Climate change mitigation Source: en.wikipedia.org/wiki/Climate_change_mitigation

Coal, oil, and natural gas remain the primary global energy sources even as renewables have begun rapidly increasing.^[1][2]

Multiple pathways exist to limit climate change to 1.5 °C or 2 °C in the context of the temperature goals set forth in the Paris Agreement.

Climate change mitigation consists of actions to limit global warming and its related effects. This is mainly reductions in human emissions of greenhouse gases (GHGs) as well as activities that reduce their concentration in the atmosphere.^[3] It is one of the ways to respond to climate change, along with adaptation.^[4] Fossil fuels emit most carbon dioxide(CO₂) and greenhouse gas as a whole.^[5] The most important challenge is to stop burning coal, oil, and gas and use only clean energy. Due to massive price drops, wind power and solar photovoltaics (PV) are increasingly out-competing oil, gas and coal^[6] though these require energy storage and improved electrical grids. As low-emission energy is deployed at large scale, transport and heating can shift to these mostly electric sources.^[7] Mitigation of climate change may also be achieved by changes in agriculture (to reduce greenhouse gas emissions from agriculture), transport, forest-management (reforestation and preservation), waste management, buildings, and industrial systems.^[8] Methane emissions, which have a high short-term impact, can be targeted by reductions in dairy products and meat consumption^[9] by imposing meat tax.^[10]

Political and economical responses to date include forms of carbon pricing by carbon taxes and carbon emission trading, reductions of fossil fuel subsidies, making national promises and laws, subsidies, simplified regulations for the integration of low-carbon energy and divestment from fossil fuel finance.

Almost all countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC).^[11] The ultimate objective of the UNFCCC is to stabilize atmospheric concentrations of GHGs at a level that would prevent dangerous human interference with the climate system.^[12] In 2010, Parties to the UNFCCC agreed that future global warming should be limited to below 2 °C (3.6 °F) relative to the pre-industrial level.^[13] With the Paris Agreement of 2015, this was confirmed.^[14]

The current trajectory of global greenhouse gas emissions is not consistent with limiting global warming to below 1.5 or 2 °C despite the limit being economically beneficial globally and to many top GHG emitters such as China and India.^[15][16]

Goals of stabilizing greenhouse gas concentrations[edit]

If CO₂ emissions would only stop growing this would not stabilize the GHG concentration in the atmosphere.^[17]

Stabilizing the atmospheric concentration of CO₂ at a constant level would require emissions to be effectively eliminated.^[17]

The UNFCCC aims to stabilize greenhouse gas (GHG) concentrations 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.^[18] Currently human activities are adding CO₂ to the atmosphere faster than natural processes can remove it.^[17]

Needed emissions cuts[edit]

In 2018, human activities were estimated to have caused approximately 1.0 °C of global warming above pre-industrial levels, with a likely range of 0.8 °C to 1.2 °C.^[19]

According to the emissions gap report of the United Nations Environment Programme for limiting warming to 1.5 °C GHG emissions should be cut from the level of 2020 by 76% by 2030.^[20]

According to the Special Report on Global Warming of 1.5 °C limiting warming below or close to 1.5 °C (2.7 °F) would require to decrease net CO₂ emissions by around 45% by 2030 from the level of 2010 and reach net zero by 2050. For limiting global warming to below 2 °C (3.6 °F), CO₂ emissions should decline by 25% by 2030 and by 100% by 2075. Non-CO₂ emissions need to be strongly reduced at similar levels in both scenarios.^[21]

In 2022, the Intergovernmental Panel on Climate Change (IPCC) released its Sixth Assessment Report on climate change, warning that greenhouse gas emissions must peak before 2025 at the latest and decline 43% by 2030, in order to likely limit global warming to 1.5°C (2.7°F).^[22][23] Secretary-general of the United Nations, António Guterres, clarified that for this "Main emitters must drastically cut emissions starting this year".^[24]

Carbon reduction[edit]

Carbon sequestration is the process of storing carbon dioxide in a solid and dissolved forms for very long periods.^[25] It is a tremendous process which could reduce the anthropogenic carbon footprint at a stable state.^[26] However, the cost of the process could be cost inefficient and the safety of the process on other ecological cycles is uncertain.^[27]

Calculations[edit]

The IPCC works with the concept of a fixed carbon emissions budget. If emissions remain on the current level of 42 GtCO₂, the carbon budget for 1.5 °C could be exhausted in 2028.^[28] The rise in temperature to that level would occur with some delay between 2030 and 2052.^[29] Even if it was possible to achieve negative emissions in the future, 1.5 °C must not be exceeded at any time to avoid the loss of ecosystems.^[30]

In the Special Report on Global Warming of 1.5 °C, the IPCC emphasized the benefits of keeping global warming below this level.^[31] Emissions pathways with no or limited overshoot would require rapid and far-reaching transitions in energy, land, urban and infrastructure including transport and buildings, and industrial systems.^[32] Pathways that aim for limiting warming to 1.5 °C by 2100 after a temporary temperature overshoot rely on large-scale deployment of carbon dioxide removal (CDR) measures, which are uncertain and entail clear risks.^[33]

Effects[edit]

Climate change mitigation scenarios from the IPCC Fifth Assessment Report state that there will be 1.5 °C (2.7 °F) of warming by the end of the 21st century if emissions immediately decline and go to net zero by 2050.^[34] In the other end of the scenarios, there will be a 4.8 °C (8.6 °F) amount of warming if emissions continue upwards until they are triple current levels. The amount of sea level rise will also depend on the future emissions scenarios.^[35]

The intended effects and purpose of climate change mitigation is to prevent and mitigate detrimental direct and indirect effects of climate change, especially effects on humans and human civilization (e.g. national security) or, broadly, to enable a just future for all on a thriving planet. It has been described as protection of humanity.^[36][37]

Drivers of global warming[edit]

By sectors and countries[edit]

Global greenhouse gas emissions by sector, 2016.^[38] For climate change mitigation goals, pathways and mechanisms to effectively transform all sectors have to be developed and implemented at a rapid rate.

Global CO₂ emissions by region from fossil fuels combustion, 2019 (not accounting for extradomestic production / imports-footprints)

Emission responsibility allotments by country/region and industry^[39]

Climate change is driven by:

• greenhouse gas emissions
• loss of carbon sinks such as of tropical forests
• various smaller factors such contrails of airplanes (Earth's albedo^[40] and the Solar cycle can also have an effect on the climate but are not responsible for current climate change)
• feedback effects in the Earth system that alter any of the above and/or climate inertia whereby mitigation at certain degrees or types becomes difficult or only causes slow response by the climate system.

By greenhouse gas[edit]

Carbon dioxide (CO₂) is the dominant emitted greenhouse gas, while methane (CH₄) emissions almost have the same short-term impact.^[43] Nitrous oxide (N₂O) and fluorinated gases (F-Gases) play a minor role. With the Kyoto Protocol, the reduction of almost all anthropogenic greenhouse gases has been addressed.^[44]

GHG emissions are measured in CO₂ equivalents determined by their global warming potential (GWP), which depends on their lifetime in the atmosphere. Estimations largely depend on the ability of oceans and land sinks to absorb these gases. Short-lived climate pollutants (SLCPs) including methane, hydrofluorocarbons (HFCs), tropospheric ozone and black carbon persist in the atmosphere for a period ranging from days to 15 years as compared to carbon dioxide which can remain in the atmosphere for millennia.^[45] Reducing SLCP emissions can cut the ongoing rate of global warming by almost half and reduce the projected Arctic warming by two-thirds.^[46]

GHG emissions in 2019 were estimated at 57.4 GtCO₂e, while CO₂ emissions alone made up 42.5 Gt including land-use change (LUC).^[47]

While mitigation measures for decarbonization are essential on the longer-term, they could result in weak near-term warming because sources of carbon emissions often also co-emit air pollution. Hence, pairing measures that target carbon dioxide with measures targeting non-CO₂ pollutants – short-lived climate pollutants, which have faster effects on the climate, is essential for climate goals.^[48]

Carbon dioxide (CO₂)[edit]

• Fossil fuel: oil, gas and coal (89%) are the major driver of anthropogenic global warming with annual emissions of 35.6 GtCO₂ in 2019.^[42][49]
• Cement production (4%) is estimated at 1.42 GtCO₂^[42]
• Land-use change (LUC) is the imbalance of deforestation and reforestation. Estimations are very uncertain at 4.5 GtCO₂.^[41] Wildfires alone cause annual emissions of about 7 GtCO₂^[50][51]
• Non-energy use of fuels, carbon losses in coke ovens, and flaring in crude oil production.^[49]

Methane (CH₄)[edit]

Historical and future temperature projections showing importance of mitigating short-lived climate pollutants like methane

Methane has a high immediate impact with a 5-year global warming potential of up to 100.^[43] Given this, the current 389 Mt of methane emissions^[52] has about the same short-term global warming effect as CO₂ emissions, with a risk to trigger irreversible changes in climate and ecosystems. For methane, a reduction of about 30% below current emission levels would lead to a stabilization in its atmospheric concentration.^[17]

• Fossil fuels (32%), again, account for most of the methane emissions including coal mining (12% of methane total), gas distribution and leakages (11%) as well as gas venting in oil production (9%).^[52][5]
• Livestock (28%) with cattle (21%) as the dominant source, followed by buffalo (3%), sheep (2%), and goats (1.5%).^[52][53]
• Human waste and wastewater (21%): When biomass waste in landfills and organic substances in domestic and industrial wastewater is decomposed by bacteria in anaerobic conditions, substantial amounts of methane are generated.^[5]
• Rice cultivation (10%) on flooded rice fields is another agricultural source, where anaerobic decomposition of organic material produces methane.^[5]

Nitrous oxide (N
₂O)[edit]

N₂O has a high GWP and significant Ozone Depleting Potential (ODP). It is estimated that the global warming potential of N₂O over 100 years is 265 times greater than CO₂.^[54] For N₂O, a reduction of more than 50% would be required for a stabilization.^[17]

• Most emissions (56%) by agriculture, especially meat production: cattle (droppings on pasture), fertilizers, animal manure.^[5]
• Combustion of fossil fuels (18%) and bio fuels.^[55]
• Industrial production of adipic acid and nitric acid.

F-Gases[edit]

Fluorinated gases include hydrofluorocarbons (HFC), perfluorocarbons (PFC), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃). They are used by switchgear in the power sector, semiconductor manufacture, aluminium production and a large unknown source of SF₆.^[56] Continued phase down of manufacture and use of HFCs under the Kigali Amendment to the Montreal Protocol will help reduce HFC emissions and concurrently improve the energy efficiency of appliances that use HFCs like air conditioners, freezers and other refrigeration devices.

Black carbon[edit]

Black carbon is formed through the incomplete combustion of fossil fuels, biofuel, and biomass. It is not a greenhouse gas but a climate forcing agent. Black carbon can absorb sunlight and reduce albedo when deposited on snow and ice. Indirect heating can be caused by the interaction with clouds.^[57] Black carbon stays in the atmosphere for only several days to weeks.^[58] Emissions may be mitigated by upgrading coke ovens, installing particulate filters on diesel-based engines, reducing routine flaring, and minimizing open burning of biomass.

By other characteristics[edit]

The responsibility for anthropogenic climate change differs substantially among individuals, e.g. between groups or cohorts.

Generational[edit]

Researchers report that, on average, the elderly played "a leading role in driving up GHG emissions in the past decade and are on the way to becoming the largest contributor" due to factors such as demographic transition, low informed concern about climate change and high expenditures on carbon-intensive products like energy which is used i.a. for heating rooms and private transport.^[59][60] They are less affected by climate change impacts,^[61] but have e.g. the same vote-weights for the available electoral options.

Wealth[edit]

Studies find that the most affluent citizens of the world are responsible for most environmental impacts, and robust action by them is necessary for prospects of moving towards safer environmental conditions.^[62][63]

According to a 2020 report by Oxfam and the Stockholm Environment Institute,^[64][65] the richest 1% of the global population have caused twice as much carbon emissions as the poorest 50% over the 25 years from 1990 to 2015.^[66][67][68] This was, respectively, during that period, 15% of cumulative emissions compared to 7%.^[69] The bottom half of the population is directly-responsible for less than 20% of energy footprints and consume less than the top 5% in terms of trade-corrected energy. The largest disproportionality was identified to be in the domain of transport, where e.g. the top 10% consume 56% of vehicle fuel and conduct 70% of vehicle purchases.^[70] However, wealthy individuals are also often shareholders and typically have more influence^[71] and, especially in the case of billionaires, may also direct lobbying efforts, direct financial decisions, and/or control companies:

Companies, investors and politicians[edit]

Sometimes, top contributors to greenhouse gas emissions are identified as the companies emitting most GHGs.^[72][73][71] Similarly, investing asset management firms are often identified as controllers of large amounts of contemporary financial value with insufficient dedication to climate change targets, with the largest four asset managers controlling around 20% of the world's listed market values – an aggregate assets under management of $20 trillion as of 2021.^[74][75][76]

However, it may not necessarily be the structural interest of these companies to help mitigate climate change sufficiently instead of striving to generate near-maximum profit in the contemporary socioeconomic system, a globalized competitive consumption-demanding environment, and use all legal means to delay climate change action if such is beneficial (see below)^[71] – their products are being bought by consumers^[71] (for various reasons), the stock market likely underestimates (or cannot value) e.g. social benefits of climate mitigation,^[77] they are regulatable by governments,^[78] and don't have as much power as many large states (or groups of such) which e.g. have capacities of law enforcement and military, customs, legal frameworks and for business-, media-, education-, global-, trade- and industrial policies. A fraction of such policies or measures are invariably initially at least partly unpopular, and in the contemporary decision-making environment of (campaign-marketing-, party-, media-, and electoral/referendum plain votes-based) politics, unpopular decisions may be difficult for politicians to enact directly or help facilitate indirectly. The question of the largest responsibility or driver may be about who is holding (or withholding) the power (and capacity) to create and change the systems that cause climate change, such as the transportation system.^[71] While it has been pointed out that blaming drivers may not be constructive in terms of climate change mitigation, understanding these links of the supply chain may allow better understanding of the complex system or untangling the structures of power and decision-making that inhibit climate action.^[71]

Fossil fuel substitution[edit]

As most greenhouse gas emissions are due to fossil fuels, rapidly phasing out oil, gas and coal is critical. In a system based on fossil fuels, demand is expected to double until 2050. Switching to renewable energy combined with the electrification of transport and heating can lower the primary energy demand significantly.^[7] Currently, less than 20% of energy is used as electricity.^[79]

A global transition to sustainable energy across all sectors is feasible well before 2050. With dropping prices for wind and solar energy as well as storage, the transition no longer depends on economic viability but is considered as a question of political will. The sustainable energy system is more efficient and cost effective than the existing system.^[7] Investors in fossil fuels face a growing risk of stranded assets.^[80]

Unextractable fossil fuels[edit]

Potential CO₂ emissions from large fossil fuel projects 'carbon bombs' per country

Distribution of committed CO₂ emissions from developed fossil fuel reserves

For a 50% probability of limiting global warming by 2050 to 1.5 °C large amounts of fossil fuels would need to be left underground.^[81][82] In various nations oil and gas companies such as QatarEnergy, Gazprom and Saudi Aramco are planning new large fossil fuel projects, called "carbon bombs", that would defeat the 1.5 °C climate goal if not "defused" and produce greenhouse gases equivalent to a decade of CO₂ emissions from China. Researchers have identified the 425 biggest fossil fuel extraction projects globally, of which 40% as of 2020 are new projects that haven't yet started extraction.^[83] As of 2022^[update], countries like China and India are planning to boost production of coal and other fossil fuels.^[84]

According to a study, "staying within a 1.5 °C carbon budget (50% probability) implies leaving almost 40% of 'developed reserves' of fossil fuels unextracted".^[85] Climate policies-induced future lost financial profits from global stranded fossil-fuel assets would lead to major losses for freely managed wealth of investors in advanced economies in current economics.^[86]

Low-carbon energy sources[edit]

Wind and sun can be sources for large amounts of low-carbon energy at competitive production costs. But even in combination, generation of variable renewable energy fluctuates a lot. This can be tackled by extending grids over large areas with a sufficient capacity or by using energy storage (see also: forms of grid energy storage) and by other means. Load management of industrial energy consumption can help to balance the production of renewable energy production and its demand. Electricity production by biogas and hydro power can follow the energy demand. Both can be driven by variable energy prices.

The deployment of renewable energy would have to be accelerated six-fold though to stay under the 2 °C target.^[87]

The global primary energy demand exceeded 161,000 TWh in 2018.^[88] 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 are wasted. The actual amount of energy consumed is significantly lower at 116,000 TWh.^[79]

The competitiveness of renewable energy is a key to a rapid deployment. In 2020, onshore wind and solar photovoltaics were the cheapest source for new bulk electricity generation in many regions.^[89] Storage requirements cause additional costs. A carbon price can increase the competitiveness of renewable energy.

^* = 2018. All other values for 2019.

Solar energy[edit]

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.^[94]

• Solar photovoltaics (PV) has become the cheapest way to produce electric energy in many regions of the world, with production costs down to 0.015 US$/KWh in desert regions.^[95] The growth of photovoltaics is exponential and has doubled every three years since the 1990s. In the summer, PV power generation follows the daily demand curve.^[96]
• A different technology is concentrated solar power (CSP) using mirrors or lenses to concentrate a large area of sunlight onto a receiver. With CSP, the energy can be stored for a few hours, providing supply in the evening. This can outweigh the higher costs compared to PV.
• Solar water heating has doubled between 2010 and 2019. Total installed solar water heating systems provide a capacity of 501 GW_th, with 67% of the global share in China.^[97] Photovoltaic thermal hybrid solar collectors combine PV and solar heating.
• Floating solar^[98][99]
• Solar panels over canals^[100][101]
• Agrivoltaics^{[102][103][104]}

Wind power[edit]

The Shepherds Flat Wind Farm is an 845 megawatt (MW) nameplate capacity, wind farm in the US state of Oregon, each turbine is a nameplate 2 or 2.5 MW electricity generator.

Regions in the higher northern and southern latitudes have the highest potential for wind power.^[105] Installed capacity has reached 650 GW in 2019. Offshore wind power currently has a share of about 10% of new installations.^[106] Offshore wind farms are more expensive but the units deliver more energy per installed capacity with less fluctuations. In most regions, wind power generation is higher in the winter when PV output is low. For this reason, combinations of wind and solar power are recommended.

Hydro power[edit]

The 22,500 MW nameplate capacity Three Gorges Dam in the People's Republic of China, the largest hydroelectric power station in the world

Hydroelectricity plays a leading role in countries like Brazil, Norway and China.^[107] but there are geographical limits and environmental issues.^[108] Tidal power can be used in coastal regions.

Bioenergy[edit]

Biogas plants can provide dispatchable electricity generation, and heat when needed.^[109] A common concept is the co-fermentation of energy crops mixed with manure in agriculture. Burning plant-derived biomass releases CO₂, but it has still been classified as a renewable energy source in the EU and UN legal frameworks because photosynthesis cycles the CO₂ back into new crops. How a fuel is produced, transported and processed has a significant impact on lifecycle emissions. Transporting fuels over long distances and excessive use of nitrogen fertilisers can reduce the emissions savings made by the same fuel compared to natural gas by between 15 and 50 per cent.^[110] Renewable biofuels are starting to be used in aviation.

Nuclear power[edit]

A comparison of price changes for energy from nuclear fission and from other sources

In most 1.5 °C pathways of the Intergovernmental Panel on Climate Change's Special Report on Global Warming of 1.5 °C the share of nuclear power is increased.^[111] The main advantage of nuclear energy is the ability to deliver large amounts of base load when renewable energy is not available.^[112]

On the other hand, environmental and security risks could outweigh the benefits. As of 2019, no country has found a final solution to nuclear waste which can cause future damage and costs over more than one million years.^[113][114] Separated plutonium and enriched uranium could be used for nuclear weapons, which is considered to be a strategical motivation for countries to promote nuclear power. The according risks are comparable to climate change.^{[115][114][116][117]} The Fukushima disaster is estimated to cost taxpayers ~$187 billion^[118] and radioactive waste management is estimated to cost the EU ~$250 billion by 2050.^[119]

The construction of new nuclear reactors currently takes about 10 years, substantially longer than scaling up the deployment of wind and solar. The largest drawback of nuclear energy is often considered to be the large construction and operating costs when compared to alternatives of sustainable energy sources whose costs are decreasing and which are the fastest-growing source of electricity generation.^{[120][121][122][123][124]} Nuclear power avoided 2–3% of total global GHG emissions in 2021. Limited uranium-235 supply inhibits substantial expansion scenarios with novel nuclear technologies^[125][126] Nevertheless, China is building a significant number of new power plants, albeit significantly fewer reactors than originally planned. As of 2019^[update] the cost of extending nuclear power plant lifetimes is competitive with other electricity generation technologies, including new solar and wind projects.^[127] New projects are reported to be highly dependent on public subsidies.^[128]

Nuclear fusion[edit]

Nuclear fusion research, in the form of the ITER and other experimental projects, is underway but fusion energy is not likely to be commercially widespread before 2050.^{[129][130][131][132]}

Carbon neutral and negative fuels[edit]

Fossil fuel may be phased-out with carbon-neutral and carbon-negative pipeline and transportation fuels created with power-to-gas and gas to liquids technologies.^{[133][134][135]}

Natural gas[edit]

Natural gas, which is mostly methane, is viewed as a bridge fuel since it produces about half as much CO₂ as burning coal.^[136] Gas-fired power plants can provide the required flexibility in electricity production in combination wind and solar energy.^[137] But methane is itself a potent greenhouse gas, and it currently leaks from production wells, storage tanks, pipelines, and urban distribution pipes for natural gas.^[138] In a low-carbon scenario, gas-fueled power plants could still continue operation if methane was produced using power-to-gas technology with renewable energy sources. Another possibility is to convert the natural gas to hydrogen and use the latter instead to run the thermal power stations.

Energy efficiency and non-fossil fuel storage[edit]

Wind energy and photovoltaics can deliver large amounts of electric energy but not at any time and place. One approach is the conversation into storable forms of energy. This generally leads to losses in efficiency. A study by Imperial College London calculated the lowest levelised cost of different systems for mid-term and seasonal storage. In 2020, pumped hydro (PHES), compressed air (CAES) and Li-on batteries are most cost effective depending on charging rhythm. For 2040, a more significant role for Li-on and hydrogen is projected.^[139]

• Li-on batteries are widely used in battery storage power stations and, as of 2020^[update], are starting to be used in vehicle-to-grid storage.^[140] They provide a sufficient round-trip efficiency of 75–90 %.^[141] However their production can cause environmental problems.^[142] Levelized costs for battery storage have drastically fallen to 0.15 US$/KWh^[89]
• Hydrogen may be useful for seasonal energy storage.^[143] The low efficiency of 30% of the reconversion to electricity must improve dramatically before hydrogen storage can offer the same overall energy efficiency as batteries.^[141] Thermal energy in the conversion process can be used for district heating. For the electricity grid a German study estimated high costs of 0.176 €/KWh for reconversion concluding that substituting the electricity grid expansion entirely with hydrogen reconversion systems does not make sense from an economic standpoint.^[144] The concept of solar hydrogen is discussed for remote desert projects where grid connections to demand centers are not available.^[145] Because it has more energy per unit volume sometimes it may be better to use hydrogen in ammonia.^[146]

Super grids[edit]

Sketch of a possible super grid. The red squares represent the total surfaces needed for solar collectors of Concentrating Solar Thermal Power (CSP) plants to provide the present electricity demands.

Long-distance power lines help to minimize storage requirements. A continental transmission network can smoothen local variations of wind energy. With a global grid, even photovoltaics could be available all day and night. The strongest high-voltage direct current (HVDC) connections are quoted with losses of only 1.6% per 1000 km^[147] with a clear advantage compared to AC. HVDC is currently only used for point-to-point connections. Meshed HVDC grids are reported to be ready-to-use in Europe^[148] and to be in operation in China by 2022.^[149]

China has built many HVDC connections within the country and supports the idea of a global, intercontinental grid as a backbone system for the existing national AC grids.^[150] A super grid in the US in combination with renewable energy could reduce GHG emissions by 80%.^[151]

Smart grid and load management[edit]

Instead of expanding grids and storage for more power, electricity demand can be adjusted on the consumer side. This can flatten demand peaks. Traditionally, the energy system has treated consumer demand as fixed. Instead, data systems can combine with advanced software to pro-actively manage demand and respond to energy market prices.^[152]

Time of use tariffs are a common way to motivate electricity users to reduce their peak load consumption. On a household level, charging electric vehicles or running heat pumps combined with hot water storage when wind or sun energy are available reduces electricity costs.

Dynamic demand plans have devices passively shut off when stress is sensed on the electrical grid. This method may work very well with thermostats, when power on the grid sags a small amount, a low power temperature setting is automatically selected reducing the load on the grid. Refrigerators or heat pumps can reduce their consumption when clouds pass over solar installations. Consumers need to have a smart meter in order for the utility to calculate credits. Smart Scheduling of activities and processes can adjust demand to fluctuating supply.^[153][154]

Demand response devices can receive all sorts of messages from the grid. The message could be a request to use a low power mode similar to dynamic demand, to shut off entirely during a sudden failure on the grid, or notifications about the current and expected prices for power. This allows electric cars to recharge at the least expensive rates independent of the time of day. Vehicle-to-grid uses a car's battery to supply the grid temporarily.^[155][156] Smart grids could also monitor/control residential devices that are noncritical during periods of peak power consumption, and return their function during nonpeak hours.^[157]

Further flexibility techniques by which smart grids can help manage the variability of renewable energy (VRE) and increase efficiency include VRE forecasting methodologies.^[158]

Energy conservation and efficiency[edit]

In the European Investment Bank Climate Survey EU citizens said that in Europe, energy should be the most prioritised area of action against climate change.

Improved energy efficiency in buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third, and help control global emissions of greenhouse gases.^[159]

Service labels like Energy Star provide information on the energy consumption of products. A procurement toolkit to assist individuals and businesses buy energy efficient products that use low GWP refrigerants was developed by the Sustainable Purchasing Leadership Council.^[160] A trial of estimated financial energy cost of refrigerators alongside EU energy-efficiency class (EEEC) labels online found that the approach of labels involves a trade-off between financial considerations and higher cost requirements in effort or time for the product-selection from the many available options – which are often unlabelled and don't have any EEEC-requirement for being bought, used or sold within the EU. Moreover, in this one trial the labeling was ineffective in shifting purchases towards more sustainable options.^[161][162] Beyond establishing higher efficiency of household appliances such as fridges and washing machines^[163] (or smaller ovens and non-use of drying machines), facilitating (less or) greener travel, installation of heat pumps, energy audits,^[164] and reducing room heating are also important.^[165] Energy efficiency of appliances as well as cooking techniques/choices have a substantial impact on GHGs from foods.^[166][167] In order for consumers to efficiently conserve energy, they – especially tenants – may need to have access to the (up to real-time) data of their electricity use and knowledge about efficient conservation options. Moreover, the most effective energy conservation options may not be in households but the industry or e.g. public venues.^{[citation needed]}

The cogeneration of electric energy and district heat also improves efficiency.^{[citation needed]}

Head of the IEA declared the failure by governments and businesses to accelerate energy efficiency efforts as "inexplicable", with IEA analysis showing that greater efficiency could be achieved with existing technologies and measures.^[165]

Research and development[edit]

Scientific research and development can improve available technological options such as of smart grids, green hydrogen, energy efficiency, emerging energy sources like floating solar and of energy storage, as well as assisting in the design and practical implementation of efficient, timely and – e.g. socially – viable global and regional fossil fuel substitution strategies. Key components of such work may include peer review criticism, replication, review, standardization, production of (often initially conflicting) conclusions, implementation and analysis of trials, and the development of alternatives.^{[168][169][170]}

Carbon sinks and removal[edit]

About 58% of CO₂ emissions have been absorbed by carbon sinks, including plant growth, soil uptake, and ocean uptake (2020 Global Carbon Budget).

World protected area map with total percentage of each country under protection, where countries in lighter colors have more protected land

Carbon sequestration is the storing of carbon in to a reservoir called a carbon sink such as growing forests, swamps,^[171] wetlands/peatlands^[172][173] (due to which some call for bans of the sale/supply of turf),^[174] and (cultivated) algae^{[175][176][177]} or through artificial carbon dioxide removal such as direct air capture. Carbon dioxide removal is vital in climate change mitigation even with the best case scenarios of reducing carbon dioxide emissions as levels of CO₂ in the atmosphere are already at damaging levels.^[178]

Conserving areas by protecting areas can boost the carbon sequestration capacity.^{[179][180][181]} The European Union, through the EU Biodiversity Strategy for 2030 targets to protect 30% of the sea territory and 30% of the land territory by 2030. In 2021, seven countries (the G7) pledged to protect or preserve at least 30% of the world's land and 30% of the world's oceans to halt biodiversity loss.^[182] A survey by the United Nations Development Programme of public opinion on climate change found that forests and land conservation policies were the most popular solutions of climate change mitigation.^[183]

Researchers have raised the concern that the use of carbon offsets – such as by maintaining forests, reforestation or carbon capture – as well as renewable energy certificates^[184] allow polluting companies a business-as-usual approach to continue releasing greenhouse gases^[78][185] and for being, inappropriately trusted, untried techno-fixes.^[186] This also includes the 2022 IPCC report on climate change critiziced for containing "a lot of pipe dreams", relying on large negative emissions technologies.^[187] A review of studies by the Stanford Solutions Project concluded that relying on Carbon capture and storage/utilization (CCS/U) is a dangerous distraction, with it (in most and large-scale cases) being expensive, increasing air pollution and mining, inefficient and unlikely to be deployable at the scale required in time.^[188]

Carbon storage in land ecosystems[edit]

Transferring land rights to indigenous inhabitants is argued to efficiently conserve forests.

Globally, protecting healthy soils and restoring the soil carbon sponge could remove 7.6 billion tons of carbon dioxide from the atmosphere annually, which is more than the annual emissions of the US.^[189][190] 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. The 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.^[189]

Afforestation[edit]

Afforestation is the establishment of trees where there was previously no tree cover. Scenarios for new plantations covering up to 4000 Mha (6300 x 6300 km) calculate with a cumulative physical carbon biosequestration of more than 900 GtC (2300 GtCO₂) until 2100.^[191] However, these are not considered a viable alternative to aggressive emissions reduction,^[192] such as the Trillion Tree Campaign,^[193][194] as the plantations would need to be so large, they would eliminate most natural ecosystems or reduce food production.^[195]

Preventing deforestation and desertification[edit]

Avoided deforestation reduces CO₂ emissions at a rate of 1 tonne of CO₂ per $1–5 in opportunity costs from lost agriculture. Cutting trees for woodfuel, the main source of energy for the poor, and clearing forests for agriculture are major drivers of desertification and deforestation.

Tropical deforestation leads to substantial warming from non-CO₂-impacts. The deforestation to prevent for climate change mitigation is the tropical deforestation. Standing tropical forests help cool the average global temperature by more than 1 °C.^[196]

Land-rights[edit]

Transferring rights over land from public domain to its indigenous inhabitants, who have had a stake for millennia in preserving the forests that they depend on, is argued to be a cost-effective strategy to conserve forests.^[197] This includes the protection of such rights entitled in existing laws, such as the Forest Rights Act in India, where concessions to land continue to go mostly to powerful companies.^[197] The transferring of such rights in China, perhaps the largest land reform in modern times, has been argued to have increased forest cover.^[198][199] Granting title of the land has shown to have two or three times less clearing than even state run parks, notably in the Brazilian Amazon. Even while the largest cause of deforestation in the world's second largest rainforest in the Congo is smallholder agriculture and charcoal production, areas with community concessions have significantly less deforestation as communities are incentivized to manage the land sustainably, even reducing poverty.^[200] Conservation methods that exclude humans, called "fortress conservation", and even evict inhabitants from protected areas often lead to more exploitation of the land as the native inhabitants then turn to work for extractive companies to survive.^[198]

Addressing drivers of deforestation[edit]

Five broad food policy categories^[201]

As enforcement of forest protection may not sufficiently address the drivers behind deforestation – the largest of which being the production of beef in the case of the Amazon rainforest – it may also need policies. These could effectively ban and/or progressively discourage deforestation-associated trade via e.g. product information requirements, satellite monitoring like the Global Forest Watch, related eco-tariffs, and product certifications.^{[202][203][204]}

Preventing permafrost leaks[edit]

The global warming induced thawing of the permafrost, which stores about two times the amount of the carbon currently released in the atmosphere,^[205] releases the potent greenhouse gas, methane, in a positive feedback cycle that is feared to lead to a tipping point called runaway climate change. While the permafrost is about 14 degrees Fahrenheit, a blanket of snow insulates it from the colder air above which could be 40 degrees below zero Fahrenheit.^[206] A method proposed to prevent such a scenario is to bring back large herbivores such as seen in Pleistocene Park, where they keep the ground cooler by reducing snow cover height by about half and eliminating shrubs and thus keeping the ground more exposed to the cold air.^[207] There have been suggestions that for this purpose, de-extinction and/or rewilding the Arctic could be used, which have been criticized for likely being both inefficient and ineffective.^[208][209]

Reforestation[edit]

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.^[210][211]

Reforestation is the restocking of existing depleted forests or where there was once recently forests. Reforestation could save at least 1 GtCO₂/year, at an estimated cost of $5–15/tCO₂.^[212] 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.^[213][214] Promoting regrowth on abandoned farmland could offset years of carbon emissions.^[215] Russia, the United States and Canada have the most land suitable for reforestation.^[216]

Planting new trees can be expensive, especially for the poor who often live in areas of deforestation, and can be a risky investment as, for example, studies in the Sahel have found that 80 percent of planted trees die within two years. Instead, helping native species sprout naturally is much cheaper and more likely to survive, with even long deforested areas still containing an "underground forest" of living roots and tree stumps that are still able to regenerate. This could include pruning and coppicing the tree to accelerate its growth and that also provides woodfuel, a major source of deforestation. Such practices, called farmer-managed natural regeneration, are centuries old but the biggest obstacle towards implementing natural regrowth of trees are legal ownership of the trees by the state, often as a way of selling such timber rights to business people, leading to seedlings being uprooted by locals who saw them as a liability. Legal aid for locals^[217][218] and pressure to change the law such as in Mali and Niger where ownership of trees to residents was allowed has led to what has been called the largest positive environmental transformation in Africa, with it being possible to discern from space the border between Niger and the more barren land in Nigeria, where the law has not changed.^[210][211]

Researchers, including from the European Commission, found that, in terms of environmental services, it is better to avoid deforestation than to allow for deforestation to subsequently reforest, as the former leads to i.a. irreversible effects in terms of biodiversity loss and soil degradation.^[219] Additionally, the effects of af- or reforestation will be farther in the future than keeping existing forests intact.^[220] It takes much longer − several decades − for the benefits for global warming to manifest to the same carbon sequestration benefits from mature trees in tropical forests and hence from limiting deforestation.^[221] Mackey and Dooley consider "the protection and recovery of carbon-rich and long-lived ecosystems, especially natural forests" "the major climate solution".^[222] The global annual net loss of trees is estimated to be approximately 10 billion.^[223][224]

Proforestation[edit]

Proforestation is promoting forests to capture their full ecological potential.^[225] Restoring all degraded forests all over the world could capture about 205 GtC (750 GtCO₂).^[226] Secondary forests that have regrown in abandoned farmland are found to have less biodiversity than the original old-growth forests and original forests store 60% more carbon than these new forests.^[213] Allowing proforestation in some secondary forests will increase their accumulated carbon and biodiversity over time. Strategies for proforestation include rewilding,^[227] such as reintroducing apex predators and keystone species as, for example, predators keep the population of herbivores in check (which reduce the biomass of vegetation). Another strategy is establishing wildlife corridors connecting isolated protected areas.^[228][229]

Carbon storage in water ecosystems[edit]

The Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC) estimated in 2013 that one-third of humankind's annual emissions of CO₂ are absorbed by the oceans.^[230] Absorption by phytoplankton is very uncertain^[231] but may be 40% of all CO₂ emissions.^[232] However, dissolved CO₂ in water leads to ocean acidification, which harms marine life^[233] as acidification lowers the level of carbonate ions available for calcifying organisms to form their shells such as the plankton species that contribute to the foundation of the ocean food webs and acidification also impacts on a broad range of other physiological and ecological processes.^[234] Blue carbon refers to carbon dioxide removed from the atmosphere by the world's ocean ecosystems through plant and macroalgae growth^[235] and the accumulation and burial of organic matter in the soil.

Wetlands[edit]

Wet areas have lower oxygen levels dissolved than in the air and so oxygen reliant decomposition of organic matter by microbes into CO₂ is decreased. Peatland globally covers just 3% of the land's surface^[236] but stores up to 550 gigatonnes of carbon, representing 42% of all soil carbon and exceeds the carbon stored in all other vegetation types, including the world's forests.^[237] The threat to peatlands include draining the areas for agriculture and cutting down trees for lumber as the trees help hold and fix the peatland.^{[238][239][240]} Restoration of degraded peatlands can be done by blocking drainage channels in the peatland, and allowing natural vegetation to recover.^[228][241]

Coastal waters[edit]

(A) untrawled seamount and (B) a trawled seamount. Bottom trawling has destroyed many coastal habitats, one of the largest sinks of carbon.

Mangroves, salt marshes and seagrasses make up the majority of the ocean's vegetated habitats but only equal 0.05% of the plant biomass on land and stash carbon 40 times faster than tropical forests.^[228] 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 make other species thrive, thus increasing biomass in that area. In addition, oyster reefs mitigate the effects of climate change by reducing the force of waves from hurricanes and reduce the erosion from rising sea levels.^[242]

Synthetic carbon dioxide removal[edit]

Direct air capture[edit]

Direct air capture is a process of capturing CO₂ directly from the ambient air (as opposed to capturing from point sources) and generating a concentrated stream of CO₂ for sequestration or utilization or production of carbon-neutral fuel and windgas.^[243] Artificial processes vary, and concerns have been expressed about the long-term effects of some of these processes.^[244]

Carbon capture and storage[edit]

Schematic showing both terrestrial and geological sequestration of carbon dioxide emissions from a large point source, for example burning natural gas

Carbon capture and storage (CCS) is a method to mitigate climate change by capturing carbon dioxide (CO₂) from large point sources, such as cement factories or biomass power plants, and subsequently storing it away safely instead of releasing it into the atmosphere. The IPCC estimates that the costs of halting global warming would double without CCS.^[245] Norway's Sleipner gas field, beginning in 1996, stores almost a million tons of CO₂ a year to avoid penalties in producing natural gas with unusually high levels of CO₂.^[246][247]

Enhanced weathering[edit]

Enhanced weathering is the removal of carbon from the air into the earth, enhancing the natural carbon cycle where carbon is mineralized into rock. The CarbFix project couples with carbon capture and storage in power plants to turn carbon dioxide into stone in a relatively short period of two years, addressing the common concern of leakage in CCS projects which stores carbon as a gas instead. While this project used basalt rocks, olivine has also shown promise.^[248]

Geoengineering[edit]

This section is an excerpt from Solar geoengineering.[edit]

Proposed stratospheric aerosol injection research using a tethered balloon to inject aerosols into the stratosphere.

Solar geoengineering, or solar radiation modification (SRM) is a type of climate engineering in which sunlight (solar radiation) would be reflected back to space to limit or reverse human-caused climate change. It is not a substitute for reducing greenhouse gas emissions, but could act as a temporary measure to limit warming while emissions of greenhouse gases are reduced and carbon dioxide is removed. The two most studied methods for SRM are stratospheric aerosol injection and marine cloud brightening.^[249]

Solar geoengineering appears able to prevent some or much of climate change.^[250] Climate models consistently indicate that it is capable of returning global, regional, and local temperatures and precipitation closer to pre-industrial levels. Solar geoengineering's principal advantages are the speed with which it could be deployed and become active and the reversibility of its direct climatic effects. Stratospheric aerosol injection, the most widely studied method, appears technically feasible and inexpensive in terms of direct financial costs, though still out of reach for individuals, small states, or other non-state rogue actors; it would instead be the exclusive domain of large national economies or coalitions including at least one such economy.^[251] Solar geoengineering would not directly reduce carbon dioxide concentrations in the atmosphere, and thus does not address ocean acidification. Solar geoengineering's excessive and/or poorly distributed use, or sudden and sustained termination, could pose serious environmental risks. Other negative impacts are possible, but uncertain as little research has been done.^[252] Governing solar geoengineering is challenging for multiple reasons, including that few countries would likely be capable of doing it alone.^[252]

Solar Radiation Management is a geoengineering method that reduces the amount of solar energy absorbed by the greenhouse gases by reflecting the sunlight back through albedo modification.^[253] The solar geoengineering methods include placing reflective objects in space, injection of stratospheric aerosols, brightening marine clouds, and increasing albedo buildings on land etc.^[254] The potential to limit the global temperature would be highly efficient, but the costs of primary deployment and additional operational cost is very high and could have potential safety problem.^[255]

Decarbonization by sector[edit]

Transport[edit]

Alstom Citadis (left) and Eurotram (right) trams in Strasbourg on grassed track

Transportation emissions account for 15% of emissions worldwide.^[256] Increasing the use of public transport, low-carbon freight transport and cycling are important components of transport decarbonization.^[257][258]

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.^[259] Other efficiency means include improved public transport, smart mobility, carsharing and electric hybrids. Fossil-fuel powered passenger cars can be converted to electric propulsion. The production of alternative fuel without GHG emissions is only possible with high conversion losses. Furthermore, moving away from a car-dominated transport system towards low-carbon advanced public transport system is important.^[260]

Electric vehicles[edit]

Battery electric bus in Montreal

Between a quarter and three-quarters of cars on the road by 2050 are forecast to be electric vehicles. EVs use 38 megajoules per 100 km in comparison to 142 megajoules per 100 km for ICE cars.^[261] Hydrogen can be a solution for long-distance transport by trucks and hydrogen-powered ships where batteries alone are too heavy.^[262][263]

GHG emissions depend on the amount of green energy being used for battery or fuel cell production and charging. In a system mainly based on electricity from fossil fuels, emissions of electric vehicles can even exceed those of diesel combustion.^[264]

A European survey based on climate found that as of 2022, 39% of European citizens tend to prefer hybrid vehicles, while 33% prefer petrol or diesel vehicles. The least preferred type of vehicles are electric cars, preferred by 28% of Europeans.^[265]

44% Chinese car buyers are the most likely to buy an electric car, while 38% of Americans would opt for a hybrid car, 33% would prefer petrol or diesel, while only 29% would go for an electric car.^[265]

Shipping[edit]

In the shipping industry, the use of liquefied natural gas (LNG) as a marine bunker fuel is driven by emissions regulations. Ship operators have to switch from heavy fuel oil to more expensive oil-based fuels, implement costly flue gas treatment technologies or switch to LNG engines.^[266] Methane slip, when gas leaks unburned through the engine, lowers the advantages of LNG. Maersk, the largest container shipping line and vessel operator in the world, warns of stranded assets when investing into transitional fuels like LNG.^[267] The company lists green ammonia as one of the preferred fuel types of the future and has announced the first carbon-neutral vessel on the water by 2023, running on carbon-neutral methanol.^[268]

Hybrid and all electric ferries are suitable for short distances. Norway's goal is an all electric fleet by 2025.^[269] The E-ferry Ellen, which was developed in an EU-backed project, is in operation in Denmark.

Air travel[edit]

In aviation, current 180 Mt of CO₂ emissions (11% of emissions in transport) are expected to rise in most projections, at least until 2040. Aviation biofuel and hydrogen can only cover a small proportion of flights in the coming years. The market entry for hybrid-driven aircraft on regional scheduled flights is projected after 2030, for battery-powered aircraft after 2035.^[270]

In October 2016, the 191 nations of the ICAO established the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), requiring operators to purchase carbon offsets to cover their emissions above 2020 levels, starting from 2021. This is voluntary until 2027. The environmental impact of aviation increases at high altitudes.

Contrails, not only airplane greenhouse gas emissions, have a significant impact on climate change.^[271][272]

Energy[edit]

Energy consumption will need to be halved by 2050 for avoiding warming of 1.5 degrees above preindustrial levels. While this will slow economic growth it will not necessarily lead to a lower life level if it will be done in the right way.^[273]

Heating and cooling[edit]

The buildings sector accounts for 23% of global energy-related CO₂ emissions^[274] About half of the energy is used for space and water heating.^[275]

A combination of electric heat pumps and building insulation can reduce the primary energy demand significantly. Generally, electrification of heating and cooling would only reduce GHG emissions if the electric power comes from low-carbon sources. A fossil-fuel power station may only deliver 3 units of electrical energy for every 10 units of fuel energy released. Electrifying heating and cooling loads may also provide a flexible resource that can participate in demand response to integrate variable renewable resources into the grid.

Heat pumps[edit]

Outside unit of an air source heat pump

A modern heat pump typically produces around two to six times more thermal energy than electrical energy consumed, giving an effective efficiency of 200 to 600%, depending on the coefficient of performance and the outside temperature. It uses an electrically driven compressor to operate a refrigeration cycle that extracts heat energy from outdoor air and moves that heat to the space to be warmed. In the summer months, the cycle can be reversed for air conditioning. In areas with average winter temperatures well below freezing, ground source heat pumps are more efficient than air-source heat pumps. The high purchase price of a heat pump compared to resistance heaters may be offset when air conditioning is also needed.

With a market share of 30% and clean electricity, heat pumps could reduce global CO₂ emissions by 8% annually.^[276] Using ground source heat pumps could reduce around 60% of the primary energy demand and 90% of CO₂ emissions of natural gas boilers in Europe in 2050 and make handling high shares of renewable energy easier.^[277] Using surplus renewable energy in heat pumps is regarded as the most effective household means to reduce global warming and fossil fuel depletion.^[278]

Cooling[edit]

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. Slashing HFC consumption by 80% by midcentury could avoid more than 0.4 °C of global warming by the end of the century. About 90% of the emissions occur at the end of the equipment's life. Solutions include investing in proper disposal and refrigerants that are less polluting.^[279]

The energy consumption for cooling is expected 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.^[280] 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 GtCO₂e over the next four decades. ^[281] 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.

Electric resistant heating[edit]

Radiant heaters in households are cheap and widespread but less efficient than heat pumps. In areas like Norway, Brazil, and Quebec that have abundant hydroelectricity, electric heat and hot water are common. Large scale hot water tanks can be used for demand-side management and store variable renewable energy over hours or days.

Agriculture[edit]

As 25% of greenhouse gas emissions (GHGs) are coming from agriculture and land use, it is impossible to limit temperature rise to 1.5 degrees without addressing the emissions from agriculture. During 2021 United Nations Climate Change Conference, 45 countries pledged to give more than 4 billion dollars for transition to sustainable agriculture. The organization "Slow Food" expressed concern about the effectivity of the spendings, as they concentrate on technological solutions and reforestation en place of "a holistic agroecology that transforms food from a mass-produced commodity into part of a sustainable system that works within natural boundaries."^[282]

With 21% of the global methane emissions, cattle are a major driver on global warming.^[52] When rainforests are cut and the land is converted for grazing, the impact is even higher. This results in up to 335 kg CO_2eq emissions for the production of 1 kg beef in Brazil when using a 30-year time horizon.^[283] Other livestock, manure management and rice cultivation also produce relevant GHG emissions, in addition to fossil fuel combustion in agriculture.

Investment in improving and scaling up the production of dairy and meat alternatives leads to big greenhouse gas reductions compared with other investments.^[284] Also, photovoltaic-driven microbial protein production could use 10 times less land for an equivalent amount of protein compared to soybean cultivation.^[285]

Agricultural changes may require complementary laws and policies to drive and support dietary shifts, including changes in pet food,^[286] increases in organic food products,^{[287][288][289]} and substantial reductions of meat-intake (food miles usually do not play a large role).^{[290][291][292]}

Regenerative agriculture includes conservation tillage, diversity, rotation and cover crops, minimizing physical disturbance, minimizing the usage of chemicals.^[293] It has other benefits like improving the state of the soil and consequently yields.^[294] A research made by the Rodale institute suggests that a worldwide transition to regenerative agriculture can soak around 100% of the greenhouse gas emissions currently emitted by people.^[295] Restoring grasslands stores CO₂ with estimates 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.^[296] Allan Savory, as part of holistic management, claims that while large herds are often blamed for desertification, prehistoric lands supported large or larger herds and areas where herds were removed in the United States are still desertifying.^[297] Grazers, such as livestock that are not left to wander, would eat the grass and would minimize any grass growth.^{[296][298][299]} However, carbon sequestration is maximized when only part of the leaf matter is consumed by a moving herd as a corresponding amount of root matter is sloughed off too sequestering part of its carbon into the soil.^[296]

In the United States, soils account for about half of agricultural GHGs while agriculture, forestry and other land use emits 24%.^[300] The US EPA says soil management practices that can reduce the emissions of nitrous oxide (N
₂O) from soils include fertilizer usage, irrigation, and tillage.

Important mitigation options for reducing the greenhouse gas emissions from livestock include genetic selection,^[301][302] introduction of methanotrophic bacteria into the rumen,^[303][304] vaccines, feeds,^[305] toilet-training,^[306] diet modification and grazing management.^{[307][308][309]} Other options include just using ruminant-free alternatives instead, such as milk substitutes and meat analogues. Non-ruminant livestock (e.g. poultry) generates far fewer emissions.^[310]

A matrix of the progress in the adoption of management practices and approaches

Methods that enhance carbon sequestration in soil include no-till farming, residue mulching and crop rotation, all of which are more widely used in organic farming than in conventional farming.^[311][312] Because only 5% of US farmland currently uses no-till and residue mulching, there is a large potential for carbon sequestration.^[313][314]

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.^[315] The farming practice of cover crops has been recognized as climate-smart agriculture.^[316] Best management practices for European soils were described to increase soil organic carbon: conversion of arable land to grassland, straw incorporation, reduced tillage, straw incorporation combined with reduced tillage, ley cropping system and cover crops.^[317]

Agroforestry is one way to achieve sustainable intensification, which is farming method that can both boosts yield to supply the growing population and reduce greenhouse gas emissions.^[318] Agroforestry is the practice of integrating trees and shrubs into crop and animal farming systems, creating environmental benefits.^[319] Trees can absorb carbon dioxide from the air, leaves from the trees can enrich the soil, manure from livestock can nutrient crops and trees. Nitrogen can also be fixed by trees, which benefits crops.^[320] This method intensifies agriculture productivity while prevents deforestation, which all largely contribute to rising of CO₂.

Methane emissions in rice cultivation can be cut by implementing an improved water management, combining dry seeding and one drawdown, or a perfect execution of a sequence of wetting and drying. This results in emission reductions of up to 90% compared to full flooding and even increased yields.^[321]

Urban planning[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.^[322]

Effective urban planning to reduce sprawl aims to decrease the distance travelled by vehicles, lowering emissions from transportation. Personal cars are extremely inefficient at moving passengers, while public transport and bicycles are many times more efficient (as is the simplest form of human transportation, walking). All of these are encouraged by urban/community planning and are an effective way to reduce greenhouse gas emissions. Inefficient land use development practices have increased infrastructure costs as well as the amount of energy needed for transportation, community services, and buildings. Switching from cars by improving walkability and cycling infrastructure is either free or beneficial to a country's economy as a whole.^[323]

"Urban mitigation options can be categorized into three broad strategies: (1) reducing urban energy 3 consumption across all sectors, including through spatial planning and infrastructure; (2) electrification 4 and switching to net zero emissions resources; and (3) enhancing carbon stocks and uptake through 5 urban green and blue infrastructure, which can also offer multiple co-benefits."^[324]

Cities have big potential for reducing greenhouse gas emissions. They emitted 28 GtCO2-eq in the year 2020. Without any action cities supposed to emit 65 GtCO2-eq by the year 2050. With full scale mitigation action the emissions will be near zero, in the worst case they will be only 3 GtCO2-eq. City planning, supporting mixed use of space, transit, walking, cycling, sharing vehicles can reduce urban emissions by 23% – 26%. Urban forests, lakes and other blue and green infrastructure can reduce emissions directly and indirectly (trough reduce in energy demand for cooling for example).^[325]

At the same time, a growing number of citizens and government officials have begun advocating a smarter approach to land use planning. These smart growth practices include compact community development, multiple transportation choices, mixed land uses, and practices to conserve green space. These programs offer environmental, economic, and quality-of-life benefits; and they also serve to reduce energy usage and greenhouse gas emissions.

Reducing the number of cars on the road,^[326] for example through proof-of-parking requirements, corporate car sharing, road reallocation (from only car use to cycling road, ...), circulation plans, bans on on-street parking or by increasing the costs of car ownership can help in reducing traffic congestion in cities.

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 (urban agriculture, urban trees), which in turn could be served by a greater variety of non-automotive based transportation choices.

Changes in urban form, behavior programs, the circular economy, the shared economy, and digitalization trends can support systemic changes that lead to reductions in demand for transport services or expands the use of more efficient transport modes. Cities can reduce their transport-related fuel consumption by around 25% through combinations of more compact land use and the provision of less car-dependent transport infrastructure. Appropriate infrastructure, including protected pedestrian and bike pathways, can also support much greater localized active travel. Transport demand management incentives are expected to be necessary to support these systemic changes. There is mixed evidence of the effect of circular economy initiatives, shared economy initiatives, and digitalization on demand for transport services. For example, while dematerialization can reduce the amount of material that need to be transported to manufacturing facilities, an increase in online shopping with priority delivery can increase demand for freight transport. Similarly, while teleworking could reduce travel demand, increased ridesharing could increase vehicle-km travelled.^[327]

Building design[edit]

Emissions from housing are substantial,^[328] and government-supported energy efficiency programmes can make a difference.^[329]

According to the IPCC Sixth Assessment Report buildings emitted 21% of global GHG emissions in the year 2019. The report introduces a new scheme for reducing GHG emissions in buildings: SER = Sufficiency, Efficiency, Renewable. Sufficiency measures do not need very complex technology, energy supply, maintenance or replacement during the life of the building. Those include, natural ventilation, green roofs, white walls, mixed use of spaces, collective use of devices etc.^[330] There are multiple links between emissions from buildings and emissions from other sectors including those discussed in chapters 6, 7, 8, 10 and 11 in the report. Reducing GHG emissions from buildings is linked to Sharing economy and Circular economy.^[331]

With strong action to reduce energy consumption of buildings "average energy intensity of the global building stock would decrease by more than 80% by 2050."^[332]

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.^[333][334] This saves energy because it cools buildings and reduces the urban heat island effect thus reducing the use of air conditioning.

Governmental action[edit]

A study suggests that political choices that effectively delay mitigation have the largest effect on the share of costs and risks of mitigation options, followed by geophysical uncertainties, social factors influencing future energy demand and technological uncertainties.^[335]

Climate Action Tracker described the situation on 9 November 2021 as follows: the global temperature will rise by 2.7 °C by the end of the century with current policies and by 2.9 °C with nationally adopted policies. The temperature will rise by 2.4 °C if only the pledges for 2030 are implemented, by 2.1 °C if the long-term targets are also achieved. If all the announced targets are fully achieved the rise in global temperature will peak at 1.9 °C and go down to 1.8 °C by the year 2100.^[336] All the information about all climate pledges is sent to the Global Climate Action Portal - Nazca. The scientific community is checking their fulfillment.^[337]

Recent proposals suggest i.a.^{[clarification needed]} investments supporting a green recovery after the COVID-19 pandemic.^[338]

Paris agreement and Kyoto Protocol[edit]

In 2015, two official UNFCCC scientific expert bodies came to the conclusion that, "in some regions and vulnerable ecosystems, high risks are projected even for warming above 1.5 °C".^[339] This expert position was, together with the strong diplomatic voice of the poorest countries and the island nations in the Pacific, the driving force leading to the decision of the Paris Conference 2015, to lay down this 1.5 °C long-term target on top of the existing 2 °C goal.^[340]

The Paris Agreement has become the main current international agreement on combating climate change. Each country must determine, plan, and regularly report on the contribution that it undertakes to mitigate global warming.^[341] Climate change mitigation measures can be written down in national environmental policy documents like the nationally determined contributions (NDC).

The Paris agreement succeeds the 1997 Kyoto Protocol which expired in 2020. Countries that ratified the Kyoto protocol 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.

How well each individual country is on track to achieving its Paris agreement commitments can be followed on-line.^[342]

Additional commitments[edit]

In addition to the main agreements, there are many additional pledges made by international coalitions, countries, cities, regions and businesses. According to a report published in September 2019 before the 2019 UN Climate Action Summit, full implementation of all pledges, including those in the Paris Agreement, will be sufficient to limit temperature rise to 2 degrees but not to 1.5 degrees.^[343] After the report was published, additional pledges were made in the September climate summit^[344] and in December of that year.^[345]

In December 2020 another climate action summit was held and important commitments were made. The organizers stated that, including the commitments expected in the beginning of the following year, countries representing 70% of the global economy will be committed to reach zero emissions by 2050.^[346]

In September 2021 the US and EU launched the Global Methane Pledge to cut methane emissions by 30% by 2030. UK, Argentina, Indonesia, Italy and Mexico joined the initiative, "while Ghana and Iraq signaled interest in joining, according to a White House summary of the meeting, which noted those countries represent six of the top 15 methane emitters globally".^[347] Israel also joined the initiative^[348]

Some information about the pledges is collected and analyzed in the Global Climate Action portal, which enables the scientific community to check their fulfilment.^[349]

Carbon pricing[edit]

Carbon emission trade – allowance prices from 2008

Additional costs on GHG emissions can lower competitiveness of fossil fuels 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 GHG emissions were covered by a carbon price, a major increase due to the introduction of the Chinese national carbon trading scheme.^[350]

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/tCO₂ in 2021.^[351] One exception is the European Union Emission Trading Scheme where prices began to rise in 2018, exceeding €63/tCO₂ (72 $) in 2021.^[352] 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.

Latest models of the social cost of carbon calculate a damage of more than $3000 per ton CO₂ as a result of economy feedbacks and falling global GDP growth rates, while policy recommendations for a carbon price range from about $50 to $200.^[353]

Most energy taxes are still levied on energy products and motor vehicles, rather than on CO₂ emissions directly.^[354] Non-transport sectors as the agricultural sector, which produces large amounts of methane, are typically left untaxed by current policies.

The revenue of carbon pricing can used to support policies that promote carbon neutrality. Another approach the concept of a carbon fee and dividend which includes the redistribution on a per-capita basis. As a result, households with a low consumption can even benefit from carbon pricing.

Montreal protocol[edit]

Although not designed for this purpose, the Montreal Protocol has benefited climate change mitigation efforts.^[355] The Montreal Protocol is an international treaty that has successfully reduced emissions of ozone-depleting substances (for example, CFCs), which are also greenhouse gases.

Enaction of a state of emergency[edit]

Enacting a state of emergency may be composed of two elements: declaring a state of emergency that has formulated real-world i.e. legal effects and the associated enabling or ensuring of rapid complementary large-scale changes in human activity for the articulated purposes. To date, many governments have acknowledged, sometimes in the form of tentative text-form "declarations", that humanity is essentially in a state of climate emergency.

In November 2021, Greta Thunberg and other climate activists asked the United Nation to declare a level 3 systemwide climate emergency.^[356]

It has been proposed that the national security sector could play a unique role in the development of a global climate-emergency mobilisation of labour and resources to build a zero-emission economy and enact decarbonization.^[357]

Commentators and The Climate Mobilization have suggested mobilisation of resources on the scale of a war economy and other related exceptional or effective measures.^{[358][359][360][361][362]}

Costs and benefits[edit]

Globally, the benefits of keeping warming under 2 °C exceed the costs.^[363] However, some consider cost–benefit analysis unsuitable for analysing climate change mitigation as a whole but still useful for analysing the difference between a 1.5 °C target and 2 °C.^[364] The OECD has been applying economic models and qualitative assessments to inform on climate change benefits and tradeoffs.^[365]

Costs[edit]

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.^[212] Mitigation costs will vary according to how and when emissions are cut: early, well-planned action will minimise the costs.^[212]

Many economists estimate the cost of climate change mitigation at between 1% and 2% of GDP.^[364] In 2019, scientists from Australia and Germany presented the "One Earth Climate Model" showing how temperature increase can be limited to 1.5 °C for 1.7 trillion dollars a year.^[366][367] According to this study, a global investment of approximately $1.7 trillion per year would be needed to keep global warming below 1.5°C. The method used by the One Earth Climate Model does not resort to dangerous geo-engineering methods. Whereas this is a large sum, it is still far less than the subsidies governments currently provided to the ailing fossil fuel industry, estimated at more than $5 trillion per year by the International Monetary Fund.^[368][369] Abolishing fossil fuel subsidies is very important but must be done carefully to avoid making poor people poorer.^[370] Ian Parry, lead author of the 2021 IMF report "Still Not Getting Energy Prices Right: A Global and Country Update of Fossil Fuel Subsidies", said: "Some countries are reluctant to raise energy prices because they think it will harm the poor. But holding down fossil fuel prices is a highly inefficient way to help the poor, because most of the benefits accrue to wealthier households. It would be better to target resources towards helping poor and vulnerable people directly."^[371]

Benefits[edit]

By limiting climate change, some of the costs of the effects of climate change can be avoided.

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 (up to 20% of the GDP or more when including a wider range of risks and impacts), whereas mitigating climate change will only cost about 2% of the GDP. Also, delaying to take significant reductions in greenhouse gas emissions may not be a good idea, when seen from a financial perspective.^[372][373] Mitigation solutions are often evaluated in terms of costs and greenhouse gas reduction potentials, missing out on the consideration of direct effects on human well-being.^[374]

Mitigation measures may have many health co-benefits – potential measures can not only mitigate future health impacts from climate change but also improve health directly.^[375]

Climate change mitigation is also an issue of intergenerational justice^[376][377] with nonintervention thought by some to violate future people's freedom^[378][379] – conversely, mitigation may preserve societal freedoms and range of viable basic choices.

The research organization Project Drawdown identified global climate solutions and ranked them according to their benefits.^[380] Early deaths due to fossil fuel air pollution with a temperature rise to 2 °C cost more globally than mitigation would: and in India cost 4 to 5 times more.^[363] Air quality improvement is a near-term benefit among the many societal benefits from climate change mitigation, including substantial health benefits. Studies suggest that demand-side climate change mitigation solutions have largely beneficial effects on 18 constituents of well-being.^[381][382]

Sharing[edit]

One of the aspects of mitigation is how to share the costs and benefits of mitigation policies. Rich people tend to emit more GHG than poor people.^[383] Activities of the poor that involve emissions of GHGs are often associated with basic needs, such as cooking. For richer people, emissions tend to be associated with things such as eating beef, cars, frequent flying, and home heating.^[384] The impacts of cutting emissions could therefore have different impacts on human welfare according to 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):^[383]

• 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: 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. 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).^[385]
  • Comparable burdens and ability to pay: with this approach, countries would reduce emissions based on comparable burdens and their ability to take on the costs of reduction. Ways to assess burdens include monetary costs per head of population, as well as other, more complex measures, like the UNDP's Human Development Index.
  • Willingness to pay: with this approach, countries take on emission reductions based on their ability to pay along with how much they benefit^[386]from reducing their emissions.

Specific proposals[edit]

• Ad hoc: Lashof (1992) and Cline (1992) (referred to by Banuri et al., 1996, p. 106),^[383] 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).^[385] In international law, one state recognized the long-established use of another state's use of the fisheries resource. It was also recognized by the state that part of the other state's economy was dependent on that resource.

Barriers to implementation[edit]

It has been suggested that the main barriers to implementation are uncertainty, institutional void, short time horizon of policies and politicians and missing motives and willingness to start adapting. When information on climate change is held between the large numbers of actors involved it can be highly dispersed, context specific or difficult to access causing fragmentation to be a barrier. The short time horizon of policies and politicians often means that climate change policies are not implemented in favour of socially favoured societal issues. Statements are often posed to keep the illusion of political action to prevent or postpone decisions being made.^{[387][better source needed]} There may be cause for concern about metal requirement for relevant technologies such as photovoltaics.^[388] Many developing nations have made national adaptation programs which are frameworks to prioritize adaption needs.^[389]

Carbon budgets by country[edit]

An international policy to allocate carbon budgets to individual countries has not been implemented. This question raises fairness issues.^[390] With a linear reduction starting from the status quo, industrial countries would have a greater share of the remaining global budget. Using an equal share per capita globally, emission cuts in industrial countries would have to be extremely sharp.

Geopoliticial impacts[edit]

In 2019, oil and gas companies were listed by Forbes with sales of US$4.8 trillion, about 5% of the global GDP.^[391] Net importers such as China and the EU would gain advantages from a transition to low-carbon technologies driven by technological development, energy efficiency or climate change policy, while Russia, the USA or Canada could see their fossil fuel industries nearly shut down.^[392] On the other hand, countries with large areas such as Australia, Russia, China, the US, Canada and Brazil and also Africa and the Middle East have a potential for huge installations of renewable energy. The production of renewable energy technologies requires rare-earth elements with new supply chains.^[393]

Policies by country[edit]

Many countries are aiming for net zero emissions, and many have either carbon taxes or carbon emission trading.

Emission trading and carbon taxes around the world (2019)^[394]

  Carbon emission trading implemented or scheduled

  Carbon tax implemented or scheduled

  Carbon emission trading or carbon tax under consideration

Middle and high-income countries[edit]

United States[edit]

Efforts to reduce greenhouse gas emissions by the United States include energy policies which encourage efficiency through programs like Energy Star, Commercial Building Integration, and the Industrial Technologies Program.^[395]

In the absence of substantial federal action, state governments have adopted emissions-control laws such as the Regional Greenhouse Gas Initiative in the Northeast and the Global Warming Solutions Act of 2006 in California.^[396] In 2019 a new climate change bill was introduced in Minnesota. One of the targets, is making all the energy of the state carbon free, by 2030.^[397]

China[edit]

In 2020, China committed to peak emissions by 2030 and reach net zero by 2060;^[398] following the 2021 blackouts, officials indicated the 2030 target was something "to strive to" and not necessarily to be met.^[399] In order to limit warming to 1.5 °C coal plants in China without carbon capture must be phased out by 2045.^[400] The Chinese national carbon trading scheme started in 2021.

With more than 12 GtCO₂, China is the largest GHG emitter worldwide, still investing into new coal plants. On the other hand, China is also installing the largest capacities of renewable energy worldwide. In recent years, Chinese companies have flooded the world market with high-performance photovoltaic modules, resulting in competitive prices. China is also building a HVDC grid.

Chinas export-embodied emissions are estimated at a level of 1.7 GtCO₂ per year.^[401]

European Union[edit]

The climate commitments of the European Union are divided into three main categories: targets for the year 2020, 2030 and 2050. The European Union claim that their policies are in line with the goal of the Paris Agreement.^[402][403]

• Targets for 2020:^[404] Reduce GHG emissions by 20% from the level in 1990, produce 20% of energy from renewable sources, increase Energy Efficiency by 20%.
• Targets for 2030:^[405] Reduce GHG emission by 40% from the level of 1990. In 2019 The European Parliament adopted a resolution upgrading the target to 55%,^[406] produce 32% of energy from renewables, increase energy efficiency by 32.5%.
• Targets for 2050:^[402] become climate neutral.

The European Union claims that they have already achieved the 2020 target for emission reduction and have the legislation needed to achieve the 2030 targets. Already in 2018, its GHG emissions were 23% lower that in 1990.^[407]

New Zealand[edit]

New Zealand made significant pledges on climate change mitigation in 2019: reduce emissions to zero by 2050, plant 1 billion trees by 2028, and encouraging farmers to reduce emissions by 2025 or face higher taxes Already in 2019 New Zealand banned new offshore oil and gas drilling and decided the climate change issues will be examined before every important decision.^[408]

In early December 2020, Prime Minister Jacinda Ardern declared a climate change emergency and pledged that the New Zealand Government would be carbon neutral by 2025. Key goals and initiatives include requiring the public sector to buy only electric or hybrid vehicles, government buildings will have to meet new "green" building standards, and all 200 coal-fired boilers in public service buildings will be phased out.^[409][410]

Nigeria[edit]

To mitigate the adverse effect of climate change, not only did Nigeria sign the Paris agreement to reduce emission, in its national climate pledge, the Nigerian government has promised to "work towards" ending gas flaring by 2030. In order to achieve this goal, the government established a Gas Flare Commercialisation Programme to encourage investment in practices that reduce gas flaring. Also, the federal government has approved a new National Forest Policy which is aimed at "protecting ecosystems" while enhancing social development. Effort is also been made to stimulate the adoption of climate-smart agriculture and the planting of trees.^[411]

Low and middle income countries[edit]

In order to reconcile economic development with mitigating carbon emissions, developing countries need particular support, both financial and technical. One of the means of achieving this is the Kyoto Protocol's Clean Development Mechanism (CDM). The World Bank's Prototype Carbon Fund^[412] is a public private partnership that operates within the CDM.

An important point of contention, however, is how overseas development assistance not directly related to climate change mitigation is affected by funds provided to climate change mitigation.^[413] One of the outcomes of the UNFCC Copenhagen Climate Conference was the Copenhagen Accord, in which developed countries promised to provide US$30 million between 2010 and 2012 of new and additional resources.^[413] Yet it remains unclear what exactly the definition of additional is and the European Commission has requested its member states to define what they understand to be additional, and researchers at the Overseas Development Institute have found four main understandings:^[413]

1. Climate finance classified as aid, but additional to (over and above) the '0.7%' ODA target;
2. Increase on previous year's Official Development Assistance (ODA) spent on climate change mitigation;
3. Rising ODA levels that include climate change finance but where it is limited to a specified percentage; and
4. Increase in climate finance not connected to ODA.

The main point being that there is a conflict between the OECD states budget deficit cuts, the need to help developing countries adapt to develop sustainably and the need to ensure that funding does not come from cutting aid to other important Millennium Development Goals.^[413]

However, none of these initiatives suggest a quantitative cap on the emissions from developing countries. This is considered as a particularly difficult policy proposal as the economic growth of developing countries are proportionally reflected in the growth of greenhouse emissions.

In an attempt to provide more opportunities for developing countries to adapt clean technologies, UNEP and WTO urged the international community to reduce trade barriers and to conclude the Doha trade round "which includes opening trade in environmental goods and services".^[414]

In 2019 week of climate action in Latin America and the Caribbean result in a declaration in which leaders says that they will act to reduce emissions in the sectors of transportation, energy, urbanism, industry, forest conservation and land use and "sent a message of solidarity with all the people of Brazil suffering the consequences of the rainforest fires in the Amazon region, underscoring that protecting the world's forests is a collective responsibility, that forests are vital for life and that they are a critical part of the solution to climate change".^[415][416]

Carbon neutral and carbon negative countries[edit]

As of the year 2021, 3 countries became carbon negative, meaning they remove from the atmosphere more Greenhouse gas emissions then they emit. The countries are: Bhutan, Suriname, Panama. The countries formed a small coalition at 2021 United Nations Climate Change Conference and asked for help so that other countries will join it.^[417]

Legal action[edit]

In some countries, those affected by climate change may be able to sue major greenhouse gas emitters. Litigation has been attempted by entire countries and peoples, such as Palau^[418] and the Inuit,^[419] as well as non-governmental organizations such as the Sierra Club.^[420] Investor-owned coal, oil, and gas corporations could be legally and morally liable for climate-related human rights violations.^[421][422] Litigations are often carried out via collective pooling of effort and resources such as via organizations like Greenpeace,^[423] which sued a Polish coal utility^[423] and a German car manufacturer.^[424]

Requirements[edit]

Proving that some weather events are due specifically to global warming is now possible, and methodologies have been developed to show the increased risk of other events caused by global warming.^[425]

For a legal action for negligence (or similar) to succeed, "Plaintiffs ... must show that, more probably than not, their individual injuries were caused by the risk factor in question, as opposed to any other cause. This has sometimes been translated to a requirement of a relative risk of at least two."^[426] Another route (though with little legal bite) is the World Heritage Convention, if it can be shown that climate change is affecting World Heritage Sites like Mount Everest.^[427][428]

Of countries[edit]

Besides countries suing one another, there are also cases where people in a country have taken legal steps against their own government. Legal action has been taken to try to force the US Environmental Protection Agency to regulate greenhouse gas emissions under the Clean Air Act.^[429]

In the Netherlands and Belgium, organisations such as the foundation Urgenda and the Klimaatzaak^[430] in Belgium have also sued their governments as they believe their governments are not meeting the emission reductions they agreed to. Urgenda have already won their case against the Dutch government.^[431]

In 2019, 22 states, six cities and Washington, DC, in United States, sued the Trump administration for repealing the Clean Power Plan.^[432]

In 2020 a group of Swiss senior women sued their government for too weak action on stopping climate change. They claimed that the increase in heat waves caused by climate change, particularly impacts elderly people.^[433]

In November 2020 the European Court of Human Rights ordered 33 countries to respond to the climate lawsuit from four children and two adults living in Portugal. The lawsuit will be treated as a priority by the court.^[434]

In 2021, Germany's supreme constitutional court has ruled that the government's climate protection measures are insufficient to protect future generations and that the government had until the end of 2022 to improve its Climate Protection Act.^[435]

Of companies[edit]

According to a 2004 study commissioned by Friends of the Earth, ExxonMobil, and its predecessors caused 4.7 to 5.3 percent of the world's human-made carbon dioxide emissions between 1882 and 2002. The group suggested that such studies could form the basis for eventual legal action.^[436]

In 2015, Exxon received a subpoena. According to the Washington Post and confirmed by the company, the attorney general of New York, Eric Schneiderman, opened an investigation into the possibility that the company had misled the public and investors about the risks of climate change.^[437] In October 2019, the trial began.^[438] Massachusetts also sued Exxon, for hiding the impact of climate change.^[439]

In May 2021, in Milieudefensie et al v Royal Dutch Shell, the district court of The Hague ordered Royal Dutch Shell to cut its global carbon emissions by 45% by the end of 2030 compared to 2019 levels.^[440]

Societal responses[edit]

The European Investment Bank's Investment Survey 2020 found that firms with active climate policies invest more in energy efficiency.^[441]

Investment[edit]

The European Investment Bank's Investment Survey also found that Western and Northern European firms are more likely to invest in climate mitigation.^[441][442]

More firms plan to invest in climate change mitigation, specifically focusing on low-carbon sectors.^[443]

More than 1000 organizations with a worth of US$8 trillion have made commitments to fossil fuel divestment.^[444] Socially responsible investing funds allow investors to invest in funds that meet high environmental, social and corporate governance (ESG) standards.^[445] Proxy firms can be used to draft guidelines for investment managers that take these concerns into account.^[446]

As well as a policy risk, Ernst and Young identify physical, secondary, liability, transitional and reputation-based risks.^[447] Therefore, it is increasingly seen to be in the interest of investors to accept climate change as a real threat which they must proactively and independently address.

The European Investment Bank's investment survey 2021 found that during the COVID-19 pandemic, climate change was addressed by 43% of EU enterprises. Despite the pandemic's effect on businesses, the percentage of firms planning climate-related investment rose to 47%. This was a rise from 2020, when the percentage of climate related investment was at 41%.^[448][449]

In 2021, firms' investments in climate change mitigation were being hampered by uncertainty about the regulatory environment and taxation.^[450][451]

As of 2021, one current approach under development is binary "labelling" of investments as "green" according to an EU governmental body-created "taxonomy" for voluntarily financial investment redirection based on this categorization.^[452]

Funding[edit]

Funding, such as the Green Climate Fund, is often provided by nations, groups of nations and increasingly NGO and private sources. These funds are often channelled through the Global Environmental Facility (GEF). This is an environmental funding mechanism in the World Bank which is designed to deal with global environmental issues.^[453] The GEF was originally designed to tackle four main areas: biological diversity, climate change, international waters and ozone layer depletion, to which land degradation and persistent organic pollutant were added. The GEF funds projects that are agreed to achieve global environmental benefits that are endorsed by governments and screened by one of the GEF's implementing agencies.^[454]

Economics[edit]

There is a debate about a potentially critical need for new ways of economic accounting, including directly monitoring and quantifying positive real-world environmental effects such as air quality improvements and related unprofitable work like forest protection, alongside far-reaching structural changes of lifestyles^[455][456] as well as acknowledging and moving beyond the limits of current economics such as GDP.^[457] Some argue that for effective climate change mitigation degrowth has to occur, while some argue that eco-economic decoupling could limit climate change enough while continuing high rates of traditional GDP growth.^[458][459] There is also research and debate about requirements of how economic systems could be transformed for sustainability – such as how their jobs could transition harmonously into green jobs – a just transition – and how relevant sectors of the economy – like the renewable energy industry and the bioeconomy – could be adequately supported.^[460][461]

While degrowth is often believed to be associated with decreased living standards and austerity measures, many of

Physical risks of climate change top the list of business concerns for US and EU firms.^[462]

its proponents seek to expand universal public goods (such as public transport), increase health^{[463][464][465]} (fitness, wellbeing^[466] and freedom from diseases) and increase various forms of, often unconventional commons-oriented,^[467] labor. To this end, the application of both advanced technologies and reductions in various demands, including via overall reduced labor time^[468] or sufficiency-oriented strategies,^[469] are considered to be important by some.^[470][471]

On the level of international trade, domestic trade, production and product designs, policies such as for "digital product passports" have been proposed to link products with environment-related information which could be a requirement for both further measures as well as unfacilitated bottom-up consumer- and business-adaptations.^[472]

Research[edit]

It has been estimated that only 0.12% of all funding for climate-related research is spent on the social science of climate change mitigation.^[473] Vastly more funding is spent on natural science studies of climate change and considerable sums are also spent on studies of impact of and adaptation to climate change.^[473] It has been argued that this is a misallocation of resources, as the most urgent puzzle at the current juncture is to work out how to change human behavior to mitigate climate change and which measures could be used how, whereas the natural science of climate change is already well established and there will be decades and centuries to handle adaptation.^[473][474] For instance, a study concluded that forms of carbon allowances (carbon credits) – examples with some level of technical detail of which include the ECO currency system^[475][476] – could be an effective component of climate change mitigation, with the economic recovery of COVID-19 and new technical capacity having opened a favorable window of opportunity for initial test runs of such in appropriate regions, while many questions remain largely unaddressed.^{[477][478][479]}

Knowledge transfer, technology transfer,^[480][481] coordination structures, collaborative open efficient research and development,^{[482][483][484]} non-commercial forms of work and product exchange^[463] and inducing maximum efficient investments (not only by market incentives, but also via governments and policy, civil society, and others)^[485][486] could contribute to climate change mitigation. For example, a "global digital commons of knowledge, software and design, and local shared manufacturing capacities" may have the potential for helping addressing climate change.^[487]

Population planning[edit]

Since 1950, world population has tripled.^[488]

Worldwide population growth is mostly seen as a threat to food security and biodiversity^{[489][490][491]} but also considered as a challenge for climate change mitigation. Proposed measures include an improved access to family planning and access of women to education and economic opportunities.^{[492][493][494]} Targeting natalistic politics involves cultural, ethical and societal issues. Various religions discourage or prohibit some or all forms of birth control.^[495] Population size has a vastly different per capita effect on global warming in different countries.^[496]

In a 2021 paper for Sustainability Science, William J. Ripple, lead author of the World Scientists' Warning to Humanity: A Second Notice, Christopher Wolf and Eileen Crist demonstrate that "human population has been mostly ignored with regard to climate policy" and attribute this to the taboo nature of the issue given its association with population policies of the past, including forced sterilization campaigns and China's one-child policy. They take a different approach and argue that population policies can both advance social justice (such as by abolishing child marriage, expanding family planning services and reforms that improve education for women and girls) while at the same time mitigating the human impact on the climate and the earth system. They say that while overconsumption by the world's wealthy is responsible for 90% of GHG emissions, which can be redressed through eco-taxes, carbon pricing and other policies, the global human population of 7.7 billion contributes to climate change in myriad ways, including the consumption of natural resources and GHG emissions from transportation.^[497][498]

Lifestyle and behavior[edit]

The emissions of the richest 1% of the global population account for more than twice the combined share of the poorest 50%.^[499]

The IPCC Fifth Assessment Report emphasises that behaviour, lifestyle, and cultural change have a high mitigation potential in some sectors, particularly when complementing technological and structural change.^[500] Common recommendations include lowering home heating and cooling usage, burning less gasoline, supporting renewable energy sources, buying local products to reduce transportation and the use of communications technologies such as videoconferencing to reduce hypermobility.^[501][502] Other examples would be heating a room less or driving less. In general, higher consumption lifestyles have a greater environmental impact. The sources of emissions have also been shown to be highly unevenly distributed, with 45% of emissions coming from the lifestyles of just 10% of the global population.^[503] Several scientific studies have shown that when relatively rich people wish to reduce their carbon footprint, there are a few key actions they can take such as living car-free (2.4 tonnes CO₂), avoiding one round-trip transatlantic flight (1.6 tonnes) and eating a plant-based diet (0.8 tonnes).^[492]

These appear to differ significantly from the popular advice for "greening" one's lifestyle, which seem to fall mostly into the "low-impact" category: Replacing a typical car with a hybrid (0.52 tonnes); Washing clothes in cold water (0.25 tonnes); Recycling (0.21 tonnes); Upgrading light bulbs (0.10 tonnes); etc. The researchers found that public discourse on reducing one's carbon footprint overwhelmingly focuses on low-impact behaviors, and that mention of the high-impact behaviors is almost non-existent in the mainstream media, government publications, school textbooks, etc.^{[492][504][505]}

Product information requirements, satellite monitoring and product certifications are used to inform consumers how the products are contributing to climate change.^{[202][506][507]} Scientists also argue that piecemeal behavioural changes like re-using plastic bags are not a proportionate response to climate change. Though being beneficial, these debates would drive public focus away from the requirement for an energy system change of unprecedented scale to decarbonise rapidly.^[508] Moreover, policy measures such as targeted subsidies, eco-tariffs, effective sustainability certificates, legal product information requirements, CO₂ pricing,^[509] emissions allowances rationing,^[510][511] budget-allocations/labelling,^[510] targeted product-range exclusions, advertising bans, and feedback mechanisms are examples of measures that could have a more substantial positive impact consumption behavior than changes exclusively carried out by consumers and could address social issues such as consumers' inhibitive constraints of budgets, awareness and time.^[512]

91% of Chinese respondents to an EU survey, 73% of Britons, 70% of Europeans and 60% of Americans support stronger policies for climate change mitigation. 63% of EU residents, 59% of Britons, 50% of Americans and 60% of Chinese respondents are in favor of switching to renewable energy. 18% of Americans are in favor of natural gas as a source of energy. For Britons and EU citizens, nuclear energy is a more popular energy alternative.^[513]

69% of EU respondents, 71% of UK respondents, 62% of US respondents and 89% of Chinese respondents support a tax on the items and services that contribute the most to global warming.^[513]

Dietary change[edit]

The widespread adoption of a vegetarian diet could cut food-related greenhouse gas emissions by 63% by 2050.^[514] Addressing the high methane emissions by cattle, a 2016 study analyzed surcharges of 40% on beef and 20% on milk and suggests that an optimum plan would reduce emissions by 1 billion tonnes per year.^[515][516] China introduced new dietary guidelines in 2016 which aim to cut meat consumption by 50% and thereby reduce greenhouse gas emissions by 1 billion tonnes by 2030.^[517] Overall, food accounts for the largest share of consumption-based GHG emissions with nearly 20% of the global carbon footprint. Almost 15% of all anthropogenic GHG emissions has been attributed to the livestock sector alone.^[518]

The IPCC's summary of the 2019 special report stated that a shift towards plant-based diets would help to mitigate climate change.^[519] In addition to the IPCC's earlier reports, the new IPCC AR6 report includes information about cross-sectoral perspectives demand, services and social aspects of mitigation, and innovation, technology development and transfer.^[520] In particular, the IPCC AR6 Working Group 3 report stresses that reducing meat consumption will be necessary to reduce methane emissions.^[521]

A 2022 study published in Nature Food found that 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, which in turn has the potential to sequester 100 billion tons of CO₂ by the end of the century.^[522][523]

Modal shift[edit]

Heavyweight, large personal vehicles (such as cars) require a lot of energy to move and take up much urban space.^[524][525] Several alternatives modes of transport are available to replace these. The European Union has made smart mobility part of its European Green Deal^[526] and in smart cities, smart mobility is also important.^[527]

Activism[edit]

One of the September 2019 climate strikes

Environmental organizations take various actions such as Peoples Climate Marches. A major event was the global climate strike in September 2019 organized by Fridays For Future and Earth Strike.^[528] The target was to influence the climate action summit organized by the UN on 23 September.^[529] According to the organizers four million people participated in the strike on 20 September.^[530] In 2019, Extinction Rebellion organized large protests demanding to "reduce carbon emissions to zero by 2025, and create a citizens' assembly to oversee progress", including blocking roads.^[531]

Media, education and arts[edit]

Media can contribute to climate change mitigation by educating citizens about climate change such as about some of the reasons for mitigation.^{[532][533][534][535]} On the other hand, advertising and journalism also advance the climate emergency in various ways.^[536]

Content analyses found the share of media coverage of climate change to be relatively small.^[537][538] False balance refers to giving viewers an inaccurate perception of the state of affairs while trying to create the impression of neutral coverage by portraying certain questions as controversial despite there being a consensus of experts and scientists, with uncertainty or controversy being reserved for other, e.g. more specific, issues.

Research suggests that the coverage usually does not include scientific content^[539][540] and commonly showed false balance.^[541][542] It has been suggested that the "role of a free press is to inform the people"^[539] – particularly about societal problems of significance and with sufficiently unpoliticized unideological formats, shares of coverage and high quality relevant content that are appropriate.

Climate change has been called a niche topic in the media as well as a "cross-cutting issue that needs to be reflected, for example, in reporting on tax reforms, economic policy or new smartphone models" (translated).^[543] Journalists could contribute to making the coverage interesting and relevant.^[544] With climate change being a "global, complex, and abstract phenomenon", the media is considered to be a highly dependent on source of information and opinion formation about it.^[545]

News on social media may also be relevant to climate change mitigation.^[546][547]

Fiction and culture[edit]

While there are some novels of climate fiction that are based on scientific projections of climate change impacts,^{[548][549][550]} some observers have wondered why cinema appears to "ignore" climate change.^[551][552] Culture – which includes norms, prevailing paradigms of thinking or zeitgeist, lifestyles, art, elements of identity and consumption-patterns – may be an important factor of climate change mitigation.^[553][554] A study suggests that the historical and ongoing "carbon lock-in" is an outcome of the "pervasive failure in industrial, modern societies to imagine desirable ways of living that are neither wedded to the carbon economy nor dependent on narratives of progress reliant on perpetual economic growth" in terms of GDP-growth.^[555]

Education systems[edit]

Education about climate change and training of skills relevant to mitigation could be important for effective mitigation of climate change.^{[556][557][558]} It has been argued that there is a societal need for putting general problem solving skills at the center of education and that too little attention is being paid to real problem‐solving.^[559][560] As economies may partly start to orient towards sustainability, the number of "green jobs" may increase while other jobs are being lost. Such changes may make it more beneficial to develop education systems and establish ways of retraining. Increased expertise and awareness as well as a larger work-force may also facilitate further mitigation.^{[561][562][563][564]} Effectiveness of government regulation, a skilled work force and public awareness may be determinants of "mitigative capacity".^[564]

Strengthening climate education has been described as a social tipping intervention that supports and amplifies norms and values and can quickly inspire behavior change among individuals and their cohorts.^[565]

Overviews, integration and comparisons of measures[edit]

Platforms that aggregated a large number of potential climate change mitigation measures along with estimations of their effectiveness and assessed priority include Project Drawdown. The non-collaborative science-based website dedicated to the problem of climate change provides one methodological framework and modeling tool to assess impacts of technologies and practices at the global scale. On the website, solutions are incorporated into different areas such as sectors of the economy.^{[566][567][568]}

Individual climate change mitigation measures can be integrated into comprehensive strategies. Studies – including feasibility studies and policy studies – have been used to explore how countries could transform for decarbonization.^{[569][570][571]} At least one legislative package, GermanZero [de], has been created as a proposal for a feasible concrete nation-level 1.5 °C action-plan outside the political government.^[572] On the global scale, one study developed different broad scenarios of minimal energy requirements for providing decent living standards globally, finding that by 2050 energy use could generally be reduced to 1960 levels.^[471]

Research activities may help quantify interrelations between challenges of climate change mitigation – like that of variable renewable energy – and solutions. For example, comparative analyses of the overall environmental impacts of different solution combinations, of projections-based externalities-data and life-cycle assessments could be used to this end.^[573] An interdisciplinary "whole system approach" – such as for developing and considering other societal goals as well as, sometimes flexibly, taking complications into account while integrating an otherwise unmanageably large amount of problem domains, synergies, trade-offs,^[574] monitoring inputs, modelling results and data – may be important for adequate climate change mitigation.^{[575][576][577][578]}

Cybernetic research and modeling provide insights about the climate–social system of coupled feedback processes that shape or determine the trajectory of global greenhouse gas emissions over the century in the contemporary socioeconomic system.^[579]

Mitigation pathways[edit]

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Shape of mitigation[edit]

A typology of discourses aimed at delaying climate change mitigation^[580]

Climate change mitigation is interconnected with various co-benefits (such as reduced air pollution and associated health benefits)^[581] and how it is carried out (in terms of e.g. policymaking) could also determine its impacts on living standards (whether and how inequality and poverty are reduced).^[582]

Many mitigation measures are associated with new problems which depend on the shape and configuration of the mitigation. For instance, as mining for materials needed for renewable energy production increases threats to conservation areas, some strategic planning that takes such complications into consideration may be needed.^[583] There also is research into ways to recycle solar panels (including the emerging perovskite solar cells) as recycling solar panels could be important for sustainability, reduce electronic waste and create a source for materials that would otherwise need to be mined.^[584] Carbon rationing could have a larger effect on poorer households as "people in the low-income groups may have an above-average energy use, because they live in inefficient homes".^[511] However, forms of discourses about the shape of mitigation may "often lead to deadlock or a sense that there are intractable obstacles to taking action".^[580]

Tracking and monitoring[edit]

Satellites are increasingly being used for locating and measuring greenhouse gas emissions and deforestation. Earlier, scientists largely relied on or calculated estimates of greenhouse gas emissions and governments' self-reported data.^[585][586] They can also evaluate the environmental impact of policies and events such as the impact of the COVID-19 pandemic on the environment.^[587] Various other technologies are also being used for environmental monitoring.

It has been proposed that if politicians and business leaders know their actions (or inaction) are being recorded for future use, this could have immediate impacts.^[588]

While the status of most goals set for 2020 have not been evaluated in a definitive and detailed way or reported on by the media, the world failed to meet most or all international goals set for that year.^[589][590]

As the 2021 United Nations Climate Change Conference occurred in Glasgow, the group of researchers running the Climate Action Tracker reported that of countries responsible for 85% of GHG emissions, only four polities (responsible for 6% of global GHG emissions) – EU, UK, Chile and Costa Rica – have published a detailed official policy‑plan that describes the steps and ways by which 2030 mitigation targets could be realized.^[591] There are organizations that aim to transparently, neutrally and credibly monitor progress of climate change mitigation such as of pledges, goals, initiatives and other developments.^[592][349]

See also[edit]

References[edit]