In most cases, the total carbon footprint cannot be exactly calculated because of inadequate knowledge of and data about the complex interactions between contributing processes, especially which including the influence on natural processes storing or releasing carbon dioxide. For this reason, Wright, Kemp, and Williams, have suggested to define the carbon footprint as:
- 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).
Greenhouse gases (GHGs) can be emitted through land clearance and the production and consumption of food, fuels, manufactured goods, materials, wood, roads, buildings, transportation and other services. For simplicity of reporting, it is often expressed in terms of the amount of carbon dioxide, or its equivalent of other GHGs, emitted.
Most of the carbon footprint emissions for the average U.S. household come from "indirect" sources, e.g. fuel burned to produce goods far away from the final consumer. These are distinguished from emissions which come from burning fuel directly in one's car or stove, commonly referred to as "direct" sources of the consumer's carbon footprint.
The concept name of the carbon footprint originates from ecological footprint, discussion, which was developed by Rees and Wackernagel in the 1990s which estimates the number of "earths" that would theoretically be required if everyone on the planet consumed resources at the same level as the person calculating their ecological footprint. However, given that ecological footprints are a measure of failure, Anindita Mitra (CREA, Seattle) chose the more easily calculated "carbon footprint" to easily measure use of carbon, as an indicator of unsustainable energy use. In 2007, carbon footprint was used as a measure of carbon emissions to develop the energy plan for City of Lynnwood, Washington. Carbon footprints are much more specific than ecological footprints since they measure direct emissions of gases that cause climate change into the atmosphere.
Carbon footprint is one of a family of footprint indicators, which also includes water footprint and land footprint.
Measuring carbon footprints
An individual's, nation's, or organization's carbon footprint can be measured by undertaking a GHG emissions assessment or other calculative activities denoted as carbon accounting. Once the size of a carbon footprint is known, a strategy can be devised to reduce it, e.g. by technological developments, better process and product management, changed Green Public or Private Procurement (GPP), carbon capture, consumption strategies, carbon offsetting and others.
Several free online carbon footprint calculators exist, including a few supported by publicly available peer-reviewed data and calculations including the University of California, Berkeley's CoolClimate Network research consortium and CarbonStory. These websites ask you to answer more or less detailed questions about your diet, transportation choices, home size, shopping and recreational activities, usage of electricity, heating, and heavy appliances such as dryers and refrigerators, and so on. The website then estimates your carbon footprint based on your answers to these questions. A systematic literature review was conducted to objectively determine the best way to calculate individual/household carbon footprints. This review identified 13 calculation principles and subsequently used the same principles to evaluate the 15 most popular online carbon footprint calculators. A recent study’s results by Carnegie Mellon's Christopher Weber found that the calculation of carbon footprints for products is often filled with large uncertainties. The variables of owning electronic goods such as the production, shipment, and previous technology used to make that product, can make it difficult to create an accurate carbon footprint. It is important to question, and address the accuracy of Carbon Footprint techniques, especially due to its overwhelming popularity.
Carbon Footprints can be reduced through the development of alternative projects, such as solar and wind energy, which are environment friendly, renewable resources, or reforestation, the restocking of existing forests or woodlands that have previously been depleted. These examples are known as Carbon Offsetting, the counteracting of carbon dioxide emissions with an equivalent reduction of carbon dioxide in the atmosphere.
The main influences on carbon footprints include population, economic output, and energy and carbon intensity of the economy. These factors are the main targets of individuals and businesses in order to decrease carbon footprints. Production creates a large carbon footprint, scholars suggest that decreasing the amount of energy needed for production would be one of the most effective ways to decrease a carbon footprint. This is due to the fact that Electricity is responsible for roughly 37% of Carbon Dioxide emissions. Coal production has been refined to greatly reduce carbon emissions; since the 1980s, the amount of energy used to produce a ton of steel has decreased by 50%.
Average carbon footprint per person by country
The global average carbon footprint in 2007 was around 5.7 tons CO2e/cap. The EU average for this time was about 13.8 tons CO2e/cap, whereas for the U.S., Luxembourg and Australia it was over 25 tons CO2e/cap. The footprints per capita of countries in Africa and India were well below average. To set this numbers into context, assuming a global population around 9-10 billion by 2050 a carbon footprint of about 2 - 2.5 tons CO2e per capita is needed to stay within a 2 °C target. The carbon footprint calculations are based on a consumption based approach using a Multi-Regional Input-Output database, which accounts for all Greenhouse Gas (GHG) emissions in the global supply chain and allocates them to the final consumer of the purchased commodities. GHG emissions related to land use cover change are not included.
Mobility (driving, flying & small amount from public transit), shelter (electricity, heating, construction) and food are the most important consumption categories determining the carbon footprint of a person. In the EU, the carbon footprint of mobility is evenly split between direct emissions (e.g. from driving private cars) and emissions embodied in purchased products related to mobility (air transport service, emissions occurring during the production of cars and during the extraction of fuel).
The carbon footprint of U.S. households is about 5 times greater than the global average. For most U.S. households the single most important action to reduce their carbon footprint is driving less or switching to a more efficient vehicle.
Direct carbon emissions
The carbon footprint of energy
The following table compares, from peer-reviewed studies of full life cycle emissions and from various other studies, the carbon footprint of various forms of energy generation: nuclear, hydro, coal, gas, solar cell, peat and wind generation technology.
Grams of CO2equivalent per Megajoule of thermal energy
Grams of CO2equivalent per Kilowatt-hour of electrical energy
|Hydroelectricity (run of river)||
|Conc. Solar Pwr||40±15#|
Note: 3.6 MJ = megajoule(s) == 1 kW·h = kilowatt-hour(s), thus 1 g/MJ = 3.6 g/kW·h.
Legend: B = Black coal (supercritical)–(new subcritical), Br = Brown coal (new subcritical), cc = combined cycle, oc = open cycle, TL = low-temperature/closed-circuit (geothermal doublet), TH = high-temperature/open-circuit, WL = Light Water Reactors, WH = Heavy Water Reactors, #Educated estimate.
These three studies thus concluded that hydroelectric, wind, and nuclear power produced the least CO2 per kilowatt-hour of any other electricity sources. These figures do not allow for emissions due to accidents or terrorism. Wind power and solar power, emit no carbon from the operation, but do leave a footprint during construction phase and maintenance during operation. Hydropower from reservoirs also has large footprints from initial removal of vegetation and ongoing methane (stream detritus decays anaerobically to methane in bottom of reservoir, rather than aerobically to CO2 if it had stayed in an unrestricted stream).
The table above gives the carbon footprint per kilowatt-hour of electricity generated, which is about half the world's man-made CO2 output. The CO2 footprint for heat is equally significant and research shows that using waste heat from power generation in combined heat and power district heating, chp/dh has the lowest carbon footprint, much lower than micro-power or heat pumps.
This section gives representative figures for the carbon footprint of the fuel burned by different transport types (not including the carbon footprints of the vehicles or related infrastructure themselves). The precise figures vary according to a wide range of factors.
Some representative figures for CO2 emissions are provided by LIPASTO's survey of average direct emissions (not accounting for high-altitude radiative effects) of airliners expressed as CO2 and CO2 equivalent per passenger kilometre:
- Domestic, short distance, less than 463 km (288 mi): 257 g/km CO2 or 259 g/km (14.7 oz/mile) CO2e
- Long distance flights: 113 g/km CO2 or 114 g/km (6.5 oz/mile) CO2e
However, emissions per unit distance traveled is not necessarily the best indicator for the carbon footprint of air travel, because the distances covered are commonly longer than by other modes of travel. It is the total emissions for a trip that matters for a carbon footprint, not the merely rate of emissions. For example, a greatly more distant holiday destination may be chosen than if another mode of travel were used, because air travel makes the longer distance feasible in the limited time available.
- 109 g/km CO2 (Figure 2)
- Newly registered passenger cars: 127 g CO2/km
- Hybrid-electric vehicles: 92 g CO2/km
- Light commercial vehicles (LCV): 175 g CO2/km
- Passenger cars: 200 g CO2/km (322 g/mi)
- Trucks: 280 g CO2/km (450 g/mi)
- Combined: 229 g CO2/km (369 g/mi)
In 2005, the US company Amtrak's carbon dioxide equivalent emissions per passenger kilometre were 0.116 kg, about twice as high as the UK rail average (where much more of the system is electrified), and about eight times a Finnish electric intercity train.
Average carbon dioxide emissions by ferries per passenger-kilometre seem to be 0.12 kg (4.2 oz). However, 18-knot ferries between Finland and Sweden produce 0.221 kg (7.8 oz) of CO2, with total emissions equalling a CO2 equivalent of 0.223 kg (7.9 oz), while 24–27-knot ferries between Finland and Estonia produce 0.396 kg (14.0 oz) of CO2 with total emissions equalling a CO2 equivalent of 0.4 kg (14 oz).
Indirect carbon emissions: the carbon footprints of products
Several organizations offer footprint calculators for public and corporate use, and several organizations have calculated carbon footprints of products. The US Environmental Protection Agency has addressed paper, plastic (candy wrappers), glass, cans, computers, carpet and tires. Australia has addressed lumber and other building materials. Academics in Australia, Korea and the US have addressed paved roads. Companies, nonprofits and academics have addressed mailing letters and packages. Carnegie Mellon University has estimated the CO2 footprints of 46 large sectors of the economy in each of eight countries. Carnegie Mellon, Sweden and the Carbon Trust have addressed foods at home and in restaurants.
The Carbon Trust has worked with UK manufacturers on foods, shirts and detergents, introducing a CO2 label in March 2007. The label is intended to comply with a new British Publicly Available Specification (i.e. not a standard), PAS 2050, and is being actively piloted by The Carbon Trust and various industrial partners. As of August 2012 The Carbon Trust state they have measured 27,000 certifiable product carbon footprints.
Evaluating the package of some products is key to figuring out the carbon footprint. The key way to determine a carbon footprint is to look at the materials used to make the item. For example, a juice carton is made of an aseptic carton, a beer can is made of aluminum, and some water bottles either made of glass or plastic. The larger the size, the larger the footprint will be.
In a 2014 study by Scarborough et al., the real-life diets of British people were surveyed and their dietary greenhouse gas footprints estimated. Average dietary greenhouse-gas emissions per day (in kilograms of carbon dioxide equivalent) were:
- 7.19 for high meat-eaters
- 5.63 for medium meat-eaters
- 4.67 for low meat-eaters
- 3.91 for fish-eaters
- 3.81 for vegetarians
- 2.89 for vegans
The precise carbon footprint of different textiles varies considerably according to a wide range of factors. However, studies of textile production in Europe suggest the following carbon dioxide equivalent emissions footprints per kilo of textile at the point of purchase by a consumer:
- Cotton: 8
- Nylon: 5.43
- PET (e.g. synthetic fleece): 5.55
- Wool: 5.48
The carbon footprint of materials (also known as embodied carbon) varies widely. The carbon footprint of many common materials can be found in the Inventory of Carbon & Energy database, the GREET databases and models, and LCA databases via openLCA Nexus
Cement production and carbon footprint resulting from soil sealing was 8.0 Mg person−1 of total per capita CO2 emissions (Italy, year 2003); the balance between C loss due to soil sealing and C stocked in man-made infrastructures resulted in a net loss to the atmosphere, -0.6 Mg C ha−1 y−1.
Schemes to reduce carbon emissions: Kyoto Protocol, carbon offsetting, and certificates
Carbon dioxide emissions into the atmosphere, and the emissions of other GHGs, are often associated with the burning of fossil fuels, like natural gas, crude oil and coal. While this is harmful to the environment, carbon offsets can be purchased in an attempt to make up for these harmful effects.
The Kyoto Protocol defines legally binding targets and timetables for cutting the GHG emissions of industrialized countries that ratified the Kyoto Protocol. Accordingly, from an economic or market perspective, one has to distinguish between a mandatory market and a voluntary market. Typical for both markets is the trade with emission certificates:
Mandatory market mechanisms
To reach the goals defined in the Kyoto Protocol, with the least economical costs, the following flexible mechanisms were introduced for the mandatory market:
The CDM and JI mechanisms requirements for projects which create a supply of emission reduction instruments, while Emissions Trading allows those instruments to be sold on international markets.
- Projects which are compliant with the requirements of the CDM mechanism generate Certified Emissions Reductions (CERs).
- Projects which are compliant with the requirements of the JI mechanism generate Emission Reduction Units (ERUs).
The CERs and ERUs can then be sold through Emissions Trading. The demand for the CERs and ERUs being traded is driven by:
- Shortfalls in national emission reduction obligations under the Kyoto Protocol.
- Shortfalls amongst entities obligated under local emissions reduction schemes.
Nations which have failed to deliver their Kyoto emissions reductions obligations can enter Emissions Trading to purchase CERs and ERUs to cover their treaty shortfalls. Nations and groups of nations can also create local emission reduction schemes which place mandatory carbon dioxide emission targets on entities within their national boundaries. If the rules of a scheme allow, the obligated entities may be able to cover all or some of any reduction shortfalls by purchasing CERs and ERUs through Emissions Trading. While local emissions reduction schemes have no status under the Kyoto Protocol itself, they play a prominent role in creating the demand for CERs and ERUs, stimulating Emissions Trading and setting a market price for emissions.
A well-known mandatory local emissions trading scheme is the EU Emissions Trading Scheme (EU ETS).
New changes are being made to the trading schemes. The EU Emissions Trading Scheme is set to make some new changes within the next year. The new changes will target the emissions produced by flight travel in and out of the European Union.
Voluntary market mechanisms
In contrast to the strict rules set out for the mandatory market, the voluntary market provides companies with different options to acquire emissions reductions. A solution, comparable with those developed for the mandatory market, has been developed for the voluntary market, the Verified Emission Reductions (VER). This measure has the great advantage that the projects/activities are managed according to the quality standards set out for CDM/JI projects but the certificates provided are not registered by the governments of the host countries or the Executive Board of the UNO. As such, high quality VERs can be acquired at lower costs for the same project quality. However, at present VERs can not be used in the mandatory market.
The voluntary market in North America is divided between members of the Chicago Climate Exchange and the Over The Counter (OTC) market. The Chicago Climate Exchange is a voluntary yet legally binding cap-and-trade emission scheme whereby members commit to the capped emission reductions and must purchase allowances from other members or offset excess emissions. The OTC market does not involve a legally binding scheme and a wide array of buyers from the public and private spheres, as well as special events that want to go carbon neutral. Being carbon neutral refers to achieving net zero carbon emissions by balancing a measured amount of carbon released with an equivalent amount sequestered or offset, or buying enough carbon credits to make up the difference.
There are project developers, wholesalers, brokers, and retailers, as well as carbon funds, in the voluntary market. Some businesses and nonprofits in the voluntary market encompass more than just one of the activities listed above. A report by Ecosystem Marketplace shows that carbon offset prices increase as it moves along the supply chain—from project developer to retailer.
While some mandatory emission reduction schemes exclude forest projects, these projects flourish in the voluntary markets. A major criticism concerns the imprecise nature of GHG sequestration quantification methodologies for forestry projects. However, others note the community co-benefits that forestry projects foster. Project types in the voluntary market range from avoided deforestation, afforestation/reforestation, industrial gas sequestration, increased energy efficiency, fuel switching, methane capture from coal plants and livestock, and even renewable energy. Renewable Energy Certificates (RECs) sold on the voluntary market are quite controversial due to additionality concerns. Industrial Gas projects receive criticism because such projects only apply to large industrial plants that already have high fixed costs. Siphoning off industrial gas for sequestration is considered picking the low hanging fruit; which is why credits generated from industrial gas projects are the cheapest in the voluntary market.
The size and activity of the voluntary carbon market is difficult to measure. The most comprehensive report on the voluntary carbon markets to date was released by Ecosystem Marketplace and New Carbon Finance in July 2007.
ÆON of Japan is firstly approved by Japanese authority to indicate carbon footprint on three private brand goods in October 2009.
Ways to reduce carbon footprint
The most common way to reduce the carbon footprint of humans is to Reduce, Reuse, Recycle, Refuse. In manufacturing this can be done by recycling the packing materials, by selling the obsolete inventory of one industry to the industry who is looking to buy unused items at lesser price to become competitive. Nothing should be disposed off into the soil, all the ferrous materials which are prone to degrade or oxidize with time should be sold as early as possible at reduced price.
This can also be done by using reusable items such as thermoses for daily coffee or plastic containers for water and other cold beverages rather than disposable ones. If that option isn't available, it is best to properly recycle the disposable items after use. When one household recycles at least half of their household waste, they can save 1.2 tons of carbon dioxide annually.
Another easy option is to drive less. By walking or biking to the destination rather than driving, not only is a person going to save money on gas, but they will be burning less fuel and releasing fewer emissions into the atmosphere. However, if walking is not an option, one can look into carpooling or mass transportation options in their area.
Yet another option for reducing the carbon footprint of humans is to use less air conditioning and heating in the home. By adding insulation to the walls and attic of one's home, and installing weather stripping or caulking around doors and windows one can lower their heating costs more than 25 percent. Similarly, one can very inexpensively upgrade the "insulation" (clothing) worn by residents of the home. For example, it's estimated that wearing a base layer of long underwear (top and bottom) made from a lightweight, super insulating fabric like microfleece (aka Polartec®, Capilene®) can conserve as much body heat as a full set of clothing, allowing a person to remain warm with the thermostat lowered by over 5 °C. These measures all help because they reduce the amount of energy needed to heat and cool the house. One can also turn down the heat while sleeping at night or away during the day, and keep temperatures moderate at all times. Setting the thermostat just 2 degrees lower in winter and higher in summer could save about 1 ton of carbon dioxide each year.
Choice of diet is a major influence on a person's carbon footprint. Animal sources of protein (especially red meat), rice (typically produced in high methane-emitting paddies), foods transported long distance and/or via fuel-inefficient transport (e.g., highly perishable produce flown long distance) and heavily processed and packaged foods are among the major contributors to a high carbon diet. Scientists at the University of Chicago have estimated "that the average American diet – which derives 28% of its calories from animal foods – is responsible for approximately one and a half more tonnes of greenhouse gasses – as CO2 equivalents – per person, per year than a fully plant-based, or vegan, diet." Their calculations suggest that even replacing one third of the animal protein in the average American's diet with plant protein (e.g., beans, grains) can reduce the diet's carbon footprint by half a tonne. Exchanging two thirds of the animal protein with plant protein is roughly equivalent to switching from a Toyota Camry to a Prius. Finally, throwing food out not only adds its associated carbon emissions to a person or household's footprint, it adds the emissions of transporting the wasted food to the garbage dump and the emissions of food decomposition, mostly in the form of the highly potent greenhouse gas, methane.
The carbon handprint movement emphasizes individual forms of carbon offsetting, like using more public transportation or planting trees in deforested regions, to reduce one's carbon footprint and increase their "handprint."
Furthermore, the carbon footprint in the food industry can be reduced by optimizing the supply chain. A life cycle or supply chain carbon footprint study can provide useful data which will help the business to identify critical areas for improvement and provides a focus. Such studies also demonstrate a company’s commitment to reducing carbon footprint now ahead of other competitors as well as preparing companies for potential regulation. In addition to increased market advantage and differentiation eco-efficiency can also help to reduce costs where alternative energy systems are implemented.
A July 2017 study published in Environmental Research Letters argued that the most significant way individuals could mitigate their own carbon footprint is to have fewer children, followed by living without a vehicle, forgoing air travel and adopting a plant-based diet.
- 4 Degrees and Beyond International Climate Conference
- 2000-watt society
- Avoiding dangerous climate change
- Carbon accounting
- Carbon cycle
- Carbon diet
- Carbon intensity
- Carbon literacy
- Carbon lock-in
- Chief green officer
- Climate footprint
- Ecological footprint
- Energy neutral design
- Energy policy
- Enterprise carbon accounting
- Environmental impact of aviation
- Food miles
- Greenhouse debt
- Greenhouse gas emissions accounting
- Global warming
- Green conventions
- Greenhouse gas inventory
- Hyper-mobile travellers
- Land footprint
- Life cycle assessment
- List of countries by carbon dioxide emissions per capita
- List of countries by greenhouse gas emissions per capita
- Low carbon diet
- Medical tourism
- Open Carbon World
- Relative cost of electricity generated by different sources
- Runoff footprint
- Water footprint
- Weighted average cost of carbon
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October 2006, Number 268
- Wiedmann, T. and J. Minx (2008). A Definition of 'Carbon Footprint'. Ecological Economics Research Trends. C. C. Pertsova: Chapter 1, pp. 1–11. Nova Science Publishers, Inc, Hauppauge NY, USA. catalog also available as ISA-UK Research Report 07/01
- World Energy Council Report (2004). Comparison of energy systems using life cycle assessment.
- Energetics (2007). The reality of carbon neutrality.
- The GHG Protocol
- Walkers Carbon Footprint
- Generally accepted definition: Carbon Footprint
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