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The UN defines mitigation in the context of climate change, as a human intervention to reduce the sources or enhance the sinks of greenhouse gases. Examples include using fossil fuels more efficiently for industrial processes or electricity generation, switching to renewable energy (solar energy or wind power), improving the insulation of buildings, and expanding forests and other "sinks" to remove greater amounts of carbon dioxide from the atmosphere. Some assert that also non-renewable sources of energy such as nuclear power should be seen as a way of reducing carbon emissions. The International Atomic Energy Agency advocates this approach. However, even while reporting to the UN, the IAEA is independent from it and in no way affiliated with the UNFCCC.
Scientific consensus on global warming, together with the precautionary principle and the fear of abrupt climate change is leading to increased effort to develop new technologies and sciences and carefully manage others in an attempt to mitigate global warming. Most means of mitigation appear effective only for preventing further warming, not at reversing existing warming. The Stern Review identifies several ways of mitigating climate change. These include reducing demand for emissions-intensive goods and services, increasing efficiency gains, increasing use and development of low-carbon technologies, and reducing fossil fuel emissions.
The energy policy of the European Union has set a target of limiting the global temperature rise to 2 °C (3.6 °F) compared to preindustrial levels, of which 0.8 °C has already taken place and another 0.5–0.7 °C is already committed. The 2 °C rise is typically associated in climate models with a carbon dioxide equivalent concentration of 400–500 ppm by volume; the current (April 2011) level of carbon dioxide alone is 393 ppm by volume, and rising at 1-3 ppm annually. Hence, to avoid a very likely breach of the 2 °C target, CO2 levels would have to be stabilised very soon; this is generally regarded as unlikely, based on current programs in place to date. The importance of change is illustrated by the fact that world economic energy efficiency is presently improving at only half the rate of world economic growth.
 Greenhouse gas concentrations and stabilizationUnited Nations Framework Convention on Climate Change (UNFCCC) has the ultimate objective of preventing "dangerous" anthropogenic (i.e., human) interference of the climate system. As is stated in Article 2 of the Convention, this requires that greenhouse gas (GHG) concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can proceed in a sustainable fashion.
A distinction needs to be made between stabilizing GHG emissions and GHG concentrations.  The two are not the same. The most important GHG emitted by human activities is carbon dioxide (chemical formula: CO2). Stabilizing emissions of CO2 at current levels would not lead to a stabilization in the atmospheric concentration of CO2. In fact, stabilizing emissions at current levels would result in the atmospheric concentration of CO2 continuing to rise over the 21st century and beyond (see the graphs opposite).
The reason for this is that human activities are adding CO2 to the atmosphere far faster than natural processes can remove it (see carbon dioxide in Earth's atmosphere for a more complete explanation). This is analogous to a flow of water into a bathtub. So long as the tap runs water (analogous to the emission of carbon dioxide) into the tub faster than water escapes through the plughole (the natural removal of carbon dioxide from the atmosphere), then the level of water in the tub (analogous to the concentration of carbon dioxide in the atmosphere) will continue to rise.
Stabilizing the atmospheric concentration of the other greenhouse gases humans emit also depends on how fast their emissions are added to the atmosphere, and how fast the GHGs are removed. Stabilization for these gases is described in the later section on non-CO2 GHGs.
 Methods and meansenergy conservation methods include increasing the fuel efficiency of vehicles (often through hybrid, plug-in hybrid, and electric cars and improving conventional automobiles), individual-lifestyle changes and changing business practices. Newly developed technologies and currently available technologies including renewable energy (such as solar power, tidal and ocean energy, geothermal power, and wind power) and more controversially nuclear power and the use of carbon sinks, carbon credits, and taxation are aimed more precisely at countering continued greenhouse gas emissions. The ever-increasing global population and the planned growth of national GDPs based on current technologies are counter-productive to most of these proposals.
 Alternative energy sources
 Renewable energyClimate change concerns and the need to reduce carbon emissions are driving increasing growth in the renewable energy industries. Some 85 countries now have targets for their own renewable energy futures, and have enacted wide-ranging public policies to promote renewables. Low-carbon renewable energy replaces conventional fossil fuels in three main areas: power generation, hot water/ space heating, and transport fuels. Scientists have advanced a plan to power 100% of the world's energy with wind, hydroelectric, and solar power by the year 2030. The authors estimate the cost at USD 100 trillion, and wind turbines would occupy one percent of the earth's surface area.
In terms of power generation, renewable energy currently provides 18 percent of total electricity generation worldwide and this percentage is growing each year. Renewable power generators are spread across many countries, and wind power alone already provides a significant share of electricity in some areas: for example, 14 percent in the U.S. state of Iowa, 40 percent in the northern German state of Schleswig-Holstein, and 20 percent in Denmark. Some countries get most of their power from renewables, including Iceland (100 percent), Brazil (85 percent), Austria (62 percent), New Zealand (65 percent), and Sweden (54 percent).
Solar water heating makes an important and growing contribution in many countries, most notably in China, which now has 70 percent of the global total (180 GWth). Worldwide, total installed solar water heating systems meet a portion of the water heating needs of over 70 million households. The use of biomass for heating continues to grow as well. In Sweden, national use of biomass energy has surpassed that of oil. Direct geothermal heating is also growing rapidly.
Renewable biofuels for transportation, such as ethanol fuel and biodiesel, have contributed to a significant decline in oil consumption in the United States since 2006. The 93 billion liters of biofuels produced worldwide in 2009 displaced the equivalent of an estimated 68 billion liters of gasoline, equal to about 5 percent of world gasoline production.
 Nuclear powernuclear renaissance has been used to refer to a possible nuclear power industry revival, driven by rising fossil fuel prices and new concerns about meeting greenhouse gas emission limits. At the same time, various barriers to a nuclear renaissance have been identified. These barriers include unfavourable economics compared to other sources of energy and slowness in addressing climate change.
New reactors under construction in Finland and France, which were meant to lead a nuclear renaissance, have been delayed and are running over-budget. China has 20 new reactors under construction, and there are also a considerable number of new reactors being built in South Korea, India, and Russia. At least 100 older and smaller reactors will "most probably be closed over the next 10-15 years".
Nuclear power brings with it important waste disposal, safety, and security risks which are unique among low-carbon energy sources. Public attitudes towards nuclear power remain ambiguous in many developed countries, with significant anti-nuclear opposition even when majority opinion is in favour. However some Nuclear reactor 'waste' byproducts are of high value and used in many radiopharmaceuticals, for example, Yttrium-90 and Technetium 99m have a wide and valuable use in Oncology and diagnostic medicine.
 Carbon intensity of fossil fuelsMost mitigation proposals imply — rather than directly state — an eventual reduction in global fossil fuel production. Also proposed are direct quotas on global fossil fuel production.
 Fuel switchingNatural gas (predominantly methane) combustion produces less greenhouses gases per energy unit gained than oil which in turn produces less than coal, principally because coal has a larger ratio of carbon to hydrogen. The combustion of natural gas emits almost 30 percent less carbon dioxide than oil, and just under 45 percent less carbon dioxide than coal. In addition, there are also other environmental benefits.
A study performed by the Environmental Protection Agency (EPA) and the Gas Research Institute (GRI) in 1997 sought to discover whether the reduction in carbon dioxide emissions from increased natural gas (predominantly methane) use would be offset by a possible increased level of methane emissions from sources such as leaks and emissions. The study concluded that the reduction in emissions from increased natural gas use strongly outweighs the detrimental effects of increased methane emissions. Thus the increased use of natural gas in the place of other, dirtier fossil fuels can serve to lessen the emission of greenhouse gases in the United States.
 Carbon capture and storagecarbon dioxide (CO2) from large point sources such as power plants and subsequently storing it away safely instead of releasing it into the atmosphere. The Intergovernmental Panel on Climate Change says CCS could contribute between 10% and 55% of the cumulative worldwide carbon-mitigation effort over the next 90 years. The International Energy Agency says CCS is "the most important single new technology for CO2 savings" in power generation and industry. Though it requires up to 40% more energy to run a CCS coal power plant than a regular coal plant, CCS could potentially capture about 90% of all the carbon emitted by the plant. Norway, which first began storing CO2, has cut its emissions by almost a million tons a year, or about 3% of the country's 1990 levels. As of late 2011, the total CO2 storage capacity of all 14 projects in operation or under construction is over 33 million tonnes a year. This is broadly equivalent to preventing the emissions from more than six million cars from entering the atmosphere each year.
 Energy efficiency and conservationinsulating a home allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature. Installing fluorescent lights or natural skylights reduces the amount of energy required to attain the same level of illumination compared to using traditional incandescent light bulbs. Compact fluorescent lights use two-thirds less energy and may last 6 to 10 times longer than incandescent lights.
Energy efficiency has proved to be a cost-effective strategy for building economies without necessarily growing energy consumption. For example, the state of California began implementing energy-efficiency measures in the mid-1970s, including building code and appliance standards with strict efficiency requirements. During the following years, California's energy consumption has remained approximately flat on a per capita basis while national U.S. consumption doubled. As part of its strategy, California implemented a "loading order" for new energy resources that puts energy efficiency first, renewable electricity supplies second, and new fossil-fired power plants last.
Energy conservation is broader than energy efficiency in that it encompasses using less energy to achieve a lesser energy service, for example through behavioural change, as well as encompassing energy efficiency. Examples of conservation without efficiency improvements would be heating a room less in winter, driving less, or working in a less brightly lit room. As with other definitions, the boundary between efficient energy use and energy conservation can be fuzzy, but both are important in environmental and economic terms. This is especially the case when actions are directed at the saving of fossil fuels.
Reducing energy use is seen as a key solution to the problem of reducing greenhouse gas emissions. According to the International Energy Agency, improved energy efficiency in buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third, and help control global emissions of greenhouse gases.
 Transportenergy efficient technologies, such as plug-in hybrid electric vehicles, and development of new technologies, such as hydrogen cars, may reduce the consumption of petroleum and emissions of carbon dioxide. A shift from air transport and truck transport to electric rail transport would reduce emissions significantly.
Increased use of biofuels (such as ethanol fuel and biodiesel that can be used in today's diesel and gasoline engines) could also reduce emissions if produced environmentally efficiently, especially in conjunction with regular hybrids and plug-in hybrids. For electric vehicles, the reduction of carbon emissions will improve further if the way the required electricity is generated is low-carbon (from renewable energy sources).
Effective urban planning to reduce sprawl would decrease Vehicle Miles Travelled (VMT), lowering emissions from transportation. Increased use of public transport can also reduce greenhouse gas emissions per passenger kilometer.
 Urban planningUrban planning also has an effect on energy use. Between 1982 and 1997, the amount of land consumed for urban development in the United States increased by 47 percent while the nation's population grew by only 17 percent. Inefficient land use development practices have increased infrastructure costs as well as the amount of energy needed for transportation, community services, and buildings.
At the same time, a growing number of citizens and government officials have begun advocating a smarter approach to land use planning. These smart growth practices include compact community development, multiple transportation choices, mixed land uses, and practices to conserve green space. These programs offer environmental, economic, and quality-of-life benefits; and they also serve to reduce energy usage and greenhouse gas emissions.
Approaches such as New Urbanism and Transit-oriented development seek to reduce distances travelled, especially by private vehicles, encourage public transit and make walking and cycling more attractive options. This is achieved through medium-density, mixed-use planning and the concentration of housing within walking distance of town centers and transport nodes.
Smarter growth land use policies have both a direct and indirect effect on energy consuming behavior. For example, transportation energy usage, the number one user of petroleum fuels, could be significantly reduced through more compact and mixed use land development patterns, which in turn could be served by a greater variety of non-automotive based transportation choices.
 Building designEmissions from housing are substantial, and government-supported energy efficiency programmes can make a difference.
For institutions of higher learning in the United States, greenhouse gas emissions depend primarily on total area of buildings and secondarily on climate. If climate is not taken into account, annual greenhouse gas emissions due to energy consumed on campuses plus purchased electricity can be estimated with the formula, E=aSb, where a =0.001621 metric tonnes of CO2 equivalent/square foot or 0.0241 metric tonnes of CO2 equivalent/square meter and b = 1.1354.
New buildings can be constructed using passive solar building design, low-energy building, or zero-energy building techniques, using renewable heat sources. Existing buildings can be made more efficient through the use of insulation, high-efficiency appliances (particularly hot water heaters and furnaces), double- or triple-glazed gas-filled windows, external window shades, and building orientation and siting. Renewable heat sources such as shallow geothermal and passive solar energy reduce the amount of greenhouse gasses emitted. In addition to designing buildings which are more energy efficient to heat, it is possible to design buildings that are more energy efficient to cool by using lighter-coloured, more reflective materials in the development of urban areas (e.g. by painting roofs white) and planting trees. This saves energy because it cools buildings and reduces the urban heat island effect thus reducing the use of air conditioning.
 Eliminating waste methaneMethane is a significantly more powerful greenhouse gas than carbon dioxide. Burning one molecule of methane generates one molecule of carbon dioxide. Accordingly, burning methane which would otherwise be released into the atmosphere (such as at oil wells, landfills, coal mines, waste treatment plants, etc.) provides a net greenhouse gas emissions benefit. However, reducing the amount of waste methane produced in the first place has an even greater beneficial impact, as might other approaches to productive use of otherwise-wasted methane.
In terms of prevention, vaccines are in the works in Australia to reduce significant global warming contributions from methane released by livestock via flatulence and eructation.
 Sinks and negative emissionsA carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period, such as a growing forest. A negative carbon dioxide emission on the other hand is a permanent removal of carbon dioxide out of the atmosphere, such as directly capturing carbon dioxide in the atmosphere and storing it in geologic formations underground.
 Reforestation and avoided deforestationAlmost 20% (8 GtCO2/year) of total greenhouse-gas emissions were from deforestation in 2007. The Stern Review found that, based on the opportunity costs of the landuse that would no longer be available for agriculture if deforestation were avoided, emission savings from avoided deforestation could potentially reduce CO2 emissions for under $5/tCO2, possiblly as little as $1/tCO2. Afforestation and reforestation could save at least another 1GtCO2/year, at an estimated cost of $5/tCO2 to $15/tCO2. The Review determined these figures by assessing 8 countries responsible for 70% of global deforestation emissions.
Pristine temperate forest has been shown to store three times more carbon than IPCC estimates took into account, and 60% more carbon than plantation forest. Preventing these forests from being logged would have significant effects.
Further significant savings from other non-energy-related-emissions could be gained through cuts to agricultural emissions, fugitive emissions, waste emissions, and emissions from various industrial processes. Using evidence from Mozambique, a typical low income country where agriculture is the dominant provider of income for most citizens, researchers from the Overseas Development Institute found a positive correlation between increased production intensification and reduced land conversion, and crop returns, economic growth and food security.
 Negative carbon dioxide emissionsCreating negative carbon dioxide emissions literally removes carbon from the atmosphere. Examples are direct air capture, biochar, bio-energy with carbon capture and storage and enhanced weathering technologies. These processes are sometimes considered as variations of sinks or mitigation, and sometimes as geoengineering.
In combination with other mitigation measures, sinks in combination with negative carbon emissions are considered crucial for meeting the 350 ppm target, and even the less conservative 450 ppm target.
 GeoengineeringGeoengineering is seen by some[who?] as an alternative to mitigation and adaptation, but by others[who?] as an entirely separate response to climate change. In a literature assessment, Barker et al. (2007) described geoengineering as a type of mitigation policy. IPCC (2007) concluded that geoengineering options, such as ocean fertilization to remove CO2 from the atmosphere, remained largely unproven. It was judged that reliable cost estimates for geoengineering had not yet been published.
Chapter 28 of the National Academy of Sciences report Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base (1992) defined geoengineering as "options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry." They evaluated a range of options to try to give preliminary answers to two questions: can these options work and could they be carried out with a reasonable cost. They also sought to encourage discussion of a third question — what adverse side effects might there be. The following types of option were examined: reforestation, increasing ocean absorption of carbon dioxide (carbon sequestration) and screening out some sunlight. NAS also argued "Engineered countermeasures need to be evaluated but should not be implemented without broad understanding of the direct effects and the potential side effects, the ethical issues, and the risks.". In July 2011 a report by the United States Government Accountability Office on geoengineering found that "[c]limate engineering technologies do not now offer a viable response to global climate change."
 Carbon dioxide removalCarbon dioxide removal has been proposed as a method of reducing the amount of radiative forcing. A variety of means of artificially capturing and storing carbon, as well as of enhancing natural sequestration processes, are being explored. The main natural process is photosynthesis by plants and single-celled organisms (see biosequestration). Artificial processes vary, and concerns have been expressed about the long-term effects of some of these processes.
 Carbon air captureIt is notable that the availability of cheap energy and appropriate sites for geological storage of carbon may make carbon dioxide air capture viable commercially. It is, however, generally expected that carbon dioxide air capture may be uneconomic when compared to carbon capture and storage from major sources — in particular, fossil fuel powered power stations, refineries, etc. In such cases, costs of energy produced will grow significantly. However, captured CO2 can be used to force more crude oil out of oil fields, as Statoil and Shell have made plans to do. CO2 can also be used in commercial greenhouses, giving an opportunity to kick-start the technology. Some attempts have been made to use algae to capture smokestack emissions, notably the GreenFuel Technologies Corporation, who have now shut down operations.
 Solar radiation managementThe main purpose of solar radiation management seek to reflect sunlight and thus reduce global warming.
 Sulfate aerosolsThe ability of stratospheric sulfate aerosols to create a global dimming effect has made them a possible candidate for use in geoengineering projects.
 Pacala and Socolow: 15 programsPacala and Socolow of Princeton  have proposed a program to reduce CO2 emissions by 1 billion metric tons per year − or 25 billion tons over the 50-year period. The proposed 15 different programs, any seven of which could achieve the goal, are:
- more efficient vehicles − increase fuel economy from 30 to 60 mpg (7.8 to 3.9 L/100 km) for 2 billion vehicles,
- reduce use of vehicles − improve urban design to reduce miles driven from 10,000 to 5,000 miles (16,000 to 8,000 km) per year for 2 billion vehicles,
- efficient buildings − reduce energy consumption by 25%,
- improve efficiency of coal plants from today's 40% to 60%,
- replace 1,400 GW (gigawatt) of coal power plants with natural gas,
- capture and store carbon emitted from 800 GW of new coal plants,
- capture and reuse hydrogen created by No. 6 above,
- capture and store carbon from coal to syn fuels conversion at 30 million barrels per day (4,800,000 m3/d),
- displace 700 GW of coal power with nuclear,
- add 2 million 1 MW wind turbines (50 times current capacity),
- displace 700 GW of coal with 2,000 GW (peak) solar power (700 times current capacity),
- produce hydrogen fuel from 4 million 1 MW wind turbines,
- use biomass to make fuel to displace oil (100 times current capacity),
- stop de-forestation and re-establish 300 million hectares of new tree plantations,
- conservation tillage − apply to all crop land (10 times current usage).
 Societal controlsAnother method being examined is to make carbon a new currency by introducing tradeable "Personal Carbon Credits". The idea being it will encourage and motivate individuals to reduce their 'carbon footprint' by the way they live. Each citizen will receive a free annual quota of carbon that they can use to travel, buy food, and go about their business. It has been suggested that by using this concept it could actually solve two problems; pollution and poverty, old age pensioners will actually be better off because they fly less often, so they can cash in their quota at the end of the year to pay heating bills, etc.
 Populationpopulation control as a means for mitigating global warming. Proposed measures include improving access to family planning and reproductive health care and information, reducing natalistic politics, public education about the consequences of continued population growth, and improving access of women to education and economic opportunities.
Population control efforts are impeded by there being somewhat of a taboo in some countries against considering any such efforts. Also, various religions discourage or prohibit some or all forms of birth control.
Population size has a different per capita effect on global warming in different countries, since the per capita production of anthropogenic greenhouse gases varies greatly by country.
 Non-CO2 greenhouse gasesCO2 is not the only GHG relevant to mitigation, and governments have acted to regulate the emissions of other GHGs emitted by human activities (anthropogenic GHGs). The emissions caps agreed to by most developed countries under the Kyoto Protocol regulate the emissions of almost all the anthropogenic GHGs. These gases are CO2, methane (chemical formula: CH4), nitrous oxide (N2O), the hydrofluorocarbons (abbreviated HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6).
Stabilizing the atmospheric concentrations of the different anthropogenic GHGs requires an understanding of their different physical properties. Stabilization depends both on how quickly GHGs are added to the atmosphere and how fast they are removed. The rate of removal is measured by the atmospheric lifetime of the GHG in question (see the main GHG article for a list). Here, the lifetime is defined as the time required for a given perturbation of the GHG in the atmosphere to be reduced to 37% of its initial amount. Methane has a relatively short atmospheric lifetime of about 12 years, while N2O's lifetime is about 110 years. For methane, a reduction of about 30% below current emission levels would lead to a stabilization in its atmospheric concentration, while for N2O, an emissions reduction of more than 50% would be required.
Another physical property of the anthropogenic GHGs relevant to mitigation is the different abilities of the gases to trap heat (in the form of infrared radiation). Some gases are more effective at trapping heat than others, e.g., SF6 is 22,200 times more effective a GHG than CO2 on a per-kilogram basis. A measure for this physical property is the global warming potential (GWP), and is used in the Kyoto Protocol.
Although not designed for this purpose, the Montreal Protocol has probably benefitted climate change mitigation efforts. The Montreal Protocol is an international treaty that has successfully reduced emissions of ozone-depleting substances (e.g., CFCs), which are also greenhouse gases.
 Costs and benefits
 CostsThe Stern Review proposes stabilising the concentration of greenhouse-gas emissions in the atmosphere at a maximum of 550ppm CO2e by 2050. The Review estimates that this would mean cutting total greenhouse-gas emissions to three quarters of 2007 levels. The Review further estimates that the cost of these cuts would be in the range −1.0 to +3.5% of World GDP, (i.e. GWP), with an average estimate of approximately 1%. Stern has since revised his estimate to 2% of GWP. For comparison, the Gross World Product (GWP) at PPP was estimated at $74.5 trillion in 2010, thus 2% is approximately $1.5 trillion. The Review emphasises that these costs are contingent on steady reductions in the cost of low-carbon technologies. Mitigation costs will also vary according to how and when emissions are cut: early, well-planned action will minimise the costs.
One way of estimating the cost of reducing emissions is by considering the likely costs of potential technological and output changes. Policy makers can compare the marginal abatement costs of different methods to assess the cost and amount of possible abatement over time. The marginal abatement costs of the various measures will differ by country, by sector, and over time.
 Benefits With high confidence, they suggested that up to the year 2050, an effort to cap greenhouse gas (GHG) emissions at 550 ppm would benefit developing countries significantly. This was judged to be especially the case when combined with enhanced adaptation. By 2100, however, it was still judged likely that there would be significant climate change impacts. This was judged to be the case even with aggressive mitigation and significantly enhanced adaptive capacity.
 SharingOne of the aspects of mitigation is how to share the costs and benefits of mitigation policies. There is no scientific consensus over how to share these costs and benefits (Toth et al., 2001). In terms of the politics of mitigation, the UNFCCC's ultimate objective is to stabilize concentrations of GHG in the atmosphere at a level that would prevent "dangerous" climate change (Rogner et al., 2007). There is, however, no widespread agreement on how to define "dangerous" climate change.
GHG emissions are an important correlate of wealth, at least at present (Banuri et al., 1996, pp. 91–92). Wealth, as measured by per capita income (i.e., income per head of population), varies widely between different countries. Activities of the poor that involve emissions of GHGs are often associated with basic needs, such as heating to stay tolerably warm. In richer countries, emissions tend to be associated with things like cars, central heating, etc. The impacts of cutting emissions could therefore have different impacts on human welfare according wealth.
 Distributing emissions abatement costsThere have been different proposals on how to allocate responsibility for cutting emissions (Banuri et al., 1996, pp. 103–105):
- Egalitarianism: this system interprets the problem as one where each person has equal rights to a global resource, i.e., polluting the atmosphere.
- Basic needs and Rawlsian criteria: this system would have emissions allocated according to basic needs, as defined according to a minimum level of consumption. Consumption above basic needs would require countries to buy more emission rights. This can be related to Rawlsian philosophy. From this viewpoint, developing countries would need to be at least as well off under an emissions control regime as they would be outside the regime.
- Proportionality and polluter-pays principle: Proportionality reflects the ancient Aristotelian principle that people should receive in proportion to what they put in, and pay in proportion to the damages they cause. This has a potential relationship with the "polluter-pays principle", which can be interpreted in a number of ways:
- Historical responsibilities: this asserts that allocation of emission rights should be based on patterns of past emissions. Two-thirds of the stock of GHGs in the atmosphere at present is due to the past actions of developed countries (Goldemberg et al., 1996, p. 29).
- Comparable burdens and ability to pay: with this approach, countries would reduce emissions based on comparable burdens and their ability to take on the costs of reduction. Ways to assess burdens include monetary costs per head of population, as well as other, more complex measures, like the UNDP's Human Development Index.
- Willingness to pay: with this approach, countries take on emission reductions based on their ability to pay along with how much they benefit from reducing their emissions.
 Specific proposals
- Ad hoc: Lashof (1992) and Cline (1992) (referred to by Banuri et al., 1996, p. 106), for example, suggested that allocations based partly on GNP could be a way of sharing the burdens of emission reductions. This is because GNP and economic activity are partially tied to carbon emissions.
- Equal per capita entitlements: this is the most widely cited method of distributing abatement costs, and is derived from egalitarianism (Banuri et al., 1996, pp. 106–107). This approach can be divided into two categories. In the first category, emissions are allocated according to national population. In the second category, emissions are allocated in a way that attempts to account for historical (cumulative) emissions.
- Status quo: with this approach, historical emissions are ignored, and current emission levels are taken as a status quo right to emit (Banuri et al., 1996, p. 107). An analogy for this approach can be made with fisheries, which is a common, limited resource. The analogy would be with the atmosphere, which can be viewed as an exhaustible natural resource (Goldemberg et al., 1996, p. 27). In international law, one state recognized the long-established use of another state's use of the fisheries resource. It was also recognized by the state that part of the other state's economy was dependent on that resource.
 Governmental and intergovernmental actionMany countries, both developing and developed, are aiming to use cleaner technologies (World Bank, 2010, p. 192). Use of these technologies aids mitigation and could result in substantial reductions in CO2 emissions. Policies include targets for emissions reductions, increased use of renewable energy, and increased energy efficiency. It is often argued that the results of climate change are more damaging in poor nations, where infrastructures are weak and few social services exist. The Commitment to Development Index is one attempt to analyze rich country policies taken to reduce their disproportionate use of the global commons. Countries do well if their greenhouse gas emissions are falling, if their gas taxes are high, if they do not subsidize the fishing industry, if they have a low fossil fuel rate per capita, and if they control imports of illegally cut tropical timber.
 Kyoto ProtocolThe main current international agreement on combating climate change is the Kyoto Protocol, which came into force on 16 February 2005. The Kyoto Protocol is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). Countries that have ratified this protocol have committed to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases.
 Successor to the Kyoto ProtocolSee Post–Kyoto Protocol negotiations on greenhouse gas emissions
 Alternatives to the Kyoto Protocol and successor
 Emissions taxAn emissions tax on greenhouse gas emissions requires individual emitters to pay a fee, charge or tax for every tonne of greenhouse gas released into the atmosphere. Most environmentally related taxes with implications for greenhouse gas emissions in OECD countries are levied on energy products and motor vehicles, rather than on CO2 emissions directly.
Emission taxes can be both cost effective and environmentally effective. Difficulties with emission taxes include their potential unpopularity, and the fact that they cannot guarantee a particular level of emissions reduction. Emissions or energy taxes also often fall disproportionately on lower income classes. In developing countries, institutions may be insufficiently developed for the collection of emissions fees from a wide variety of sources.
 Making the emitting of CO2 illegalOne of the biggest problem seems to revolve around the fact that the countries decide on a average "allowed emission amount" per capita (which many believe should actually actually not exist at all). Many people, including prominent ones such as Ken Caldeira believe that a acceptable GHG emission per capita would be 0 tonnes (or -alternatively, very close to that, say 0,001 tonnes or so  The current protocol however has huge allowed amounts of emissions (between 3 and 10 tonnes) per capita and is as such extremely negligent.
Although 0,001 tonnes per capita would be acceptable, it can be expected that most people won't accept this and a better approach might be to just get rid entirely of this emission reduction-positive approach with the successor and replace it with a emitted GHG-negative approach. Some prominent people like Ken Caldeira have opted for this approach aswell. Obviously, it should be possible to still emit CO2, yet when emitting more than 0 tonnes of GHG, a sort of "fine" needs to be payed (carbon credits). This is much similar as what it is now, except for the method we employ.
 Encouraging use changes
 SubsidiesA program of subsidization balanced against expected flood costs could pay for conversion to 100% renewable power by 2030. The proponents of such a plan expect the cost to generate and transmit power in 2020 will be less than 4 cents per kilowatt hour (in 2007 dollars) for wind, about 4 cents for wave and hydroelectric, from 4 to 7 cents for geothermal, and 8 cents per kwh for solar, fossil, and nuclear power.
 Carbon emissions tradingWith the creation of a market for trading carbon dioxide emissions within the Kyoto Protocol, it is likely that London financial markets will be the centre for this potentially highly lucrative business; the New York and Chicago stock markets may have a lower trade volume than expected as long as the US maintains its rejection of the Kyoto.
However, emissions trading may delay the phase-out of fossil fuels.
The European Union Emission Trading Scheme (EU ETS) is the largest multi-national, greenhouse gas emissions trading scheme in the world. It commenced operation on 1 January 2005, and all 25 member states of the European Union participate in the scheme which has created a new market in carbon dioxide allowances estimated at 35 billion Euros (US$43 billion) per year. The Chicago Climate Exchange was the first (voluntary) emissions market, and is soon to be followed by Asia's first market (Asia Carbon Exchange). A total of 107 million metric tonnes of carbon dioxide equivalent have been exchanged through projects in 2004, a 38% increase relative to 2003 (78 Mt CO2e).
Twenty three multinational corporations have come together in the G8 Climate Change Roundtable, a business group formed at the January 2005 World Economic Forum. The group includes Ford, Toyota, British Airways and BP. On 9 June 2005 the Group published a statement stating that there was a need to act on climate change and claiming that market-based solutions can help. It called on governments to establish "clear, transparent, and consistent price signals" through "creation of a long-term policy framework" that would include all major producers of greenhouse gases.
The Regional Greenhouse Gas Initiative is a proposed carbon trading scheme being created by nine North-eastern and Mid-Atlantic American states; Connecticut, Delaware, Maine, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island and Vermont. The scheme was due to be developed by April 2005 but has not yet been completed.
 ImplementationImplementation puts into effect climate change mitigation strategies and targets. These can be targets set by international bodies or voluntary action by individuals or institutions. This is the most important, expensive and least appealing aspect of environmental governance.
 FundingImplementation requires funding sources but is often beset by disputes over who should provide funds and under what conditions. A lack of funding can be a barrier to successful strategies as there are no formal arrangements to finance climate change development and implementation. Funding is often provided by nations, groups of nations and increasingly NGO and private sources. These funds are often channelled through the Global Environmental Facility (GEF). This is an environmental funding mechanism in the World Bank which is designed to deal with global environmental issues. The GEF was originally designed to tackle four main areas: biological diversity, climate change, international waters and ozone layer depletion, to which land degradation and persistent organic pollutant were added. The GEF funds projects that are agreed to achieve global environmental benefits that are endorsed by governments and screened by one of the GEF’s implementing agencies.
 ProblemsThere are numerous issues which result in a current perceived lack of implementation. It has been suggested that the main barriers to implementation are, Uncertainty, Fragmentation, Institutional void, Short time horizon of policies and politicians and Missing motives and willingness to start adapting. The relationships between many climatic processes can cause large levels of uncertainty as they are not fully understood and can be a barrier to implementation. When information on climate change is held between the large numbers of actors involved it can be highly dispersed, context specific or difficult to access causing fragmentation to be a barrier. Institutional void is the lack of commonly accepted rules and norms for policy processes to take place, calling into question the legitimacy and efficacy of policy processes. The Short time horizon of policies and politicians often means that climate change policies are not implemented in favour of socially favoured societal issues. Statements are often posed to keep the illusion of political action to prevent or postpone decisions being made. Missing motives and willingness to start adapting is a large barrier as it prevents any implementation.
 OccurrenceDespite a perceived lack of occurrence, evidence of implementation is emerging internationally. Some examples of this are the initiation of NAPA’s and of joint implementation. Many developing nations have made National Adaptation Programs of Action (NAPAs) which are frameworks to prioritize adaption needs. The implementation of many of these is supported by GEF agencies. Many developed countries are implementing ‘first generation’ institutional adaption plans particularly at the state and local government scale. There has also been a push towards joint implementation between countries by the UNFCC as this has been suggested as a cost effective way for objectives to be achieved.
 Territorial policies
 United StatesEfforts to reduce greenhouse gas emissions by the United States include energy policies which encourage efficiency through programs like Energy Star, Commercial Building Integration, and the Industrial Technologies Program. On 12 November 1998, Vice President Al Gore symbolically signed the Kyoto Protocol, but he indicated participation by the developing nations was necessary prior its being submitted for ratification by the United States Senate.
In 2007, Transportation Secretary Mary Peters, with White House approval, urged governors and dozens of members of the House of Representatives to block California’s first-in-the-nation limits on greenhouse gases from cars and trucks, according to e-mails obtained by Congress. The U.S. Climate Change Science Program is a group of about twenty federal agencies and US Cabinet Departments, all working together to address global warming.
The Bush administration pressured American scientists to suppress discussion of global warming, according to the testimony of the Union of Concerned Scientists to the Oversight and Government Reform Committee of the U.S. House of Representatives. "High-quality science" was "struggling to get out," as the Bush administration pressured scientists to tailor their writings on global warming to fit the Bush administration's skepticism, in some cases at the behest of an ex-oil industry lobbyist. "Nearly half of all respondents perceived or personally experienced pressure to eliminate the words 'climate change,' 'global warming' or other similar terms from a variety of communications." Similarly, according to the testimony of senior officers of the Government Accountability Project, the White House attempted to bury the report "National Assessment of the Potential Consequences of Climate Variability and Change," produced by U.S. scientists pursuant to U.S. law. Some U.S. scientists resigned their jobs rather than give in to White House pressure to underreport global warming.
In the absence of substantial federal action, state governments have adopted emissions-control laws such as the Regional Greenhouse Gas Initiative in the Northeast and the Global Warming Solutions Act of 2006 in California.
 Developing countriesIn order to reconcile economic development with mitigating carbon emissions, developing countries need particular support, both financial and technical. One of the means of achieving this is the Kyoto Protocol's Clean Development Mechanism (CDM). The World Bank's Prototype Carbon Fund is a public private partnership that operates within the CDM.
An important point of contention, however, is how overseas development assistance not directly related to climate change mitigation is affected by funds provided to climate change mitigation. One of the outcomes of the UNFCC Copenhagen Climate Conference was the Copenhagen Accord, in which developed countries promised to provide US $30 million between 2010–2012 of new and additional resources. Yet it remains unclear what exactly the definition of additional is and the European Commission has requested its member states to define what they understand to be additional, and researchers at the Overseas Development Institute have found 4 main understandings:
- Climate finance classified as aid, but additional to (over and above) the ‘0.7%’ ODA target;
- Increase on previous year's Official Development Assistance (ODA) spent on climate change mitigation;
- Rising ODA levels that include climate change finance but where it is limited to a specified percentage; and
- Increase in climate finance not connected to ODA.
In July 2005 the U.S., China, India, Australia, as well as Japan and South Korea, agreed to the Asia-Pacific Partnership for Clean Development and Climate. The pact aims to encourage technological development that may mitigate global warming, without coordinated emissions targets. The highest goal of the pact is to find and promote new technology that aid both growth and a cleaner environment simultaneously. An example is the Methane to Markets initiative which reduces methane emissions into the atmosphere by capturing the gas and using it for growth enhancing clean energy generation. Critics[who?] have raised concerns that the pact undermines the Kyoto Protocol.
However, none of these initiatives suggest a quantitative cap on the emissions from developing countries. This is considered as a particularly difficult policy proposal as the economic growth of developing countries are proportionally reflected in the growth of greenhouse emissions. Critics[who?] of mitigation often argue that, the developing countries' drive to attain a comparable living standard to the developed countries would doom the attempt at mitigation of global warming. Critics[who?] also argue that holding down emissions would shift the human cost of global warming from a general one to one that was borne most heavily by the poorest populations on the planet.
In an attempt to provide more opportunities for developing countries to adapt clean technologies, UNEP and WTO urged the international community to reduce trade barriers and to conclude the Doha trade round "which includes opening trade in environmental goods and services".
 Non-governmental approachesWhile many of the proposed methods of mitigating global warming require governmental funding, legislation and regulatory action, individuals and businesses can also play a part in the mitigation effort.
 Choices in personal actions and business operationsEnvironmental groups encourage individual action against global warming, often aimed at the consumer. Common recommendations include lowering home heating and cooling usage, burning less gasoline, supporting renewable energy sources, buying local products to reduce transportation, turning off unused devices, and various others.
A geophysicist at Utrecht University has urged similar institutions to hold the vanguard in voluntary mitigation, suggesting the use of communications technologies such as videoconferencing to reduce their dependence on long-haul flights.
 Air travel and shipmentClimate scientist Kevin Anderson raised concern about the growing effect of rapidly increasing global air transport on the climate in a paper and a presentation in 2008, suggesting that reversing this trend is necessary. Part of the difficulty is that when aviation emissions are made at high altitude, the climate impacts are much greater than otherwise. Others have been raising the related concerns of the increasing hypermobility of individuals, whether traveling for business or pleasure, involving frequent and often long distance air travel, as well as air shipment of goods.
 Business opportunities and risksOn 9 May 2005 Jeff Immelt, the chief executive of General Electric (GE), announced plans to reduce GE's global warming related emissions by one percent by 2012. "GE said that given its projected growth, those emissions would have risen by 40 percent without such action."
On 21 June 2005 a group of leading airlines, airports and aerospace manufacturers pledged to work together to reduce the negative environmental impact of aviation, including limiting the impact of air travel on climate change by improving fuel efficiency and reducing carbon dioxide emissions of new aircraft by fifty percent per seat kilometre by 2020 from 2000 levels. The group aims to develop a common reporting system for carbon dioxide emissions per aircraft by the end of 2005, and pressed for the early inclusion of aviation in the European Union's carbon emission trading scheme.
 Legal actionIn some countries, those affected by climate change may be able to sue major producers, in a parallel to the lawsuits against tobacco companies. Although proving that particular weather events are due specifically to global warming may never be possible, methodologies have been developed to show the increased risk of such events caused by global warming.
For a legal action for negligence (or similar) to succeed, "Plaintiffs ... must show that, more probably than not, their individual injuries were caused by the risk factor in question, as opposed to any other cause. This has sometimes been translated to a requirement of a relative risk of at least two." Another route (though with little legal bite) is the World Heritage Convention, if it can be shown that climate change is affecting World Heritage Sites like Mount Everest.
Legal action has also been taken to try to force the U.S. Environmental Protection Agency to regulate greenhouse gas emissions under the Clean Air Act, and against the Export-Import Bank and OPIC for failing to assess environmental impacts (including global warming impacts) under NEPA.
According to a 2004 study commissioned by Friends of the Earth, ExxonMobil and its predecessors caused 4.7 to 5.3 percent of the world's man-made carbon dioxide emissions between 1882 and 2002. The group suggested that such studies could form the basis for eventual legal action.
 See also
- 4 Degrees and Beyond International Climate Conference
- Alternative propulsion
- Avoiding Dangerous Climate Change
- Black carbon
- Carbon diet
- Carbon negative fuel
- Climate bond
- Contraction and Convergence
- Green IT
- Hell and High Water: Global Warming
- Iron fertilization
- Low carbon diet
- Mitigation of peak oil
- Oil phase-out
- Stratospheric sulfur aerosols (geoengineering)
- Zero-carbon economy
- Environmental impact of the coal industry
 By country
- Debate over China's economic responsibilities for climate change mitigation
- European Climate Change Programme
- Mitigation of global warming in Australia
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