Carbon footprint

The concept and name of the carbon footprint was derived from the ecological footprint concept,[15] which was developed by William E. Rees and Mathis Wackernagel in the 1990s at the University of British Columbia. While carbon footprints are usually reported in tons of emissions (CO₂-equivalent) per year, ecological footprints are usually reported in comparison to what the planet can renew. This assesses the number of "earths" that would be required if everyone on the planet consumed resources at the same level as the person calculating their ecological footprint. The carbon footprint is one part of the ecological footprint. Carbon footprints are more focused than ecological footprints since they merely measure emissions of gases that cause climate change into the atmosphere.

Carbon footprint is one of a family of footprint indicators,[16] which also include ecological footprints, water footprints and land footprints.

The idea of a personal carbon footprint was popularized by a large advertising campaign of the fossil fuel company BP in 2005, designed by Ogilvy.[10][15] It instructed people to calculate their personal footprints and provided ways for people to "go on a low-carbon diet".[17] This strategy, also employed by other major fossil fuel companies[18] borrowed heavily from previous campaigns by the tobacco industry[19] and plastics industry to shift the blame for negative consequences of those industries (under-age smoking,[20] cigarette butt pollution,[21] and plastic pollution[22]) onto individual choices.

BP made no attempt to reduce its own carbon footprint, instead expanding its oil drilling into the 2020s.[23][24] However, the strategy had some success, with a rise in consumers concerned about their own personal actions, and creation of multiple carbon footprint calculators.[10]

Direct or 'scope 1' carbon emissions come from sources that are directly from the site that is producing a product or delivering a service.[37][38] An example for industry would be the emissions related to burning a fuel on site. On the individual level, emissions from personal vehicles or gas burning stoves would fall under scope 1.

Consumption-based CO₂ emissions per capita, 2017

Indirect carbon emissions are emissions from sources upstream or downstream from the process being studied, also known as scope 2 or scope 3 emissions.[37]

Examples of upstream, indirect carbon emissions may include:[39]

• Transportation of materials/fuels
• Any energy used outside of the production facility
• Wastes produced outside of the production facility

Examples of downstream, indirect carbon emissions may include:[13]

• Any end-of-life process or treatments
• Product and waste transportation
• Emissions associated with selling the product

Scope 2 emissions are the other indirect related to purchased electricity, heat, and/or steam used on site.[38]

Scope 3 emissions are all other indirect emissions derived from the activities of an organisation but from sources which they do not own or control.[40] 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.[41]

In the US, the EPA has broken down electricity emission factors by state.[42]

In the UK, DEFRA provides emission factors going back to 2002 covering scope 1, 2 and 3.[43] DEFRA no longer provide international emission factors and refer visitors to the IEA who provide free highlights and paid for details covering Scope 1 and 2.[44]

According to The World Bank, the global average carbon footprint in 2014 was 4.97 metric tons CO₂/cap.[5] The EU average for 2007 was about 13.8 tons CO₂e/cap, whereas for the U.S., Luxembourg and Australia it was over 25 tons CO₂e/cap. In 2017, the average for the USA was about 20 metric tons CO₂e.[lower-alpha 1]

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). In low carbon economies such as Sweden and France the majority of household carbon is in imported goods 65% and 51% respectively.[47]

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.[48]

As well as calculating carbon footprints for whole countries, it is also possible to calculate the footprint of regions, cities, and neighbourhoods.[49]

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:[53]

• 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 travelled 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 merely the rate of emissions. For example, because air travel makes rapid long-distance travel feasible, a holiday destination may be chosen that is much more distant than if another mode of travel were used.[54]

CO₂ emissions per passenger-kilometre (pkm) for all road travel for 2011 in Europe as provided by the European Environment Agency:[55]

• 109 g/km CO₂ (Figure 2)

For vehicles, average figures for CO₂ emissions per kilometer for road travel for 2013 in Europe, normalized to the NEDC test cycle, are provided by the International Council on Clean Transportation:[56]

• Newly registered passenger cars: 127 g CO₂/km
• Hybrid-electric vehicles: 92 g CO₂/km
• Light commercial vehicles (LCV): 175 g CO₂/km

Average figures for the United States are provided by the US Environmental Protection Agency,[57] based on the EPA Federal Test Procedure, for the following categories:

• 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)

Food contributes 10-30% of a household’s carbon footprint, mainly attributed to agricultural practices like food production and transportation. Meat products have larger carbon footprints than plant products like vegetables and grains due to inefficient conversion of plant energy to animals, and the release of methane from manure.[63] In a 2014 study by Scarborough et al., the real-life diets of British people were surveyed and their dietary greenhouse gas footprints estimated.[64] 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:[65]

• Cotton: 8
• Nylon: 5.43
• PET (e.g. synthetic fleece): 5.55
• Wool: 5.48

Accounting for durability and energy required to wash and dry textile products, synthetic fabrics generally have a substantially lower carbon footprint than natural ones.[66]

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,[67] the GREET databases and models,[68] and LCA databases via openLCA Nexus.[69] The carbon footprint of any manufactured product should be verified by a third-party.[70]

Cement production gives a major contribution to CO₂ emissions.

A July 2017 study published in Environmental Research Letters found that the most significant way individuals could mitigate their own carbon footprint is to have one less child ("an average for developed countries of 58.6 tonnes CO₂-equivalent (tCO₂e) emission reductions per year"), followed by living car-free (2.4 tonnes CO₂-equivalent per year), forgoing air travel (1.6 tonnes CO₂-equivalent per trans-Atlantic trip) and adopting a plant-based diet (0.8 tonnes CO₂-equivalent per year).[84][85] The study also found that most government resources on climate change focus on actions that have a relatively modest effect on greenhouse gas emissions, and concludes that "a US family who chooses to have one fewer child would provide the same level of emissions reductions as 684 teenagers who choose to adopt comprehensive recycling for the rest of their lives".[85]

An option is to drive less. Walking, biking, carpooling, mass transportation and combining trips result in burning less fuel and releasing fewer emissions into the atmosphere.

The 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 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[86] "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."[87] 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, but it also 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.

Recycling station in a park to promote reduce, reuse, recycle.

Options to reduce the carbon footprint of humans include Reduce, Reuse, Recycle, Refuse. This can 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.[88]

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.[89] For example, it's estimated that wearing a base layer of long underwear with top and bottom, made from a lightweight, super-insulating fabric like microfleece, 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.[89][90] 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.[88]

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."[91][92]

Windmills located in a field to conserve energy.

The most powerful industrial climate actions are:[93] refrigerant management (90 billion tonnes of CO₂e 2017–2050,[94] since refrigerants have thousands of times the warming potential of CO₂); land-based wind turbines for electricity (85 billion); reduced food waste (71 billion); and restoring tropical forests by ending use of the land for other purposes (61 billion). They calculate benefits cumulatively to 2050, rather than annually, because industrial actions have long lead times.[95]

A product, service, or company's carbon footprint can be affected by several factors including, but not limited to:

• Energy sources
• Offsite electricity generation
• Materials

These factors can also change with location or industry. However, there are some general steps that can be taken to reduce carbon footprint on a larger scale.

In 2016, the EIA reported that in the US electricity is responsible for roughly 37% of Carbon Dioxide emissions, making it a potential target for reductions.[96] Possibly the cheapest way to do this is through energy efficiency improvements. The ACEEE reported that energy efficiency has the potential to save the US over 800 billion kWh per year, based on 2015 data.[97] Some potential options to increase energy efficiency include, but are not limited to:[98]

• Waste heat recovery systems
• Insulation for large buildings and combustion chambers
• Technology upgrades, ie different light sources, lower consumption machines

Carbon footprint from energy consumption can be reduced through the development of nuclear power (a zero carbon emissions energy source) and alternative energy projects, such as solar and wind energy, which are renewable resources.

Reforestation, the restocking of existing forests or woodlands that have previously been depleted, is an example of Carbon Offsetting, the counteracting of carbon dioxide emissions with an equivalent reduction of carbon dioxide in the atmosphere.[99] Carbon offsetting can reduce a companies overall carbon footprint by offering a carbon credit.

Supply chain emissions (scope 3) are on average 11.4 times higher than operational emissions,[100] more than double previous estimates, due to suppliers improving their emissions accounting. Therefore, there is an increasing focus on companies reducing their emissions coming from their suppliers as a way to reduce risks and capture opportunities.

A life cycle or supply chain carbon footprint study can provide useful data which will help the business to identify specific and critical areas for improvement. By calculating or predicting a process’ carbon footprint high emissions areas can be identified and steps can be taken to reduce in those areas. Collecting real data from suppliers emissions, setting a strategy focused on hot-spots and incentivizing suppliers are still barriers for companies. Nevertheless, solutions exist and the focus should be on improving year-on-year.[101]

CO₂ projection

To reach the goals defined in the Kyoto Protocol, with the least economical costs, the following flexible mechanisms were introduced for the mandatory market:

• Clean Development Mechanism (CDM)
• Joint Implementation (JI)
• Emissions trading

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.[102]

Other nations are scheduled to start participating in Emissions Trading Schemes within the next few years. These nations include China, India and the United States.[102]

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 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.[103]

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.[104] 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 Taskforce on Scaling Voluntary Carbon Markets (TSVCM), an initiative led by ex-governor of the Bank of England Mark Carney, aims to bring more outstanding quality and integrity to the voluntary carbon markets. The TSVCM during 2023 will seek to create a set of Core Carbon Principles (CCPs) and mechanisms to simplify companies access to high-integrity credits and provide banks and investors confidence for financing carbon projects and trading credits.

The size and activity of the voluntary carbon market are difficult to measure. The market size of voluntary carbon offsets market in 2021 is expected to hit $1 billion.[105]

There are many simple changes that can be made to the everyday lifestyle of a person that would reduce their GHG footprint. Reducing energy consumption within a household can include lowering one's dependence on air conditioning and heating, using LED lamps, choosing ENERGY STAR appliances, recycling, using cold water to wash clothes, avoiding a dryer, and eating less meat. Another adjustment would be reducing one's reliance on gas combustion-based motor vehicles, which produce many GHGs.[37] One could also lower their footprint by taking direct flights during air traveling. While making these changes won't bring down one's carbon footprint overnight, they will make a significant difference long term.[106]

Sustainable living refers to ways of living that are found to be sustainable within the Earth system or by which one purposely attempts to reduce an individual's or society's use of the Earth's natural resources, and one's personal resources. Studies found that systemic change for "decarbonization" of humanity's economic structures[107] or root-cause system changes above politics are required[108] for a substantial impact on global warming. Such changes may result in sustainable lifestyles, along with associated products, services and expenditures,[109] being structurally supported and becoming sufficiently prevalent and effective in terms of collective greenhouse gas emission reductions.

In order to decrease CO₂ emissions, the reliance of fossil fuels must be lowered. These fuels produce much CO₂ across all forms of their usage. Alternatively, renewable sources are cleaner for the environment.[13]

Household energy conservation measures include increasing insulation in construction, using fuel-efficient vehicles and ENERGY STAR appliances, and unplugging electrical items when not in use.

Reducing methane gas emissions can be accomplished in several ways. Capturing CH₄ emissions from coal mines and landfills, are two ways of reducing these emissions. Manure management and livestock operations is another possible solution. Motor vehicles use fossil fuels, which produces CO₂, but fossil fuels also produce CH₄ as a byproduct. Thus, better technology for these vehicles to avoid leakage as well as technologies that reduce their use would be beneficial.[13]

Nitrous oxide (N₂O) is often given off as a byproduct in various ways. Nylon production and fossil fuel usage are two ways that N₂O is given off as a byproduct. Thus, improving technology for nylon production and the gathering of fossil fuels would greatly reduce nitrous oxide emissions. Also, many fertilizers have a nitrogenous base. A decrease in usage of these fertilizers, or changing their components, are more ways to reduce N₂O emissions.[13]

Although fluorinated gases are not produced on a massive scale, they have the worst effect on the environment. A reduction of fluorinated gas emissions can be done in many ways. Many industries that emit these gases can capture or recycle them. These same industries can also invest in more advanced technology that will not produce these gases. A reduction of leakage within power grids and motor vehicles will also decrease the emissions of fluorinated gases. There are also many air conditioning systems that emit fluorinated gases, thus an update in technology would decrease these emissions.[13]