Climate change mitigation/ja: Difference between revisions

{{excerpt|sustainable energy/ja#化石燃料の切り替えと緩和|paragraphs=1-2|file=no}}

{{Main/ja|2 = :en:Energy conservation|3 = :en:Efficient energy use}}

Some scientists say that avoiding meat and dairy foods is the single biggest way an individual can reduce their environmental impact. The widespread adoption of a vegetarian diet could cut food-related greenhouse gas emissions by 63% by 2050. China introduced new dietary guidelines in 2016 which aim to cut meat consumption by 50% and thereby reduce greenhouse gas emissions by 1{{nbsp}}Gt per year by 2030. Overall, food accounts for the largest share of consumption-based greenhouse gas emissions. It is responsible for nearly 20% of the global carbon footprint. Almost 15% of all anthropogenic greenhouse gas emissions have been attributed to the livestock sector.

A shift towards [[plant-based diets]] would help to mitigate climate change. In particular, reducing meat consumption would help to reduce methane emissions. If high-income nations switched to a plant-based diet, vast amounts of land used for animal agriculture could be allowed to [[Restoration ecology|return to their natural state]]. This in turn has the potential to sequester 100 billion tonnes of {{CO2}} by the end of the century. A comprehensive analysis found that plant based diets reduce emissions, water pollution and land use significantly (by 75%), while reducing the destruction of wildlife and usage of water.

[[File:GHG by diet groups.svg|thumb|right|Environmental footprint of 55,504 UK citizens by diet group (''Nat Food'' 4, 565–574, 2023).]]

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=== Family size ===

{{Further|Individual action on climate change#Family size}}[[File:World population (UN).svg|thumb|right|upright=1.35|Since 1950, world population has tripled.]]<nowiki> </nowiki>[[Projections of population growth|Population growth]] has resulted in higher greenhouse gas emissions in most regions, particularly Africa. However, economic growth has a bigger effect than population growth. Rising incomes, changes in consumption and dietary patterns, as well as population growth, cause pressure on land and other natural resources. This leads to more greenhouse gas emissions and fewer carbon sinks. Some scholars have argued that humane policies to slow population growth should be part of a broad climate response together with policies that end fossil fuel use and encourage sustainable consumption. Advances in female education and [[Sexual and reproductive health|reproductive health]], especially voluntary [[family planning]], can contribute to reducing population growth.

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== Preserving and enhancing carbon sinks ==

[[File:Carbon Dioxide Partitioning.svg|thumb|upright=1.35|right|About 58% of {{CO2}} emissions have been absorbed by [[carbon sinks]], including plant growth, soil uptake, and ocean uptake ([[Global Carbon Project#Global Carbon Budget|2020 Global Carbon Budget]]).]]

{{Main|Carbon dioxide removal|Carbon sequestration|Carbon sink}}

An important mitigation measure is "preserving and enhancing [[carbon sink]]s". This refers to the management of Earth's natural [[carbon sink]]s in a way that preserves or increases their capability to remove CO₂ from the atmosphere and to store it durably. Scientists call this process also [[carbon sequestration]]. In the context of climate change mitigation, the IPCC defines a ''sink'' as "Any process, activity or mechanism which removes a greenhouse gas, an aerosol or a precursor of a greenhouse gas from the atmosphere". Globally, the two most important carbon sinks are vegetation and the [[ocean]].

To enhance the ability of [[ecosystem]]s to sequester carbon, changes are necessary in agriculture and forestry. Examples are preventing [[deforestation]] and restoring natural ecosystems by [[reforestation]]. Scenarios that limit global warming to 1.5&nbsp;°C typically project the large-scale use of [[Carbon dioxide removal|carbon dioxide removal methods]] over the 21st century. There are concerns about over-reliance on these technologies, and their environmental impacts. But ecosystem restoration and reduced conversion are among the mitigation tools that can yield the most emissions reductions before 2030.

Land-based mitigation options are referred to as "AFOLU mitigation options" in the 2022 IPCC report on mitigation. The abbreviation stands for "agriculture, forestry and other land use" The report described the economic mitigation potential from relevant activities around forests and ecosystems as follows: "the conservation, improved management, and restoration of forests and other ecosystems (coastal wetlands, [[peatlands]], savannas and grasslands)". A high mitigation potential is found for reducing deforestation in tropical regions. The economic potential of these activities has been estimated to be 4.2 to 7.4 gigatonnes of carbon dioxide equivalent (GtCO₂ -eq) per year.

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=== Forests ===

{{Further|Carbon sequestration#Forestry|Deforestation and climate change|Reducing emissions from deforestation and forest degradation}}

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====Conservation====

{{Main|Deforestation#Control|Proforestation|Wildfire#Prevention}}

[[File:Shennongjia virgin forest.jpg|thumb|Transferring [[land rights]] to indigenous inhabitants is argued to efficiently conserve forests.]]

The [[Stern Review]] on the economics of climate change stated in 2007 that curbing [[deforestation]] was a highly cost-effective way of reducing greenhouse gas emissions. About 95% of deforestation occurs in the tropics, where clearing of land for agriculture is one of the main causes. One forest conservation strategy is to transfer rights over land from public ownership to its indigenous inhabitants. Land concessions often go to powerful extractive companies. Conservation strategies that exclude and even evict humans, called [[fortress conservation]], often lead to more exploitation of the land. This is because the native inhabitants turn to work for extractive companies to survive.

[[Proforestation]] is promoting forests to capture their full ecological potential. This is a mitigation strategy as [[secondary forest]]s that have regrown in abandoned farmland are found to have less biodiversity than the original [[old-growth forest]]s. Original forests store 60% more carbon than these new forests. Strategies include [[Rewilding (conservation biology)|rewilding]] and establishing [[wildlife corridor]]s.

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====Afforestation, reforestation and preventing desertification====

{{Seealso|Desertification#Countermeasures}}

[[Afforestation]] is the establishment of trees where there was previously no tree cover. Scenarios for new plantations covering up to 4000 million hectares (Mha) (6300 x 6300&nbsp;km) suggest cumulative carbon storage of more than 900&nbsp;GtC (2300&nbsp;Gt{{CO2}}) until 2100. But they are not a viable alternative to aggressive emissions reduction. This is because the plantations would need to be so large they would eliminate most natural ecosystems or reduce food production. One example is the [[Trillion Tree Campaign]]. However, preserving [[biodiversity]] is also important and for example not all [[grassland]]s are suitable for conversion into forests. Grasslands can even turn from [[carbon sink]]s to [[carbon source]]s. [[File:Coppice stool.jpg|thumb|right|Helping existing roots and tree stumps regrow even in long deforested areas is argued to be more efficient than planting trees. Lack of legal ownership to trees by locals is the biggest obstacle preventing regrowth.]]

[[Reforestation]] is the restocking of existing depleted forests or in places where there were recently forests. Reforestation could save at least 1{{nbsp}}GtCO₂ per year, at an estimated cost of $5–15 per tonne of carbon dioxide (tCO₂). Restoring all degraded forests all over the world could capture about 205&nbsp;GtC (750&nbsp;Gt{{CO2}}). With increased [[intensive agriculture]] and [[urbanisation]], there is an increase in the amount of abandoned farmland. By some estimates, for every acre of original [[old-growth forest]] cut down, more than 50 acres of new [[secondary forest]]s are growing. In some countries, promoting regrowth on abandoned farmland could offset years of emissions.

Planting new trees can be expensive and a risky investment. For example, about 80 per cent of planted trees in the [[Sahel]] die within two years. Reforestation has higher carbon storage potential than afforestation. Even long-deforested areas still contain an "underground forest" of living roots and tree stumps. Helping native species sprout naturally is cheaper than planting new trees and they are more likely to survive. This could include [[pruning]] and [[coppicing]] to accelerate growth. This also provides woodfuel, which is otherwise a major source of deforestation. Such practices, called [[farmer-managed natural regeneration]], are centuries old but the biggest obstacle towards implementation is ownership of the trees by the state. The state often sells timber rights to businesses which leads to locals uprooting seedlings because they see them as a liability. Legal aid for locals and changes to property law such as in Mali and Niger have led to significant changes. Scientists describe them as the largest positive environmental transformation in Africa. It is possible to discern from space the border between Niger and the more barren land in Nigeria, where the law has not changed.

[[Rangeland]]s account for more half the world’s land and could sequester 35% of terrestrial carbon. [[Pastoralism|Pastoralist]]s are those who move with their herds that feed and migrate over often [[extensive farming|unenclosed grazeland]]s. Such land is usually unable to grow any other kind of food. Rangelands coevolved with large wild herds, many of which have decreased or gone extinct, and [[nomadic pastoralism|pastoralist]]s’ herds replace such wild herds and thus help maintain the ecosystem. However, the movement of herds grazing on large areas over vast distances is increasingly restricted by governments, who often grant exclusive title to lands for more profitable uses which restricts pastoralists to more enclose spaces. This has led to the overgrazing of the land and [[desertification]], as well as [[nomadic conflict|conflict]].

===Soils===

{{Further|Carbon sequestration#Agriculture|Carbon farming|}}

There are many measures to increase soil carbon. This makes it complex and hard to measure and account for. One advantage is that there are fewer trade-offs for these measures than for [[Bioenergy with carbon capture and storage|BECCS]] or afforestation, for example.

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Globally, protecting healthy soils and restoring the soil carbon sponge could remove 7.6 billion tonnes of carbon dioxide from the atmosphere annually. This is more than the annual emissions of the US. Trees capture {{CO2}} while growing above ground and [[Plant root exudates|exuding]] larger amounts of carbon below ground. Trees contribute to the building of a [[soil carbon sponge]]. Carbon formed above ground is released as {{CO2}} immediately when wood is burned. If dead wood remains untouched, only some of the carbon returns to the atmosphere as decomposition proceeds.

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Farming can deplete soil carbon and render soil incapable of supporting life. However, [[conservation farming]] can protect carbon in soils, and repair damage over time. The farming practice of [[cover crop]]s is a form of [[carbon farming]]. Methods that enhance carbon sequestration in soil include [[no-till farming]], residue mulching and [[crop rotation]]. Scientists have described the best management practices for European soils to increase soil organic carbon. These are conversion of arable land to grassland, straw incorporation, reduced tillage, straw incorporation combined with reduced tillage, [[Ley farming|ley cropping]] system and cover crops.

Another mitigation option is the production of [[biochar]] and its storage in soils This is the solid material that remains after the [[pyrolysis]] of [[biomass]]. Biochar production releases half of the carbon from the biomass—either released into the atmosphere or captured with CCS—and retains the other half in the stable biochar. It can endure in soil for thousands of years. Biochar may increase the [[soil fertility]] of [[acidic soil]]s and increase [[agricultural productivity]]. During production of biochar, heat is released which may be used as [[bioenergy]].

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=== Wetlands ===

{{Further|Carbon sequestration#Wetlands|Wetland#Climate change mitigation}}

Wetland restoration is an important mitigation measure. It has moderate to great mitigation potential on a limited land area with low trade-offs and costs. Wetlands perform two important functions in relation to climate change. They can [[Carbon sink|sequester carbon]], converting carbon dioxide to solid plant material through [[photosynthesis]]. They also store and regulate water. Wetlands store about 45 million tonnes of carbon per year globally.

Some [[Wetland methane emissions|wetlands are a significant source of methane emissions]]. Some also emit [[nitrous oxide]]. [[Peat]]land globally covers just 3% of the land's surface. But it stores up to 550 gigatonnes (Gt) of carbon. This represents 42% of all soil carbon and exceeds the carbon stored in all other vegetation types, including the world's forests. The threat to peatlands includes draining the areas for agriculture. Another threat is cutting down trees for lumber, as the trees help hold and fix the peatland. Additionally, peat is often sold for compost. It is possible to restore degraded peatlands by blocking drainage channels in the peatland, and allowing natural vegetation to recover.

[[Mangrove]]s, [[salt marsh]]es and [[seagrass]]es make up the majority of the ocean's vegetated habitats. They only equal 0.05% of the plant biomass on land. But they store carbon 40 times faster than tropical forests. [[Bottom trawling]], [[dredging]] for coastal development and [[fertiliser runoff]] have damaged coastal habitats. Notably, 85% of [[oyster reef]]s globally have been removed in the last two centuries. Oyster reefs clean the water and help other species thrive. This increases biomass in that area. In addition, oyster reefs mitigate the effects of climate change by reducing the force of waves from hurricanes. They also reduce the erosion from rising sea levels. Restoration of coastal wetlands is thought to be more cost-effective than restoration of inland wetlands.

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=== Deep ocean ===

{{Further|Carbon sequestration#Sequestration techniques in oceans|Ocean acidification#Technologies to remove carbon dioxide from the ocean|Blue carbon}}

These options focus on the carbon which ocean reservoirs can store. They include [[ocean fertilization]], [[ocean alkalinity enhancement]] or [[enhanced weathering]].The IPCC found in 2022 ocean-based mitigation options currently have only limited deployment potential. But it assessed that their future mitigation potential is large. It found that in total, ocean-based methods could remove 1–100&nbsp;Gt of {{CO2}} per year. Their costs are in the order of US$40–500 per tonne of {{CO2}}. Most of these options could also help to reduce [[ocean acidification]]. This is the drop in pH value caused by increased atmospheric CO₂ concentrations.

The recovery of whale populations can play a role in mitigation as [[whale]]s play a significant part in [[nutrient recycling]] in the ocean. This occurs through what is referred to as the [[whale pump]], where whales’ liquid feces stay at the surface of the ocean. [[Phytoplankton]] live near the surface of the ocean in order use sunlight to photosynthesize and rely on much of the carbon, nitrogen and iron of the feces. As the phytoplankton form the [[Primary production|base]] of the [[marine food chain]] this increases ocean biomass and thus the amount of carbon sequestrated in it.

Blue carbon management is another type of ocean-based biological [[carbon dioxide removal]] (CDR). It can involve land-based as well as ocean-based measures. The term usually refers to the role that [[tidal marsh]]es, [[mangrove]]s and [[seagrass]]es can play in carbon sequestration. Some of these efforts can also take place in deep ocean waters. This is where the vast majority of ocean carbon is held. These ecosystems can contribute to climate change mitigation and also to [[ecosystem-based adaptation]]. Conversely, when blue carbon ecosystems are degraded or lost they release carbon back to the atmosphere. There is increasing interest in developing blue carbon potential. Scientists have found that in some cases these types of ecosystems remove far more carbon per area than terrestrial forests. However, the long-term effectiveness of blue carbon as a carbon dioxide removal solution remains under discussion.

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===Enhanced weathering===

{{Main|Enhanced weathering}}

Enhanced weathering could remove 2–4&nbsp;Gt of {{CO2}} per year. This process aims to accelerate natural [[weathering]] by spreading finely ground [[Silicate mineral|silicate]] rock, such as [[basalt]], onto surfaces. This speeds up chemical reactions between rocks, water, and air. It [[Carbon dioxide removal|removes carbon dioxide]] from the atmosphere, permanently storing it in solid [[carbonate mineral]]s or ocean [[alkalinity]].

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== Other methods to capture and store CO₂ ==

{{Main|Direct air capture|Carbon capture and storage|Bioenergy with carbon capture and storage}}

[[File:Carbon sequestration-2009-10-07.svg|thumb|upright=1.35|Schematic showing both terrestrial and geological sequestration of carbon dioxide emissions from a large point source, for example burning natural gas]]

In addition to traditional land-based methods to remove carbon dioxide (CO₂) from the air, other technologies are under development. These could reduce CO₂ emissions and lower existing atmospheric CO₂ levels. [[Carbon capture and storage]] (CCS) is a method to mitigate climate change by capturing CO₂ from large [[Point source pollution|point sources]], such as cement factories or [[Bioenergy with carbon capture and storage|biomass]] power plants. It then stores it away safely instead of releasing it into the atmosphere. The IPCC estimates that the costs of halting global warming would double without CCS.

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Among the most viable carbon dioxide removal methods considered alongside solar radiation modification, biochar soil amendment is already being deployed commercially. Studies indicate that the carbon it contains remains stable in soils for centuries, giving it a durable potential of removing gigatonnes of CO2 per year. Expert assessments place the net cost of removing CO2 with biochar between US$30 and $120 per tonne. Market data show that biochar supplied 94% of all durable CDR credits delivered in 2023, demonstrating current scalability. Stratospheric aerosol injection (SAI), by comparison, could reduce global temperature quickly by dispersing sulfate aerosols in the stratosphere; however, deployment at climatically relevant scale would require the design and certification of a new fleet of high‑altitude aircraft, a process estimated to take a decade or more, and ongoing operating costs of about US$18 billion for each degree Celsius of cooling. While models confirm that SAI would lower global mean temperature, there are potential side effect including ozone depletion, altered

regional precipitation patterns, and the risk of a sudden "termination shock" warming if the programme were interrupted. These systemic risks are absent from biochar deployment.

[[Bioenergy with carbon capture and storage]] (BECCS) expands on the potential of CCS and aims to lower atmospheric CO₂ levels. This process uses [[biomass]] grown for [[bioenergy]]. The biomass yields energy in useful forms such as electricity, heat, biofuels, etc. through consumption of the biomass via combustion, fermentation, or pyrolysis. The process captures the CO₂ that was extracted from the atmosphere when it grew. It then stores it underground or via land application as [[biochar]]. This effectively [[Carbon dioxide removal|removes it from the atmosphere]]. This makes BECCS a negative emissions technology (NET).

Scientists estimated the potential range of negative emissions from BECCS in 2018 as 0–22&nbsp;Gt per year. {{As of|2022}}, BECCS was capturing approximately 2 million tonnes per year of CO₂ annually. The cost and availability of biomass limits wide deployment of BECCS.{{rp|10}} BECCS currently forms a big part of achieving climate targets beyond 2050 in modelling, such as by the [[Integrated assessment modelling|Integrated Assessment Models]] (IAMs) associated with the IPCC process. But many scientists are sceptical due to the risk of loss of biodiversity.

[[Direct air capture]] is a process of capturing {{co2}} directly from the ambient air. This is in contrast to CCS which captures carbon from point sources. It generates a concentrated stream of {{CO2}} for [[Carbon sequestration|sequestration]], [[Carbon capture and utilization|utilisation]] or production of [[carbon-neutral fuel]] and [[windgas]].

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== Mitigation by sector ==

{{See also|Greenhouse gas emissions#Emissions by sector}}

| total_width       = 500

| image1           = Greenhouse Gas Emissions by Economic Sector.svg

| caption1         = Taking into account direct and indirect emissions, industry is the sector with the highest share of global emissions.

| image2           = Global GHG Emissions by Sector 2016.png

| caption2         = 2016 global greenhouse gas emissions by sector.Percentages are calculated from estimated global emissions of all Kyoto Greenhouse Gases, converted to {{CO2}} equivalent quantities (Gt{{CO2}}e).

}}

=== Buildings ===

{{Further|Energy-efficient buildings|Sustainable architecture|Green building|Low-energy house|Air conditioning paradox}}

The building sector accounts for 23% of global energy-related {{CO2}} emissions. About half of the energy is used for space and [[water heating]]. Building insulation can reduce the primary energy demand significantly. [[Heat pump]] loads may also provide a flexible resource that can participate in [[demand response]] to integrate variable renewable resources into the grid. [[Solar water heating]] uses thermal energy directly. Sufficiency measures include moving to smaller houses when the needs of households change, mixed use of spaces and the collective use of devices. Planners and civil engineers can construct new buildings using [[passive solar building design]], [[low-energy building]], or [[zero-energy building]] techniques. In addition, 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.

Refrigeration and air conditioning account for about 10% of global {{CO2}} emissions caused by fossil fuel-based energy production and the use of fluorinated gases. Alternative cooling systems, such as [[passive cooling]] building design and [[passive daytime radiative cooling]] surfaces, can reduce air conditioning use. Suburbs and cities in hot and arid climates can significantly reduce energy consumption from cooling with daytime radiative cooling.

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Energy consumption for cooling is likely to rise significantly due to increasing heat and availability of devices in poorer countries. Of the 2.8 billion people living in the hottest parts of the world, only 8% currently have air conditioners, compared with 90% of people in the US and Japan. By combining energy efficiency improvements and decarbonising electricity for air conditioning with the transition away from super-polluting refrigerants, the world could avoid cumulative greenhouse gas emissions of up to 210–460 Gt{{CO2}}-eq over the next four decades. A shift to renewable energy in the cooling sector comes with two advantages: Solar energy production with mid-day peaks corresponds with the load required for cooling and additionally, cooling has a large potential for load management in the electric grid.

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=== Urban planning ===

{{Main|Climate change and cities}}

[[File:BikesInAmsterdam 2004 SeanMcClean.jpg|right|thumb|[[Bicycle]]s have almost no [[carbon footprint]].]]

Cities emitted 28&nbsp;GtCO₂-eq in 2020 of combined CO₂ and {{CH4}} emissions. This was from producing and consuming goods and services. Climate-smart [[urban planning]] aims to reduce [[urban sprawl|sprawl]] to reduce the distance travelled. This lowers emissions from transportation. Switching from cars by improving [[walkability]] and [[cycling infrastructure]] is beneficial to a country's economy as a whole.

[[Urban forestry]], lakes and other blue and green infrastructure can reduce emissions directly and indirectly by reducing energy demand for cooling. Methane emissions from [[municipal solid waste]] can be reduced by segregation, [[compost]]ing, and recycling.

=== Transport ===

{{Main|Sustainable transport|Phase-out of fossil fuel vehicles}}

[[File:2015- Passenger electric vehicle (EV) annual sales - BloombergNEF.svg|thumb|Sales of electric vehicles (EVs) indicate a trend away from gas-powered vehicles that generate greenhouse gases.]]

Transportation accounts for 15% of emissions worldwide. Increasing the use of public transport, low-carbon freight transport and [[cycling]] are important components of transport decarbonisation.

[[Electric vehicle]]s and environmentally friendly rail help to reduce the consumption of fossil fuels. In most cases, electric trains are more efficient than air transport and truck transport. Other efficiency means include improved public transport, [[smart mobility]], carsharing and [[hybrid vehicle|electric hybrids]]. Fossil-fuel for passenger cars can be included in emissions trading. Furthermore, moving away from a [[car]]-dominated transport system towards low-carbon advanced public transport system is important.

Heavyweight, large personal vehicles (such as cars) require a lot of energy to move and take up much urban space. Several alternatives modes of transport are available to replace these. The European Union has made smart mobility part of its [[European Green Deal]]. In [[Smart city|smart cities]], smart mobility is also important.[[File:Societe de transport de Montreal bus 36-902 - 08.jpg|thumb|[[Battery electric bus]] in [[Montreal]]]]

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==== Shipping ====

{{Further|Environmental effects of shipping#Greenhouse gas emissions}}

In the shipping industry, the use of [[liquefied natural gas]] (LNG) as a marine bunker fuel is driven by emissions regulations. Ship operators must switch from [[heavy fuel oil]] to more expensive oil-based fuels, implement costly flue gas treatment technologies or switch to [[Marine LNG Engine|LNG engines]]. Methane slip, when gas leaks unburned through the engine, lowers the advantages of LNG. [[Maersk]], the world's biggest container shipping line and vessel operator, warns of [[stranded asset]]s when investing in transitional fuels like LNG. The company lists green [[ammonia]] as one of the preferred fuel types of the future. It has announced the first carbon-neutral vessel on the water by 2023, running on carbon-neutral [[methanol]]. Cruise operators are trialling partially [[hydrogen-powered ship]]s.

==== Air transport ====

{{Further|environmental impact of aviation}}

[[File:CO2 emissions fraction of Aviation (%25).png|thumb|Between 1940 and 2018, aviation [[CO2 emissions|CO₂ emissions]] grew from 0.7% to 2.65% of all {{CO2}} emissions.]]

Jet airliners contribute to climate change by emitting carbon dioxide, [[nitrogen oxides]], [[Condensation trails|contrails]] and particulates. Their [[radiative forcing]] is estimated at 1.3–1.4 that of {{CO2}} alone, excluding induced [[cirrus cloud]]. In 2018, global commercial operations generated 2.4% of all {{CO2}} emissions.

The aviation industry has become more fuel efficient. But overall emissions have risen as the volume of air travel has increased.By 2020, aviation emissions were 70% higher than in 2005 and they could grow by 300% by 2050.

It is possible to reduce aviation's environmental footprint by better [[fuel economy in aircraft]]. Optimising flight routes to lower non-{{CO2}} effects on climate from nitrogen oxides, particulates or contrails can also help. [[Aviation biofuel]], [[carbon emission trading]] and [[carbon offsetting]], part of the 191 nation ICAO's [[Carbon Offsetting and Reduction Scheme for International Aviation]] (CORSIA), can lower {{CO2}} emissions. [[Short-haul flight ban]]s, train connections, personal choices and [[aviation taxation and subsidies|taxation on flights]] can lead to fewer flights. [[Hybrid electric aircraft]] and [[electric aircraft]] or [[hydrogen-powered aircraft]] may replace fossil fuel-powered aircraft.

Experts expect emissions from aviation to rise in most projections, at least until 2040. They currently amount to 180&nbsp;Mt of {{CO2}} or 11% of transport emissions. [[Aviation biofuel]] and hydrogen can only cover a small proportion of flights in the coming years. Experts expect hybrid-driven aircraft to start commercial regional scheduled flights after 2030. Battery-powered aircraft are likely to enter the market after 2035. Under CORSIA, flight operators can purchase [[carbon offset]]s to cover their emissions above 2019 levels. CORSIA will be compulsory from 2027.

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=== Agriculture, forestry and land use ===

[[File:Environmental-impact-of-food-by-life-cycle-stage.png|thumb|upright=1.35|[[Greenhouse gas emissions]] across the [[supply chain]] for different foods, showing which type of food should be encouraged and which discouraged from a mitigation perspective]]

{{See also|Greenhouse gas emissions from agriculture|Environmental impact of meat production|4=Sustainable agriculture}}

Almost 20% of greenhouse gas emissions come from the agriculture and forestry sector. To significantly reduce these emissions, annual investments in the agriculture sector need to increase to $260 billion by 2030. The potential benefits from these investments are estimated at $4.3 trillion by 2030, offering a substantial economic return of 16-to-1.

Mitigation measures in the food system can be divided into four categories. These are demand-side changes, ecosystem protections, mitigation on farms, and mitigation in [[supply chains]]. On the demand side, limiting [[food waste]] is an effective way to reduce food emissions. Changes to a diet less reliant on animal products such as [[plant-based diets]] are also effective.

With 21% of global methane emissions, cattle are a major driver of global warming. When rainforests are cut and the land is converted for grazing, the impact is even higher. In Brazil, producing 1&nbsp;kg of beef can result in the emission of up to 335&nbsp;kg CO₂-eq.

Important mitigation options for reducing the greenhouse gas emissions from livestock include genetic selection, introduction of [[Methanotroph|methanotrophic bacteria]] into the rumen, diet modification and grazing management. Other options are diet changes towards [[ruminant]]-free alternatives, such as [[milk substitute]]s and [[meat analogue]]s. Non-ruminant livestock, such as poultry, emit far fewer GHGs.

It is possible to cut methane emissions in rice cultivation by improved water management, combining dry seeding and one drawdown, or executing a [[alternate wetting and drying|sequence of wetting and drying]]. This results in emission reductions of up to 90% compared to full flooding and even increased yields.

Reducing the usage of [[Fertilizer#Nitrogen_fertilizers|nitrogen fertilizers]] through [[nutrient management]] could avoid nitrous oxide emissions equal to 2.77 - 11.48 gigatons of carbon dioxide from 2020 to 2050.

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=== Industry ===

  | caption= Global [[List of countries by carbon dioxide emissions|carbon dioxide emissions]] by country in 2023:

  | label1 = China

  | label2 = United States

  | label3 = European Union

  | label4 = India

  | label5 = Russia

  | label6 = Japan

Industry is the largest emitter of greenhouse gases when direct and indirect emissions are included. [[Electrification]] can reduce emissions from industry. [[Green hydrogen]] can play a major role in [[energy-intensive industries]] for which electricity is not an option. Further mitigation options involve the steel and cement industry, which can switch to a less polluting production process. Products can be made with less material to reduce emission-intensity and industrial processes can be made more efficient. Finally, [[circular economy]] measures reduce the need for new materials. This also saves on emissions that would have been released from the mining of collecting of those materials.

Another sector with a significant carbon footprint is the steel sector, which is responsible for about 7% of global emissions. Emissions can be reduced by using [[electric arc furnaces]] to melt and recycle scrap steel. To produce virgin steel without emissions, [[blast furnace]]s could be replaced by hydrogen [[direct reduced iron]] and [[electric arc furnace]]s. Alternatively, carbon capture and storage solutions can be used.

Coal, gas and oil production often come with significant methane leakage. In the early 2020s some governments recognised the scale of the problem and introduced regulations. [[Methane leaks]] at oil and gas wells and processing plants are cost-effective to fix in countries which can easily trade gas internationally. There are leaks in countries where gas is cheap; such as Iran, and Turkmenistan. Nearly all this can be stopped by replacing old components and preventing routine flaring. [[Coalbed methane]] may continue leaking even after the mine has been closed. But it can be captured by drainage and/or ventilation systems. Fossil fuel firms do not always have financial incentives to tackle methane leakage.

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===Health and well-being===

{{Further|Effects of climate change on human health#Benefits from climate change mitigation and adaptation}}

{{See also|Health and environmental impact of the coal industry|Health and environmental impact of the petroleum industry}}

== Negative side effects ==

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== Costs and funding ==

{{Main|Economics of climate change mitigation#Assessing costs and benefits|Economic analysis of climate change}}

Mitigation costs will vary according to how and when emissions are cut. Early, well-planned action will minimise the costs. Globally, the benefits of keeping warming under 2&nbsp;°C exceed the costs, which according to [[The Economist]] are affordable.

Economists estimate the cost of climate change mitigation at between 1% and 2% of [[Gross domestic product|GDP]]. While this is a large sum, it is still far less than the subsidies governments provide to the ailing fossil fuel industry. The [[International Monetary Fund]] estimated this at more than $5 trillion per year.

Globally, limiting warming to 2&nbsp;°C may result in higher economic benefits than economic costs. The economic repercussions of mitigation vary widely across regions and households, depending on policy design and level of [[international cooperation]]. Delayed global cooperation increases policy costs across regions, especially in those that are relatively carbon intensive at present. Pathways with uniform carbon values show higher mitigation costs in more carbon-intensive regions, in fossil-fuels exporting regions and in poorer regions. Aggregate quantifications expressed in GDP or monetary terms undervalue the economic effects on households in poorer countries. The actual effects on welfare and well-being are comparatively larger.

[[Cost–benefit analysis]] may be unsuitable for analysing climate change mitigation as a whole. But it is still useful for analysing the difference between a 1.5&nbsp;°C target and 2&nbsp;°C. One way of estimating the cost of reducing emissions is by considering the likely costs of potential technological and output changes. Policymakers 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.

[[Eco-tariff]]s on only imports contribute to reduced global export [[Competition (economics)|competitiveness]] and to [[deindustrialisation]].

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=== Avoided costs of climate change effects ===

{{See also|Economic impacts of climate change}}

It is possible to avoid some of the costs of the [[effects of climate change]] by limiting climate change. According to the [[Stern Review]], inaction can be as high as the equivalent of losing at least 5% of global gross domestic product (GDP) each year, now and forever. This can be up to 20% of GDP or more when including a wider range of risks and impacts. But mitigating climate change will only cost about 2% of GDP. Also it may not be a good idea from a financial perspective to delay significant reductions in greenhouse gas emissions.

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=== Distributing emissions abatement costs ===

There have been different proposals on how to allocate responsibility for cutting emissions. These include [[egalitarianism]], [[basic needs]] according to a minimum level of consumption, proportionality and the [[Polluter pays principle|polluter-pays principle]]. A specific proposal is "equal per capita entitlements". This approach has 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 or cumulative emissions.

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===Funding===

{{main|Climate finance|Economics of climate change mitigation#Finance}}

In order to reconcile economic development with mitigating carbon emissions, developing countries need particular support. This would be both financial and technical. The IPCC found that accelerated support would also tackle inequities in financial and economic vulnerability to climate change. One way to achieve this is the Kyoto Protocol's [[Clean Development Mechanism]] (CDM).

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== Policies ==

=== National policies ===

[[File:Total CO2 emissions by country in 2017 vs per capita emissions (top 40 countries).svg|thumb|Although China is the leading producer of {{CO2}} emissions in the world with the U.S. second, per capita the U.S. leads China by a fair margin (data from 2017).]]Climate change mitigation policies can have a large and complex impact on the socio-economic status of individuals and countries This can be both positive and negative. It is important to design policies well and make them inclusive. Otherwise climate change mitigation measures can impose higher financial costs on poor households.

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An evaluation was conducted on 1,500 climate policy interventions made between 1998 and 2022. The interventions took place in 41 countries and across 6 continents, which together contributed 81% of the world's total emissions as of 2019. The evaluation found 63 successful interventions that resulted in significant emission reductions; the total {{CO2}} release averted by these interventions was between 0.6 and 1.8 billion metric tonnes. The study focused on interventions with at least 4.5% emission reductions, but the researchers noted that meeting the reductions required by the Paris Agreement would require 23 billion metric tonnes per year. Generally, carbon pricing was found to be most effective in [[Developed country|developed countries]], while regulation was most effective in the [[Developing country|developing countries]]. Complementary policy mixes benefited from synergies, and were mostly found to be more effective interventions than the implementation of isolated policies.

* '''Other''' policies include the ''Establishing an Independent climate advisory body''.

* '''Non market based''' policies include the Implementing or tighening of ''Regulatory standards''. These set technology or performance standards. They can be effective in addressing the [[market failure]] of informational barriers.

*Among '''market based''' policies, the ''carbon price'' has been found to be the most effective (at least for developed economies), and has its own section below. Additional ''market based'' policy instruments for climate change mitigation include:

''Emissions taxes'' These often require domestic emitters to pay a fixed fee or tax for every tonne of CO₂ emissions they release into the atmosphere. [[Methane emissions]] from fossil fuel extraction are also occasionally taxed. But methane and nitrous oxide from agriculture are typically not subject to tax.

<br />''Removing unhelpful subsidies:'' Many countries provide subsidies for activities that affect emissions. For example, significant [[fossil fuel subsidies]] are present in many countries. [[Fossil fuel phase-out#Phase-out of fossil fuel subsidies|Phasing-out fossil fuel subsidies]] is crucial to address the climate crisis. It must however be done carefully to avoid protests and making poor people poorer.

<br />''Creating helpful subsidies'': Creating subsidies and financial incentives. One example is [[Energy subsidy|energy subsidies]] to support clean generation which is not yet commercially viable such as tidal power.

<br />''Tradable permits'': A [[carbon emission trading|permit system]] can limit emissions.

==== Carbon pricing ====

{{Main|Carbon price}}

[[File:ETS-allowance-prices.svg|thumb|upright=1.35|Carbon emission trade – allowance prices from 2008]]

Imposing additional costs on greenhouse gas emissions can make fossil fuels less competitive and accelerate investments into low-carbon sources of energy. A growing number of countries raise a fixed [[carbon tax]] or participate in dynamic [[carbon emission trading]] (ETS) systems. In 2021, more than 21% of global greenhouse gas emissions were covered by a carbon price. This was a big increase from earlier due to the introduction of the [[Chinese national carbon trading scheme]].

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Trading schemes offer the possibility to limit emission allowances to certain reduction targets. However, an oversupply of allowances keeps most ETS at low price levels around $10 with a low impact. This includes the Chinese ETS which started with $7/t{{CO2}} in 2021. One exception is the [[European Union Emission Trading Scheme]] where prices began to rise in 2018. They reached about €80/t{{CO2}} in 2022. This results in additional costs of about €0.04/KWh for coal and €0.02/KWh for gas combustion for electricity, depending on the [[emission intensity]]. Industries which have high energy requirements and high emissions often pay only very low energy taxes, or even none at all.

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While this is often part of national schemes, [[carbon offsets and credits]] can be part of a voluntary market as well such as on the international market. Notably, the company [[Blue Carbon (company)|Blue Carbon]] of the [[UAE]] has bought ownership over an area equivalent to the United Kingdom to be preserved in return for carbon credits.

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=== International agreements ===

{{Main|Politics of climate change}}

{{See also|Climate change#Policies and politics|Climate change mitigation framework}}

[[International cooperation]] is considered a ''critical enabler'' for climate action Almost all countries are parties to the [[United Nations Framework Convention on Climate Change]] (UNFCCC). The ultimate objective of the UNFCCC is to stabilise atmospheric concentrations of greenhouse gases at a level that would prevent dangerous human interference with the climate system.

Although not designed for this purpose, the [[Montreal Protocol]] has benefited climate change mitigation efforts. The Montreal Protocol is an international treaty that has successfully reduced emissions of [[ozone-depleting substance]]s such as [[Chlorofluorocarbon|CFCs]]. These are also greenhouse gases.

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==== Paris Agreement ====

[[File:ParisAgreement.svg|thumb|[[Paris Agreement#Parties and signatories|Signatories (yellow) and parties (blue)]] to the [[Paris Agreement]]]]

{{excerpt|Paris Agreement|paragraphs=1|file=no}}

== History ==

{{See also|Climate change mitigation framework|History of climate change policy and politics|Kyoto Protocol#Chronology|Paris Agreement#Development}}

Historically efforts to deal with climate change have taken place at a multinational level. They involve attempts to reach a consensus decision at the United Nations, under the [[United Nations Framework Convention on Climate Change]] (UNFCCC). This is the dominant approach historically of engaging as many international governments as possible in taking action on a worldwide public issue. The [[Montreal Protocol]] in 1987 is a precedent that this approach can work. But some critics say the top-down framework of only utilising the UNFCCC consensus approach is ineffective. They put forward counter-proposals of bottom-up governance. At this same time this would lessen the emphasis on the UNFCCC.

The [[Kyoto Protocol]] to the UNFCCC adopted in 1997 set out legally binding emission reduction commitments for the "Annex 1" countries. The Protocol defined three international policy instruments ("[[Flexibility mechanisms|Flexibility Mechanisms]]") which could be used by the Annex 1 countries to meet their emission reduction commitments. According to Bashmakov, use of these instruments could significantly reduce the costs for Annex 1 countries in meeting their emission reduction commitments.

The Paris Agreement reached in 2015 succeeded the [[Kyoto Protocol]] which expired in 2020. [[List of Kyoto Protocol signatories|Countries that ratified the Kyoto protocol]] committed to reduce their emissions of carbon dioxide and five other greenhouse gases, or engage in [[carbon emissions trading]] if they maintain or increase emissions of these gases.

In 2015, the UNFCCC's "structured expert dialogue" came to the conclusion that, "in some regions and vulnerable ecosystems, high risks are projected even for warming above 1.5&nbsp;°C". Together with the strong diplomatic voice of the poorest countries and the island nations in the Pacific, this expert finding was the driving force leading to the decision of the 2015 [[2015 United Nations Climate Change Conference|Paris Climate Conference]] to lay down this 1.5&nbsp;°C long-term target on top of the existing 2&nbsp;°C goal.