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Undid revision 1012666836 by Efbrazil (talk) this article is not about climate change only
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Undid revision 1012667959 by Femkemilene (talk) As written, it is only about air pollution. The edit is to create balance, not to make the article about climate change. I also fixed typos. Please reconsider.
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'''Sustainable energy''' is [[energy]] produced and used in such a way that it "meets the needs of the present without compromising the ability of future generations to meet their own needs."{{Sfn|Kutscher|Milford|Kreith|2019|p=5-6}} It is similar to the concepts of '''green energy''' and '''clean energy''' in its consideration of environmental impacts, however formal definitions of sustainable energy also include economic and social impacts.
'''Sustainable energy''' is [[energy]] produced and used in such a way that it "meets the needs of the present without compromising the ability of future generations to meet their own needs."{{Sfn|Kutscher|Milford|Kreith|2019|p=5-6}} It is similar to the concepts of '''green energy''' and '''clean energy''' in its consideration of environmental impacts, however formal definitions of sustainable energy also include economic and social impacts.


The [[energy transition]] to meet the world's needs for electricity, heating, cooling, and power for transport in a sustainable way is widely considered to be one of the greatest challenges facing humanity in the 21st century. Production and consumption of energy emits over 70% of the human-caused [[Greenhouse-gas emissions|greenhouse gas emissions]] that cause [[climate change]]. Worldwide, nearly a billion people lack [[Electrification|access to electricity]], and around 3 billion rely on smoky fuels such as wood, [[charcoal]] or animal dung to cook. [[Air pollution]] from fossil fuels is estimated to cause 3 million deaths each year, and air pollution from use of dirty cooking fuels is estimated to cause around 4 million deaths each year.
The [[energy transition]] to meet the world's needs for electricity, heating, cooling, and power for transport in a sustainable way is widely considered to be one of the greatest challenges facing humanity in the 21st century. Production and consumption of energy emits over 70% of the human-caused [[Greenhouse-gas emissions|greenhouse gas emissions]] that cause [[climate change]], which the [[World Health Organization]] has called the greatest threat to global health in the 21st century. Worldwide, energy demands are increasing and nearly a billion people still lack [[Electrification|access to electricity]], with around 3 billion relying on smoky fuels such as wood, [[charcoal]] or animal dung to cook.


In general, renewable energy sources such as [[solar energy|solar]], [[wind energy|wind]], and [[Hydroelectricity|hydroelectric]] energy are widely considered to be sustainable. However, aspects of some renewable energy projects, such as the clearing of forests for the production of [[biofuel]]s, can lead to similar worse environmental damage than using fossil fuel energy. [[Nuclear power]] is a [[Low-carbon power|low-carbon]] source and has a safety record comparable to wind and solar,<ref>{{Cite web|title=What are the safest and cleanest sources of energy?|url=https://ourworldindata.org/safest-sources-of-energy|access-date=2021-01-04|website=Our World in Data|last=Ritchie|first=Hannah|date=10 February 2020}}</ref> but [[radioactive waste]] and the risk of major [[Nuclear and radiation accidents and incidents|accidents]] are disadvantages of this technology.
In general, renewable energy sources such as [[solar energy|solar]], [[wind energy|wind]], and [[Hydroelectricity|hydroelectric]] energy are widely considered to be sustainable. However, aspects of some renewable energy projects, such as the clearing of forests for the production of [[biofuel]]s, can also lead to environmental damage. [[Nuclear power]] is a [[Low-carbon power|low-carbon]] source and has a safety record comparable to wind and solar,<ref>{{Cite web|title=What are the safest and cleanest sources of energy?|url=https://ourworldindata.org/safest-sources-of-energy|access-date=2021-01-04|website=Our World in Data|last=Ritchie|first=Hannah|date=10 February 2020}}</ref> but [[radioactive waste]] and the risk of major [[Nuclear and radiation accidents and incidents|accidents]] are disadvantages of this technology.


Moderate amounts of wind and solar energy, which are [[Variable renewable energy|variable energy sources]], can be integrated into the electrical grid without additional infrastructure such as [[grid energy storage]] and [[Demand response|demand-response]] measures. These sources generated 8.5% of worldwide electricity in 2019, a share that has grown rapidly.<ref name=":4">{{Cite web|url=https://yearbook.enerdata.net/renewables/wind-solar-share-electricity-production.html|title=Wind & Solar Share in Electricity Production Data|website=Enerdata}}</ref> Costs of wind, solar, and batteries are projected to continue falling due to innovation and [[economies of scale]] from increased investment.
Moderate amounts of wind and solar energy, which are [[Variable renewable energy|variable energy sources]], can be integrated into the electrical grid without additional infrastructure such as [[grid energy storage]] and [[Demand response|demand-response]] measures. These sources generated 8.5% of worldwide electricity in 2019, a share that has grown rapidly.<ref name=":4">{{Cite web|url=https://yearbook.enerdata.net/renewables/wind-solar-share-electricity-production.html|title=Wind & Solar Share in Electricity Production Data|website=Enerdata}}</ref> Costs of wind, solar, and batteries are projected to continue falling due to innovation and [[economies of scale]] from increased investment.

Revision as of 17:39, 17 March 2021

Buildings in the Solar Settlement at Schlierberg produce more energy than they consume. They incorporate rooftop solar panels and are built for maximum energy efficiency.
Coal, oil, and natural gas remain the primary global energy sources even as renewables have begun rapidly increasing.[1]

Sustainable energy is energy produced and used in such a way that it "meets the needs of the present without compromising the ability of future generations to meet their own needs."[2] It is similar to the concepts of green energy and clean energy in its consideration of environmental impacts, however formal definitions of sustainable energy also include economic and social impacts.

The energy transition to meet the world's needs for electricity, heating, cooling, and power for transport in a sustainable way is widely considered to be one of the greatest challenges facing humanity in the 21st century. Production and consumption of energy emits over 70% of the human-caused greenhouse gas emissions that cause climate change, which the World Health Organization has called the greatest threat to global health in the 21st century. Worldwide, energy demands are increasing and nearly a billion people still lack access to electricity, with around 3 billion relying on smoky fuels such as wood, charcoal or animal dung to cook.

In general, renewable energy sources such as solar, wind, and hydroelectric energy are widely considered to be sustainable. However, aspects of some renewable energy projects, such as the clearing of forests for the production of biofuels, can also lead to environmental damage. Nuclear power is a low-carbon source and has a safety record comparable to wind and solar,[3] but radioactive waste and the risk of major accidents are disadvantages of this technology.

Moderate amounts of wind and solar energy, which are variable energy sources, can be integrated into the electrical grid without additional infrastructure such as grid energy storage and demand-response measures. These sources generated 8.5% of worldwide electricity in 2019, a share that has grown rapidly.[4] Costs of wind, solar, and batteries are projected to continue falling due to innovation and economies of scale from increased investment.

Proposed pathways for limiting global warming to 1.5 °C describe rapid implementation of low-emission methods of producing electricity and heat, and a shift towards more use of electricity in sectors such as transport. The pathways also include measures to reduce energy consumption; and use of low-carbon fuels, such as hydrogen produced by renewable electricity or with carbon capture and storage. Achieving these goals will require government policies including carbon pricing, energy-specific policies, and phase-out of fossil fuel subsidies.

Definitions

The concept of sustainable development, for which energy is a key component, was described by the United Nations Brundtland Commission in its 1987 report Our Common Future. It defined sustainable development as development that "meets the needs of the present without compromising the ability of future generations to meet their own needs."[2] This description of sustainable development has since been referenced in many definitions and explanations of sustainable energy.[5][6][7][2] No single interpretation of how the concept of sustainability applies to energy has gained worldwide acceptance.[8] The UN Economic Commission for Europe, and various scholars in the field, include several aspects of sustainability in their working definitions:

  • Environmental aspects include greenhouse gas emissions, impacts on biodiversity and ecosystems, the production of hazardous waste and toxic emissions,[8] water consumption,[9] and depletion of non-renewable resources.[7]
  • Economic and social aspects include having reliable energy be affordable for all people,[8][7] and energy security so that each country has constant access to sufficient energy.[8][10]

Environmental issues

The current energy system contributes to many environmental issues, including climate change, air pollution, biodiversity loss, the release of toxics into the environment and water scarcity. Energy production and consumption is responsible for 72% of annual human-caused greenhouse gas emissions as of 2014. Generation of electricity and heat contributes 31% of human-caused greenhouse gas emissions, use of energy in transport contributes 15%, and use of energy in manufacturing and construction contributes 12%. An additional 5% is released through processes associated with fossil fuel production, and 8% through various other forms of fuel combustion.[11][12]

The combustion of coal releases precursor elements which form into ground-level ozone and acid rain, especially if the coal is not cleaned before combustion.[13] An estimated 3 million people die each year as a consequence of ambient air pollution, with major contributions from coal and biomass burning.[14] Oil spills during transport at sea harms marine life; when oil ignites instead toxic gases are released to the atmosphere.[15] Around 10% of global water use goes to energy production, mainly for cooling thermal energy plants. In already dry regions, this contributes to water scarcity. Bioenergy production, coal mining and processing and oil extraction also require large amounts of water.[16]

Biodiversity is greatly impacted by climate change, while additional threats from fossil fuel extraction. Low-carbon sources of energy also have the potential to be detrimental to biodiversity, with the best locations for bioenergy production in places of high ecological value.[17] Onshore wind and solar, when built in protected areas or wilderness, may also pose a risk to biodiversity.[18]

Energy access

Map of people with access to energy. Lack of access is most pronounced in India, Sub-Saharan Africa and South-East Asia.
Two-thirds of people without access to electricity live in sub-Saharan Africa.

Providing sustainable energy is widely viewed as one of the greatest challenges facing humanity in the 21st century, both in terms of meeting the needs of the present and in terms of effects on future generations.[19][20]

As of 2016, 940 million (13% of the world) people do not have access to electricity; two-thirds of whom live in sub-Saharan Africa.[21] The lack of electricity exacerbates the coronavirus pandemic, with half of health facilities having no or poor access to electricity in six surveyed countries in Asia and Africa.[22]

In developing countries, over 2.5 billion people rely on traditional cookstoves[23] and open fires to burn biomass or coal for heating and cooking. This practice causes harmful indoor air pollution, resulting in an estimated 3.8 million deaths annually, particularly among young children and women who spend much time near the hearth.[24] As of 2017, improved access to clean cooking fuels consistently lag improvements in getting more access to electricity.[25] Additionally, serious local environmental damage, including desertification, can be caused by excessive harvesting of wood and other combustible material.[26]

The United Nations Sustainable Development Goal 7 calls for "access to affordable, reliable, sustainable and modern energy for all" by 2030.[27] According to a 2019 report by the IEA, in sub-Saharan Africa "current and planned efforts to provide access to modern energy services barely outpace population growth" and would still leave over half a billion people without electricity and over a billion without clean cooking by 2030.[28]

Energy conservation

Countries such as the U.S. and Canada use twice as much energy per capita as Japan or western Europe, and 100 times as much energy per capita as some African countries.
Global energy usage is highly unequal. Countries such as the U.S. and Canada use 100 times as much energy per capita as some African countries.

Increasing energy efficiency is one of the most important ways to reduce energy-related pollution while also delivering economic benefits and improving quality of life. For some countries, efficiency can improve energy security by reducing dependence on fossil fuel imports. Efficiency has the potential to slow the growth of energy demand to allow rising clean energy supplies to make deep cuts in fossil fuel use.[29] The International Energy Agency (IEA) estimates that 40% of greenhouse gas emission reductions needed for the Paris agreement can be achieved by increasing energy efficiency.[30][31]

Between 2015 in 2018, each year saw less improvement in energy efficiency compared to the previous. In transport, consumer preferences for bigger cars is part of the driver of the slowdown. Globally, governments did not strongly increase their ambitions in energy efficiency policy over this period either.[31] Policies to improve efficiency can include building codes, performance standards, and carbon pricing.[32] Energy efficiency and renewable energy are often considered the twin pillars of sustainable energy.[33][34]

Behavioural changes are another important way to conserve energy. In the International Energy Agency scenario for reaching net zero greenhouse gas emissions in 2050, several significant behavioural changes are described, about half of them deriving from transport. In their scenario, some business flights are replaced by videoconferencing, cycling and walking increase in popularity, and more people use public transport.[35]

Renewable energy sources

The terms "sustainable energy" and "renewable energy" are often used interchangeably. However, renewable energy projects sometimes raise significant sustainability concerns. Renewable energy technologies are essential contributors to sustainable energy as they generally contribute to world energy security, and reduce dependence on fossil fuel resources thus mitigating greenhouse gas emissions.[36]

Solar

11 MW solar power plant near Serpa, Portugal

In 2019, solar power provided around 3% of global electricity.[4] Most of this is in the form of solar panels based on photovoltaic cells (PV). Costs of solar PV have dropped rapidly, which is driving a strong growth in worldwide capacity.[37] Solar panels are mounted on top of building or used in solar parks connected to the electrical grid. Typical panels convert less than 20% of the sunlight that hits them into electricity, as higher efficiency materials are more expensive.[38] The cost of electricity from new solar farms is competitive with, or in many places cheaper than, existing coal plants.[39]

Concentrated solar power produces heat to drive a heat engine. Because the heat is stored, this type of solar power is dispatchable: it can be produced when needed.[40] Solar thermal heating and cooling systems are used for many applications: hot water, heating and cooling buildings, drying and desalination.[41] Globally in 2018, it provided 1.5% of heating and cooling final energy demand.[42]

Wind power

Wind power stations in Xinjiang, China

Wind turbines are turned by the kinetic energy of wind and, in 2019, their electric generators provided approximately 6% of global electricity supply.[4] Wind farms consist of many individual wind turbines, which are connected to the electric power transmission network. New onshore wind is often cheaper than existing coal plants, and competitive with natural gas and nuclear.[39] Although construction and maintenance costs are higher at sea some analysts forecast that, because the winds are steadier and stronger than on land, with future larger blades offshore wind power will become cheaper than onshore wind in the mid-2030s.[43]

Onshore wind farms, often built in wild or rural areas, have a visual impact on the landscape.[44] The noise and flickering light created by the turbines can be annoying, and restricts the construction near densily populated areas. In terms of wildlife, bat populations may be strongly impacted by collusions.[45] Turbine blades are not fully recyclable yet, and research continues on how to manufacture blades which are easier to recycle.[46] Wind power, in contrast to nuclear and fossil fuel plants, does not consume water to produce power.[47] Little energy is needed for wind turbine construction compared to the energy produced by the wind power plant itself.[48]

Hydropower

Hydroelectric dams are one of the most widely deployed sources of renewable energy.

Hydroelectric plants convert the energy of moving water into electricity. On average, hydropower ranks amoung the energy sources with the lowest levels of greenhouse gas emissions per unit of energy produced, but levels of emissions vary enormously between projects.[49] In 2019, hydropower supplied 16% of the world's electricity, down from a high of nearly 20% in the mid-to-late 20th century.[50][51] It produced 60% of electricity in Canada and nearly 80% in Brazil.[50] Reservoir-based hydropower plants provide a highly flexible, dispatchable electricity supply. They can be combined with wind and solar power to provide peak load and to compensate when wind and sun are less available.[52]

In conventional hydropower, a reservoir is created behind a dam. In most cases, the biological matter that becomes submerged in the flooding of the reservoir decomposes, becoming a source of carbon dioxide and methane.[53] These greenhouse gas emissions are particularly large in tropical regions.[54] In turn, deforestation and climate change can reduce energy generation from hydroelectric dams.[52] Depending on location, the implementation of large-scale dams can displace residents and cause significant local environmental damage.[52]

In general, run-of-the-river hydroelectricity facilities have less environmental impact than reservoir-based facilities, but their ability to generate power depends on river flow, which can vary with daily and seasonal weather conditions.[55]

Geothermal

Cooling towers at Larderello geothermal power plant

Geothermal energy is produced by tapping into the heat that exists below the earth's crust.[56] Heat can be obtained by drilling into the ground and then carried by a heat-transfer fluid such as water, brine or steam.[56] Geothermal energy can be harnessed for electricity generation and for heating. The use of geothermal energy is concentrated in regions where heat extraction is economical: a combination of heat, flow and high permeability is needed.[57] Worldwide in 2018, geothermal provided 0.6% of heating and cooling final energy demand in buildings.[42]

Geothermal energy is a renewable resource because thermal energy is constantly replenished from neighbouring hotter regions.[58] The greenhouse gas emissions of geothermal electric stations are on average 45 grams of carbon dioxide per kilowatt-hour of electricity, or less than 5 percent of that of conventional coal-fired plants.[59] Geothermal energy carries a risk of inducing earthquakes, needs effective protection to avoid water pollution, and emits toxic emissions which can be captured.[60]

Bioenergy

Kenyan dairy farmer lighting biogas lamp
Biogas can provide both heat and light where electricity is not available.
Sugarcane plantation to produce ethanol in Brazil

Biomass is a versatile and common source of renewable energy. If the production of biomass is well-managed, carbon emissions can be significantly offset by the absorption of carbon dioxide by the plants during their lifespans.[61] Biomass can either be burned to produce heat and to generate electricity or converted to modern biofuels such as biodiesel and ethanol.[62][63] Biofuels are often produced from corn or sugar cane. They are used to power transport, often blended with liquid fossil fuels.[61]

Use of farmland for growing biomass can result in less land being available for growing food. Since photosynthesis only captures a small fraction of the energy in sunlight, and crops also require significant amounts of energy to harvest, dry, and transport, a lot of land is needed to produce biomass.[64] If biomass is harvested from crops, such as tree plantations, the cultivation of these crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilizers.[65][66] In some cases, these impacts can actually result in higher overall carbon emissions compared to using petroleum-based fuels.[66][67]

In the United States, corn-based ethanol has replaced less than 10% of motor gasoline use since 2011, but has consumed around 40% of the annual corn harvest in the country.[66] In Malaysia and Indonesia, the clearing of forests to produce palm oil for biodiesel has led to serious social and environmental effects, as these forests are critical carbon sinks and habitats for endangered species.[68]

More sustainable sources of biomass include crops grown on soil unsuitable for food production, algae and waste.[61] If the biomass source is agricultural or municipal waste, burning it or converting it into biogas also provides a way to dispose of this waste.[65] Second-generation biofuels, produced from non-food plants, reduce competition with food production, but may have other negative effects including trade-offs with conservation areas and local air pollution.[61]

According to the UK Committee on Climate Change in the long term all uses of biomass must maximise carbon sequestration, for example by using it in conjunction with carbon capture and storage (BECCS) when the biomass is burned,[69] and move "away from using biofuels in surface transport, biomass for heating buildings, or biomass for generating power without CCS".[70] Due to lack of technologically feasible alternatives, aviation biofuel may one of the best uses of biomass, providing that some carbon is captured and stored during manufacture of the fuel.[69]

Marine energy

Marine energy represents the smallest share of the energy market. It encompasses tidal power, which is approaching maturity, and wave power, which is earlier in its development. Two tidal barrage systems, in France and in Korea, make up 90% of total production. While single devices pose little risk to the environment, the impacts of multi-array devices are less well known.[71]

Non-renewable energy sources

(Fossil) fuel switching

A woman in rural Rajasthan carries firewood. Using firewood for cooking is labour-intensive and causes harmful air pollution.

For a given unit of energy produced, the life-cycle greenhouse-gas emissions of natural gas are around 40 times the emissions of wind or nuclear energy, but much less than that of coal. Natural gas produces significantly less air pollution than coal. It produces around half the emissions of coal when used to generate electricity, and around two-thirds the emissions of coal when used to produce heat. Reducing methane leaks in the process of extracting and transporting natural gas further decreases emissions.[72] Building gas-fired power plants and gas pipelines is promoted as a way to phase out coal and wood burning pollution, and increase energy supply in some African countries with fast growing populations or economies,[28] however this practice is controversial. Developing natural gas infrastructure risks the creation of carbon lock-in and stranded assets.[73][74] Switching cooking from dirty fuels such as wood or kerosene to LPG, biogas or electricity provides significant health benefits.[75]

Nuclear power

Nuclear power plants have been used since the 1950s to produce a low-carbon supply of electricity, without creating local air pollution. In 2020, nuclear power plants in over 30 countries generated 10% of global electricity.[76] Nuclear power's lifecycle greenhouse gas emissions (including the mining and processing of uranium), are similar to the emissions from renewable energy sources.[77]

There is considerable controversy over whether nuclear power can be considered sustainable, with debates revolving around the risk of nuclear accidents, the cost and construction time needed to build new plants, the generation of radioactive nuclear waste, and the potential for nuclear energy to contribute to nuclear proliferation. These concerns spurred the anti-nuclear movement. Public support for nuclear energy is often low as a result of safety concerns, however for each unit of energy produced, nuclear energy is far safer than fossil fuel energy and comparable to renewable sources.[78] The uranium ore used to fuel nuclear fission plants is a non-renewable resource, but sufficient quantities exist to provide a supply for hundreds of years.[79]

Various new forms of nuclear energy are in development, hoping to address the drawbacks of conventional nuclear. Nuclear power based on thorium, rather than uranium, may be able to provide higher energy security for countries that do not have a large supply of uranium.[80] Small modular reactors may also have several advantages over current large reactors: it should be possible to build them faster, and their modularization would allow for cost reductions via learning-by-doing.[81] Several countries are attempting to develop nuclear fusion reactors, which would generate very small amounts of waste and carry lower risk of explosions.[82]

Sustainable energy systems

Carbon capture and storage

The greenhouse gas emissions of fossil fuel and biomass power plants can be significantly reduced through carbon capture and storage (CCS), however deployment of this technology is still very limited, with only 21 large-scale CCS plants in operation worldwide as of 2020.[83] The CCS process is expensive, with costs depending considerably on the location's proximity to suitable geology for carbon dioxide storage.[43][84] CCS can be retrofitted to existing power plants, but is more energy-intensive in that case.[85] Most studies use a working assumption that CCS can capture 85–90% of the CO2 emissions from a power plant.[86][87] If 90% of emitted CO2 is captured from a coal-fired power plant, its uncaptured emissions would still be many times greater than the emissions of nuclear, solar, or wind energy per unit of electricity produced.[88][89]

When CCS is used to capture emissions from burning biomass in a process known as bioenergy with carbon capture and sequestration (BECCS), the overall process can result in net carbon dioxide removal from the atmosphere. The BECCS process can also result in net positive emissions depending on how the biomass material is grown, harvested, and transported.[90] As of 2014, the lowest-cost mitigation pathways for meeting the 2 °C target typically describe massive deployment of BECCS.[90] However, using BECCS at the scale described in these pathways would require more resources than are currently available worldwide. For example, to capture 10 billion tons of CO2 per year would require biomass from 40 percent of the world's current cropland.[90]

Managing intermittent energy sources

Solar and wind are variable renewable energy sources that supply electricity intermittently depending on the weather and the time of day.[91][92] Most electric grids were constructed for non-intermittent energy sources such as coal-fired power plants.[93] As larger amounts of solar and wind energy are integrated into the grid, changes have to be made to the energy system to ensure that the supply of electricity is matched to demand.[94]

Various sources of flexibility are available. Often, wind and solar production is complementary on a daily and season scale: in many places there is more wind during the night and in winter, when solar energy production is low.[94] Linking different geographical regions through long-distance transmission lines allows for further cancelling out of variability.[95] Energy demand can be shifted in time through energy demand management and the use of smart grids, matching the times when variable energy production is highest. With storage, energy produced in excess can be released when needed.[94] The final mismatch may be covered via overproduction of variable energy (and curtailing further excess), and by using dispatchable energy, such as hydro, bioenergy, natural gas, or nuclear plants.[96]

As of 2019, the cost and logistics of energy storage is a significant challenge, although the cost of battery systems has plunged dramatically.[97] For instance, a 2019 study found that for solar and wind energy to replace all fossil fuel generation for a week of extreme cold in the eastern and midwest United States, energy storage capacity would have to increase from the 11 GW in place at that time to between 230 GW and 280 GW, depending on how much nuclear power is retired.[97]

Energy storage

Construction of salt tanks to store thermal energy

Energy storage helps overcome barriers for intermittent renewable energy, and is therefore an important aspect of a sustainable energy system.[98] The most commonly used storage method is pumped-storage hydroelectricity, which requires locations with large differences in height and access to water.[98] Battery storage power stations and home energy storage are being deployed widely.[99] Some lithium-ion batteries contain cobalt, now largely mined in Congo some unsustainably. Responsible sourcing of cobalt[100] and more diverse geographical sourcing may ensure a more stable supply-chain. Environmental impacts can be reduced by downcycling and recycling.[101] Batteries typically have capacity to store enough electricity to last for short periods; research is ongoing into technology with sufficient capacity to last through seasons.[102] Pumped hydro storage and power-to-gas with capacity for multi-month usage has been implemented in some locations.[103][104]

As of 2018, thermal energy storage is typically not as convenient as burning fossil fuels. High upfront costs form a barrier for implementation. Seasonal thermal energy storage requires large capacity; it has been implemented in some high-latitude regions for household heat.[105]

Hydrogen

Hydrogen can be burned to produce heat or can power fuel cells to generate electricity, with zero emissions at the point of usage. The overall lifecycle emissions of hydrogen depend on how it is produced. Very little of the world's current supply of hydrogen is currently created from sustainable sources. Nearly all of it is produced from fossil fuels, which results in high greenhouse gas emissions. With carbon capture and storage technologies, 80 – 90% of the carbon dioxide emitted during the production of hydrogen could be removed.[106]

Hydrogen can be produced through electrolysis, by using electricity to split water molecules into hydrogen and oxygen, and if the electricity is generated sustainably, the resultant fuel will also be sustainable. This process is currently more expensive than creating hydrogen from fossil fuels, and the efficiency of energy conversion is inherently low.[106] Hydrogen can be produced when there is a surplus of intermittent renewable electricity, then stored and used to generate heat or to re-generate electricity. Further conversion to ammonia allows the energy to be more easily stored at room temperature in liquid form.[107]

There is potential for hydrogen to play a significant role in decarbonising energy systems because in certain sectors, replacing fossil fuels with direct use of electricity would be very difficult.[106] Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals.[108] Steelmaking is considered to be the use of hydrogen which would be most effective in limiting greenhouse gas emissions in the short-term.[108]

Sectors

Electricity generation

As of 2018, about a quarter of all electricity generation came from modern renewable sources (excluding the traditional use of biomass). The growth of renewable energy usage has been significantly faster in this sector than in heating and transport.[109] Those sectors rely more heavily on fossil fuels, gas for heating and oil for transport, and there are fewer alternatives for those compared to power, where nuclear, wind, solar and hydro all provide low-carbon energy.[110]

Electrification is a key part of using energy sustainably. Many options exist to produce electricity sustainably, but sustainably producing fuels or heat at large scales is relatively difficult.[111] Specifically, massive electrification in the heat and transport sector may be needed to make these sectors sustainable, with heat pumps and electric vehicles playing important roles.[112]

Heating and cooling

A large fraction of the world population cannot afford sufficient cooling or live in poorly designed houses. In addition to air conditioning, which requires electrification and additional power demand, passive building design and urban planning will be needed to ensure cooling needs are met in a sustainable way.[113] Similarly, many households in the developing and developed world suffer from fuel poverty and cannot heat their houses enough.[114] Existing heating practices are often polluting. Alternatives to fossil fuel heating include electrification (heat pumps, or the less efficient electric heater), geothermal, biomass, solar thermal, and waste heat.[115][116][117] The costs of all these technologies strongly depend on location, and uptake of the technology sufficient for deep decarbonisation requires stringent policy interventions.[117]

Transport

Group of cyclists in Beijing
Cycling is a sustainable method of transport.

There are multiple ways to make transport more sustainable. Public transport frequently emits less per passenger than personal vehicles such as cars, especially with high occupancy.[118][119] Transport can be made cleaner and healthier by stimulating nonmotorised transport such as cycling, particularly in cities.[120] The energy efficiency of cars has increased as a consequence of technological progress.[121]

It is easier to sustainably produce electricity than it is to sustainably produce liquid fuels. Therefore, adoption of electric vehicles is a way to make transport more sustainable;[112] Hydrogen vehicles may be an option for larger vehicles which have not yet been widely electrified, such as long distance lorries.[122] Many of the techniques needed to lower emissions from shipping and aviation are still in early in their development.[123]

Industry

Of final energy demand, over one third is used by industry. Most of that energy is deployed in thermal processes: generating steam, drying and refrigeration. The share of renewable energy in industry was 14.5% in 2017, which mostly include low-temperature heat supplied by bioenergy and electricity. The more energy intensive part of industry have the lowest shares of renewable energy, as they face limitations to meet heat demand over 200 °C.[124] For some industrial processes, such as steel production, commercialization of technologies that have not yet been built or operated at full scale is needed to eliminate greenhouse gas emissions.[125] The production of plastic, cement and fertilizers also requires significant amounts of energy, with limited possibilities available to decarbonise.[126]

Pathways for climate change mitigation

Bangui Wind Farm in the Philippines
Workers construct a solar panel array structure in Malawi.

Cost–benefit analysis work has been done by a disparate array of specialists and agencies to determine the best path to decarbonizing the energy supply of the world.[127][128] The IPCC's 2018 Special Report on Global Warming of 1.5 °C says that for limiting warming to 1.5 °C and avoiding the worst effects of climate change, "global net human-caused emissions of CO2 would need to fall by about 45% from 2010 levels by 2030, reaching net zero around 2050." As part of this report, the IPCC's working group on climate change mitigation reviewed a variety of previously-published papers that describe pathways (i.e. scenarios and portfolios of mitigation options) to stabilize the climate system through changes in energy, land use, agriculture, and other areas.

The pathways that are consistent with limiting warning to approximately 1.5 °C describe a rapid transition towards producing electricity through lower-emission methods, and increasing use of electricity instead of other fuels in sectors such as transport.[129] These pathways have the following characteristics (unless otherwise stated, the following values are the median across all pathways):

  • Renewable energy: The proportion of primary energy supplied by renewables increases from 15% in 2020 to 60% in 2050.[130] The proportion of primary energy supplied by biomass increases from 10% to 27%,[131] with effective controls on whether land use is changed in the growing of biomass.[132] The proportion from wind and solar increases from 1.8% to 21%.[131]
  • Nuclear energy: The proportion of primary energy supplied by nuclear power increases from 2.1% in 2020 to 4% in 2050. Most pathways describe an increase in use of nuclear power, but some describe a decrease. The reason for the wide range of possibilities is that deployment of nuclear energy "can be constrained by societal preferences."[133]
  • Coal and oil: Between 2020 and 2050, the proportion of primary energy from coal declines from 26% to 5%, and the proportion from oil declines from 35% to 13%.[131]
  • Natural gas: In most pathways, the proportion of primary energy supplied by natural gas decreases, but in some pathways, it increases. Using the median values across all pathways, the proportion of primary energy from natural gas declines from 23% in 2020 to 13% in 2050.[131]
  • Carbon capture and storage: Pathways describe more use of carbon capture and storage for bioenergy and fossil fuel energy.[133]
  • Electrification: In 2020, around 20% of final energy use is provided by electricity. By 2050, this proportion more than doubles in most pathways.[134]
  • Energy conservation: Pathways describe methods to increase energy efficiency and reduce energy demand in all sectors (industry, buildings, and transport). With these measures, pathways show energy usage to remain around the same between 2010 and 2030, and increase slightly by 2050.[135]

Government policies

According to the IPCC, both explicit carbon pricing and complementary energy-specific policies are necessary mechanisms to limit global warming to 1.5 °C. Some studies estimate that combining a carbon tax with energy-specific policies would be more cost-effective than a carbon tax alone.[136]

Energy-specific programs and regulations have historically been the mainstays of efforts to reduce fossil fuel emissions. Successful cases include the building of nuclear reactors in France in the 1970s and 1980s, and fuel efficiency standards in the United States which conserved billions of barrels of oil.[137] Other examples of energy-specific policies include energy-efficiency requirements in building codes, banning new coal-fired electricity plants, performance standards for electrical appliances, and support for electric vehicle use.[138][136] Fossil fuel subsidies form a significant barrier to the energy transition.[139]

Carbon taxes are an effective way to encourage movement towards a low-carbon economy, while providing a source of revenue that can be used to lower other taxes[140] or to help lower-income households afford higher energy costs.[141] Carbon taxes have encountered strong political pushback in some jurisdictions, whereas energy-specific policies tend to be politically safer.[137] According to the OECD, climate change cannot be curbed without carbon taxes on energy, but 70% of energy-related CO2 emissions were not taxed at all in 2018.[142]

Energy security is another major policy goal. Historically, energy independence has been the focus of energy security policy, with countries wanting to become less dependent on oil exporters. With the integration of variable renewables, countries are increasingly considering the benefits of interdependence to compensate for intermittency.[143] The market for metals and minerals required for sustainable energy is sometimes dominated by a small group of countries or companies, raising geopolitical concerns.[144]

In 2020, the International Energy Agency warned that the economic turmoil caused by the coronavirus outbreak may prevent or delay companies from investing in green energy.[145][146] The outbreak could potentially spell a slowdown in the world's clean energy transition if no action is undertaken, but also offers possibilities for a green recovery.[147]

See also

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