Fossil fuel related CO2 emissions compared to five of IPCCs emissions scenarios. The dips are related to global recessions. Data from IPCC SRES scenarios; Data spreadsheet included with International Energy Agencys CO2 Emissions from Fuel Combustion 2010 - Highlights; and Supplemental IEA data. Image source: Skeptical Science Global average surface temperature 1880 to 2009. The Global dimming, from sulfate aerosol air pollution, between 1950 to 1980 is believed to have mitigated global warming somewhat. Global carbon dioxide emissions from human activities 1800–2007.[1] Greenhouse gas emissions by sector. See World Resources Institute for a detailed breakdown. Climate change mitigation are actions to limit the magnitude and/or rate of long-term climate change.[2] Climate change mitigation generally involves reductions in human (anthropogenic) emissions of greenhouse gases (GHGs).[3] Mitigation may also be achieved by increasing the capacity of carbon sinks, e.g., through reforestation.[3] By contrast, adaptation to global warming are actions taken to manage the eventual (or unavoidable) impacts of global warming,[4] e.g., by building dikes in response to sea level rise.[5] Examples of mitigation include switching to low-carbon energy sources, such as renewable and nuclear energy, and expanding forests and other sinks to remove greater amounts of carbon dioxide from the atmosphere.[3] Energy efficiency may also play a role,[6] for example, through improving the insulation of buildings.[7] Another approach to climate change mitigation is climate engineering.[8] The main international treaty on climate change is the United Nations Framework Convention on Climate Change (UNFCCC),[9] which in 2002 adopted the objective to prevent dangerous anthropogenic interference with the climate system.[10] In 2010, Parties to the UNFCCC agreed that future global warming should be limited to below 2.0 °C (3.6 °F) relative to the pre-industrial level.[11] Some analyses suggest that staying within the 2 °C guardrail would require annual global emissions of greenhouse gases[12] to peak before the year 2020, and decline significantly thereafter,[13] with emissions in 2050 reduced by 30-50% compared to 1990 levels.[14] Recent analyses by the United Nations Environment Programme[15] and International Energy Agency[16][17][18] suggest that current policies (as of 2013) are too weak to follow that pathway for staying within the 2 °C guardrail. Other recent analyses challenge both that pathway (as being inadequate to stay within the guardrail) and the 2 °C guardrail itself (as being inadequate for the needed degree and timeliness of mitigation).[19][20][21][22][23][24] Contents 1 Background 1.1 Greenhouse gas concentrations and stabilization 1.2 Energy consumption by power source 2 Methods and means 2.1 Alternative energy sources 2.1.1 Renewable energy 2.1.2 Nuclear power 2.1.3 Fuel switching 2.2 Energy efficiency and conservation 2.3 Sinks and negative emissions 2.3.1 Reforestation and avoided deforestation 2.3.2 Carbon capture and storage 2.3.3 Negative carbon dioxide emissions 2.4 Geoengineering 2.4.1 Carbon dioxide removal 2.4.2 Solar radiation management 2.5 Non-CO2 greenhouse gases 3 By sector 3.1 Transport 3.2 Urban planning 3.2.1 Building design 3.3 Societal controls 3.3.1 Population 4 Costs and benefits 4.1 Costs 4.2 Benefits 4.3 Sharing 4.3.1 Distributing emissions abatement costs 4.3.2 Specific proposals 5 Governmental and intergovernmental action 5.1 Kyoto Protocol 5.2 Temperature targets 5.3 Encouraging use changes 5.3.1 Emissions tax 5.3.2 Making the emitting of CO2 illegal 5.3.3 Subsidies 5.3.4 Carbon emissions trading 5.4 Implementation 5.4.1 Funding 5.4.2 Problems 5.4.3 Occurrence 5.5 Territorial policies 5.5.1 United States 5.5.2 Developing countries 6 Non-governmental approaches 6.1 Choices in personal actions and business operations 6.1.1 Air travel and shipment 6.2 Business opportunities and risks 6.3 Legal action 7 See also 7.1 By country 8 Notes 9 References 10 External links 10.1 European Union 10.2 USA 10.3 Academic Background[edit] Greenhouse gas concentrations and stabilization[edit] See also: Greenhouse gas § Removal from the atmosphere and global warming potential refer to caption and adjacent text Stabilizing CO2 emissions at their present level would not stabilize its concentration in the atmosphere.[25] refer to caption and adjacent text Stabilizing the atmospheric concentration of CO2 at a constant level would require emissions to be effectively eliminated.[25] One of the issues often discussed in relation to climate change mitigation is the stabilization of greenhouse gas concentrations in the atmosphere. The United 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.[26] There are a number of anthropogenic greenhouse gases. These include carbon dioxide (chemical formula: CO 2), methane (CH 4), nitrous oxide (N 2O), and a group of gases referred to as halocarbons.[27] The emissions reductions necessary to stabilize the atmospheric concentrations of these gases varies.[25] CO 2 is the most important of the anthropogenic greenhouse gases (see radiative forcing).[28] There is a difference between stabilizing CO 2 emissions and stabilizing atmospheric concentrations of CO 2.[29] 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 Earths atmosphere for a more complete explanation).[25] This is analogous to a flow of water into a bathtub.[30] 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 atmospheric CO 2 concentrations would require anthropogenic CO 2 emissions to be reduced by 80% relative to the peak emissions level.[31] An 80% reduction in emissions would stabilize CO 2 concentrations for around a century, but even greater reductions would be required beyond this.[25][31] 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. Projections Projections of future greenhouse gas emissions are highly uncertain.[32] In the absence of policies to mitigate climate change, GHG emissions could rise significantly over the 21st century.[33] Numerous assessments have considered how atmospheric GHG concentrations could be stabilized.[34] The lower the desired stabilization level, the sooner global GHG emissions must peak and decline.[35] GHG concentrations are unlikely to stabilize this century without major policy changes.[33] refer to caption and adjacent text Projected carbon dioxide emissions and atmospheric concentrations over the 21st century for reference and mitigation scenarios. Rate of world energy usage per day, from 1970 to 2010. Every fossil fuel source has increased in large amounts between 1970 and 2010, dominating all other energy sources. Hydroelectricity has increased at a slow steady rate over this same period, nuclear entered a period of rapid growth between 1970 and 1990 before levelling off. Other Renewables, between 2000 and 2010 have, having started from a low usage rate, began to enter into a period of rapid growth. 1000TWh=1PWh.[36] Energy consumption by power source[edit] To create lasting climate change mitigation, the replacement of high carbon emission intensity power sources, such as conventional fossil fuels - oil, coal and natural gas - with low-carbon power sources is required. Fossil fuels supply humanity with the vast majority of our energy demands, and at a growing rate. In 2012 the IEA noted that coal accounted for half the increased energy use of the prior decade, growing faster than all renewable energy sources.[37] Both hydroelectricity and nuclear power together provide the majority of the generated low-carbon power fraction of global total power consumption. Hydropower-Internalised Costs and Externalised Benefits; Frans H. Koch; International Energy Agency (IEA)-Implementing Agreement for Hydropower Technologies and Programmes; 2000. Fuel type Average total global power consumption in TW[38] 1980 2004 2006 Oil 4.38 5.58 5.74 Gas 1.80 3.45 3.61 Coal 2.34 3.87 4.27 Hydroelectric 0.60 0.93 1.00 Nuclear power 0.25 0.91 0.93 Geothermal, wind, solar energy, wood 0.02 0.13 0.16 Total 9.48 15.0 15.8 Source: The USA Energy Information Administration Change and use of energy, by source, in units of (PWh) in that year.[39] Fossil Nuclear All renewables Total 1990 83.374 6.113 13.082 102.569 2000 94.493 7.857 15.337 117.687 2008 117.076 8.283 18.492 143.851 Change 2000–2008 22.583 0.426 3.155 26.164 Methods and means[edit] See also: Emission intensity Refer to caption and image description This graph shows the projected contribution of various energy sources to world primary electricity consumption (PEC).[40] It is based on a climate change mitigation scenario, in which GHG emissions are substantially reduced over the 21st century. In the scenario, emission reductions are achieved using a portfolio of energy sources, as well as reductions in energy demand. Also available in greyscale. Assessments often suggest that GHG emissions can be reduced using a portfolio of low-carbon technologies.[41] At the core of most proposals is the reduction of greenhouse gas (GHG) emissions through reducing energy waste and switching to low-carbon power sources of energy. As the cost of reducing GHG emissions in the electricity sector appears to be lower than in other sectors, such as in the transportation sector, the electricity sector may deliver the largest proportional carbon reductions under an economically efficient climate policy.[42] Other frequently discussed means include energy conservation, increasing fuel economy in automobiles (which includes the use of electric hybrids), charging plug-in hybrids and electric cars by low-carbon electricity, making individual-lifestyle changes[43] (e.g., cycling instead of driving),[44] and changing business practices. A range of energy technologies may contribute to climate change mitigation.[45] These include renewable energy sources such as solar power, tidal, ocean energy, geothermal power, and wind power; nuclear power, the use of carbon sinks, and carbon capture and storage. For example, Pacala and Socolow of Princeton [46] have proposed a 15 part program to reduce CO2 emissions by 1 billion metric tons per year − or 25 billion tons over the 50-year period using todays technologies as a type of Global warming game.[47] Another consideration is how future socio-economic development proceeds. Development choices (or pathways) can lead differences in GHG emissions.[48] Political and social attitudes may affect how easy or difficult it is to implement effective policies to reduce emissions.[49] Alternative energy sources[edit] Renewable energy[edit] Main articles: Renewable energy, Renewable energy commercialization and Renewable energy debate The 22,500 MW nameplate capacity Three Gorges Dam in the Peoples Republic of China, the largest hydroelectric power station in the world. Solar cookers use sunlight as energy source for outdoor cooking. The Shepherds Flat Wind Farm is an 845 megawatt (MW) nameplate capacity, wind farm in the U.S. state of Oregon, each turbine is a nameplate 2 or 2.5 MW electricity generator. The 150 MW Andasol solar power station is a commercial parabolic trough solar thermal power plant, located in Spain. The Andasol plant uses tanks of molten salt to store solar energy so that it can continue generating electricity for 7.5 hours after the sun has stopped shining.[50] Renewable energy flows involve natural phenomena such as sunlight, wind, tides, plant growth, and geothermal heat, as the International Energy Agency explains:[51] Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources. Climate change concerns[52][53][54] and the need to reduce carbon emissions are driving increasing growth in the renewable energy industries.[55][56][57] Low-carbon renewable energy replaces conventional fossil fuels in three main areas: power generation, hot water/ space heating, and transport fuels.[58] In 2011, the share of renewables in electricity generation worldwide grew for the fourth year in a row to 20.2%, with the global share of electricity from hydro power staying roughly constant at 16.3%.[59] Renewable energy use has grown much faster than anyone anticipated.[60] The Intergovernmental Panel on Climate Change (IPCC) has said that there are few fundamental technological limits to integrating a portfolio of renewable energy technologies to meet most of total global energy demand.[61] At the national level, at least 30 nations around the world already have renewable energy contributing more than 20% of energy supply. As of 2012, renewable energy accounts for almost half of new electricity capacity installed and costs are continuing to fall.[62] Public policy and political leadership helps to level the playing field and drive the wider acceptance of renewable energy technologies.[63] As of 2011, 118 countries have targets for their own renewable energy futures, and have enacted wide-ranging public policies to promote renewables.[64][65] Leading renewable energy companies include BrightSource Energy, First Solar, Gamesa, GE Energy, Goldwind, Sinovel, Suntech, Trina Solar, Vestas and Yingli.[66][67] The incentive to use 100% renewable energy has been created by global warming and other ecological as well as economic concerns.[60] Mark Z. Jacobson says producing all new energy with wind power, solar power, and hydropower by 2030 is feasible and existing energy supply arrangements could be replaced by 2050. Barriers to implementing the renewable energy plan are seen to be primarily social and political, not technological or economic. Jacobson says that energy costs with a wind, solar, water system should be similar to todays energy costs.[68] According to a 2011 projection by the (IEA)International Energy Agency, solar power generators may produce most of the worlds electricity within 50 years, dramatically reducing harmful greenhouse gas emissions.[69] Critics of the 100% renewable energy approach include Vaclav Smil and James E. Hansen. Smil and Hansen are concerned about the variable output of solar and wind power, NIMBYism, and a lack of infrastructure.[70] Economic analysts expect market gains for renewable energy (and efficient energy use) following the 2011 Japanese nuclear accidents.[71][72] In his 2012 State of the Union address, President Barack Obama restated his commitment to renewable energy and mentioned the long-standing Interior Department commitment to permit 10,000 MW of renewable energy projects on public land in 2012.[73] Globally, there are an estimated 3 million direct jobs in renewable energy industries, with about half of them in the biofuels industry.[74] Some countries, with favorable geography, geology and weather well suited to an economical exploitation of renewable energy sources, already get most of their electricity from renewables, including from geothermal energy in Iceland (100 percent), and Hydroelectric power in Brazil (85 percent), Austria (62 percent), New Zealand (65 percent), and Sweden (54 percent).[75] Renewable power generators are spread across many countries, with wind power providing a significant share of electricity in some regional 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. 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.[75] 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.[75] Nuclear power[edit] See also: Nuclear renaissance and Comparisons of life-cycle greenhouse gas emissions Blue Cherenkov light being produced near the core of the Fission powered Advanced Test Reactor Since about 2001 the term nuclear 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.[76] However, in March 2011 the Fukushima nuclear disaster in Japan and associated shutdowns at other nuclear facilities raised questions among some commentators over the future of nuclear power.[77][78][79] Platts has reported that the crisis at Japans Fukushima nuclear plants has prompted leading energy-consuming countries to review the safety of their existing reactors and cast doubt on the speed and scale of planned expansions around the world.[80] The World Nuclear Association has reported that nuclear electricity generation in 2012 was at its lowest level since 1999.[81] Several previous international studies and assessments,[82][83][84] suggested that as part of the portfolio of other low-carbon energy technologies, nuclear power will continue to play a role in reducing greenhouse gas emissions. Historically, nuclear power usage is estimated to have prevented the atmospheric emission of 64 gigatonnes of CO2-equivalent as of 2013.[85] Public concerns about nuclear power include the fate of spent nuclear fuel, nuclear safety, and security risks which are considered unique among low-carbon energy sources. A Yale University review published in the Journal of Industrial Ecology analyzing CO2 life cycle assessment emissions from nuclear power determined that: The collective LCA literature indicates that life cycle GHG emissions from nuclear power are only a fraction of traditional fossil sources and comparable to renewable technologies.[86] Uncertainty surrounding the future GHG emissions of nuclear power have to do with the potential for a declining uranium ore grade without a corresponding increase in the efficiency of enrichment methods. In a scenario analysis of future global nuclear development, as it could be effected by a decreasing global uranium market of average ore grade, the analysis determined that depending on conditions, median life cycle nuclear power GHG emissions could be between 9 to 110 g CO2-eq/kWh by 2050.[86] During his presidential campaign, Barack Obama stated, Nuclear power represents more than 70% of our noncarbon generated electricity. It is unlikely that we can meet our aggressive climate goals if we eliminate nuclear power as an option. [87] This graph illustrates nuclear power is the USAs largest contributor of non-greenhouse-gas-emitting electric power generation, comprising nearly three-quarters of the non-emitting sources. Nuclear power may be uncompetitive compared with fossil fuel energy sources in countries without a carbon tax program, and in comparison to a fossil fuel plant of the same power output, nuclear power plants take a longer amount of time to construct.[88][89][90][91] refer to caption and image description Global public support for energy sources, based on a survey by Ipsos (2011).[92] Two new, first of their kind, EPR reactors under construction in Finland and France have been delayed and are running over-budget.[93][94][95] However learning from experience, two further EPR reactors under construction in China are on, and ahead, of schedule respectively.[96] As of 2013, according to the IAEA and the European Nuclear Society, worldwide there were 68 civil nuclear power reactors under construction in 15 countries.[97][98] China has 29 of these nuclear power reactors under construction, as of 2013, with plans to build many more,[98][99] while in the US the licenses of almost half its reactors have been extended to 60 years,[100] and plans to build another dozen are under serious consideration.[101] 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.[102] This is probable only if one does not factor in the ongoing Light Water Reactor Sustainability Program, created to permit the extension of the life span of the USAs 104 nuclear reactors to 60 years. The licenses of almost half of the USAs reactors have been extended to 60 years as of 2008.[100] Two new AP1000 reactors are, as of 2013, being constructed at Vogtle Electric Generating Plant. Public opinion about nuclear power varies widely between countries.[103][104] A poll by Gallup International (2011)[105] assessed public opinion in 47 countries. The poll was conducted following a tsumani and earthquake which caused an accident at the Fukushima nuclear power plant in Japan. 49% stated that they held favourable views about nuclear energy, while 43% held an unfavourable view.[106] Another global survey by Ipsos (2011)[107] assessed public opinion in 24 countries. Respondents to this survey showed a clear preference for renewable energy sources over coal and nuclear energy (refer to graph opposite).[92] Ipsos (2012)[108] found that solar and wind were viewed by the public as being more environmentally friendly and more viable long-term energy sources relative to nuclear power and natural gas. However, solar and wind were viewed as being less reliable relative to nuclear power and natural gas. In 2012 a poll done in the UK found that 63% of those surveyed support nuclear power, and with opposition to nuclear power at 11%.[109] In Germany, strong anti-nuclear sentiment led to eight of the seventeen operating reactors being permanently shut down following the March 2011 Fukushima nuclear disaster.[110] Nuclear fusion research, in the form of the International Thermonuclear Experimental Reactor is underway. Fusion powered electricity generation was initially believed to be readily achievable, as fission power had been. However, the extreme requirements for continuous reactions and plasma containment led to projections being extended by several decades. In 2010, more than 60 years after the first attempts, commercial power production was still believed to be unlikely before 2050.[111] Fuel switching[edit] See also: Emission intensity Most 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.[112][113] Natural gas emits far fewer greenhouse gases (i.e. CO2 and Methane - CH4) than coal when burned at power plants, but evidence has been emerging that this benefit could be completely negated by methane leakage at gas drilling fields and other earlier points in the production lifecycle. 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 outweighs the detrimental effects of increased methane emissions. More recent peer-reviewed studies have challenged the findings of this study, with researchers from the National Oceanic and Atmospheric Administration (NOAA) reconfirming findings of high rates of methane (CH4) leakage from natural gas fields. A 2011 study [114] by noted climate research scientist, Tom Wigley,[115] found that while carbon dioxide (CO2) emissions from fossil fuel combustion may be reduced by using natural gas rather than coal to produce energy, it also found that additional methane (CH4) from leakage adds to the radiative forcing of the climate system, offsetting the reduction in CO2 forcing that accompanies the transition from coal to gas. The study looked at methane leakage from coal mining; changes in radiative forcing due to changes in the emissions of sulfur dioxide and carbonaceous aerosols; and differences in the efficiency of electricity production between coal- and gas-fired power generation. On balance, these factors more than offset the reduction in warming due to reduced CO2 emissions. When gas replaces coal there is additional warming out to 2,050 with an assumed leakage rate of 0%, and out to 2,140 if the leakage rate is as high as 10%. The overall effects on global-mean temperature over the 21st century, however, are small. Petron et al. (2013) [116] and Alvarez et al. (2012)[117] note that estimated that leakage from gas infrastructure is likely to be underestimated. These studies indicate that the exploitation of natural gas as a cleaner fuel is questionable. Energy efficiency and conservation[edit] Main articles: Efficient energy use and Energy conservation A spiral-type integrated compact fluorescent lamp, use has grown among North American consumers since its introduction in the mid-1990s.[118] Efficient energy use, sometimes simply called energy efficiency, is the goal of efforts to reduce the amount of energy required to provide products and services. For example, insulating 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.[119] 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, Californias 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.[120] 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.[121] 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 worlds energy needs in 2050 by one third, and help control global emissions of greenhouse gases.[122] Sinks and negative emissions[edit] Main articles: Carbon sink and Negative carbon dioxide emission A 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. The Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC) notes that one third of humankind’s annual emissions of CO2 are absorbed by the oceans. The oceans act as a carbon sink, that is, a reservoir that accumulates and stores carbon via its physicochemical and biological processes.[123] Unfortunately, this vital service comes with the cost of ocean acidification. The ecological effects of ocean acidification are still largely unknown. Research so far has focussed on how acidification lowers pH and the level of carbonate ions available for calcifying organisms to form their shells. These organisms include plankton species that contribute to the foundation of the Southern Ocean food web. However acidification may impact on a broad range of other physiological and ecological processes, such as fish respiration, larval development and changes in the solubility of both nutrients and toxins.[124] According to the CSIRO [125] the Southern Ocean is absorbing increasing amounts of carbon dioxide, with potentially significant impacts on marine life.[126] Reforestation and avoided deforestation[edit] Managed grazing methods are argued to be able to restore grasslands, thereby significantly decreasing atmospheric CO2 levels.[127] Main articles: Deforestation, Reforestation and Biosequestration Almost 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.[128] 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.[129] 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.[128] 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.[130] Restoring grasslands store CO2 from the air into plant material. Grazing livestock, usually not left to wander, would eat the grass and would minimize any grass growth while grass left alone would eventually grow to cover its own growing buds, preventing them from photosynthesizing and killing the plant.[131] A method proposed to restore grasslands uses fences with many small paddocks and moving herds from one paddock to another after a day a two in order to mimick natural grazers and allowing the grass to grow optimally.[131][132][133] It is estimated that increasing the carbon content of the soils in the world’s 3.5 billion hectares of agricultural grassland by 1% would offset nearly 12 years of CO2 emissions.[131] Allan Savory, as part of holistic management, claims that while large herds are often blamed for desertification, prehistoric lands used to support large or larger herds and areas where herds were removed in the United States are still desertifying.[127] Carbon capture and storage[edit] Schematic showing both terrestrial and geological sequestration of carbon dioxide emissions from a coal-fired plant. Main article: Carbon capture and storage Carbon capture and storage (CCS) is a method to mitigate climate change by capturing carbon 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.[134] 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.[134] Norway, which first began storing CO2, has cut its emissions by almost a million tons a year, or about 3% of the countrys 1990 levels.[134] 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.[135] Negative carbon dioxide emissions[edit] Main article: Negative carbon dioxide emission Creating 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,[136][137] and sometimes as geoengineering.[138] In combination with other mitigation measures, sinks in combination with negative carbon emissions are considered crucial for meeting the 350 ppm target,[139][140] and even the less conservative 450 ppm target.[136] Geoengineering[edit] Main article: geoengineering Geoengineering 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.[141] IPCC (2007) concluded that geoengineering options, such as ocean fertilization to remove CO2 from the atmosphere, remained largely unproven.[142] 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.[143] 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..[143] 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.[144] Carbon dioxide removal[edit] Main articles: Carbon dioxide removal, Greenhouse gas remediation and Carbon sequestration See also: Carbon air capture Carbon 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.[138] It 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.[citation needed] However, captured CO2 can be used to force more crude oil out of oil fields, as Statoil and Shell have made plans to do.[145] 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,[146] notably the GreenFuel Technologies Corporation, who have now shut down operations.[147] Solar radiation management[edit] Main article: Solar radiation management See also: Stratospheric sulfate aerosols (geoengineering) The main purpose of solar radiation management seek to reflect sunlight and thus reduce global warming. The ability of stratospheric sulfate aerosols to create a global dimming effect has made them a possible candidate for use in geoengineering projects.[148] Non-CO2 greenhouse gases[edit] CO2 is not the only GHG relevant to mitigation,[149] 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.[150] 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.[25] Methane has a relatively short atmospheric lifetime of about 12 years, while N2Os 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.[25] Methane is a significantly more powerful greenhouse gas than carbon dioxide. Burning one molecule of methane generates one molecule of carbon dioxide, indicating there may be no net benefit in using gas as a fuel source.[114][116] Reducing the amount of waste methane produced in the first place and moving away from use of gas as a fuel source will have a 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.[151] 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.[152] A measure for this physical property is the global warming potential (GWP), and is used in the Kyoto Protocol.[153] Although not designed for this purpose, the Montreal Protocol has probably benefitted climate change mitigation efforts.[154] The Montreal Protocol is an international treaty that has successfully reduced emissions of ozone-depleting substances (e.g., CFCs), which are also greenhouse gases. By sector[edit] Transport[edit] Bicycles have almost no carbon footprint compared to cars, and canal transport may represent a positive option for certain types of freight in the 21st century[155] Main article: Sustainable transport Modern energy-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.[156][157] For electric vehicles, the reduction of carbon emissions will improve further if the way the required electricity is generated is low-carbon power in origin. Urban planning[edit] Main article: Urban planning 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. Between 1982 and 1997, the amount of land consumed for urban development in the United States increased by 47 percent while the nations population grew by only 17 percent.[158] 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 greennhouse 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 design[edit] Main articles: Sustainable architecture and Green building Emissions from housing are substantial,[159] and government-supported energy efficiency programmes can make a difference.[160] For institutions of higher learning in the United States, greenhouse gas emissions depend primarily on total area of buildings and secondarily on climate.[161] 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.[162] 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.[163][164] This saves energy because it cools buildings and reduces the urban heat island effect thus reducing the use of air conditioning. Societal controls[edit] Another 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.[citation needed] Population[edit] Population density by country Various organizations promote population control as a means for mitigating global warming.[165][166][167][168][169] 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.[170] 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.[171] Costs and benefits[edit] Main article: Economics of climate change mitigation Costs[edit] The 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%.[128] Stern has since revised his estimate to 2% of GWP.[172] For comparison, the Gross World Product (GWP) at PPP was estimated at $74.5 trillion in 2010,[173] 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.[128] 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.[128] Benefits[edit] Total extreme weather cost and number of events costing more than $1 billion in the United States from 1980 to 2011. Yohe et al. (2007) assessed the literature on sustainability and climate change.[174] 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 effects of global warming. This was judged to be the case even with aggressive mitigation and significantly enhanced adaptive capacity. Sharing[edit] One 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).[175] In terms of the politics of mitigation, the UNFCCCs ultimate objective is to stabilize concentrations of GHG in the atmosphere at a level that would prevent dangerous climate change (Rogner et al., 2007).[176] 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).[177] 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 costs[edit] There have been different proposals on how to allocate responsibility for cutting emissions (Banuri et al., 1996, pp. 103–105):[177] 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).[178] 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 UNDPs 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[edit] Ad hoc: Lashof (1992) and Cline (1992) (referred to by Banuri et al., 1996, p. 106),[177] 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).[178] In international law, one state recognized the long-established use of another states use of the fisheries resource. It was also recognized by the state that part of the other states economy was dependent on that resource. Governmental and intergovernmental action[edit] Main article: Politics of global warming Many countries, both developing and developed, are aiming to use cleaner technologies (World Bank, 2010, p. 192).[179] 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 Protocol[edit] Main article: Kyoto Protocol The 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. Temperature targets[edit] Refer to caption and image description The graph on the right shows three pathways to meet the UNFCCCs 2 °C target, labelled global technology, decentralised solutions, and consumption change. Each pathway shows how various measures (e.g., improved energy efficiency, increased use of renewable energy) could contribute to emissions reductions. Image credit: PBL Netherlands Environmental Assessment Agency.[180] Actions to mitigate climate change are sometimes based on the goal of achieving a particular temperature target. One of the targets that has been suggested is to limit the future increase in global mean temperature (global warming) to below 2 °C, relative to the pre-industrial level.[181][182] The 2 °C target was adopted in 2010 by Parties to the United Nations Framework Convention on Climate Change.[183] Most countries of the world are Parties to the UNFCCC.[184] The target had been adopted in 1996 by the European Union Council.[185] Temperatures have increased by 0.8 °C compared to the pre-industrial level, and another 0.5–0.7 °C is already committed.[186] 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.[187][188] The importance of change is illustrated by the fact that world economic energy efficiency is improving at only half the rate of world economic growth.[189] Encouraging use changes[edit] Emissions tax[edit] See also: carbon tax, energy tax and fee and dividend An 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.[190] 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.[190] Emission taxes can be both cost-effective and environmentally effective.[190] Difficulties with emission taxes include their potential unpopularity, and the fact that they cannot guarantee a particular level of emissions reduction.[190] 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.[190] Making the emitting of CO2 illegal[edit] Another option is to replace the emission reduction-positive approach[clarification needed] proposed with the Kyoto protocol and its successor with an emitted GHG-negative approach.[clarification needed] Scientist Ken Caldeira has proposed making greenhouse gas-emitting devices illegal.[191] Subsidies[edit] According to Mark Z. Jacobson, a program of subsidization balanced against expected flood costs could pay for conversion to 100% renewable power by 2030.[192] Jacobson, and his colleague Mark Delucchi, suggest that the cost to generate and transmit power in 2020 will be less than 4 cents per kilowatt hour (in 20
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