Climate change mitigation facts for kids

Demand reduction

We can reduce demand for products and services that cause greenhouse gas emissions in three different ways. Firstly, we can reduce demand by behavioural and cultural changes. One example would be changes in diet, especially the decision to eat less meat, an effective action individuals take to fight climate change. Secondly, we can reduce demand by improving infrastructure. An example would be a good public transport network. Lastly, changes in end-use technology can reduce energy demand. For instance a well-insulated house emits less than a poorly-insulated house.

Mitigation options that reduce demand for products or services help people make personal choices to reduce their carbon footprint. This could be in their choice of transport or food. So these mitigation options have many social aspects that focus on demand reduction. We can call these demand-side mitigation actions. For example, people with high socio-economic status often cause more greenhouse gas emissions than those from a lower status. If they reduce their emissions and promote green policies, these people could become low-carbon lifestyle role models. However, there are many psychological variables that influence consumers. These include awareness and perceived risk. Government policies can support or hinder demand-side mitigation options. For example, public policy can promote circular economy concepts which would support climate change mitigation. Reducing greenhouse gas emissions is linked to the sharing economy.

There is a debate regarding the correlation of economic growth and emissions. It seems economic growth no longer necessarily means higher emissions.

Energy conservation and efficiency

Global primary energy demand exceeded 161,000 terawatt hours (TWh) in 2018. This refers to electricity, transport and heating including all losses. In transport and electricity production, fossil fuel usage has a low efficiency of less than 50%. Large amounts of heat in power plants and in motors of vehicles go to waste. The actual amount of energy consumed is significantly lower at 116,000 TWh.

Energy conservation is the effort made to reduce the consumption of energy by using less of an energy service. One way is to use energy more efficiently. For instance we would use less energy than before to produce the same service. Another way is to reduce the amount of service used. An example of this would be to drive less. Energy conservation is at the top of the sustainable energy hierarchy. We can conserve energy by reducing wastage and losses. We can improve efficiency by upgrading technology, and improving operations and maintenance.

Efficient energy use is the process of reducing the amount of energy required to provide products and services. We sometimes simply call it energy efficiency. Improved energy efficiency in buildings ("green buildings"), industrial processes and transportation could reduce the world's energy needs in 2050 by one third. This would help reduce global emissions of greenhouse gases. For example, insulating a building allows it to use less heating and cooling energy to achieve and maintain thermal comfort. Improvements in energy efficiency are generally achieved by adopting a more efficient technology or production process. Another way is to use commonly accepted methods to reduce energy losses.

Lifestyle changes

Individual action on climate change can include personal choices in many areas. These include diet, travel, household energy use, consumption of goods and services, and family size. People who wish to reduce their carbon footprint can take high-impact actions such as avoiding frequent flying and petrol-fuelled cars, eating mainly a plant-based diet, having fewer children, using clothes and electrical products for longer, and electrifying homes. These approaches are more practical for people in high-income countries with high-consumption lifestyles. Naturally, it is more difficult for those with lower income statuses to make these changes. This is because choices like electric-powered cars may not be available. Excessive consumption is more to blame for climate change than population increase. High-consumption lifestyles have a greater environmental impact, with the richest 10% of people emitting about half the total lifestyle emissions.

Dietary change

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 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 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.

Preserving and enhancing carbon sinks

An important mitigation measure is one the IPCC Sixth Assessment Report calls "preserving and enhancing carbon sinks". This refers to the management of Earth's natural carbon sinks in a way that preserves or increases their capability to remove CO₂ from the atmosphere and to store it durably. We call this 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 ecosystems 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 °C typically project the large-scale use of 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.

Forests

Conservation

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 forests that have regrown in abandoned farmland are found to have less biodiversity than the original old-growth forests. Original forests store 60% more carbon than these new forests. Strategies include rewilding and establishing wildlife corridors.

Mitigation measures in forestry are slow. They often have trade-offs with food prices. And they can lead to spill-over effects on climate from indirect land use change. Additionally, the long-term success of forestry mitigation measures depends on careful consideration of their ecological impact and their integration into broader sustainable land use practices.

Afforestation and reforestation

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 km) suggest cumulative carbon storage of more than 900 GtC (2300 GtCO₂) 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.

Reforestation is the restocking of existing depleted forests or in places where there were recently forests. Reforestation could save at least 1 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 GtC (750 GtCO₂). With increased intensive agriculture and urbanization, 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 forests 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 percent of planted trees in the Sahel die within two years. Reforestation has higher carbon storage potential than afforestation. In mangroves reforestation is predicted to provide 60% more carbon uptake per hectare in the 40 years after planting. Estuarine and coastal wetland ecosystems could see a 4.3-5.1% increase in annual CO₂ uptake by reforesting available mangrove areas. 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.

Soils

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 BECCS or afforestation, for example.

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 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.

Methods that enhance carbon sequestration in soil include no-till farming, residue mulching and crop rotation. Organic farming makes more use of these techniques than conventional farming does. Because only 5% of US farmland currently uses no-till and residue mulching, there is a large potential for carbon sequestration.

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 crops is a form of climate-smart agriculture. 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 cropping system and cover crops.

Regenerative agriculture includes conservation tillage, diversity, rotation and cover crops. It also includes minimizing physical disturbance and supporting carbon sequestration in soils. It has other benefits like improving the state of the soil and consequently yields.

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 soils and increase agricultural productivity. During production of biochar, heat is released which may be used as bioenergy.

Wetlands

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 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 wetlands are a significant source of methane emissions. Some also emit nitrous oxide. Peatland 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.

Mangroves, salt marshes and seagrasses 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 fertilizer runoff have damaged coastal habitats. Notably, 85% of oyster reefs 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.

Deep ocean

These options focus on the carbon we can store in ocean reservoirs. 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 Gt of CO₂ per year. Their costs are in the order of 40–500 USD 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.

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 marshes, mangroves and seagrasses 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.

Enhanced weathering

Enhanced weathering could remove 2–4 Gt of CO₂ per year. This process aims to accelerate natural weathering by spreading finely ground silicate rock, such as basalt, onto surfaces. This speeds up chemical reactions between rocks, water, and air. It removes carbon dioxide from the atmosphere, permanently storing it in solid carbonate minerals or ocean alkalinity. Cost estimates are in the 50-200 USD per tonne range of CO₂.

Other methods to capture and store CO₂

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 sources, such as cement factories or 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.

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 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 Gt per year. As of 2022^[update], BECCS was capturing approximately 2 million tonnes per year of CO₂ annually. The cost and availability of biomass limits wide deployment of BECCS. BECCS currently forms a big part of achieving climate targets beyond 2050 in modelling, such as by the 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 CO
2 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 sequestration, utilization or production of carbon-neutral fuel and windgas. Artificial processes vary, and there are concerns about the long-term effects of some of these processes.

Mitigation by sector

Buildings

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. We 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.

Heat pumps efficiently heat buildings, and cool them by air conditioning. A modern heat pump typically transports around three to five times more thermal energy than electrical energy consumed. The amount depends on the coefficient of performance and the outside temperature.

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.

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 with the transition away from super-polluting refrigerants, the world could avoid cumulative greenhouse gas emissions of up to 210–460 GtCO₂-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. Additionally, cooling has a large potential for load management in the electric grid.

Transport

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

Electric vehicles 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 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 cities, smart mobility is also important.

The World Bank is helping lower income countries buy electric buses. Their purchase price is higher than diesel buses. But lower running costs and health improvements due to cleaner air can offset this higher price.

Between one quarter and three quarters of cars on the road by 2050 are forecast to be electric vehicles. Hydrogen may be a solution for long-distance heavy freight trucks, if batteries alone are too heavy.

Shipping

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 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 assets 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 ships.

Hybrid and all electric ferries are suitable for short distances. Norway's goal is an all electric fleet by 2025.

Air transport

Jet airliners contribute to climate change by emitting carbon dioxide, nitrogen oxides, 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 bans, train connections, personal choices and 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 leat until 2040. They currently amount to 180 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 offsets to cover their emissions above 2019 levels. CORSIA will be compulsory from 2027.

Agriculture, forestry and land use

Almost 20% of greenhouse gas emissions come from the agriculture and forestry sector. 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 kg of beef can result in the emission of up to 335 kg CO₂-eq. Other livestock, manure management and rice cultivation also emit greenhouse gases, in addition to fossil fuel combustion in agriculture.

Important mitigation options for reducing the greenhouse gas emissions from livestock include genetic selection, introduction of methanotrophic bacteria into the rumen, vaccines, feeds, diet modification and grazing management. Other options are diet changes towards ruminant-free alternatives, such as milk substitutes and meat analogues. 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 sequence of wetting and drying. This results in emission reductions of up to 90% compared to full flooding and even increased yields.

Industry

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.

The decarbonisation of cement production requires new technologies, and therefore investment in innovation. Bioconcrete is one possibility to reduce emissions. But no technology for mitigation is yet mature. So CCS will be necessary at least in the short-term. Blast furnaces could be replaced by hydrogen direct reduced iron and electric arc furnaces.

Coal, gas and oil production often come with significant methane leakage. In the early 2020s some governments recognized 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, Russia, 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.

Co-benefits

Health and well-being

The health benefits from climate change mitigation are significant. Potential measures can not only mitigate future health impacts from climate change but also improve health directly. Climate change mitigation is interconnected with various health co-benefits, such as those from reduced air pollution. Air pollution generated by fossil fuel combustion is both a major driver of global warming and the cause of a large number of annual deaths. Some estimates are as high as 8.7 million excess deaths during 2018. Mitigation policies can also promote healthier diets such as less red meat, more active lifestyles, and increased exposure to green urban spaces. Access to urban green spaces provides benefits to mental health as well. The increased use of green and blue infrastructure can reduce the urban heat island effect. This reduces heat stress on people. Studies suggest that efforts to reduce consumption of goods and services have largely beneficial effects on 18 constituents of well-being.

Future sustainable pathways scenarios may result in an annual reduction of 1.18 million air pollution-related deaths, 5.86 million diet-related deaths, and 1.15 million deaths due to physical inactivity, across nine countries by 2040. These benefits were attributable to the mitigation of direct greenhouse gas emissions and the accompanying actions that reduce exposure to harmful pollutants, as well as improved diets and safe physical activity. Globally the cost of limiting warming to 2 °C is less than the value of the extra years of life due to cleaner air - and in India and China much less.

In the transportation sector mitigation strategies could enable more equitable access to transportation services and reduce congestion.

Addressing inequality can assist with climate change mitigation efforts. Placing health as a key focus of the Nationally Determined Contributions could present an opportunity to increase ambition and realise health co-benefits.

Climate change adaptation

Some mitigation measures have co-benefits in the area of climate change adaptation. This is for example the case for many nature-based solutions. Examples in the urban context include urban green and blue infrastructure which provide mitigation as well as adaptation benefits. This can be in the form of urban forests and street trees, green roofs and walls, urban agriculture and so forth. The mitigation is achieved through the conservation and expansion of carbon sinks and reduced energy use of buildings. Adaptation benefits come for example through reduced heat stress and flooding risk.

Costs and funding

Several factors affect mitigation cost estimates. One is the baseline. This is a reference scenario that the alternative mitigation scenario is compared with. Others are the way costs are modelled, and assumptions about future government policy. Cost estimates for mitigation for specific regions depend on the quantity of emissions allowed for that region in future, as well as the timing of interventions.

Mitigation costs will vary according to how and when emissions are cut. Early, well-planned action will minimize the costs. Globally, the benefits of keeping warming under 2 °C exceed the costs.

Economists estimate the cost of climate change mitigation at between 1% and 2% of GDP. Whereas 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.

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 °C target and 2 °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.

Avoided costs of climate change effects

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.

Mitigation solutions are often evaluated in terms of costs and greenhouse gas reduction potentials. This fails to take into account the direct effects on human well-being.

Distributing emissions abatement costs

Mitigation at the speed and scale required to limit warming to 2 °C or below implies deep economic and structural changes. These raise multiple types of distributional concerns across regions, income classes and sectors.

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. 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.

Funding

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).

Policies

Municipal policies and urban planning

Cities have a big potential to reduce greenhouse gas emissions. They emitted 28 GtCO2-eq in 2020 of combined CO₂ and CH
4 emissions. This was from producing and consuming goods and services. Climate-smart urban planning aims to reduce sprawl to reduce the distance travelled. This lowers emissions from transportation. It supports mixed use of space and transit. Walking, cycling and sharing vehicles can reduce urban emissions. Urban forestry, lakes and other blue and green infrastructure can reduce emissions directly and indirectly by reducing energy demand for cooling. Personal cars are extremely inefficient at moving passengers. Public transport and bicycles are many times more efficient in an urban context. Switching from cars by improving walkability and cycling infrastructure is either free or beneficial to a country's economy as a whole. Methane emissions from municipal solid waste can be reduced by segregation, composting, and recycling.

National policies

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.

The most effective and economically efficient approach of achieving lower emissions in the energy sector is to apply a combination of measures. These include market-based instruments such as taxes and permits, standards, and information policies.

Types of national policies that would support climate change mitigation include:

• Regulatory standards: These set technology or performance standards. They can be effective in addressing the market failure of informational barriers. If the costs of regulation are less than the benefits of addressing the market failure, standards can result in net benefits. One example is fuel-efficiency standards for cars.
• Market-based instruments such as emission taxes and charges. An emissions tax requires domestic emitters to pay a fixed fee or tax for every tonne of CO₂-eq GHG emissions they release into the atmosphere. If every emitter were to face the same level of tax, emitters would choose the lowest cost way of achieving emission reductions first. In the real world, however, markets are not perfect. This means that an emissions tax may deviate from this ideal. Distributional and equity considerations usually result in differential tax rates for different sources.
• Tradable permits: A permit system can limit emissions. A number of permits are distributed equal to the emission limit. Each liable entity must hold the number of permits equal to its actual emissions. A tradable permit system can be cost-effective if costs are not excessive. There must also be no significant imperfections in the permit market and markets relating to emitting activities.
• Voluntary agreements: These are agreements between governments, often in the form of public agencies, and industry. Agreements may relate to general issues, such as research and development. In other cases they may involve quantitative targets. There is, however, the risk that participants in the agreement will free ride. They can do this by not complying with the agreement or by benefitting from the agreement while bearing no cost.
• Informational instruments: Poor information is a barrier to improving energy efficiency or reducing emissions. Examples of policies in this area include increasing public awareness of energy saving with home heating and insulation or emissions from meat and dairy products. However some say that it is politically toxic for a politician to ask people to eat less meat.
• Research and development policies: Some areas, such as soil, may differ by country and so need national research. Technologies may need financial support to reach commercial scale, for example floating wind power.
• Low carbon power: Governments may relax planning regulations on solar power and onshore wind. They may also partly finance technologies considered risky by the private sector, such as nuclear.
• Demand-side management: This aims to reduce energy demand, e.g. through energy audits, labelling, and regulation.
• Adding or removing subsidies:
  • A subsidy for greenhouse gas emissions reductions pays entities a specific amount per tonne of CO₂-eq for every tonne of greenhouse gas reduced or sequestered. Subsidies are generally less efficient than taxes. But distributional and competitiveness issues sometimes result when energy/emission taxes are coupled with subsidies or tax exceptions.
  • Creating subsidies and financial incentives. One example is energy subsidies to support clean generation which is not yet commercially viable such as tidal power.
  • Phasing-out of unhelpful subsidies. Many countries provide subsidies for activities that affect emissions. Examples are subsidies in the agriculture and energy sectors, and indirect subsidies for transport.
• A Green Marshall Plan. This calls for global central bank money creation to fund green infrastructure.
• Market liberalization: Energy markets have been restructured in several countries and regions. These policies mainly aim to increase competition in the market. But they can also have a significant impact on emissions.

Phasing out fossil fuel subsidies