Climate change mitigation

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

Climate change mitigation consists of actions to limit global warming and its related effects. This involves reductions in human emissions of greenhouse gases (GHGs) as well as activities that reduce their concentration in the atmosphere.[2]

Fossil fuel combustion accounts for 89% of all CO
2
emissions and 68% of all GHG emissions.[3] The most important challenge is to eliminate the use of coal, oil and gas and substitute them with clean energy sources. Due to massive price drops, wind power and solar photovoltaics (PV) are increasingly out-competing oil, gas and coal[4] though these require energy storage and improved electrical grids. Once that low-emission energy is deployed at large scale, transport and heating can shift to these mostly electric sources.[5]

Mitigation of climate change may also be achieved by changes in agriculture, reforestation and forest preservation and improved waste management.[6] Methane emissions, which have a high short-term impact, can be targeted by reductions in cattle and more generally by reducing meat consumption.

Political and economical responses include carbon taxes and other emission pricing models, abolishing fossil fuel 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).[7] 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.[8] 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.[9] With the Paris Agreement of 2015 this was confirmed.[10]

With the Special Report on Global Warming of 1.5 °C, the International Panel on Climate Change has emphasized the benefits of keeping global warming below this level.[11] 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.[12] 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.[13]

The current trajectory of global greenhouse gas emissions does not appear to be 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.[14][15]

Greenhouse gas concentrations and stabilization[edit]

refer to caption and adjacent text
Stabilizing CO2 emissions at their present level would not stabilize its concentration in the atmosphere.[16]
refer to caption and adjacent text
Stabilizing the atmospheric concentration of CO2 at a constant level would require emissions to be effectively eliminated.[16]

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.[17] Currently human activities are adding CO2 to the atmosphere faster than natural processes can remove it.[16]

The IPCC works with the concept of a fixed carbon emissions budget. If emissions remain on the current level of 42 GtCO
2
, the carbon budget for 1.5 °C could be exhausted in 2028.[18] The rise in temperature to that level would occur with some delay between 2030 and 2052.[19] 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.[20]

After leaving room for emissions for food production for 9 billion people and to keep the global temperature rise below 2 °C, emissions from energy production and transport will have to peak almost immediately in the developed world and decline at about 10% each year until zero emissions are reached around 2030.[21][22][23][24][needs update]

If emissions will be reduced to zero, the warming might stop in 10 – 20 years.[25] Potential feedback effects lead to a high degree of uncertainty in any projection. Climate change mitigation scenarios from the IPCC Fifth Assessment Report cover a range from 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, or 4.8 °C (8.6 °F) if emissions continue upwards until they are triple current levels.

Drivers of global warming[edit]

GHG emissions 2019 by gas type
without land-use change
using 100 year GWP
Total: 51.8 GtCO
2
e[26]

  CO
2
mostly by fossil fuel (72%)
  CH4 methane (19%)
  N
2
O
nitrous oxide (6%)
  Fluorinated gases (3%)

CO
2
emissions by fuel type[27]

  coal (39%)
  oil (34%)
  gas (21%)
  cement (4%)
  others (1.5%)

Carbon dioxide (CO
2
) is the dominant emitted greenhouse gas, while Methane (CH
4
) emissions almost have the same short-term impact.[28] 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.[29]

GHG emissions are measured in CO
2
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.[30] Reducing SLCP emissions can cut the ongoing rate of global warming by almost half and reduce the projected Arctic warming by two-thirds.[31]

GHG emissions in 2019 were estimated at 57.4 GtCO
2
e, while CO
2
emissions alone made up 42.5 Gt including land-use change (LUC).[32]

Carbon dioxide (CO
2
)
[edit]

  • Fossil fuel: oil, gas and coal (89%) are the major driver of anthropogenic global warming with annual emissions of 35.6 GtCO
    2
    in 2019.[27][33]
  • Cement production (4%) is estimated at 1.42 GtCO
    2
    [27]
  • Land-use change (LUC) is the imbalance of deforestation and reforestation. Estimations are very uncertain at 4.5 GtCO
    2
    .[26] Wildfires alone cause annual emissions of about 7 GtCO
    2
    [34][35]
  • Non-energy use of fuels, carbon losses in coke ovens, and flaring in crude oil production.[33]

Methane (CH4)[edit]

Methane has a high immediate impact with a 5-year global warming potential of up to 100.[28] Given this, the current 389 Mt of methane emissions[36] has about the same short-term global warming effect as CO
2
emissions, with a risk to trigger off 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.[16]

  • 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%).[36][3]
  • Livestock (28%) with cattle (21%) as the dominant source, followed by buffalo (3%), sheep (2%), and goats (1.5%).[36][37]
  • 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.[3]
  • Rice cultivation (10%) on flooded rice fields is another agricultural source, where anaerobic decomposition of organic material produces methane.[3]

Nitrous oxide (N
2
O
)
[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.[38] For N2O, a reduction of more than 50% would be required for a stabilization.[16]

  • Most emissions (56%) by agriculture, especially meat production: cattle (droppings on pasture), fertilizers, animal manure.[3]
  • Combustion of fossil fuels (18%) and bio fuels.[39]
  • Industrial production of adipic acid and nitric acid.

F-Gases[edit]

Fluorinated gases include hydrofluorocarbons (HFC), perfluorocarbons (PFC), and sulfur hexafluoride (SF6). They are used by switchgear in the power sector, semi-conducture manufacture, aluminium production and a large unknown source of SF6.[40] Continued phase down of manufacture and use of hydrofluorocarbons (HFCs) under the Montreal Protocol will help reduce HFC emissions and concurrently improve the energy efficiency of appliances that use HFCs like air conditioners, freezers and refrigerators.

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.[41] Black carbon stays in the atmosphere for only several days to weeks.[42] Emissions may be mitigated by upgrading coke ovens, installing particulate filters on diesel-based engines and minimizing open burning of biomass.

Fossil fuel substitution[edit]

As most greenhouse gas emissions are due to fossil fuels, rapidly phasing out oil, gas and coal is critical.[43] 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.[5] Currently, less than 20% of energy is used as electricity.[44]

A global transition to 100% renewable 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.[5]

The risk of the stranding of assets (i.e. climate-related asset stranding) can be of help to get operators of fossil fuel power plants to convert their power plants (i.e. running it on a renewable fuel source), in order to decrease its emissions (completely).[45][46] In some cases, installations that were part of the fossil fuel industry can even be converted to not just completely stop emitting carbon, but even aid the climate change mitigation effort by storing carbon away. One example is an oil well that is repurposed to pump CO2 into rocks below the seabed.

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. 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.[47]

The global primary energy demand exceeded 161,000 TWh in 2018.[48] 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.[44]

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.[49] Storage requirements cause additional costs. On the other hand, a price on carbon emissions can increase the competitiveness of renewable energy.

installed[50]
TWp
growth
TW/yr[50]
production
per installed
capacity*[51]
energy
TWh/yr*[51]
growth
TWh/yr*[51]
levelized cost
US¢/KWh[52]
Av. auction prices
US¢/KWh[53]
Cost development
2010-2019[52]
Solar PV 0.580 0.098 13% 549 123 6.8 3.9 -82%
Solar CSP 0.006 0.0006 13% 6.3 0.5 18.2 7.5 -47%
Wind Offshore 0.028 0.0045 33% 68 11.5 11.5 8.2 -30%
Wind Onshore 0.594 0.05 25% 1194 118 5.3 4.3 -38%
Hydro 1.310 0.013 38% 4267 90 4.7 +27%
Bioenergy 0.12 0.006 51% 522 27 6.6 -13%
Geothermal 0.014 0.00007 74% 13.9 0.7 7.3 +49%

* = 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.[54]
  • Solar photovoltaics has become the cheapest way to produce electric energy in many regions of the world, with production costs down to 0.015 - 0.02 US$/KWh in desert regions.[55] The growth of photovoltaics is exponential and has doubled every three years since the 1990s.
  • A different technology is concentrated solar power (CSP) using mirrors or lenses to concentrate a large area of sunlight onto a receiver. With CSP, the energy can be saved up for a few hours. Prices in Chile are expected to fall below 0.05 US$/KWh in 2020.[56]
  • Solar water heating makes an important and growing contribution in many countries, most notably in China, which now has 70 percent of the global total (180 GWh). Worldwide, total installed solar water heating systems meet a portion of the water heating needs of over 70 million households.[57]

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.[58] Installed capacity has reached 650 GW in 2019. Offshore wind power currently has a share of about 10% of new installations.[59] Offshore wind farms are more expensive but the units deliver more energy per installed capacity with less fluctuations.

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.[60] but there are geographical limits and environmental issues.[61] Tidal power can be used in coastal regions.

Bioenergy[edit]

Biogas plants can provide dispatchable electricity generation, and heat when needed.[62] A common concept is the co-fermentation of energy crops mixed with manure in agriculture. Burning plant-derived biomass releases CO
2
, but it has still been classified as a renewable energy source in the EU and UN legal frameworks because photosynthesis cycles the CO
2
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.[63] Renewable biofuels are starting to be used in aviation.

Nuclear power[edit]

In most 1.5 °C pathways nuclear power increases its share.[64] The main advantage is the ability to deliver large amounts of base load when renewable energy is not available.[citation needed] It has been repeatedly classified as a climate change mitigation technology.[65]

On the other hand, nuclear power comes with environmental risks which could outweigh the benefits. Apart from nuclear accidents, the disposal of radioactive waste can cause damage and costs over more than one million years. Separated plutonium could be used for nuclear weapons.[66][67] Public opinion about nuclear power varies widely between countries.[68][69]

As of 2019 the cost of extending nuclear power plant lifetimes is competitive with other electricity generation technologies, including new solar and wind projects.[70] New projects are reported to be highly dependent on public subsidies.[71]

Nuclear fusion research, in the form of the International Thermonuclear Experimental Reactor is underway but fusion is not likely to be commercially widespread before 2050.[72]

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.[73][74][75]

Natural gas[edit]

Natural gas, which is mostly methane, is viewed as a bridge fuel since it produces about half as much CO
2
as burning coal.[76] Gas-fired power plants can provide the required flexibility in electricity production in combination wind and solar energy.[77] 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.[78] 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 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.[79]

  • Li-on batteries are widely used in battery storage power stations and, as of 2020, are starting to be used in vehicle-to-grid storage.[80] They provide a sufficient round-trip efficiency of 75-90 %.[81] However their production can cause environmental problems.[82] Levelized costs for battery storage have drastically fallen to 0.15 US$/KWh[49]
  • Hydrogen may be useful for seasonal energy storage.[83] The low efficiency of 30% must improve dramatically before hydrogen storage can offer the same overall energy efficiency as batteries.[81] 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.[84] The concept of solar hydrogen is discussed for remote desert projects where grid connections to demand centers are not available.[85] Because it has more energy per unit volume sometimes it may be better to use hydrogen in ammonia.[86]

Super grids[edit]

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[87] 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[88] and to be in operation in China by 2022.[89]

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.[90] A super grid in the US in combination with renewable energy could reduce GHG emissions by 80%.[91]

Smart grid and load management[edit]

Instead of expanding grids and storage for more power, there are a variety of ways to affect the size and timing of electricity demand on the consumer side. Identifying and shifting electrical loads can reduce power bills by taking advantage of lower off-peak rates and flatten demand peaks. Traditionally, the energy system has treated consumer demand as fixed and used centralised supply options to manage variable demand. Now, better data systems and emerging onsite storageand generation technologies can combine with advanced, automated demand control software to pro-actively manage demand and respond to energy market prices.[92]

Time of use metering is a common way to motivate electricity users to reduce their peak load consumption. For instance, running dishwashers and laundry at night after the peak has passed, 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. For instance millions of refrigerators reduce their consumption when clouds pass over solar installations. Consumers need to have a smart meter in order for the utility to calculate credits.

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 or fuel cell to supply the grid temporarily.

Decarbonization of transport[edit]

In a system completely based on renewable energy, the transport sector can be emission free. Electric vehicles and ferries are the most effective way to use renewable energy. Between a quarter and three-quarters of cars on the road by 2050 are forecast to be electric vehicles.[93] Hydrogen can be a solution for long-distance transport by trucks and hydrogen-powered ships where batteries alone are too heavy.[94][95] Passenger cars using hydrogen are already produced in small numbers. While being more expensive than battery powered cars, they can refuel much faster, and may offer higher ranges up to 700 km.[96][97] The main disadvantage of hydrogen is the low efficiency of only 30%. When used for vehicles, more than twice as much energy is needed compared to a battery powered electric car.[98]

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.[99]

In aviation, current 180 Mt of CO
2
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.[100]

Decarbonization of heating[edit]

The buildings sector accounts for 23% of global energy-related CO2 emissions[101] About half of the energy is used for space and water heating.[102] A combination of electric heat pumps and building insolation can reduce the primary energy demand significantly. Generally, electrification of heating 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 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 three times more thermal energy than electrical energy consumed, giving an effective efficiency of 300%, depending on the coefficient of performance. 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 CO
2
emissions by 8% annually.[103] Using ground source heat pumps could reduce around 60% of the primary energy demand and 90% of CO
2
emissions of natural gas boilers in Europe in 2050 and make handling high shares of renewable energy easier.[104] Using surplus renewable energy in heat pumps is regarded as the most effective household means to reduce global warming and fossil fuel depletion.[105]

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.

Zero heating building[edit]

With advances in ultra low U-value glazing a Passive House-based (nearly) zero heating building is proposed to supersede nearly-zero energy buildings. The zero-heating building reduces on the passive solar design and makes the building more opened to conventional architectural design. The annual specific space heating demand for the zero-heating house should not exceed 3 kWh/m2a. Removing the need for heating is the best approach to de-carbonize heating.

Energy conservation[edit]

Reducing energy use is seen as a key solution to the problem of reducing greenhouse gas emissions. According to the International Energy Agency, improved energy efficiency in buildings, industrial processes and transportation could reduce the world's energy needs in 2050 by one third, and help control global emissions of greenhouse gases.[106]

Energy efficiency[edit]

Energy efficiency means using the least amount of energy to perform a task or the ability of a piece of equipment to use the least amount of energy to perform a task. To conserve energy or reduce electricity costs, individual consumers or businesses may deliberately purchase energy efficient products that use refrigerants with low global warming potential (GWP) or products that are ENERGY STAR certified.[107] In general, the more the number of ENERGY STARS, the more efficient the product is. A procurement toolkit[108] to assist individuals and businesses buy energy efficient products that use low GWP refrigerants was developed by the Sustainable Purchasing Leadership Council[109] and is available for use. Products with refrigerants include household refrigerators and freezers, commercial stand-alone refrigerators and freezers, lab-grade refrigerators and freezers, commercial ice makers, vending machines, water dispensers, water coolers, room air conditioners and vehicles. Efficiency covers a wide range of means from building insulation to public transport. The cogeneration of electric energy and district heat also improves efficiency.

Lifestyle and behavior[edit]

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.[110] 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.[111] 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).[112]

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.[112][113][114]

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.[115]

Dietary change[edit]

The widespread adoption of a vegetarian diet could cut food-related greenhouse gas emissions by 63% by 2050.[116] 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.[117][118] 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.[119] Overall, food accounts for the largest share of consumption-based GHG emissions with nearly 20% of the global carbon footprint.

Modal shift[edit]

Heavyweight, large personal vehicles (such as cars) require a lot of energy to move and take up much urban space.[120][121] Several alternatives modes of transport are available to replace these. The European Union has made smart mobility part of its European Green Deal[122] and in smart cities, smart mobility is also important.[123]

Carbon sinks and removal[edit]

About 58% of CO
2
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.

A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period, such as a growing forest. Carbon dioxide removal on the other hand is a permanent removal of carbon dioxide out of the atmosphere. Examples are direct air capture, enhanced weathering technologies such as storing it in geologic formations underground and biochar. These processes are sometimes considered variations of sinks or mitigation,[124][125] and sometimes as geoengineering.[126] In combination with other mitigation measures, carbon sinks and removal are crucial for meeting the 2 degree target.[127]

The Antarctic Climate and Ecosystems Cooperative Research Centre (ACE-CRC) notes that one third of humankind's annual emissions of CO
2
are absorbed by the oceans.[128] However, this also leads to ocean acidification, which may harm marine life.[129] Acidification lowers the level of carbonate ions available for calcifying organisms to form their shells. These organisms include plankton species that contribute to the foundation of the Southern Ocean food web. However acidification may impact on a broad range of other physiological and ecological processes, such as fish respiration, larval development and changes in the solubility of both nutrients and toxins.[130]

Conserving areas by protecting areas can boost the carbon sequestration capacity.[131][132][133] 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. Also, Campaign for Nature's 30x30 for Nature Petition tries to let governments agree to the same goal during the Convention on Biodiversity COP15 Summit.[134] has the same target. In 2021, 7 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.[135] The One Earth Climate Model advises a protection of 50% of our lands and oceans. It also stresses the importance of rewilding,[136] like other reports.[137][138] The reason being that predators (which are often keystone species) keep the population of herbivores in check (which reduce the biomass of vegetation), and also impact their feeding behavior.[137]

Proforestation, avoided deforestation, reforestation and afforestation[edit]

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

Almost 20 percent (8 GtCO2/year) of total greenhouse-gas emissions were from deforestation in 2007.[needs update] It is estimated that avoided deforestation reduces CO2 emissions at a rate of 1 tonne of CO2 per $1–5 in opportunity costs from lost agriculture. Reforestation, which is restocking of depleted forests, could save at least another 1 GtCO2/year, at an estimated cost of $5–15/tCO2.[139] According to research conducted at ETH Zurich, restoring all degraded forests all over the world could capture about 205 billion tons of carbon in total (which is about 2/3rd of all carbon emissions, bringing global warming down to below 2 °C[citation needed]).[140][141] Afforestation is where there was previously no forest. According to research by Tom Crowther et al., there is still enough room to plant an additional 1.2 trillion trees. This amount of trees would cancel out the last 10 years of CO2 emissions and sequester 160 billion tons of carbon.[142][143][144][145] This vision is being executed by the Trillion Tree Campaign. Other studies[146][147] have found large-scale afforestation can do more harm than good or such plantations are estimated to have to be prohibitively massive to reduce emissions. Proforestation, which is maintaining or growing existing forests to their ecological potential, maintains and optimizes carbon sequestration or carbon dioxide removal from the atmosphere while limiting climate change.

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.[148] This includes the protection of such rights entitled in existing laws, such as India's Forest Rights Act.[148] The transferring of such rights in China, perhaps the largest land reform in modern times, has been argued to have increased forest cover.[149][150] 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.[151][152] Conservation methods that exclude humans and even evict inhabitants from protected areas (called "fortress conservation") often lead to more exploitation of the land as the native inhabitants then turn to work for extractive companies to survive.[149]

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, even though they do not have the same biodiversity as the original forests and original forests store 60% more carbon than these new secondary forests.[153][154] According to a study in Science, promoting regrowth on abandoned farmland could offset years of carbon emissions.[155] Research by the university ETH Zurich estimates that Russia, the United States and Canada have the most land suitable for reforestation.[156][157]

According to a big survey of the United Nations Development Programme of public opinion on climate change, forests and land conservation policies were the most popular solutions of climate change mitigation, followed by renewable energy, and climate-friendly farming techniques.[158]

Avoided desertification[edit]

Restoring grasslands stores CO2 from the air in plant material. Grazing livestock, usually not left to wander, would eat the grass and would minimize any grass growth. However, grass left alone would eventually grow to cover its own growing buds, preventing them from photosynthesizing and the dying plant would stay in place.[159] A method proposed to restore grasslands uses fences with many small paddocks and moving herds from one paddock to another after a day or two in order to mimic natural grazers and allowing the grass to grow optimally.[159][160][161] Additionally, when part of the leaf matter is consumed by an animal in the herd, a corresponding amount of root matter is sloughed off too as it would not be able to sustain the previous amount of root matter and while most of the lost root matter would rot and enter the atmosphere, part of the carbon is sequestered into the soil.[159] It is estimated that increasing the carbon content of the soils in the world's 3.5 billion hectares of agricultural grassland by 1% would offset nearly 12 years of CO2 emissions.[159] 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.[162]

Additionally, the global warming induced thawing of the permafrost, which stores about two times the amount of the carbon currently released in the atmosphere,[163] 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.[164] 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.[165]

Protecting healthy soils and recovering damaged soils could remove 5.5 billion tons of carbon dioxide from the atmosphere annually, which is approximately equal to the annual emissions of the USA.[166]

Blue carbon[edit]

Estimates of the economic value of blue carbon ecosystems per hectare. Based on 2009 data from UNEP/GRID-Arendal.[167][168]

Blue carbon refers to carbon dioxide removed from the atmosphere by the world's ocean ecosystems, mostly algae, mangroves, salt marshes, seagrasses and macroalgae, through plant growth and the accumulation and burial of organic matter in the soil.[167][169][170]

Historically the ocean, atmosphere, soil, and terrestrial forest ecosystems have been the largest natural carbon (C) sinks. "Blue carbon" designates carbon that is fixed via the largest ocean ecosystems, rather than traditional land ecosystems, like forests. Oceans cover 70% of the planet, consequently ocean ecosystem restoration has the greatest blue carbon development potential. 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. Despite their small footprint, they can store a comparable amount of carbon per year and are highly efficient carbon sinks. Seagrasses, mangroves and salt marshes can capture carbon dioxide (CO
2
) from the atmosphere by sequestering the C in their underlying sediments, in underground and below-ground biomass, and in dead biomass.[171][172]

In plant biomass such as leaves, stems, branches or roots, blue carbon can be sequestered for years to decades, and for thousands to millions of years in underlying plant sediments. Current estimates of long-term blue carbon C burial capacity are variable, and research is ongoing.[172] Although vegetated coastal ecosystems cover less area and have less aboveground biomass than terrestrial plants they have the potential to impact longterm C sequestration, particularly in sediment sinks.[173] One of the main concerns with Blue Carbon is the rate of loss of these important marine ecosystems is much higher than any other ecosystem on the planet, even compared to rainforests. Current estimates suggest a loss of 2-7% per year, which is not only lost carbon sequestration, but also lost habitat that is important for managing climate, coastal protection, and health.[173]

Peatlands[edit]

Peat extraction in East Frisia, Germany. Peat extraction degrades peatland and is possible as many peatlands are currently not protected.

Peatland globally 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.[174] Across the world, peat covers just 3% of the land's surface, but stores one-third of the Earth's soil carbon.[175] Restoration of degraded peatlands can be done by blocking drainage channels in the peatland, and allowing natural vegetation to recover.[137]

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 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.[176] The International Energy Agency says CCS is "the most important single new technology for CO2 savings" in power generation and industry.[177][better source needed] 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.[178][177] According to a Sierra Club analysis, the US Kemper Project, which was due to be online in 2017, is the most expensive power plant ever built for the watts of electricity it will generate.[179]

Carbon dioxide removal[edit]

Carbon dioxide removal has been proposed as a method of reducing the amount of radiative forcing. A variety of means of artificially capturing and storing carbon, as well as of enhancing natural sequestration processes, are being explored. The main natural process is photosynthesis by plants and single-celled organisms (see biosequestration). Artificial processes vary, and concerns have been expressed about the long-term effects of some of these processes.[180]

It is notable that the availability of cheap energy and appropriate sites for geological storage of carbon may make carbon dioxide air capture viable commercially. It is, however, generally expected that carbon dioxide air capture may be uneconomic when compared to carbon capture and storage from major sources — in particular, fossil fuel powered power stations, refineries, etc. As in the case of the US Kemper Project with carbon capture, costs of energy produced will grow significantly. CO2 can also be used in commercial greenhouses, giving an opportunity to kick-start the technology.

Enhanced weathering[edit]

Enhanced weathering or accelerated weathering refers to geoengineering approaches intended to remove carbon dioxide from the atmosphere by using specific natural or artificially created minerals which absorb carbon dioxide and transform it in other substances through chemical reactions occurring in the presence of water (for example in the form of rain, groundwater or seawater).

Enhanced weathering research considers how natural processes of rocks' and minerals' weathering (in particular chemical weathering) may be enhanced to sequester CO2 from the atmosphere to be stored in form of another substance in solid carbonate minerals or ocean alkalinity. Since the carbon dioxide is usually first removed from ocean water, these approaches would attack the problem by first reducing ocean acidification.

This technique requires the extraction or production of large quantities of materials, crushing them and spreading them over large areas (for example fields or beaches); Besides extracting minerals for the purpose of enhanced weathering, also alkaline industrial silicate minerals (such as steel slags, construction & demolition waste, ash from biomass incineration) can be utilized.[181] In a 2020 techno-economical analysis, the cost of utilizing this method on cropland was estimated at US$80–180 per tonne of CO2. This is comparable with other methods of removing carbon dioxide from the atmosphere currently available (BECCS (US$100–200 per tonne of CO2)- Bio-Energy with Carbon Capture and Storage) and direct air capture and storage (US$100–300 per tonne of CO2). In contrast, the cost of reforestation was estimated lower than (US$100 per tonne of CO2).[182]

It has the side effect of altering the natural salinity of the seas.

Geoengineering[edit]

Chapter 28 of the National Academy of Sciences report Policy Implications of Greenhouse Warming: Mitigation, Adaptation, and the Science Base (1992) defined geoengineering as "options that would involve large-scale engineering of our environment in order to combat or counteract the effects of changes in atmospheric chemistry."[183] They evaluated a range of options to try to give preliminary answers to two questions: can these options work and could they be carried out with a reasonable cost. They also sought to encourage discussion of a third question — what adverse side effects might there be. Increasing ocean absorption of carbon dioxide (carbon sequestration) and screening out some sunlight were evaluated. NAS also argued "Engineered countermeasures need to be evaluated but should not be implemented without broad understanding of the direct effects and the potential side effects, the ethical issues, and the risks."[183] In July 2011 a report by the United States Government Accountability Office on geoengineering found that "[c]limate engineering technologies do not now offer a viable response to global climate change."[184]

Solar radiation management[edit]

refer to caption and image description
Proposed solar geoengineering using a tethered balloon to inject sulfate aerosols into the stratosphere.

Solar geoengineering, or solar radiation modification (SRM) is a proposed type of climate engineering in which sunlight (solar radiation) would be reflected back to space to limit or reverse human-caused climate change. Most methods would increase the planetary albedo (reflectivity), for example with stratospheric aerosol injection. Although most techniques would have global effects, localized protective or restorative methods have also been proposed to protect natural heat reflectors including sea ice, snow, and glaciers.[185][186][187]

Solar geoengineering appears able to prevent some or much of climate change.[188] 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 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. Solar geoengineering could serve as a response if climate change impacts are greater than expected or as a temporary, complementary measure while atmospheric greenhouse gas concentrations are lowered through emissions reductions and carbon dioxide removal. Solar geoengineering would not directly reduce carbon dioxide concentrations in the atmosphere, and thus does not address ocean acidification. Solar geoengineering's excessive, poorly distributed, or sudden and sustained termination would pose serious environmental risks. Other negative impacts are possible. Governing solar geoengineering is challenging for multiple reasons.

Solar Radiation Modification (SRM) methods involve reducing the amount of incoming solar radiation reaching the surface and reducing optical thickness and cloud lifetime. The variability of the climate system would make it difficult to detect the efficacy or side-effects of SRM intervention.[189] Uncertainties including technological maturity, physical understanding and potential impacts constrain the ability to implement SRM in the near future.[190]

By sector[edit]

Agriculture[edit]

Managed grazing methods are argued to be able to restore grasslands, thereby significantly decreasing atmospheric CO2 levels.[162]

With 21% of the global methane emissions, cattle are a major driver on global warming.[36] When rainforests are cut and the land is converted for grazing, the impact is even higher. This results in up to 335 kg CO2eq emissions for the production of 1 kg beef in Brazil when using a 30 year time horizon.[191] Other livestock, manure management and rice cultivation also produce relevant GHG emissions, in addition to fossil fuel combustion in agriculture.

Regenerative agriculture includes conservation tillage, diversity, rotation and cover crops, minimizing physical disturbance, minimizing the usage of chemicals.[192] It has other benefits like improving the state of the soil and consequently yields.[193]

In the United States, soils account for about half of agricultural greenhouse gas emissions while agriculture, forestry and other land use emits 24%.[194] The US EPA says soil management practices that can reduce the emissions of nitrous oxide (N
2
O
) from soils include fertilizer usage, irrigation, and tillage.

Important mitigation options for reducing the greenhouse gas emissions from livestock (especially ruminants) include genetic selection[195][196] introduction of methanotrophic bacteria into the rumen,[197][198] diet modification and grazing management.[199][200][201] 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.[202]

Methods that enhance carbon sequestration in soil include no-till farming, residue mulching, cover cropping, and crop rotation, all of which are more widely used in organic farming than in conventional farming.[203][204] Because only 5% of US farmland currently uses no-till and residue mulching, there is a large potential for carbon sequestration.[205][206]

A 2015 study found that farming can deplete soil carbon and render soil incapable of supporting life; however, the study also showed that conservation farming can protect carbon in soils, and repair damage over time.[207] The farming practice of cover crops has been recognized as climate-smart agriculture.[208] Best management practices for European soils were described to be 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.[209]

In terms of prevention, vaccines are being developed in Australia to reduce the significant global warming contributions from methane released by livestock via flatulence and eructation.[210][needs update]

A project to mitigate climate change with agriculture was launched in 2019 by the "Global EverGreening Alliance". The target is to sequester carbon from the atmosphere with Agroforestry. By 2050 the restored land should sequestrate 20 billion of carbon annually[211]

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.[212]

Transport[edit]

Transportation emissions account for roughly 15% of emissions worldwide.[213] Energy-efficient technologies, such as electric vehicles and environmentally friendly rail help to reduce the consumption of fossil fuels. Using electric trains over the far less efficient air transport and truck transport significantly reduces emissions.[214] Other frequently discussed efficiency means include public transport, smart mobility solutions (carsharing, ...), increasing fuel economy in automobiles (which includes the use of electric hybrids), charging plug-in hybrids and electric cars by low-carbon electricity. Also important is the cost of implementing sustainable transport solutions. Existing (fossil-fuel powered) passenger cars can for example be converted to electric propulsion by swapping the internal combustion engine with an electric engine and building in batteries (instead of simply buying a new vehicle which is designed from the start as an electric vehicle). The latter may or may not be more expensive. Another option is to simply keep the existing internal combustion engine but instead run it on an emissionless fuel (i.e. hydrogen, ...). This avoids the cost of needing to buy a different engine and battery system.

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.[215] 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.[216] 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.[217]

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.[218]

Effective urban planning to reduce sprawl aims to decrease Vehicle Miles Travelled (VMT), 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.[219]

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.

A reduction in the quantity of cars that are on the road,[220] i.e. 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.

Building design[edit]

Emissions from housing are substantial,[221] and government-supported energy efficiency programmes can make a difference.[222]

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.[223][224] This saves energy because it cools buildings and reduces the urban heat island effect thus reducing the use of air conditioning.

Societal controls[edit]

Another method being examined[by whom?] is to make carbon a new currency by introducing tradeable "personal carbon credits". The idea being it will encourage and motivate individuals to reduce their 'carbon footprint' by the way they live. Each citizen will receive a free annual quota of carbon that they can use to travel, buy food, and go about their business. It has been suggested that by using this concept it could actually solve two problems; pollution and poverty, old age pensioners will actually be better off because they fly less often, so they can cash in their quota at the end of the year to pay heating bills and so forth.[citation needed]

Population[edit]

Various organizations[citation needed] promote human population planning as a means for mitigating global warming.[225] Proposed measures include improving access to family planning and reproductive health care and information, reducing natalistic politics, public education about the consequences of continued population growth, and improving access of women to education and economic opportunities.

According to a 2017 study published in Environmental Research Letters, having one less child would have a much more substantial effect on greenhouse gas emissions compared with for example living car free or eating a plant-based diet.[112] However this has been criticised: both as a category mistake for assigning descendants emissions to their ancestors[226] and for the very long timescale of reductions.[227]

Population control efforts are impeded by there being somewhat of a taboo in some countries against considering any such efforts.[228] Also, various religions discourage or prohibit some or all forms of birth control. Population size has a vastly different per capita effect on global warming in different countries, since the per capita production of anthropogenic greenhouse gases varies greatly by country.[229]

By country[edit]

Costs and benefits[edit]

Globally, the benefits of keeping warming under 2 °C exceed the costs.[230] 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.[231] The OECD has been applying economic models and qualitative assessments to inform on climate change benefits and tradeoffs.[232]

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.[139] Mitigation costs will vary according to how and when emissions are cut: early, well-planned action will minimise the costs.[139]

Many economists estimate the cost of climate change mitigation at between 1% and 2% of GDP.[231] 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.[233][234] 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.[235][236] Abolishing fossil fuel subsidies is very important but must be done carefully to avoid making poor people poorer.[237]

Benefits[edit]

By addressing climate change, we can avoid the costs associated with the effects of climate change. According to the Stern Review, inaction can be as high as the equivalent of losing at least 5% of global gross domestic product (GDP) each year, now and forever (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.[238][239]

The research organization Project Drawdown identified global climate solutions and ranked them according to their benefits.[240] 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.[230]

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.[241] 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.[242] 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):[241]

  • 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).[243]
    • 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[citation needed] from reducing their emissions.

Specific proposals[edit]

  • Ad hoc: Lashof (1992) and Cline (1992) (referred to by Banuri et al., 1996, p. 106),[241] 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).[243] In international law, one state recognized the long-established use of another state's use of the fisheries resource. It was also recognized by the state that part of the other state's economy was dependent on that resource.

Governmental and intergovernmental action[edit]

In 2019 a report was published by the United Nations saying that to limit the temperature rise to 2 °C, the world will need to cut emissions by 2.7% each year from 2020 to 2030, and triple the climate targets. To limit the temperature rise to 1.5 °C the world would need to cut emissions by 7.6% each year from 2020 to 2030 and increase its climate commitments five-fold. Even if all the Paris Agreement pledges as they are in 2019, are fulfilled the temperature will rise by 3.2 degrees this century.[14][15][needs update]

A report published in September 2019 before the 2019 UN Climate Action Summit says, that the full implementation of all pledges made by international coalitions, countries, cities, regions and businesses (not only those in the Paris Agreement) will be sufficient to limit temperature rise to 2 degrees but not to 1.5 degrees.[244][needs update] Additional pledges were made in the September climate summit[245] and in December.[246] All the information about all climate pledges is sent to the Global Climate Action Portal - Nazca. The scientific community is checking their fulfillment.[247]

Recent proposals suggest investments supporting a green recovery after the COVID-19 pandemic.[248]

Paris agreement and Kyoto Protocol[edit]

Refer to caption and image description
The graph shows multiple pathways to limit climate change to 1.5 °C or 2 °C. All pathways include negative emission technologies such as afforestation and bio-energy with carbon capture and storage.

The main current international agreement on combating climate change is the Paris agreement. The Paris Agreement's long-term temperature goal is to keep the increase in global average temperature to well below 2 °C above pre-industrial levels; and to pursue efforts to limit the increase to 1.5 °C. Each country must determine, plan, and regularly report on the contribution that it undertakes to mitigate global warming.[249] 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, and is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC).[citation needed] 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.[250]

Additional commitments[edit]

Except 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.[251] After the report was published, additional pledges were made in the September climate summit[245] and in December of that year.[246]

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.[252]

All the information about the pledges is collected and analyzed in the Global Climate Action portal, which enables the scientific community to check their fulfilment.[253]

Temperature targets[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.[254]

Official long-term target of 1.5 °C

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".[255] 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.[256]

Encouraging use changes[edit]

Citizens for climate action at the People's Climate March (2017).

Emissions tax and trading[edit]

Additional costs on GHG emissions can lower competitiveness of fossil fuels and accelerate investments into low-carbon sources of energy.

For greenhouse gases, a growing number of countries participate in various emissions trading systems. After years with cheap certificates caused by an oversupply, prices in the European Union Emission Trading Scheme began to rise in 2018, reaching €40/tCO
2
(46 $) in March 2021.[257] 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. The German Environment Agency estimates the environmental damage between €180 (206 $) and €640 (731 $) per ton CO
2
depending on the rate of time preference.[258]

Carbon taxes are an alternative or additional approach that provide incentives for GHG reductions.

Most environmentally related taxes are still levied on energy products and motor vehicles, rather than on CO2 emissions directly.[259] As such, non-transport sectors as the agricultural sector which produces large amounts of methane are typically left untaxed by current policies. Also, revenue of the emissions taxes are not always used to offset the emissions directly. Emission taxes can be both cost-effective and environmentally effective. Difficulties with emission taxes include their potential unpopularity, and the fact that they cannot guarantee a particular level of emissions reduction. In developing countries, institutions may be insufficiently developed for the collection of emissions fees from a wide variety of sources.[259]

Investment[edit]

Another indirect method of encouraging uses of renewable energy, and pursue sustainability and environmental protection, is that of prompting investment in this area through legal means, something that is already being done at national level as well as in the field of international investment.[260][clarification needed]

As well as a policy risk, Ernst and Young identify physical, secondary, liability, transitional and reputation-based risks.[261] 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.

Carbon emission trading[edit]

Carbon emissions trading is a form of emissions trading that specifically targets carbon dioxide (calculated in tonnes of carbon dioxide equivalent or tCO2) and it currently constitutes the bulk of emissions trading.

This form of permit trading is a common method countries utilize in order to meet their obligations specified by the Kyoto Protocol; namely the reduction of carbon emissions in an attempt to reduce (mitigate) future climate change.

Under Carbon trading, a country or a polluter having more emissions of carbon is able to purchase the right to emit more and the country or entity having fewer emissions sells the right to emit carbon to other countries or entities. The countries or polluting entities emitting more carbon thereby satisfy their carbon emission requirements, and the trading market results in the most cost-effective carbon reduction methods being exploited first.

Implementation[edit]

Since 2000, rising CO
2
emissions in China and the rest of world have eclipsed the output of the United States and Europe.[262]
Per person, the United States generates carbon dioxide at a far faster rate than other primary regions.[262]

Implementation puts into effect climate change mitigation strategies and targets. These can be targets set by international bodies or voluntary action by individuals or institutions. This is the most important, expensive and least appealing aspect of environmental governance.[263]

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.[263] 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.[264]

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.[265] 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.[265] 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, whereas the natural science of climate change is already well established and there will be decades and centuries to handle adaptation.[265]

Problems[edit]

There are numerous issues which result in a current perceived lack of implementation.[263] It has been suggested that the main barriers to implementation are Uncertainty, Fragmentation, Institutional void, Short time horizon of policies and politicians and Missing motives and willingness to start adapting. The relationships between many climatic processes can cause large levels of uncertainty as they are not fully understood and can be a barrier to implementation. When information on climate change is held between the large numbers of actors involved it can be highly dispersed, context specific or difficult to access causing fragmentation to be a barrier. Institutional void is the lack of commonly accepted rules and norms for policy processes to take place, calling into question the legitimacy and efficacy of policy processes. The Short time horizon of policies and politicians often means that climate change policies are not implemented in favour of socially favoured societal issues. Statements are often posed to keep the illusion of political action to prevent or postpone decisions being made. Missing motives and willingness to start adapting is a large barrier as it prevents any implementation.[266] The issues that arise with a system which involves international government cooperation, such as cap and trade, could potentially be improved with a polycentric approach where the rules are enforced by many small sections of authority as opposed to one overall enforcement agency.[267] Concerns about metal requirement and/or availability for essential decarbonization technologies such as photovoltaics, nuclear power, and (plug-in hybrid) electric vehicles have also been expressed as obstacles.[268]

Occurrence[edit]

Despite a perceived lack of occurrence,[clarification needed] evidence of implementation is emerging internationally. Some examples of this are the initiation of NAPA's and of joint implementation. Many developing nations have made National Adaptation Programs of Action (NAPAs) which are frameworks to prioritize adaption needs.[269] The implementation of many of these is supported by GEF agencies.[270] Many developed countries are implementing 'first generation'[clarification needed] institutional adaption plans particularly at the state and local government scale.[269] There has also been a push towards joint implementation between countries by the UNFCCC as this has been suggested as a cost-effective way for objectives to be achieved.[271]

Montreal protocol[edit]

Although not designed for this purpose, the Montreal Protocol has benefited climate change mitigation efforts.[272] The Montreal Protocol is an international treaty that has successfully reduced emissions of ozone-depleting substances (for example, CFCs), which are also greenhouse gases.

Territorial policies[edit]

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

Carbon taxes and emission trading worldwide
Emission trading and carbon taxes around the world (2019)[273]
  Carbon emission trading implemented or scheduled
  Carbon tax implemented or scheduled
  Carbon emission trading or carbon tax under consideration

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.[274]

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.[275] 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.[276]

China[edit]

As to 2019, China implements more than 100 policies to fight climate change. China said in the Paris Agreement that its emission will begin to fall by 2030, but it will possibly occur by 2026. This can position China as a leader on the issue because it is the biggest emitter of GHG emissions, so if it really reduces them, the significance will be large.[277]

European Union[edit]

The climate commitments of the European Union are divided into 3 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.[278][279]

Targets for the year 2020:[280]

  • Reduce GHG emissions by 20% from the level in 1990.
  • Produce 20% of energy from renewable sources.
  • Increase Energy Efficiency by 20%.

Targets for the year 2030:[281]

  • Reduce GHG emission by 40% from the level of 1990. In 2019 The European Parliament adopted a resolution upgrading the target to 55%[282]
  • Produce 32% of energy from renewables.
  • Increase energy efficiency by 32.5%.

Targets for the year 2050:[283]

  • Become climate neutral.

Implementation:

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.[284]

New Zealand[edit]

New Zealand made significant pledges on climate change mitigation in the year 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.[285]

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.[286][287]

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.[288]

Developing 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[289] 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.[290] 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.[290] 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:[290]

  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.[290]

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".[291]

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".[292][293]

Non-governmental approaches[edit]

While many of the proposed methods of mitigating global warming require governmental funding, legislation and regulatory action, individuals and businesses can also play a part in the mitigation effort.

Choices in personal actions and business operations[edit]

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.[294][295]

Investor response[edit]

More than 1000 organizations with a worth of 8 trillion dollars have made commitments to fossil fuel divestment.[296] Socially responsible investing funds allow investors to invest in funds that meet high environmental, social and corporate governance (ESG) standards.[297] Proxy firms can be used to draft guidelines for investment managers that take these concerns into account.[298]

Air travel[edit]

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.

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[299] and the Inuit,[300] as well as non-governmental organizations such as the Sierra Club.[301] Although proving that particular weather events are due specifically to global warming may never be possible,[302] methodologies have been developed to show the increased risk of such events caused by global warming.[303]

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."[304] 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.[305][306]

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.[307]

In the Netherlands and Belgium, organisations such as the foundation Urgenda and the Klimaatzaak[308] in Belgium have also sued their governments as they believe their governments aren't meeting the emission reductions they agreed to. Urgenda have already won their case against the Dutch government.[309]

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.[310]

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.[311] In October 2019, the trial began.[312] Massachusetts also sued Exxon, for hiding the impact of climate change.[313]

In 2019, 22 states, six cities and Washington DC in United States, sued the Trump administration for repealing the Clean Power Plan.[314]

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.[315]

In November 2020 the European Court of Human Rights ordered 33 countries to respond to the climate lawsuit from 4 children and 2 adults living in Portugal. The lawsuit will be treated as a priority by the court.[316]

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.[317]

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.[318]

Activism[edit]

Many people standing on steps of large public building holding banners with signs, including "Act For Climate" and "Go Nuclear."
Protesters at a People's Climate March in Helsinki, Finland in November 2015

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.[319] The target was to influence the climate action summit organized by the UN on September 23.[320] According to the organizers four million people participated in the strike on September 20.[321] In 2019, Extinction Rebellion organized massive protests demanding to "reduce carbon emissions to zero by 2025, and create a citizens' assembly to oversee progress", including blocking roads.[322]

See also[edit]

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Sources[edit]

IPCC reports[edit]

AR4 Working Group I Report

AR4 Working Group III Report

AR5 Working Group III Report
SR15 Special Report

IRENA[edit]

by the International Renewable Energy Agency

Other sources[edit]

Further reading[edit]