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Carbon footprint

A carbon footprint is a "measure of the impact human activities have on the environment in terms of the amount of greenhouse gases produced, measured in units of carbon dioxide". It is meant to be useful for individuals, nations and organizations to conceptualize their personal (or organizational) impact in contributing to global warming. A conceptual tool in response to carbon footprints are carbon offsets, or the mitigation of carbon emissions through the development of alternative projects such as solar or wind energy or reforestation. The carbon footprint is a subset of the ecological footprint, which includes all human demands on the biosphere.

Defining a carbon footprint

The carbon footprint is a measure of the exclusive global amount of carbon dioxide and other greenhouse gases emitted by a human activity or accumulated over the full life cycle of a product or service (see Wiedmann and Minx, 2008).

The life cycle concept of the carbon footprint means that it is all-encompassing and includes all possible causes that give rise to carbon emissions. In other words, all direct (on-site, internal) and indirect emissions (off-site, external, embodied, upstream, downstream) need to be taken into account.

Normally, a carbon footprint is expressed as a equivalent (usually in kilograms or tonnes), which accounts for the same global warming effects of different greenhouse gases (UK Parliamentary Office of Science and Technology POST, 2006). Carbon footprints can be calculated using a Life Cycle Assessment (LCA) method, or can be restricted to the immediately attributable emissions from energy use of fossil fuels. In both cases however, as the term usually indicates the amount of emissions generated through the actions of people, what is important is not only the total amount of energy use, but also how the energy was produced in the first place (e.g. from fossil fuels or renewable resources).

An alternative definition of the carbon footprint is the total amount of carbon dioxide attributable to the actions of an individual (which includes emissions through their energy use, but other unforeseen emissions as well) over a period of one year. This definition underlies the personal carbon calculators. The term owes its origins to the idea that a footprint is what has been left behind as a result of the individual's activities. Carbon footprints can either consider only direct emissions (typically from energy used in the home and in transport, including travel by cars, airplanes, rail and other public transport), or can also include indirect emissions (including CO2 emissions as a result of goods and services consumed). Bottom-up calculations sum attributable CO2 emissions from individual actions; top-down calculations take total emissions from a country (or other low-level entity) and divide these emissions among the residents (or other participants in that entity).

Reducing a carbon footprint

The carbon footprint can be efficiently and effectively reduced by using a Carbon Diet or applying the following steps:

Life Cycle Assessment (LCA) to accurately determine the current carbon footprint
Identification of hot-spots in terms of energy consumption and associated -emissions
Where possible, changing to another electricity company to switch to buying electricity from renewable sources (from wind turbines, solar panels or hydroelectrical plants -or- from nuclear power plants
Optimisation of energy efficiency and, thus, reduction of -emissions and reduction of other GHG emissions contributed from production processes
Identification of solutions to neutralise the emissions that cannot be eliminated by energy saving measures. This last step includes carbon offsetting; investment in projects that aim at the reducing emissions, for instance tree planting.

Kyoto Protocol, carbon offsetting, and certificates

Carbon dioxide emissions to air (and the emissions of other GHG's) are almost exclusively associated with the conversion of energy carriers like natural gas, crude oil, etc.

The Kyoto Protocol defines legally binding targets and timetables for cutting the greenhouse-gas 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:

The mandatory market

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

The CDM and JI mechanisms specify requirements for projects which create a supply of emission reduction instruments, whilst 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 Emissions 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 CO2 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 Emission Trading Scheme (EU ETS).

The voluntary market

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.

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.

Criticism of the term

Criticism of the concept of a carbon footprint is generally based on disagreement with one or more of the following assumptions usually underlying the calculation of a carbon footprint:

That carbon emissions are a significant cause of global warming.
That human activity is a significant cause of these emissions.
That it is possible to attribute all or most emissions to particular individuals.
That individual initiative is necessary because market forces or legislation will not be powerful and timely enough.
That each individual should therefore calculate and attempt to reduce his share of carbon emissions.
Sometimes, that each person should be given as a target an equal share of emissions, or some other share.

Criticisms derived from rejection of these assumptions may therefore include:

That other causes, such as methane emissions, are more important.
That human activity is not as significant a cause as natural processes such as vulcanism or solar radiation.
That many emissions cannot reasonably be attributed to any individual. E.g. should emissions from commuting be attributed to commuters or consumers of what they produce?
That market forces or political action will correct human activity in sufficient time.
That population growth invalidates the calculations,
That one cannot limit everyone to equal emissions, for example those in urbanized societies may be unable to avoid some emissions, while less-developed countries may not have the technology to mitigate others.

Another criticism relates to ambiguity of the term carbon footprint, which can either also include greenhouse gasses other than carbon dioxide, or can alternatively assess only carbon dioxide itself. For a range of consumables, the non-CO₂ greenhouse gasses like methane, nitrous oxide, or CFCs (in CO₂-equivalents) make up a non-negligible part of the global warming impact. An appropriate term according to the more encompassing definition could be climate footprint.

Carbon Labelling

A carbon label, which shows the life cycle carbon emissions or carbon footprint embodied in a product in bringing it to the shelf, was introduced in the UK in March 2007 by the Carbon Trust. The label is closely linked to a collaboration between The Carbon Trust and The British Standards Institute. The label is intended to comply with a new British Standard, PAS2050, (

) and is being actively piloted by The Carbon Trust and various industrial partners (

).
Examples of products which already feature this carbon footprint label include Walkers Crisps, a smoothie product from Innocent Drinks, and a shampoo product produced by Boots Group.

Age-related carbon footprint

A number of studies have calculated the carbon footprint of organisations and nations. One UK (2007) study examined age-related carbon emissions based on expenditure and consumption. The study found that on average people aged 50-65 years have a higher carbon footprint than any other age group. Individuals aged 50-55 years old have a carbon footprint of approximately 13.5 tonnes/capita per year compared to the UK average of 12 tonnes.

Carbon footprint by energy type

The following table compares the carbon footprint of various forms of energy generation, from a study of full life cycle emissions by the Swedish utility Vattenfall of Nuclear, Hydro, Coal, Gas, Solar Cell, Peat and Wind generation technology (and ), from the US EPA figures and from various other studies.

Carbon footprint by generation technology
Technology	g/kWh Vattenfall (Sweden)	g/kWh EPA	g/kWh other
Gas (thermal)	1170
Coal	980	950
Oil		900
Natural gas		600
Gas (combined cycle)	450
Solar photovoltaic	50
Wind	5.5
Nuclear	6
Nuclear			3.10 Forsmark Nuclear Power Plant
Nuclear			5.05 Torness Nuclear Power Station
Hydroelectric	3	11

The Vattenfall study thus concluded that hydroelectric and nuclear power produced the least CO₂ per kilowatt-hour of any of their electricity sources. These figures do not allow for emissions due to accidents or terrorism.

Holidays as extra environmental burden

An analysis of the carbon footprint of Christmas in the UK shows that consumption of items such as food, travel, lighting and gifts at Christmas produces as much as 650 kg of carbon dioxide (CO2) emissions per person - equal to 5.5% of the UK annual carbon footprint. Over Christmas, the average person could produce as much as:

26 kg of CO2 from Christmas food
96 kg of CO2 from Christmas Car travel
218 kg of CO2 from extravagant lighting displays
310 kg of CO2 on Christmas Shopping

Christmas carbon emissions could be reduced by up to 60 per cent to about 250 kg.

Notes

References

Parliamentary Office of Science and Technology POST (2006). Carbon footprint of electricity generation. 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. https://www.novapublishers.com/catalog/product_info.php?products_id=5999, also available as ISA-UK Research Report 07/01 from http://www.isa-research.co.uk/reports.html.
World Energy Council Report (2004). Comparison of energy systems using life cycle assessment.
Energetics (2007). The reality of carbon neutrality.