emissions associated with selling the product. The GHG Protocol says it is important to calculate upstream and downstream emissions. There could be some double counting. This is because upstream emissions of one person's consumption patterns could be someone else's downstream emissions
Other indirect carbon emissions (Scope 3) Scope 3 emissions are all other indirect emissions derived from the activities of an organization. But they are from sources they do not own or control. The GHG Protocol's Corporate Value Chain (Scope 3) Accounting and Reporting Standard allows companies to assess their entire value chain emissions impact and identify where to focus reduction activities.
Scope 3 emission sources include emissions from suppliers and product users. These are also known as the value chain. Transportation of goods, and other indirect emissions are also part of this scope. In 2022 about 30% of US companies reported Scope 3 emissions. The International Sustainability Standards Board is developing a recommendation to include Scope 3 emissions in all GHG reporting.
Purpose and strengths
The current rise in global average temperature is more rapid than previous changes. It is primarily caused by humans burning fossil fuels.Allen, M.R., O.P. Dube, W. Solecki, F. Aragón-Durand, W. Cramer, S. Humphreys, M. Kainuma, J. Kala, N. Mahowald, Y. Mulugetta, R. Perez, M.Wairiu, and K. Zickfeld, 2018: Chapter 1: Framing and Context. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 49-92. . The increase in greenhouse gases in the atmosphere is also due to deforestation and agricultural and industrial practices. These include cement production. The two most notable greenhouse gases are carbon dioxide and methane. Greenhouse gas emissions, and hence humanity's carbon footprint, have been increasing during the 21st century. The Paris Agreement aims to reduce greenhouse gas emissions enough to limit the rise in global temperature to no more than 1.5 °C above pre-industrial levels.
The carbon footprint concept makes comparisons between the climate impacts of individuals, products, companies and countries. A carbon footprint label on products could enable consumers to choose products with a lower carbon footprint if they want to help limit climate change. For meat products, as an example, such a label could make it clear that beef has a higher carbon footprint than chicken.