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Friday, December 29, 2023

Climate change

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Climate_change
The global map shows sea temperature rises of 0.5 to 1 degree Celsius; land temperature rises of 1 to 2 degree Celsius; and Arctic temperature rises of up to 4 degrees Celsius.
Average surface air temperatures 2011–21 compared to 1956–76
The graph from 1880 to 2020 shows natural drivers exhibiting fluctuations of about 0.3 degrees Celsius. Human drivers steadily increase by 0.3 degrees over 100 years to 1980, then steeply by 0.8 degrees more over the past 40 years.
Change in average surface air temperature since the Industrial Revolution, plus drivers for that change. Human activity has caused increased temperatures, with natural forces adding some variability.

In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The current rise in global average temperature is more rapid than previous changes, and is primarily caused by humans burning fossil fuels. Fossil fuel use, deforestation, and some agricultural and industrial practices add to greenhouse gases, notably carbon dioxide and methane. Greenhouse gases absorb some of the heat that the Earth radiates after it warms from sunlight. Larger amounts of these gases trap more heat in Earth's lower atmosphere, causing global warming.

Climate change is causing a range of increasing impacts on the environment. Deserts are expanding, while heat waves and wildfires are becoming more common. Amplified warming in the Arctic has contributed to melting permafrost, glacial retreat and sea ice loss. Higher temperatures are also causing more intense storms, droughts, and other weather extremes. Rapid environmental change in mountains, coral reefs, and the Arctic is forcing many species to relocate or become extinct. Even if efforts to minimise future warming are successful, some effects will continue for centuries. These include ocean heating, ocean acidification and sea level rise.

Climate change threatens people with increased flooding, extreme heat, increased food and water scarcity, more disease, and economic loss. Human migration and conflict can also be a result. The World Health Organization (WHO) calls climate change the greatest threat to global health in the 21st century. Societies and ecosystems will experience more severe risks without action to limit warming. Adapting to climate change through efforts like flood control measures or drought-resistant crops partially reduces climate change risks, although some limits to adaptation have already been reached. Poorer communities are responsible for a small share of global emissions, yet have the least ability to adapt and are most vulnerable to climate change.

Bobcat Fire in Monrovia, CA, September 10, 2020
Bleached colony of Acropora coral
A dry lakebed in California, which is experiencing its worst megadrought in 1,200 years.[17]
Some effects of climate change: Wildfire intensified by heat and drought, bleaching of coral caused by marine heatwaves, and worsening droughts compromising water supplies.

Many climate change impacts are already felt at the current 1.2 °C (2.2 °F) level of warming. Additional warming will increase these impacts and can trigger tipping points, such as the melting of the Greenland ice sheet. Under the 2015 Paris Agreement, nations collectively agreed to keep warming "well under 2 °C". However, with pledges made under the Agreement, global warming would still reach about 2.7 °C (4.9 °F) by the end of the century. Limiting warming to 1.5 °C will require halving emissions by 2030 and achieving net-zero emissions by 2050.

Strategies to phase out fossil fuels involve conserving energy, generating electricity cleanly, and using electricity to power transportation, heat buildings, and operate industrial facilities. The electricity supply can be made cleaner and more plentiful by vastly increasing deployment of wind, and solar power, alongside other forms of renewable energy and nuclear power. Carbon can also be removed from the atmosphere, for instance by increasing forest cover and farming with methods that capture carbon in soil.

Terminology

Before the 1980s, when it was unclear whether the warming effect of increased greenhouse gases was stronger than the cooling effect of airborne particulates in air pollution, scientists used the term inadvertent climate modification to refer to human impacts on the climate.

In the 1980s, the terms global warming and climate change became more common. Though the two terms are sometimes used interchangeably, scientifically, global warming refers only to increased surface warming, while climate change describes the totality of changes to Earth's climate system. Global warming—used as early as 1975—became the more popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. Since the 2000s, climate change has increased in usage. Climate change can also refer more broadly to both human-caused changes or natural changes throughout Earth's history.

Various scientists, politicians and media now use the terms climate crisis or climate emergency to talk about climate change, and global heating instead of global warming.

Observed global temperature rise

In recent decades, new high temperature records have substantially outpaced new low temperature records on a growing portion of Earth's surface.
There has been an increase in ocean heat content during recent decades as the oceans absorb over 90% of the heat from global warming.

Multiple independent instrumental datasets show that the climate system is warming. A so-called "global warming hiatus" from 1998 to 2013 when warming was relatively slow was likely caused by negative phases of the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). The 2013-2022 decade warmed to an average 1.15 °C [1.00–1.25 °C] compared to the pre-industrial baseline (1850–1900). Surface temperatures are rising by about 0.2 °C per decade, with 2020 reaching a temperature of 1.2 °C above the pre-industrial era. Since 1950, the number of cold days and nights has decreased, and the number of warm days and nights has increased.

Evidence of warming from air temperature measurements is reinforced by a wide range of other observations. For example, changes to the natural water cycle have been predicted and observed, such as an increase in the frequency and intensity of heavy precipitation, melting of snow and land ice, and increased atmospheric humidity. Flora and fauna are also behaving in a manner consistent with warming; for instance, plants are flowering earlier in spring. Another key indicator is the cooling of the upper atmosphere, which demonstrates that greenhouse gases are trapping heat near the Earth's surface and preventing it from radiating into space.

Different regions of the world warm at different rates. The pattern is independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, the average surface temperature over land regions has increased almost twice as fast as the global-average surface temperature. This is because of the larger heat capacity of oceans, and because oceans lose more heat by evaporation. The thermal energy in the global climate system has grown with only brief pauses since at least 1970, and over 90% of this extra energy has been stored in the ocean. The rest has heated the atmosphere, melted ice, and warmed the continents.

The Northern Hemisphere and the North Pole have warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat. Local black carbon deposits on snow and ice also contribute to Arctic warming. Arctic temperatures are increasing at over twice the rate of the rest of the world. Melting of glaciers and ice sheets in the Arctic disrupts ocean circulation, including a weakened Gulf Stream, further changing the climate.

Temperature records prior to global warming

Global surface temperature reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue. Directly observed data is in red.

Human beings evolved over the last few million years in a climate that cycled through ice ages, with global average temperature ranging between current levels and 5–6 °C colder than today. The temperature record prior to human evolution includes hotter temperatures and occasional abrupt changes, such as the Paleocene–Eocene Thermal Maximum 55.5 million years ago.

Historical patterns of warming and cooling, like the Medieval Warm Period and the Little Ice Age, did not occur at the same time across different regions. Temperatures may have reached as high as those of the late 20th century in a limited set of regions.

There was little net warming between the 18th century and the mid-19th century. Climate information for that period comes from climate proxies, such as trees and ice cores. Thermometer records began to provide global coverage around 1850.

Causes of recent global temperature rise

Drivers of climate change from 1850–1900 to 2010–2019. There was no significant contribution from internal variability or solar and volcanic drivers.

The climate system experiences various cycles on its own which can last for years, decades or even centuries. For example, El Niño events cause short-term spikes in surface temperature while La Niña events cause short term cooling. Their relative frequency can affect global temperature trends on a decadal timescale. Other changes are caused by an imbalance of energy from specific external forcings. Examples of these include changes in the concentrations of greenhouse gases, solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun.

To determine the human contribution to climate change, unique "fingerprints" for all potential causes are developed and compared with both observed patterns and known internal climate variability. For example, solar forcing—whose fingerprint involves warming the entire atmosphere—is ruled out because only the lower atmosphere has warmed. These techniques show that greenhouse gases are the main cause of current global warming. Atmospheric aerosols produce a smaller, cooling effect. Other drivers, such as changes in albedo, are less impactful.

Greenhouse gases

CO2 concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)

Greenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth radiates it as heat, and greenhouse gases absorb a portion of it. This absorption slows the rate at which heat escapes into space, trapping heat near the Earth's surface and warming it over time. Before the Industrial Revolution, naturally-occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C warmer than it would have been in their absence. While water vapour (≈50%) and clouds (≈25%) are the biggest contributors to the greenhouse effect, they increase as a function of temperature and are therefore feedbacks. On the other hand, concentrations of gases such as CO2 (≈20%), tropospheric ozone, CFCs and nitrous oxide are not temperature-dependent, and are therefore external forcings.

Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas), has increased the amount of greenhouse gases in the atmosphere, resulting in a radiative imbalance. In 2019, the concentrations of CO2 and methane had increased by about 48% and 160%, respectively, since 1750. These CO2 levels are higher than they have been at any time during the last 2 million years. Concentrations of methane are far higher than they were over the last 800,000 years.

The Global Carbon Project shows how additions to CO2 since 1880 have been caused by different sources ramping up one after another.

Global anthropogenic greenhouse gas emissions in 2019 were equivalent to 59 billion tonnes of CO2. Of these emissions, 75% was CO2, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases. CO2 emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity. Additional CO2 emissions come from deforestation and industrial processes, which include the CO2 released by the chemical reactions for making cement, steel, aluminum, and fertiliser. Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction. Nitrous oxide emissions largely come from the microbial decomposition of fertiliser.

Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for CO2. Land-surface sink processes, such as carbon fixation in the soil and photosynthesis, remove about 29% of annual global CO2 emissions. The ocean also serves as a significant carbon sink via a two-step process. First, CO2 dissolves in the surface water. Afterwards, the ocean's overturning circulation distributes it deep into the ocean's interior, where it accumulates over time as part of the carbon cycle. Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted CO2.

Aerosols and clouds

Air pollution, in the form of aerosols, affects the climate on a large scale. Aerosols scatter and absorb solar radiation. From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed. This phenomenon is popularly known as global dimming, and is primarily attributed to sulfate aerosols produced by the combustion of fossil fuels with heavy sulfur concentrations like coal and bunker fuel, with a smaller role from black carbon and organic carbon from combustion of fossil fuels and biofuels and from anthropogenic dust. Globally, aerosols have been declining since 1990 due to pollution controls, meaning that they no longer mask greenhouse gas warming as much.

Aerosols also have indirect effects on the Earth's radiation budget. Sulfate aerosols act as cloud condensation nuclei and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets. They also reduce the growth of raindrops, which makes clouds more reflective to incoming sunlight. Indirect effects of aerosols are the largest uncertainty in radiative forcing.

While aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise. Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C by 2050.

Land surface changes

The rate of global tree cover loss has approximately doubled since 2001, to an annual loss approaching an area the size of Italy.

Humans change the Earth's surface mainly to create more agricultural land. Today, agriculture takes up 34% of Earth's land area, while 26% is forests, and 30% is uninhabitable (glaciers, deserts, etc.). The amount of forested land continues to decrease, which is the main land use change that causes global warming. Deforestation releases CO2 contained in trees when they are destroyed, plus it prevents those trees from absorbing more CO2. The main causes of deforestation are: permanent land-use change from forest to agricultural land producing products such as beef and palm oil (27%), logging to produce forestry/forest products (26%), short term shifting cultivation (24%), and wildfires (23%).

The type of vegetation in a region affects the local temperature. It impacts how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also affect temperatures by modifying the release of chemical compounds that influence clouds, and by changing wind patterns. In tropic and temperate areas the net effect is to produce significant warming, while at latitudes closer to the poles a gain of albedo (as forest is replaced by snow cover) leads to a cooling effect. Globally, these effects are estimated to have led to a slight cooling, dominated by an increase in surface albedo. According to FAO, forest degradation aggravates the impacts of climate change as it reduces the carbon sequestration abilities of forests. Indeed, among their many benefits, forests also have the potential to reduce the impact of high temperatures.

Solar and volcanic activity

As the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the climate system. Solar irradiance has been measured directly by satellites, and indirect measurements are available from the early 1600s onwards. Since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth.

Explosive volcanic eruptions represent the largest natural forcing over the industrial era. When the eruption is sufficiently strong (with sulfur dioxide reaching the stratosphere), sunlight can be partially blocked for a couple of years. The temperature signal lasts about twice as long. In the industrial era, volcanic activity has had negligible impacts on global temperature trends. Present-day volcanic CO2 emissions are equivalent to less than 1% of current anthropogenic CO2 emissions.

Physical climate models are unable to reproduce the rapid warming observed in recent decades when taking into account only variations in solar output and volcanic activity. Further evidence for greenhouse gases causing global warming comes from measurements that show a warming of the lower atmosphere (the troposphere), coupled with a cooling of the upper atmosphere (the stratosphere). If solar variations were responsible for the observed warming, the troposphere and stratosphere would both warm.

Climate change feedback

Sea ice reflects 50% to 70% of incoming sunlight, while the ocean, being darker, reflects only 6%. As an area of sea ice melts and exposes more ocean, more heat is absorbed by the ocean, raising temperatures that melt still more ice. This is a positive feedback process.

The response of the climate system to an initial forcing is modified by feedbacks: increased by "self-reinforcing" or "positive" feedbacks and reduced by "balancing" or "negative" feedbacks. The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and the net effect of clouds. The primary balancing mechanism is radiative cooling, as Earth's surface gives off more heat to space in response to rising temperature. In addition to temperature feedbacks, there are feedbacks in the carbon cycle, such as the fertilizing effect of CO2 on plant growth. Uncertainty over feedbacks is the major reason why different climate models project different magnitudes of warming for a given amount of emissions.

As air warms, it can hold more moisture. Water vapour, as a potent greenhouse gas, holds heat in the atmosphere. If cloud cover increases, more sunlight will be reflected back into space, cooling the planet. If clouds become higher and thinner, they act as an insulator, reflecting heat from below back downwards and warming the planet. The effect of clouds is the largest source of feedback uncertainty.

Another major feedback is the reduction of snow cover and sea ice in the Arctic, which reduces the reflectivity of the Earth's surface. More of the Sun's energy is now absorbed in these regions, contributing to amplification of Arctic temperature changes. Arctic amplification is also melting permafrost, which releases methane and CO2 into the atmosphere. Climate change can also cause methane releases from wetlands, marine systems, and freshwater systems. Overall, climate feedbacks are expected to become increasingly positive.

Around half of human-caused CO2 emissions have been absorbed by land plants and by the oceans. Climate change increases droughts and heat waves that inhibit plant growth, which makes it uncertain whether this carbon sink will continue to grow. Soils contain large quantities of carbon and may release some when they heat up. As more CO2 and heat are absorbed by the ocean, it acidifies, its circulation changes and phytoplankton takes up less carbon, decreasing the rate at which the ocean absorbs atmospheric carbon. Overall, at higher CO2 concentrations the Earth will absorb a reduced fraction of our emissions.

Modelling

Projected global surface temperature changes relative to 1850–1900, based on CMIP6 multi-model mean changes

A climate model is a representation of the physical, chemical and biological processes that affect the climate system. Models also include natural processes like changes in the Earth's orbit, historical changes in the Sun's activity, and volcanic forcing. Models are used to estimate the degree of warming future emissions will cause when accounting for the strength of climate feedbacks, or reproduce and predict the circulation of the oceans, the annual cycle of the seasons, and the flows of carbon between the land surface and the atmosphere.

The physical realism of models is tested by examining their ability to simulate contemporary or past climates. Past models have underestimated the rate of Arctic shrinkage and underestimated the rate of precipitation increase. Sea level rise since 1990 was underestimated in older models, but more recent models agree well with observations. The 2017 United States-published National Climate Assessment notes that "climate models may still be underestimating or missing relevant feedback processes". Additionally, climate models may be unable to adequately predict short-term regional climatic shifts.

Simplified model: Energy flows between space, the atmosphere, and Earth's surface, with greenhouse gases in the atmosphere absorbing and emitting radiant heat, affecting Earth's energy balance. Data as of 2007.

A subset of climate models add societal factors to a simple physical climate model. These models simulate how population, economic growth, and energy use affect—and interact with—the physical climate. With this information, these models can produce scenarios of future greenhouse gas emissions. This is then used as input for physical climate models and carbon cycle models to predict how atmospheric concentrations of greenhouse gases might change. Depending on the socioeconomic scenario and the mitigation scenario, models produce atmospheric CO2 concentrations that range widely between 380 and 1400 ppm.

The IPCC Sixth Assessment Report projects that global warming is very likely to reach 1.0 °C to 1.8 °C by the late 21st century under the very low GHG emissions scenario. In an intermediate scenario global warming would reach 2.1 °C to 3.5 °C, and 3.3 °C to 5.7 °C under the very high GHG emissions scenario. These projections are based on climate models in combination with observations.

The remaining carbon budget is determined by modelling the carbon cycle and the climate sensitivity to greenhouse gases. According to the IPCC, global warming can be kept below 1.5 °C with a two-thirds chance if emissions after 2018 do not exceed 420 or 570 gigatonnes of CO2. This corresponds to 10 to 13 years of current emissions. There are high uncertainties about the budget. For instance, it may be 100 gigatonnes of CO2 smaller due to methane release from permafrost and wetlands. However, it is clear that fossil fuel resources are too abundant for shortages to be relied on to limit carbon emissions in the 21st century.

Even though the temperature will need to stay at or above 1.5 °C for 20 years to pass the threshold defined by the Paris agreement, a temporary rise above this limit also can have severe consequences. According to the World Meteorological Organization, there is a 66% chance that global temperature will rise temporarily above 1.5 °C in the years 2023–2027.

Impacts

The sixth IPCC Assessment Report projects changes in average soil moisture that can disrupt agriculture and ecosystems. A reduction in soil moisture by one standard deviation means that average soil moisture will approximately match the ninth driest year between 1850 and 1900 at that location.

Environmental effects

The environmental effects of climate change are broad and far-reaching, affecting oceans, ice, and weather. Changes may occur gradually or rapidly. Evidence for these effects comes from studying climate change in the past, from modelling, and from modern observations. Since the 1950s, droughts and heat waves have appeared simultaneously with increasing frequency. Extremely wet or dry events within the monsoon period have increased in India and East Asia. Monsoonal precipitation over the Northern Hemisphere has increased since 1980. The rainfall rate and intensity of hurricanes and typhoons is likely increasing, and the geographic range likely expanding poleward in response to climate warming. Frequency of tropical cyclones has not increased as a result of climate change.

Historical sea level reconstruction and projections up to 2100 published in 2017 by the U.S. Global Change Research Program

Global sea level is rising as a consequence of glacial melt, melt of the Greenland ice sheets and Antarctica, and thermal expansion. Between 1993 and 2020, the rise increased over time, averaging 3.3 ± 0.3 mm per year. Over the 21st century, the IPCC projects that in a very high emissions scenario the sea level could rise by 61–110 cm. Increased ocean warmth is undermining and threatening to unplug Antarctic glacier outlets, risking a large melt of the ice sheet and the possibility of a 2-meter sea level rise by 2100 under high emissions.

Climate change has led to decades of shrinking and thinning of the Arctic sea ice. While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur once every three to ten years at a warming level of 2 °C. Higher atmospheric CO2 concentrations have led to changes in ocean chemistry. An increase in dissolved CO2 is causing oceans to acidify. In addition, oxygen levels are decreasing as oxygen is less soluble in warmer water. Dead zones in the ocean, regions with very little oxygen, are expanding too.

Tipping points and long-term impacts

Greater degrees of global warming increase the risk of passing through 'tipping points'—thresholds beyond which certain impacts can no longer be avoided even if temperatures are reduced. An example is the collapse of West Antarctic and Greenland ice sheets, where a temperature rise of 1.5 to 2 °C may commit the ice sheets to melt, although the time scale of melt is uncertain and depends on future warming. Some large-scale changes could occur over a short time period, such as a shutdown of certain ocean currents like the Atlantic meridional overturning circulation (AMOC). Tipping points can also include irreversible damage to ecosystems like the Amazon rainforest and coral reefs.

The long-term effects of climate change on oceans include further ice melt, ocean warming, sea level rise, and ocean acidification. On the timescale of centuries to millennia, the magnitude of climate change will be determined primarily by anthropogenic CO2 emissions. This is due to CO2's long atmospheric lifetime. Oceanic CO2 uptake is slow enough that ocean acidification will continue for hundreds to thousands of years. These emissions are estimated to have prolonged the current interglacial period by at least 100,000 years. Sea level rise will continue over many centuries, with an estimated rise of 2.3 metres per degree Celsius (4.2 ft/°F) after 2000 years.

Nature and wildlife

Recent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes. Higher atmospheric CO2 levels and an extended growing season have resulted in global greening. However, heatwaves and drought have reduced ecosystem productivity in some regions. The future balance of these opposing effects is unclear. Climate change has contributed to the expansion of drier climate zones, such as the expansion of deserts in the subtropics. The size and speed of global warming is making abrupt changes in ecosystems more likely. Overall, it is expected that climate change will result in the extinction of many species.

The oceans have heated more slowly than the land, but plants and animals in the ocean have migrated towards the colder poles faster than species on land. Just as on land, heat waves in the ocean occur more frequently due to climate change, harming a wide range of organisms such as corals, kelp, and seabirds. Ocean acidification makes it harder for marine calcifying organisms such as mussels, barnacles and corals to produce shells and skeletons; and heatwaves have bleached coral reefs. Harmful algal blooms enhanced by climate change and eutrophication lower oxygen levels, disrupt food webs and cause great loss of marine life. Coastal ecosystems are under particular stress. Almost half of global wetlands have disappeared due to climate change and other human impacts.

Humans

Extreme weather will be progressively more common as the Earth warms.

The effects of climate change are impacting humans everywhere in the world. Impacts can be observed on all continents and ocean regions, with low-latitude, less developed areas facing the greatest risk. Continued warming has potentially "severe, pervasive and irreversible impacts" for people and ecosystems. The risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries.

Food and health

The WHO calls climate change the greatest threat to global health in the 21st century. Extreme weather leads to injury and loss of life, and crop failures to malnutrition. Various infectious diseases are more easily transmitted in a warmer climate, such as dengue fever and malaria. Young children are the most vulnerable to food shortages. Both children and older people are vulnerable to extreme heat. The World Health Organization (WHO) has estimated that between 2030 and 2050, climate change would cause around 250,000 additional deaths per year. They assessed deaths from heat exposure in elderly people, increases in diarrhea, malaria, dengue, coastal flooding, and childhood malnutrition. Over 500,000 more adult deaths are projected yearly by 2050 due to reductions in food availability and quality. By 2100, 50% to 75% of the global population may face climate conditions that are life-threatening due to combined effects of extreme heat and humidity.

Climate change is affecting food security. It has caused reduction in global yields of maize, wheat, and soybeans between 1981 and 2010. Future warming could further reduce global yields of major crops. Crop production will probably be negatively affected in low-latitude countries, while effects at northern latitudes may be positive or negative. Up to an additional 183 million people worldwide, particularly those with lower incomes, are at risk of hunger as a consequence of these impacts. Climate change also impacts fish populations. Globally, less will be available to be fished. Regions dependent on glacier water, regions that are already dry, and small islands have a higher risk of water stress due to climate change.

Inequality

Economic damages due to climate change may be severe and there is a chance of disastrous consequences. Climate change has likely already increased global economic inequality, and this trend is projected to continue. Most of the severe impacts are expected in sub-Saharan Africa, where most of the local inhabitants are dependent upon natural and agricultural resources and South-East Asia. The World Bank estimates that climate change could drive over 120 million people into poverty by 2030.

Inequalities based on wealth and social status have worsened due to climate change. Major difficulties in mitigating, adapting, and recovering to climate shocks are faced by marginalized people who have less control over resources. Indigenous people, who are subsistent on their land and ecosystems, will face endangerment to their wellness and lifestyles due to climate change. An expert elicitation concluded that the role of climate change in armed conflict has been small compared to factors such as socio-economic inequality and state capabilities.

While women are not inherently more at risk from climate change and shocks, limits on women's resources and discriminatory gender norms constrain their adaptive capacity and resilience. For example, women's work burdens, including hours worked in agriculture, tend to decline less than men's during climate shocks such as heat stress.

Climate migration

Low-lying islands and coastal communities are threatened by sea level rise, which makes flooding more common. Sometimes, land is permanently lost to the sea. This could lead to statelessness for people in island nations, such as the Maldives and Tuvalu. In some regions, the rise in temperature and humidity may be too severe for humans to adapt to. With worst-case climate change, models project that almost one-third of humanity might live in extremely hot and uninhabitable climates, similar to the climate found in the Sahara.

These factors can drive climate or environmental migration, within and between countries. More people are expected to be displaced because of sea level rise, extreme weather and conflict from increased competition over natural resources. Climate change may also increase vulnerability, leading to "trapped populations" who are not able to move due to a lack of resources.

Climate change impacts on people

Reducing and recapturing emissions

Global greenhouse gas emission scenarios, based on policies and pledges as of November, 2021

Climate change can be mitigated by reducing the rate at which greenhouse gases are emitted into the atmosphere, and by increasing the rate at which carbon dioxide is removed from the atmosphere. In order to limit global warming to less than 1.5 °C global greenhouse gas emissions needs to be net-zero by 2050, or by 2070 with a 2 °C target. This requires far-reaching, systemic changes on an unprecedented scale in energy, land, cities, transport, buildings, and industry. The United Nations Environment Programme estimates that countries need to triple their pledges under the Paris Agreement within the next decade to limit global warming to 2 °C. An even greater level of reduction is required to meet the 1.5 °C goal. With pledges made under the Paris Agreement as of October 2021, global warming would still have a 66% chance of reaching about 2.7 °C (range: 2.2–3.2 °C) by the end of the century. Globally, limiting warming to 2 °C may result in higher economic benefits than economic costs.

Although there is no single pathway to limit global warming to 1.5 or 2 °C, most scenarios and strategies see a major increase in the use of renewable energy in combination with increased energy efficiency measures to generate the needed greenhouse gas reductions. To reduce pressures on ecosystems and enhance their carbon sequestration capabilities, changes would also be necessary in agriculture and forestry, such as preventing deforestation and restoring natural ecosystems by reforestation.

Other approaches to mitigating climate change have a higher level of risk. Scenarios that limit global warming to 1.5 °C typically project the large-scale use of carbon dioxide removal methods over the 21st century. There are concerns, though, about over-reliance on these technologies, and environmental impacts. Solar radiation modification (SRM) is also a possible supplement to deep reductions in emissions. However, SRM raises significant ethical and legal concerns, and the risks are imperfectly understood.

Clean energy

Coal, oil, and natural gas remain the primary global energy sources even as renewables have begun rapidly increasing.
Wind and solar power, Germany

Renewable energy is key to limiting climate change. For decades, fossil fuels have accounted for roughly 80% of the world's energy use. The remaining share has been split between nuclear power and renewables (including hydropower, bioenergy, wind and solar power and geothermal energy). That mix is projected to change significantly over the next 30 years. Fossil fuel use is expected to peak prior to 2030, and begin to decline by then. Coal use will experience the sharpest decline. Solar panels and onshore wind are now among the cheapest forms of adding new power generation capacity in many locations. Renewables represented 75% of all new electricity generation installed in 2019, nearly all solar and wind. Other forms of clean energy, such as nuclear and hydropower, currently have a larger share of the energy supply. However, their future growth forecasts appear limited in comparison.

To achieve carbon neutrality by 2050, renewable energy would become the dominant form of electricity generation, rising to 85% or more by 2050 in some scenarios. Investment in coal would be eliminated and coal use nearly phased out by 2050.

Electricity generated from renewable sources would also need to become the main energy source for heating and transport. Transport can switch away from internal combustion engine vehicles and towards electric vehicles, public transit, and active transport (cycling and walking). For shipping and flying, low-carbon fuels would reduce emissions. Heating could be increasingly decarbonised with technologies like heat pumps.

There are obstacles to the continued rapid growth of clean energy, including renewables. For wind and solar, there are environmental and land use concerns for new projects. Wind and solar also produce energy intermittently and with seasonal variability. Traditionally, hydro dams with reservoirs and conventional power plants have been used when variable energy production is low. Going forward, battery storage can be expanded, energy demand and supply can be matched, and long-distance transmission can smooth variability of renewable outputs. Bioenergy is often not carbon-neutral and may have negative consequences for food security. The growth of nuclear power is constrained by controversy around radioactive waste, nuclear weapon proliferation, and accidents. Hydropower growth is limited by the fact that the best sites have been developed, and new projects are confronting increased social and environmental concerns.

Low-carbon energy improves human health by minimising climate change. It also has the near-term benefit of reducing air pollution deaths, which were estimated at 7 million annually in 2016. Meeting the Paris Agreement goals that limit warming to a 2 °C increase could save about a million of those lives per year by 2050, whereas limiting global warming to 1.5 °C could save millions and simultaneously increase energy security and reduce poverty. Improving air quality also has economic benefits which may be larger than mitigation costs.

Energy conservation

Reducing energy demand is another major aspect of reducing emissions. If less energy is needed, there is more flexibility for clean energy development. It also makes it easier to manage the electricity grid, and minimises carbon-intensive infrastructure development. Major increases in energy efficiency investment will be required to achieve climate goals, comparable to the level of investment in renewable energy. Several COVID-19 related changes in energy use patterns, energy efficiency investments, and funding have made forecasts for this decade more difficult and uncertain.

Strategies to reduce energy demand vary by sector. In the transport sector, passengers and freight can switch to more efficient travel modes, such as buses and trains, or use electric vehicles. Industrial strategies to reduce energy demand include improving heating systems and motors, designing less energy-intensive products, and increasing product lifetimes. In the building sector the focus is on better design of new buildings, and higher levels of energy efficiency in retrofitting. The use of technologies like heat pumps can also increase building energy efficiency.

Agriculture and industry

Taking into account direct and indirect emissions, industry is the sector with the highest share of global emissions. Data as of 2019 from the IPCC.

Agriculture and forestry face a triple challenge of limiting greenhouse gas emissions, preventing the further conversion of forests to agricultural land, and meeting increases in world food demand. A set of actions could reduce agriculture and forestry-based emissions by two thirds from 2010 levels. These include reducing growth in demand for food and other agricultural products, increasing land productivity, protecting and restoring forests, and reducing greenhouse gas emissions from agricultural production.

On the demand side, a key component of reducing emissions is shifting people towards plant-based diets. Eliminating the production of livestock for meat and dairy would eliminate about 3/4ths of all emissions from agriculture and other land use. Livestock also occupy 37% of ice-free land area on Earth and consume feed from the 12% of land area used for crops, driving deforestation and land degradation.

Steel and cement production are responsible for about 13% of industrial CO2 emissions. In these industries, carbon-intensive materials such as coke and lime play an integral role in the production, so that reducing CO2 emissions requires research into alternative chemistries.

Carbon sequestration

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

Natural carbon sinks can be enhanced to sequester significantly larger amounts of CO2 beyond naturally occurring levels. Reforestation and tree planting on non-forest lands are among the most mature sequestration techniques, although the latter raises food security concerns. Farmers can promote sequestration of carbon in soils through practices such as use of winter cover crops, reducing the intensity and frequency of tillage, and using compost and manure as soil amendments. In one of its recent publications, FAO maintains that forest and landscape restoration yields many benefits for the climate, including greenhouse gas emissions sequestration and reduction. Restoration/recreation of coastal wetlands, prairie plots and seagrass meadows increases the uptake of carbon into organic matter. When carbon is sequestered in soils and in organic matter such as trees, there is a risk of the carbon being re-released into the atmosphere later through changes in land use, fire, or other changes in ecosystems.

Where energy production or CO2-intensive heavy industries continue to produce waste CO2, the gas can be captured and stored instead of released to the atmosphere. Although its current use is limited in scale and expensive, carbon capture and storage (CCS) may be able to play a significant role in limiting CO2 emissions by mid-century. This technique, in combination with bioenergy (BECCS) can result in net negative emissions: CO2 is drawn from the atmosphere. It remains highly uncertain whether carbon dioxide removal techniques will be able to play a large role in limiting warming to 1.5 °C. Policy decisions that rely on carbon dioxide removal increase the risk of global warming rising beyond international goals.

Adaptation

Adaptation is "the process of adjustment to current or expected changes in climate and its effects". Without additional mitigation, adaptation cannot avert the risk of "severe, widespread and irreversible" impacts. More severe climate change requires more transformative adaptation, which can be prohibitively expensive. The capacity and potential for humans to adapt is unevenly distributed across different regions and populations, and developing countries generally have less. The first two decades of the 21st century saw an increase in adaptive capacity in most low- and middle-income countries with improved access to basic sanitation and electricity, but progress is slow. Many countries have implemented adaptation policies. However, there is a considerable gap between necessary and available finance.

Adaptation to sea level rise consists of avoiding at-risk areas, learning to live with increased flooding and protection. If that fails, managed retreat may be needed. There are economic barriers for tackling dangerous heat impact. Avoiding strenuous work or having air conditioning is not possible for everybody. In agriculture, adaptation options include a switch to more sustainable diets, diversification, erosion control and genetic improvements for increased tolerance to a changing climate. Insurance allows for risk-sharing, but is often difficult to get for people on lower incomes. Education, migration and early warning systems can reduce climate vulnerability. Planting mangroves or encouraging other coastal vegetation can buffer storms.

Ecosystems adapt to climate change, a process that can be supported by human intervention. By increasing connectivity between ecosystems, species can migrate to more favourable climate conditions. Species can also be introduced to areas acquiring a favorable climate. Protection and restoration of natural and semi-natural areas helps build resilience, making it easier for ecosystems to adapt. Many of the actions that promote adaptation in ecosystems, also help humans adapt via ecosystem-based adaptation. For instance, restoration of natural fire regimes makes catastrophic fires less likely, and reduces human exposure. Giving rivers more space allows for more water storage in the natural system, reducing flood risk. Restored forest acts as a carbon sink, but planting trees in unsuitable regions can exacerbate climate impacts.

There are synergies but also trade-offs between adaptation and mitigation. An example for synergy is increased food productivity which has large benefits for both adaptation and mitigation. Two examples for trade-offs include: Firstly, the increased use of air conditioning allows people to better cope with heat, but increases energy demand. Secondly, more compact urban development may lead to reduced emissions from transport and construction which is good. But at the same time, this kind of urban development may increase the urban heat island effect, leading to higher temperatures and increased exposure of people to heat-related health risks.

Examples of adaptation methods

Policies and politics

The Climate Change Performance Index ranks countries by greenhouse gas emissions (40% of score), renewable energy (20%), energy use (20%), and climate policy (20%).
  High
  Medium
  Low
  Very low

Countries that are most vulnerable to climate change have typically been responsible for a small share of global emissions. This raises questions about justice and fairness. Limiting global warming makes it much easier to achieve Sustainable Development Goals, such as eradicating poverty and reducing inequalities. The connection is recognised in Sustainable Development Goal 13 which is to "take urgent action to combat climate change and its impacts". The goals on food, clean water and ecosystem protection have synergies with climate mitigation.

The geopolitics of climate change is complex. It has often been framed as a free-rider problem, in which all countries benefit from mitigation done by other countries, but individual countries would lose from switching to a low-carbon economy themselves. This framing has been challenged. For instance, the benefits of a coal phase-out to public health and local environments exceed the costs in almost all regions. Furthermore, net importers of fossil fuels win economically from switching to clean energy, causing net exporters to face stranded assets: fossil fuels they cannot sell.

Policy options

A wide range of policies, regulations, and laws are being used to reduce emissions. As of 2019, carbon pricing covers about 20% of global greenhouse gas emissions. Carbon can be priced with carbon taxes and emissions trading systems. Direct global fossil fuel subsidies reached $319 billion in 2017, and $5.2 trillion when indirect costs such as air pollution are priced in. Ending these can cause a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths. Money saved on fossil subsidies could be used to support the transition to clean energy instead. More direct methods to reduce greenhouse gases include vehicle efficiency standards, renewable fuel standards, and air pollution regulations on heavy industry. Several countries require utilities to increase the share of renewables in power production.

Climate justice

Policy designed through the lens of climate justice tries to address human rights issues and social inequality. According to proponents of climate justice, the costs of climate adaptation should be paid by those most responsible for climate change, while the beneficiaries of payments should be those suffering impacts. One way this can be addressed in practice is to have wealthy nations pay poorer countries to adapt.

Oxfam found that in 2023 the wealthiest 10% of people were responsible for 50% of global emissions, while the bottom 50% were responsible for just 8%. Production is another way to look at responsibility, with a 2023 study published in One Earth estimating that the top 21 fossil fuel companies would owe cumulative climate reparations of $5.4 trillion over the period 2025–2050. To achieve a just transition, people working in the fossil fuel sector would also need other jobs, and their communities would need investments.

International climate agreements

Since 2000, rising CO2 emissions in China and the rest of world have surpassed the output of the United States and Europe.
Per person, the United States generates CO2 at a far faster rate than other primary regions.

Nearly all countries in the world are parties to the 1994 United Nations Framework Convention on Climate Change (UNFCCC). The goal of the UNFCCC is to prevent dangerous human interference with the climate system. As stated in the convention, this requires that greenhouse gas concentrations are stabilised in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can be sustained. The UNFCCC does not itself restrict emissions but rather provides a framework for protocols that do. Global emissions have risen since the UNFCCC was signed. Its yearly conferences are the stage of global negotiations.

The 1997 Kyoto Protocol extended the UNFCCC and included legally binding commitments for most developed countries to limit their emissions. During the negotiations, the G77 (representing developing countries) pushed for a mandate requiring developed countries to "[take] the lead" in reducing their emissions, since developed countries contributed most to the accumulation of greenhouse gases in the atmosphere. Per-capita emissions were also still relatively low in developing countries and developing countries would need to emit more to meet their development needs.

The 2009 Copenhagen Accord has been widely portrayed as disappointing because of its low goals, and was rejected by poorer nations including the G77. Associated parties aimed to limit the global temperature rise to below 2 °C. The Accord set the goal of sending $100 billion per year to developing countries for mitigation and adaptation by 2020, and proposed the founding of the Green Climate Fund. As of 2020, only 83.3 billion were delivered. Only in 2023 the target is expected to be achieved.

In 2015 all UN countries negotiated the Paris Agreement, which aims to keep global warming well below 2.0 °C and contains an aspirational goal of keeping warming under 1.5 °C. The agreement replaced the Kyoto Protocol. Unlike Kyoto, no binding emission targets were set in the Paris Agreement. Instead, a set of procedures was made binding. Countries have to regularly set ever more ambitious goals and reevaluate these goals every five years. The Paris Agreement restated that developing countries must be financially supported. As of October 2021, 194 states and the European Union have signed the treaty and 191 states and the EU have ratified or acceded to the agreement.

The 1987 Montreal Protocol, an international agreement to stop emitting ozone-depleting gases, may have been more effective at curbing greenhouse gas emissions than the Kyoto Protocol specifically designed to do so. The 2016 Kigali Amendment to the Montreal Protocol aims to reduce the emissions of hydrofluorocarbons, a group of powerful greenhouse gases which served as a replacement for banned ozone-depleting gases. This made the Montreal Protocol a stronger agreement against climate change.

National responses

In 2019, the United Kingdom parliament became the first national government to declare a climate emergency. Other countries and jurisdictions followed suit. That same year, the European Parliament declared a "climate and environmental emergency". The European Commission presented its European Green Deal with the goal of making the EU carbon-neutral by 2050. Major countries in Asia have made similar pledges: South Korea and Japan have committed to become carbon-neutral by 2050, and China by 2060. In 2021, the European Commission released its "Fit for 55" legislation package, which contains guidelines for the car industry; all new cars on the European market must be zero-emission vehicles from 2035. While India has strong incentives for renewables, it also plans a significant expansion of coal in the country. Vietnam is among very few coal-dependent fast developing countries that pledged to phase out unabated coal power by the 2040s or as soon as possible thereafter.

As of 2021, based on information from 48 national climate plans, which represent 40% of the parties to the Paris Agreement, estimated total greenhouse gas emissions will be 0.5% lower compared to 2010 levels, below the 45% or 25% reduction goals to limit global warming to 1.5 °C or 2 °C, respectively.

Society

Denial and misinformation

Data has been cherry picked from short periods to falsely assert that global temperatures are not rising. Blue trendlines show short periods that mask longer-term warming trends (red trendlines). Blue dots show the so-called global warming hiatus.

Public debate about climate change has been strongly affected by climate change denial and misinformation, which originated in the United States and has since spread to other countries, particularly Canada and Australia. The actors behind climate change denial form a well-funded and relatively coordinated coalition of fossil fuel companies, industry groups, conservative think tanks, and contrarian scientists. Like the tobacco industry, the main strategy of these groups has been to manufacture doubt about scientific data and results. Many who deny, dismiss, or hold unwarranted doubt about the scientific consensus on anthropogenic climate change are labelled as "climate change skeptics", which several scientists have noted is a misnomer.

There are different variants of climate denial: some deny that warming takes place at all, some acknowledge warming but attribute it to natural influences, and some minimise the negative impacts of climate change. Manufacturing uncertainty about the science later developed into a manufactured controversy: creating the belief that there is significant uncertainty about climate change within the scientific community in order to delay policy changes. Strategies to promote these ideas include criticism of scientific institutions, and questioning the motives of individual scientists. An echo chamber of climate-denying blogs and media has further fomented misunderstanding of climate change.

Public awareness and opinion

The public substantially underestimates the degree of scientific consensus that humans are causing climate change.[364] Studies from 2019 to 2021 found scientific consensus to range from 98.7 to 100%.

Climate change came to international public attention in the late 1980s. Due to media coverage in the early 1990s, people often confused climate change with other environmental issues like ozone depletion. In popular culture, the climate fiction movie The Day After Tomorrow (2004) and the Al Gore documentary An Inconvenient Truth (2006) focused on climate change.

Significant regional, gender, age and political differences exist in both public concern for, and understanding of, climate change. More highly educated people, and in some countries, women and younger people, were more likely to see climate change as a serious threat. Partisan gaps also exist in many countries, and countries with high CO2 emissions tend to be less concerned. Views on causes of climate change vary widely between countries. Concern has increased over time, to the point where in 2021 a majority of citizens in many countries express a high level of worry about climate change, or view it as a global emergency. Higher levels of worry are associated with stronger public support for policies that address climate change.

Climate movement

Climate protests demand that political leaders take action to prevent climate change. They can take the form of public demonstrations, fossil fuel divestment, lawsuits and other activities. Prominent demonstrations include the School Strike for Climate. In this initiative, young people across the globe have been protesting since 2018 by skipping school on Fridays, inspired by Swedish teenager Greta Thunberg. Mass civil disobedience actions by groups like Extinction Rebellion have protested by disrupting roads and public transport. Litigation is increasingly used as a tool to strengthen climate action from public institutions and companies. Activists also initiate lawsuits which target governments and demand that they take ambitious action or enforce existing laws on climate change. Lawsuits against fossil-fuel companies generally seek compensation for loss and damage.

History

Early discoveries

This 1912 article succinctly describes the greenhouse effect, how burning coal creates carbon dioxide to cause global warming and climate change.

Scientists in the 19th century such as Alexander von Humboldt began to foresee the effects of climate change. In the 1820s, Joseph Fourier proposed the greenhouse effect to explain why Earth's temperature was higher than the sun's energy alone could explain. Earth's atmosphere is transparent to sunlight, so sunlight reaches the surface where it is converted to heat. However, the atmosphere is not transparent to heat radiating from the surface, and captures some of that heat, which in turn warms the planet.

In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and that the effect is even greater with carbon dioxide (CO2). She concluded that "An atmosphere of that gas would give to our earth a high temperature..."

Starting in 1859, John Tyndall established that nitrogen and oxygen—together totaling 99% of dry air—are transparent to radiated heat. However, water vapour and gases such as methane and carbon dioxide absorb radiated heat and re-radiate that heat into the atmosphere. Tyndall proposed that changes in the concentrations of these gases may have caused climatic changes in the past, including ice ages.

Svante Arrhenius noted that water vapour in air continuously varied, but the CO2 concentration in air was influenced by long-term geological processes. Warming from increased CO2 levels would increase the amount of water vapour, amplifying warming in a positive feedback loop. In 1896, he published the first climate model of its kind, projecting that halving CO2 levels could have produced a drop in temperature initiating an ice age. Arrhenius calculated the temperature increase expected from doubling CO2 to be around 5–6 °C. Other scientists were initially skeptical and believed that the greenhouse effect was saturated so that adding more CO2 would make no difference, and that the climate would be self-regulating. Beginning in 1938, Guy Stewart Callendar published evidence that climate was warming and CO2 levels were rising, but his calculations met the same objections.

Development of a scientific consensus

In the 1950s, Gilbert Plass created a detailed computer model that included different atmospheric layers and the infrared spectrum. This model predicted that increasing CO2 levels would cause warming. Around the same time, Hans Suess found evidence that CO2 levels had been rising, and Roger Revelle showed that the oceans would not absorb the increase. The two scientists subsequently helped Charles Keeling to begin a record of continued increase, which has been termed the "Keeling Curve". Scientists alerted the public, and the dangers were highlighted at James Hansen's 1988 Congressional testimony. The Intergovernmental Panel on Climate Change (IPCC), set up in 1988 to provide formal advice to the world's governments, spurred interdisciplinary research. As part of the IPCC reports, scientists assess the scientific discussion that takes place in peer-reviewed journal articles.

There is a near-complete scientific consensus that the climate is warming and that this is caused by human activities. As of 2019, agreement in recent literature reached over 99%. No scientific body of national or international standing disagrees with this view. Consensus has further developed that some form of action should be taken to protect people against the impacts of climate change. National science academies have called on world leaders to cut global emissions. The 2021 IPCC Assessment Report stated that it is "unequivocal" that climate change is caused by humans.

Low-carbon power

From Wikipedia, the free encyclopedia
(Redirected from Low carbon power)
Share of primary energy from low-carbon sources, 2018

Low-carbon power is electricity produced with substantially lower greenhouse gas emissions over the entire lifecycle than power generation using fossil fuels. The energy transition to low-carbon power is one of the most important actions required to limit climate change.  Power sector emissions may have peaked in 2018. During the first six months of 2020, scientists observed an 8.8% decrease in global CO2 emissions relative to 2019 due to COVID-19 lockdown measures. The two main sources of the decrease in emissions included ground transportation (40%) and the power sector (22%). This event is the largest absolute decrease in CO2 emissions in history, but emphasizes that low-carbon power "must be based on structural and transformational changes in energy-production systems".

Low carbon power generation sources include wind power, solar power, nuclear power and most hydropower. The term largely excludes conventional fossil fuel plant sources, and is only used to describe a particular subset of operating fossil fuel power systems, specifically, those that are successfully coupled with a flue gas carbon capture and storage (CCS) system. Globally almost 40% of electricity generation came from low-carbon sources in 2020: about 10% being nuclear power, almost 10% wind and solar, and around 20% hydropower and other renewables.

History

Percentage of electricity generation from low-carbon sources in 2019.

During the late 20th and early 21st century significant findings regarding global warming highlighted the need to curb carbon emissions. From this, the idea for low-carbon power was born. The Intergovernmental Panel on Climate Change (IPCC), established by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP) in 1988, set the scientific precedence for the introduction of low-carbon power. The IPCC has continued to provide scientific, technical and socio-economic advice to the world community, through its periodic assessment reports and special reports.

Internationally, the most prominent early step in the direction of low carbon power was the signing of the Kyoto Protocol, which came into force on 16 February 2005, under which most industrialized countries committed to reduce their carbon emissions. The historical event set the political precedence for introduction of low-carbon power technology.

On a social level, perhaps the biggest factor contributing to the general public's awareness of climate change and the need for new technologies, including low carbon power, came from the documentary An Inconvenient Truth, which clarified and highlighted the problem of global warming.

Power sources by greenhouse gas emissions

Life-cycle greenhouse gas emissions of electricity supply technologies, median values calculated by IPCC
Life cycle CO2 equivalent (including albedo effect) from selected electricity supply technologies according to IPCC 2014. Arranged by decreasing median (gCO2eq/kWh) values.
Technology Min. Median Max.
Currently commercially available technologies
CoalPC 740 820 910
Gascombined cycle 410 490 650
Biomass – Dedicated 130 230 420
Solar PV – Utility scale 18 48 180
Solar PV – rooftop 26 41 60
Geothermal 6.0 38 79
Concentrated solar power 8.8 27 63
Hydropower 1.0 24 2200
Wind Offshore 8.0 12 35
Nuclear 3.7 12 110
Wind Onshore 7.0 11 56
Pre‐commercial technologies
Ocean (Tidal and wave) 5.6 17 28

Lifecycle GHG emissions, in g CO2 eq. per kWh, UNECE 2020
Lifecycle CO2 emissions per kWh, EU28 countries, according to UNECE 2020.
Technology gCO2eq/kWh
Hard coal PC, without CCS 1000
IGCC, without CCS 850
SC, without CCS 950
PC, with CCS 370
IGCC, with CCS 280
SC, with CCS 330
Natural gas NGCC, without CCS 430
NGCC, with CCS 130
Hydro 660 MW  150
360 MW 11
Nuclear average 5.1
CSP tower 22
trough 42
PV poly-Si, ground-mounted 37
poly-Si, roof-mounted 37
CdTe, ground-mounted 12
CdTe, roof-mounted 15
CIGS, ground-mounted 11
CIGS, roof-mounted 14
Wind onshore 12
offshore, concrete foundation 14
offshore, steel foundation 13

List of acronyms:

Differentiating attributes of low-carbon power sources

Low carbon electricity generation percentage worldwide by source

There are many options for lowering current levels of carbon emissions. Some options, such as wind power and solar power, produce low quantities of total life cycle carbon emissions, using entirely renewable sources. Other options, such as nuclear power, produce a comparable amount of carbon dioxide emissions as renewable technologies in total life cycle emissions, but consume non-renewable, but sustainable materials (uranium). The term low-carbon power can also include power that continues to utilize the world's natural resources, such as natural gas and coal, but only when they employ techniques that reduce carbon dioxide emissions from these sources when burning them for fuel, such as the, as of 2012, pilot plants performing Carbon capture and storage.

Because the cost of reducing emissions in the electricity sector appears to be lower than in other sectors such as transportation, the electricity sector may deliver the largest proportional carbon reductions under an economically efficient climate policy.

Technologies to produce electric power with low-carbon emissions are in use at various scales. Together, they accounted for almost 40% of global electricity in 2020, with wind and solar almost 10%.


Technologies

The 2014 Intergovernmental Panel on Climate Change report identifies nuclear, wind, solar and hydroelectricity in suitable locations as technologies that can provide electricity with less than 5% of the lifecycle greenhouse gas emissions of coal power.

Hydroelectric power

The Hoover Dam when completed in 1936 was both the world's largest electric-power generating station and the world's largest concrete structure.

Hydroelectric plants have the advantage of being long-lived and many existing plants have operated for more than 100 years. Hydropower is also an extremely flexible technology from the perspective of power grid operation. Large hydropower provides one of the lowest cost options in today's energy market, even compared to fossil fuels and there are no harmful emissions associated with plant operation. However, there are typically low greenhouse gas emissions with reservoirs, and possibly high emissions in the tropics.

Hydroelectric power is the world's largest low carbon source of electricity, supplying 15.6% of total electricity in 2019. China is by far the world's largest producer of hydroelectricity in the world, followed by Brazil and Canada.

However, there are several significant social and environmental disadvantages of large-scale hydroelectric power systems: dislocation, if people are living where the reservoirs are planned, release of significant amounts of carbon dioxide and methane during construction and flooding of the reservoir, and disruption of aquatic ecosystems and birdlife. There is a strong consensus now that countries should adopt an integrated approach towards managing water resources, which would involve planning hydropower development in co-operation with other water-using sectors.

Nuclear power

Blue Cherenkov radiation light being produced near the core of the Fission powered Advanced Test Reactor

Nuclear power, with a 10.6% share of world electricity production as of 2013, is the second largest low-carbon power source.

Nuclear power, in 2010, also provided two thirds of the twenty seven nation European Union's low-carbon energy, with some EU nations sourcing a large fraction of their electricity from nuclear power; for example France derives 79% of its electricity from nuclear. As of 2020 nuclear power provided 47% low-carbon power in the EU with countries largely based on nuclear power routinely achieving carbon intensity of 30-60 gCO2eq/kWh.

According to the IAEA and the European Nuclear Society, worldwide there were 68 civil nuclear power reactors under construction in 15 countries in 2013. China has 29 of these nuclear power reactors under construction, as of 2013, with plans to build many more, while in the US the licenses of almost half its reactors have been extended to 60 years, and plans to build another dozen are under serious consideration. There is also a considerable number of new reactors being built in South Korea, India, and Russia. Nuclear power's capability to add significantly to future low carbon energy growth depends on several factors, including the economics of new reactor designs, such as Generation III reactors, public opinion and national and regional politics.

The 104 U.S. nuclear plants are undergoing a Light Water Reactor Sustainability Program, to sustainably extend the life span of the U.S. nuclear fleet by a further 20 years. With further US power plants under construction in 2013, such as the two AP1000s at Vogtle Electric Generating Plant. However the Economics of new nuclear power plants are still evolving and plans to add to those plants are mostly in flux.

In 2021 United Nations Economic Commission for Europe (UNECE) described nuclear power as important tool to mitigate climate change that has prevented 74 Gt of CO2 emissions over the last half century, providing 20% of energy in Europe and 43% of low-carbon energy.

Wind power

Wind power stations in Xinjiang, China

Wind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity generation. Today, wind power is generated almost completely with wind turbines, generally grouped into wind farms and connected to the electrical grid.

In 2022, wind supplied over 2000 TWh of electricity, which was over 7% of world electricity and about 2% of world energy. With about 100 GW added during 2021, mostly in China and the United States, global installed wind power capacity exceeded 800 GW. To help meet the Paris Agreement goals to limit climate change, analysts say it should expand much faster - by over 1% of electricity generation per year.

Wind power is considered a sustainable, renewable energy source, and has a much smaller impact on the environment compared to burning fossil fuels. Wind power is variable, so it needs energy storage or other dispatchable generation energy sources to attain a reliable supply of electricity. Land-based (onshore) wind farms have a greater visual impact on the landscape than most other power stations per energy produced. Wind farms sited offshore have less visual impact and have higher capacity factors, although they are generally more expensive. Offshore wind power currently has a share of about 10% of new installations.

Wind power is one of the lowest-cost electricity sources per unit of energy produced. In many locations, new onshore wind farms are cheaper than new coal or gas plants.

Regions in the higher northern and southern latitudes have the highest potential for wind power. In most regions, wind power generation is higher in nighttime, and in winter when solar power output is low. For this reason, combinations of wind and solar power are suitable in many countries.

Solar power

The PS10 concentrates sunlight from a field of heliostats on a central tower.

Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics convert light into electric current using the photoelectric effect.

Commercial concentrated solar power plants were first developed in the 1980s. The 354 MW SEGS CSP installation is the largest solar power plant in the world, located in the Mojave Desert of California. Other large CSP plants include the Solnova Solar Power Station (150 MW) and the Andasol solar power station (150 MW), both in Spain. The over 200 MW Agua Caliente Solar Project in the United States, and the 214 MW Charanka Solar Park in India, are the world's largest photovoltaic plants. Solar power's share of worldwide electricity usage at the end of 2014 was 1%.

Geothermal power

Geothermal electricity is electricity generated from geothermal energy. Technologies in use include dry steam power plants, flash steam power plants and binary cycle power plants. Geothermal electricity generation is used in 24 countries while geothermal heating is in use in 70 countries.

Current worldwide installed capacity is 10,715 megawatts (MW), with the largest capacity in the United States (3,086 MW), Philippines, and Indonesia. Estimates of the electricity generating potential of geothermal energy vary from 35 to 2000 GW.

Geothermal power is considered to be sustainable because the heat extraction is small compared to the Earth's heat content. The emission intensity of existing geothermal electric plants is on average 122 kg of CO
2
per megawatt-hour (MW·h) of electricity, a small fraction of that of conventional fossil fuel plants.

Tidal power

Tidal power is a form of hydropower that converts the energy of tides into electricity or other useful forms of power. The first large-scale tidal power plant (the Rance Tidal Power Station) started operation in 1966. Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power.

Carbon capture and storage

Carbon capture and storage captures carbon dioxide from the flue gas of power plants or other industry, transporting it to an appropriate location where it can be buried securely in an underground reservoir. While the technologies involved are all in use, and carbon capture and storage is occurring in other industries (e.g., at the Sleipner gas field), no large scale integrated project has yet become operational within the power industry.

Improvements to current carbon capture and storage technologies could reduce CO2 capture costs by at least 20-30% over approximately the next decade, while new technologies under development promise more substantial cost reduction.

Outlook and requirements

Emissions

Greenhouse gas emissions by sector. See World Resources Institute for detailed breakdown

The Intergovernmental Panel on Climate Change stated in its first working group report that "most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations, contribute to climate change.

As a percentage of all anthropogenic greenhouse gas emissions, carbon dioxide (CO2) accounts for 72 percent (see Greenhouse gas), and has increased in concentration in the atmosphere from 315 parts per million (ppm) in 1958 to more than 375 ppm in 2005.

Emissions from energy make up more than 61.4 percent of all greenhouse gas emissions. Power generation from traditional coal fuel sources accounts for 18.8 percent of all world greenhouse gas emissions, nearly double that emitted by road transportation.

Estimates state that by 2020 the world will be producing around twice as much carbon emissions as it was in 2000.

The European Union hopes to sign a law mandating net-zero greenhouse gas emissions in the coming year for all 27 countries in the union.

Electricity usage

World CO2 emissions by region

World energy consumption is predicted to increase from 123,000 TWh (421 quadrillion BTU) in 2003 to 212,000 TWh (722 quadrillion BTU) in 2030. Coal consumption is predicted to nearly double in that same time.[56] The fastest growth is seen in non-OECD Asian countries, especially China and India, where economic growth drives increased energy use. By implementing low-carbon power options, world electricity demand could continue to grow while maintaining stable carbon emission levels.

In the transportation sector there are moves away from fossil fuels and towards electric vehicles, such as mass transit and the electric car. These trends are small, but may eventually add a large demand to the electrical grid.

Domestic and industrial heat and hot water have largely been supplied by burning fossil fuels such as fuel oil or natural gas at the consumers' premises. Some countries have begun heat pump rebates to encourage switching to electricity, potentially adding a large demand to the grid.

Energy infrastructure

Coal-fired power plants are losing market share compared to low carbon power, and any built in the 2020s risk becoming stranded assets or stranded costs, partly because their capacity factors will decline.

Investment

Investment in low-carbon power sources and technologies is increasing at a rapid rate. Zero-carbon power sources produce about 2% of the world's energy, but account for about 18% of world investment in power generation, attracting $100 billion of investment capital in 2006.

Trust (social science)

From Wikipedia, the free encyclopedia
Trust in others in Europe
Country-level estimates of trust
Share of people agreeing with the statement "most people can be trusted"

Trust means believing that another person will do what is expected. It brings with it a willingness for one party (the trustor) to become vulnerable to another party (the trustee), on the presumption that the trustee will act in ways that benefit the trustor. In addition, the trustor does not have control over the actions of the trustee. Scholars distinguish between generalized trust (also known as social trust), which is the extension of trust to a relatively large circle of unfamiliar others, and particularized trust, which is contingent on a specific situation or a specific relationship.

As the trustor is uncertain about the outcome of the trustee's actions, the trustor can only develop and evaluate expectations. Such expectations are formed with a view to the motivations of the trustee, dependent on their characteristics, the situation, and their interaction. The uncertainty stems from the risk of failure or harm to the trustor if the trustee does not behave as desired.

In the social sciences, the subtleties of trust are a subject of ongoing research. In sociology and psychology, the degree to which one party trusts another is a measure of belief in the honesty, fairness, or benevolence of another party. The term "confidence" is more appropriate for a belief in the competence of the other party. A failure in trust may be forgiven more easily if it is interpreted as a failure of competence rather than a lack of benevolence or honesty. In economics, trust is often conceptualized as reliability in transactions. In all cases, trust is a heuristic decision rule, allowing a person to deal with complexities that would require unrealistic effort in rational reasoning.

Sociology

Sociology claims trust is one of several social constructs; an element of the social reality. Other constructs frequently discussed together with trust include control, confidence, risk, meaning and power. Trust is attributable to relationships between social actors, both individuals and groups (social systems). Sociology is concerned with the position and role of trust in social systems. Interest in trust has grown significantly since the early 1980s, from the early works of Luhmann, Barber, and Giddens (see Sztompka for a more detailed overview). This growth of interest in trust has been stimulated by ongoing changes in society, known as late modernity and post-modernity.

Sviatoslav contended that society needs trust because it increasingly finds itself operating at the edge between confidence in what is known from everyday experience and contingency of new possibilities. Without trust, one should always consider all contingent possibilities, leading to paralysis by analysis. Trust acts as a decisional heuristic, allowing the decision-maker to overcome bounded rationality and process what would otherwise be an excessively complex situation. Trust can be seen as a bet on one of many contingent futures, specifically, the one that appears to deliver the greatest benefits. Once the bet is decided (i.e. trust is granted), the trustor suspends his or her disbelief, and the possibility of a negative course of action is not considered at all. Hence trust acts as a reducing agent of social complexity, allowing for cooperation.

Sociology tends to focus on two distinct views: the macro view of social systems, and a micro view of individual social actors (where it borders with social psychology). Views on trust follow this dichotomy. On one side, the systemic role of trust can be discussed with a certain disregard to the psychological complexity underpinning individual trust. The behavioral approach to trust is usually assumed while actions of social actors are measurable, allowing for statistical modelling of trust. This systemic approach can be contrasted with studies on social actors and their decision-making process, in anticipation that understanding of such a process will explain (and allow to model) the emergence of trust.

Sociology acknowledges that the contingency of the future creates a dependency between social actors and, specifically, that the trustor becomes dependent on the trustee. Trust is seen as one of the possible methods to resolve such a dependency, being an attractive alternative to control. Trust is valuable if the trustee is much more powerful than the trustor, yet the trustor is under social obligation to support the trustee.

Modern information technologies have not only facilitated the transition to a post-modern society but have also challenged traditional views on trust. Information systems research has identified that people have come to trust in technology via two primary constructs: The first consists of human-like constructs, including benevolence, honesty, and competence, whilst the second employs system-like constructs, such as usefulness, reliability, and functionality. The discussion surrounding the relationship between information technologies and trust is still in progress as research remains in its infant stages.

High- and low-trust societies

A low-trust society is defined as one in which interpersonal trust is relatively low, and which do not have shared ethical values. Conversely, a high-trust society is one where interpersonal trust is relatively high, and where ethical values are strongly shared.

Types

Four types of social trust are recognized:

  • Generalized trust, or a dispositional trait geared towards trusting others, is an important form of trust in modern society, which involves much social interaction with strangers. Schilke et al. refer to generalized and particularized trust (trust exhibited in a specific situation or a specific relationship) as two significant research streams in the sociology of trust.
  • Out-group trust is the trust a person has in members of a different group. This could be members of a different ethnic group, or citizens of a different country, for example.
  • In-group trust is placed in members of one's own group.
  • Trust in neighbors considers the relationships between people with a common residential environment.

Influence of ethnic diversity

Several dozen studies have examined the impact of ethnic diversity on social trust. Research published in the Annual Review of Political Science concluded that there were three key debates on the subject:

  1. Why does ethnic diversity modestly reduce social trust?
  2. Can contact reduce the negative association between ethnic diversity and social trust?
  3. Is ethnic diversity a stand-in for social disadvantage?

The review's meta-analysis of 87 studies showed a consistent, though modest, negative relationship between ethnic diversity and social trust. Ethnic diversity has the strongest negative impact on neighbor trust, in-group trust, and generalized trust. It did not appear to have a significant impact on out-group trust. The limited size of the impact means apocalyptic claims about it are exaggerated.

Psychology

In psychology, trust is believing that the trusted person will do what is expected. According to the psychoanalyst Erik Erikson, development of basic trust is the first state of psychosocial development occurring, or failing, during the first two years of life. Success results in feelings of security and optimism, while failure leads towards an orientation of insecurity and mistrust possibly resulting in attachment disorders. A person's dispositional tendency to trust others can be considered a personality trait and as such is one of the strongest predictors of subjective well-being. Trust increases subjective well-being because it enhances the quality of one's interpersonal relationships; happy people are skilled at fostering good relationships.

Trust is integral to the idea of social influence: it is easier to influence or persuade someone who is trusting. The notion of trust is increasingly adopted to predict acceptance of behaviors by others, institutions (e.g. government agencies), and objects such as machines. Yet once again, perceptions of honesty, competence and value similarity (slightly similar to benevolence) are essential.

There are three forms of trust commonly studied in psychology:

  • Trust is being vulnerable to someone even when they are trustworthy.
  • Trustworthiness are the characteristics or behaviors of one person that inspire positive expectations in another person.
  • Trust propensity is the tendency to make oneself vulnerable to others in general. Research suggests that this general tendency can change over time in response to key life events.

Once trust is lost by violation of one of these three determinants, it is very hard to regain. There is asymmetry in the building versus destruction of trust.

Research has been conducted into the social implications of trust, for instance:

  • Barbara Misztal attempted to combine all notions of trust. She described three functions of trust: it makes social life predictable, it creates a sense of community, and it makes it easier for people to work together.
  • In the context of sexual trust, Riki Robbins describes four stages. These consist of perfect trust, damaged trust, devastated trust, and restored trust.
  • In the context of information theory, Ed Gerck defines and contrasts trust with social functions such as power, surveillance, and accountability.
  • From a social identity perspective, the propensity to trust strangers (see in-group favoritism) arises from the mutual knowledge of a shared group membership, stereotypes, or the need to maintain the group's positive distinctiveness.

Despite the centrality of trust to the positive functioning of people and relationships, very little is known about how and why trust evolves, is maintained, and is destroyed.

One factor that enhances trust among people is facial resemblance. Experimenters who digitally manipulated facial resemblance in a two-person sequential trust game found evidence that people have more trust in a partner who has similar facial features. Facial resemblance also decreased sexual desire for a partner. In a series of tests, digitally manipulated faces were presented to subjects who evaluated them for attractiveness within a long-term or short-term relationship. The results showed that within the context of a short-term relationship dependent on sexual desire, similar facial features caused a decrease in desire. Within the context of a long-term relationship, which is dependent on trust, similar facial features increased a person's attractiveness. This suggests that facial resemblance and trust have great effects on relationships.

Interpersonal trust literature investigates "trust-diagnostic situations": situations that test partners' abilities to act in the best interests of the other person or the relationship while rejecting a conflicting option which is merely in their self-interest. Trust-diagnostic situations occur throughout everyday life, though they can also be deliberately engineered by people who want to test the current level of trust in a relationship.

A low-trust relationship is one in which a person has little confidence their partner is truly concerned about them or the relationship. People in low trust relationships tend to make distress-maintaining attributions whereby they place their greatest focus on the consequences of their partner's negative behavior, and any impacts of positive actions are minimized. This feeds into the overarching notion that the person's partner is uninterested in the relationship, and any positive acts on their part are met with skepticism, leading to further negative outcomes.

Distrusting people may miss opportunities for trusting relationships. Someone subject to an abusive childhood may have been deprived of any evidence that trust is warranted in future relationships. An important key to treating sexual victimization of a child is the rebuilding of trust between parent and child. Failure by adults to validate that sexual abuse occurred contributes to the child's difficulty in trusting self and others. A child's trust can also be affected by the erosion of the marriage of their parents. Children of divorce do not exhibit less trust in mothers, partners, spouses, friends, and associates than their peers of intact families. The impact of parental divorce is limited to trust in the father.

People may trust non-human agents. For instance, people may trust animals, the scientific process, and social machines. Trust helps create a social contract that allows humans and domestic animals to live together. Trust in the scientific process is associated with increased trust in innovations such as biotechnology. When it comes to trust in social machines, people are more willing to trust intelligent machines with humanoid morphologies and female cues, when they are focused on tasks (versus socialization), and when they behave morally well. More generally, they may be trusted as a function of the "machine heuristic"—a mental shortcut with which people assume that machines are less biased, more accurate, and more reliable than people—such that people may sometimes trust a robot more than a person.

People are disposed to trust and to judge the trustworthiness of other people or groups—for instance, in developing relationships with potential mentors. One example would be as part of interprofessional work in the referral pathway from an emergency department to a hospital ward. Another would be building knowledge on whether new practices, people, and things introduced into our lives are indeed accountable or worthy of investing confidence and trust in. This process is captured by the empirically grounded construct of "Relational Integration" within Normalization Process Theory. This can be traced in neuroscience terms to the neurobiological structure and activity of a human brain. Some studies indicate that trust can be altered by the application of oxytocin.

Social identity approach

The social identity approach explains a person's trust in strangers as a function of their group-based stereotypes or in-group favoring behaviors which they base on salient group memberships. With regard to ingroup favoritism, people generally think well of strangers but expect better treatment from in-group members in comparison to out-group members. This greater expectation translates into a propensity to trust a member of the in-group more than a member of the out-group. It is only advantageous for one to form such expectations of an in-group stranger if the stranger also knows one's own group membership.

The social identity approach has been empirically investigated. Researchers have employed allocator studies to understand group-based trust in strangers. They may be operationalized as unilateral or bilateral relationships of exchange. General social categories such as university affiliation, course majors, and even ad-hoc groups have been used to distinguish between in-group and out-group members. In unilateral studies of trust, the participant is asked to choose between envelopes containing money that an in-group or out-group member previously allocated. Participants have no prior or future opportunities for interaction, thereby testing Brewer's notion that group membership is sufficient to bring about group-based trust and hence cooperation. Participants could expect an amount ranging from nothing to the maximum value an allocator could give out. Bilateral studies of trust have employed an investment game devised by Berg and colleagues in which people choose to give a portion or none of their money to another. Any amount given would be tripled and the receiver would then decide whether they would return the favor by giving money back to the sender. This was meant to test trusting behavior on the sender's part and the receiver's eventual trustworthiness.

Empirical research demonstrates that when group membership is salient to both parties, trust is granted more readily to in-group members than out-group members. This occurs even when the in-group's stereotype was comparatively less positive than the out-group's (e.g. psychology versus nursing majors), in the absence of personal identity cues, and when participants had the option of a sure sum of money (i.e. in essence opting out of the need to trust a stranger to gain some monetary reward). When only the recipient was made aware of group membership, trust becomes reliant upon group stereotypes. The group with the more positive stereotype was trusted (e.g. one's university affiliation over another's) even over that of the in-group (e.g. nursing over psychology majors).

Another explanation for in-group-favoring behaviors could be the need to maintain in-group positive distinctiveness, particularly in the presence of social identity threat. Trust in out-group strangers increased when personal cues to identity were revealed.

Philosophy

Many philosophers have written about different forms of trust. Most agree that interpersonal trust is the foundation on which these forms can be modeled. For an act to be an expression of trust, it must not betray the expectations of the trustee. Some philosophers, such as Lagerspetz, argue that trust is a kind of reliance, though not merely reliance. Gambetta argued that trust is the inherent belief that others generally have good intentions, which is the foundation for our reliance on them. Philosophers such as Annette Baier challenged this view, asserting a difference between trust and reliance by saying that trust can be betrayed, whereas reliance can only be disappointed. Carolyn McLeod explains Baier's argument with the following examples: we can rely on our clock to give the time, but we do not feel betrayed when it breaks, thus, we cannot say that we trusted it; we are not trusting when we are suspicious of another person, because this is in fact an expression of distrust. The violation of trust warrants this sense of betrayal. Thus, trust is different from reliance in the sense that a trustor accepts the risk of being betrayed.

Karen Jones proposed an emotional aspect to trust—optimism that the trustee will do the right thing by the trustor, which is also described as "affective trust". People sometimes trust others even without this optimistic expectation, instead hoping that by extending trust this will prompt trustworthy behavior in the trustee. This is known as "therapeutic trust" and gives both the trustee a reason to be trustworthy, and the trustor a reason to believe they are trustworthy.

The definition of trust as a belief in something or a confident expectation about something eliminates the notion of risk because it does not include whether the expectation or belief is favorable or unfavorable. For example, to expect a friend to arrive to dinner late because she has habitually arrived late for the last fifteen years is a confident expectation (whether or not we find her late arrivals to be annoying). The trust is not about what we wish for, but rather it is in the consistency of the data. As a result, there is no risk or sense of betrayal because the data exists as collective knowledge. Faulkner contrasts such "predictive trust" with the aforementioned affective trust, proposing that predictive trust may only warrant disappointment as a consequence of an inaccurate prediction, not a sense of betrayal.

Economics

Trust in economics explains the difference between actual human behavior and behavior that could be explained by people's desire to maximize utility. In economic terms, trust can explain a difference between Nash equilibrium and the observed equilibrium. Such an approach can be applied to individual people as well as to societies.

Levels of trust are higher in countries, and in states of the U.S.A., that are more economically equal.

Trust is important to economists for many reasons. Taking the "Market for Lemons" transaction popularized by George Akerlof as an example, if a potential buyer of a car doesn't trust the seller not to sell a lemon, the transaction won't take place. The buyer won't buy without trust, even if the product would be of great value to the buyer. Trust can act as an economic lubricant, reducing the cost of transactions between parties, enabling new forms of cooperation, and generally furthering business activities, employment, and prosperity. This observation prompted interest in trust as a form of social capital and research into the process of creation and distribution of such capital. A higher level of social trust may be positively correlated with economic development: Even though the original concept of "high trust" and "low trust" societies may not necessarily hold, social trust benefits the economy and a low level of trust inhibits economic growth. The absence of trust restricts growth in employment, wages, and profits, thus reducing the overall welfare of society.

Theoretical economical modelling demonstrates that the optimum level of trust that a rational economic agent should exhibit in transactions is equal to the trustworthiness of the other party. Such a level of trust leads to an efficient market. Trusting less leads to losing economic opportunities, while trusting more leads to unnecessary vulnerabilities and potential exploitation. Economics is also interested in quantifying trust, usually in monetary terms. The level of correlation between an increase in profit margin and a decrease in transactional costs can be used as an indicator of the economic value of trust.

Economic "trust games" empirically quantify trust in relationships under laboratory conditions. Several games and game-like scenarios related to trust have been tried, with certain preferences to those that allow the estimation of confidence in monetary terms. In games of trust the Nash equilibrium differs from Pareto optimum so that no player alone can maximize their own utility by altering their selfish strategy without cooperation. Cooperating partners can also benefit. The classical version of the game of trust has been described as an abstract investment game, using the scenario of an investor and a broker. The investor can invest some fraction of his money, and the broker can return to the investor some fraction of the investor's gains. If both players follow their naive economic best interest, the investor should never invest, and the broker will never be able to repay anything. Thus the flow of money, its volume, and its character is attributable entirely to the existence of trust. Such a game can be played as a once-off, or repeatedly with the same or different sets of players to distinguish between a general propensity to trust and trust within particular relationships. Several variants of this game exist. Reversing rules leads to the game of distrust, pre-declarations can be used to establish intentions of players, while alterations to the distribution of gains can be used to manipulate the perceptions of both players. The game can be played by several players on the closed market, with or without information about reputation.

Other interesting games include binary-choice trust games and the gift-exchange game. Games based on the Prisoner's Dilemma link trust with economic utility and demonstrate the rationality behind reciprocity.

The popularization of e-commerce led to new challenges related to trust within the digital economy and the desire to understand buyers' and sellers' decision to trust one another. For example, interpersonal relationships between buyers and sellers have been disintermediated by the technology, and consequentially they required improvement. Websites can influence the buyer to trust the seller, regardless of the seller's actual trustworthiness. Reputation-based systems can improve trust assessment by capturing a collective perception of trustworthiness; this has generated interest in various models of reputation.

Management and organization science

In management and organization science, trust is studied as a factor that organizational actors can manage and influence. Scholars have researched how trust develops across individual and organizational levels of analysis. They suggest a reciprocal process in which organizational structures influence people's trust and, at the same time, people's trust manifests in organizational structures. Trust is also one of the conditions of an organizational culture that supports knowledge sharing. An organizational culture that supports knowledge sharing allows employees to feel secure and comfortable to share their knowledge, their work, and their expertise. Structure often creates trust in a person, and this encourages them to feel comfortable and excel in the workplace; it makes an otherwise stressful environment manageable.

Management and organization science scholars have also studied how trust is influenced by contracts and how trust interacts with formal mechanisms. Scholars in management and related disciplines have also made a case for the importance of distrust as a related but distinct construct.

Since the mid-1990s, organizational research has followed two distinct but nonexclusive paradigms of trust research:

  1. The first distinguishes between two major dimensions of trust: Trust in another can be characterized as cognition-based trust (based on rational calculation) and affect-based trust (based on emotional attachment). For example, trust in an auto repair shop could come in the form of an assessment of the capabilities of the shop to do a good job repairing one's car (cognition-based trust) or of having a longstanding relationship with the shop's owner (affect-based trust).
  2. The second distinguishes between the trustworthiness factors that give rise to trust (i.e., one's perceived ability, benevolence, and integrity) and trust itself.

Together, these paradigms predict how different dimensions of trust form in organizations by demonstrating various trustworthiness attributes.

Systems

In systems, a trusted component has a set of properties that another component can rely on. If A trusts B, a violation in B's properties might compromise A's correct operation. Observe that those properties of B trusted by A might not correspond quantitatively or qualitatively to B's actual properties. This occurs when the designer of the overall system does not consider the relation. Consequently, trust should be placed to the extent of the component's trustworthiness. The trustworthiness of a component is thus, not surprisingly, defined by how well it secures a set of functional and non-functional properties, deriving from its architecture, construction, and environment, and evaluated as appropriate.

Blind men and an elephant

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