Climate change

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https://en.wikipedia.org/wiki/Climate_change

Changes in surface air temperature over the past 50 years. The Arctic has warmed the most, and temperatures on land have generally increased more than sea surface temperatures.

 

Earth's average surface air temperature has increased almost 1.5 °C (about 2.5 °F) since the Industrial Revolution. Natural forces cause some variability, but the 20-year average shows the progressive influence of human activity.

Present-day climate change includes both global warming—the ongoing increase in global average temperature—and its wider effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to Earth's climate. The modern-day rise in global temperatures is driven by human activities, especially fossil fuel (coal, oil and natural gas) burning since the Industrial Revolution. Fossil fuel use, deforestation, and some agricultural and industrial practices release greenhouse gases. These gases absorb some of the heat that the Earth radiates after it warms from sunlight, warming the lower atmosphere. Earth's atmosphere now has roughly 50% more carbon dioxide, the main gas driving global warming, than it did at the end of the pre-industrial era, reaching levels not seen for millions of years.

Climate change has an increasingly large impact on the environment. Deserts are expanding, while heat waves and wildfires are becoming more common. Amplified warming in the Arctic has contributed to thawing permafrost, retreat of glaciers and sea ice decline. 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 minimize 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 calls climate change one of the biggest threats 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.

Examples of some effects of climate change: Wildfire intensified by heat and drought, bleaching of corals occurring more often due to marine heatwaves, and worsening droughts compromising water supplies.

Many climate change impacts have been observed in the first decades of the 21st century, with 2024 the warmest on record at +1.60 °C (2.88 °F) since regular tracking began in 1850. Additional warming will increase these impacts and can trigger tipping points, such as melting all 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 2.8 °C (5.0 °F) by the end of the century.

There is widespread support for climate action worldwide, and most countries aim to stop emitting carbon dioxide. Fossil fuels can be phased out by stopping subsidising them, conserving energy and switching to energy sources that do not produce significant carbon pollution. These energy sources include wind, solar, hydro, and nuclear power. Cleanly generated electricity can replace fossil fuels for powering transportation, heating buildings, and running industrial processes. Carbon can also be removed from the atmosphere, for instance by increasing forest cover and farming with methods that store carbon in soil.

Terminology

Before the 1980s, 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 at this time. In the 1980s, the terms global warming and climate change became more common, often being used interchangeably. Scientifically, global warming refers only to increased global average surface temperature, while climate change describes both global warming and its effects on Earth's climate system, such as precipitation changes.

Climate change can also be used more broadly to include changes to the climate that have happened throughout Earth's history as result of natural processes. The term anthropogenic climate change is sometimes used to describe climate change resulting from human activities.

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, usage of climate change has increased. Various scientists, politicians and media may use the terms climate crisis or climate emergency to talk about climate change, and may use the term global heating instead of global warming.

Global temperature rise

Further information: Global surface temperature

Temperatures prior to present-day global warming

Main articles: Climate variability and change; Temperature record of the last 2,000 years; and Paleoclimatology

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

Over the last few million years the climate cycled through ice ages. One of the hotter periods was the Last Interglacial, around 125,000 years ago, where temperatures were between 0.5 °C and 1.5 °C warmer than before the start of global warming. This period saw sea levels 5 to 10 metres higher than today. The most recent glacial maximum 20,000 years ago was some 5–7 °C colder. This period has sea levels that were over 125 metres (410 ft) lower than today.

Temperatures stabilized in the current interglacial period beginning 11,700 years ago. This period also saw the start of agriculture. 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. Climate information for that period comes from climate proxies, such as trees and ice cores.

Warming since the Industrial Revolution

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.

Around 1850 thermometer records began to provide global coverage. Between the 18th century and 1970 there was little net warming, as the warming impact of greenhouse gas emissions was offset by cooling from sulfur dioxide emissions. Sulfur dioxide causes acid rain, but it also produces sulfate aerosols in the atmosphere, which reflect sunlight and cause global dimming. After 1970, the increasing accumulation of greenhouse gases and controls on sulfur pollution led to a marked increase in temperature.

Ongoing changes in climate have had no precedent for several thousand years. Multiple datasets all show worldwide increases in surface temperature, at a rate of around 0.2 °C per decade. The 2014–2023 decade warmed to an average 1.19 °C [1.06–1.30 °C] compared to the pre-industrial baseline (1850–1900). Not every single year was warmer than the last: internal climate variability processes can make any year 0.2 °C warmer or colder than the average. From 1998 to 2013, negative phases of two such processes, Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) caused a short slower period of warming called the "global warming hiatus". After the "hiatus", the opposite occurred, with 2024 well above the recent average at more than +1.5 °C. This is why the temperature change is defined in terms of a 20-year average, which reduces the noise of hot and cold years and decadal climate patterns, and detects the long-term signal.

A wide range of other observations reinforce the evidence of warming. The upper atmosphere is cooling, because greenhouse gases are trapping heat near the Earth's surface, and so less heat is radiating into space. Warming reduces average snow cover and forces the retreat of glaciers. At the same time, warming also causes greater evaporation from the oceans, leading to more atmospheric humidity, more and heavier precipitation. Plants are flowering earlier in spring, and thousands of animal species have been permanently moving to cooler areas.

Differences by region

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 oceans lose more heat by evaporation and oceans can store a lot of heat. 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 surface temperatures are increasing between three and four times faster than in the rest of the world. Melting of ice sheets near the poles weakens both the Atlantic and the Antarctic limb of thermohaline circulation, which further changes the distribution of heat and precipitation around the globe.

Future global temperatures

CMIP6 multi-model projections of global surface temperature changes for the year 2090 relative to the 1850–1900 average. The current trajectory for warming by the end of the century is roughly halfway between these two extremes.

The World Meteorological Organization estimates there is almost a 50% chance of the five-year average global temperature exceeding +1.5 °C between 2024 and 2028. The IPCC expects the 20-year average to exceed +1.5 °C in the early 2030s.

The IPCC Sixth Assessment Report (2021) included projections that by 2100 global warming is very likely to reach 1.0–1.8 °C under a scenario with very low emissions of greenhouse gases, 2.1–3.5 °C under an intermediate emissions scenario, or 3.3–5.7 °C under a very high emissions scenario. The warming will continue past 2100 in the intermediate and high emission scenarios, with future projections of global surface temperatures by year 2300 being similar to millions of years ago.

The remaining carbon budget for staying beneath certain temperature increases is determined by modelling the carbon cycle and climate sensitivity to greenhouse gases. According to UNEP, global warming can be kept below 2.0 °C with a 50% chance if emissions after 2023 do not exceed 900 gigatonnes of CO₂. This carbon budget corresponds to around 16 years of current emissions.

Causes of recent global temperature rise

Main article: Causes of climate change

Physical drivers of global warming that has happened so far. Future global warming potential for long lived drivers like carbon dioxide emissions is not represented. Whiskers on each bar show the possible error range.

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 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. Atmospheric aerosols produce a smaller, cooling effect. Other drivers, such as changes in albedo, are less impactful.

Greenhouse gases

Main articles: Greenhouse gas, Greenhouse gas emissions, Greenhouse effect, and Carbon dioxide in Earth's atmosphere

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.

While water vapour (≈50%) and clouds (≈25%) are the biggest contributors to the greenhouse effect, they primarily change as a function of temperature and are therefore mostly considered to be feedbacks that change climate sensitivity. On the other hand, concentrations of gases such as CO₂ (≈20%), tropospheric ozone, CFCs and nitrous oxide are added or removed independently from temperature, and are therefore considered to be external forcings that change global temperatures.

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. 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. In 2022, the concentrations of CO₂ and methane had increased by about 50% and 164%, respectively, since 1750. These CO₂ levels are higher than they have been at any time during the last 14 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 human-caused 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, aluminium, and fertilizer. 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 fertilizer.

While methane only lasts in the atmosphere for an average of 12 years, CO₂ lasts much longer. The Earth's surface absorbs CO₂ as part of the carbon cycle. While plants on land and in the ocean absorb most excess emissions of CO₂ every year, that CO₂ is returned to the atmosphere when biological matter is digested, burns, or decays. Land-surface carbon sink processes, such as carbon fixation in the soil and photosynthesis, remove about 29% of annual global CO₂ emissions. The ocean has absorbed 20 to 30% of emitted CO₂ over the last two decades. CO₂ is only removed from the atmosphere for the long term when it is stored in the Earth's crust, which is a process that can take millions of years to complete.

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.

Around 30% of Earth's land area is largely unusable for humans (glaciers, deserts, etc.), 26% is forests, 10% is shrubland and 34% is agricultural land. Deforestation is the main land use change contributor to global warming, as the destroyed trees release CO₂, and are not replaced by new trees, removing that carbon sink. Between 2001 and 2018, 27% of deforestation was from permanent clearing to enable agricultural expansion for crops and livestock. Another 24% has been lost to temporary clearing under the shifting cultivation agricultural systems. 26% was due to logging for wood and derived products, and wildfires have accounted for the remaining 23%. Some forests have not been fully cleared, but were already degraded by these impacts. Restoring these forests also recovers their potential as a carbon sink.

Local vegetation cover 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 modify 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, and forest restoration can make local temperatures cooler. At latitudes closer to the poles, there is a cooling effect as forest is replaced by snow-covered (and more reflective) plains. Globally, these increases in surface albedo have been the dominant direct influence on temperature from land use change. Thus, land use change to date is estimated to have a slight cooling effect.

Other factors

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. Smaller contributions come from black carbon (from combustion of fossil fuels and biomass), and from 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 energy 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. The effect of decreasing sulfur content of fuel oil for ships since 2020 is estimated to cause an additional 0.05 °C increase in global mean temperature by 2050.

Solar and volcanic activity

Further information: Solar activity and climate

The Fourth National Climate Assessment ("NCA4", USGCRP, 2017) includes charts illustrating that neither solar nor volcanic activity can explain the observed warming.

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, in contrast to the warming of the lower atmosphere (the troposphere). The upper atmosphere (the stratosphere) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling. This is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.

Explosive volcanic eruptions can release gases, dust and ash that partially block sunlight and reduce temperatures, or they can send water vapour into the atmosphere, which adds to greenhouse gases and increases temperatures. These impacts on temperature only last for several years, because both water vapour and volcanic material have low persistence in the atmosphere. volcanic CO₂ emissions are more persistent, but they are equivalent to less than 1% of current human-caused CO₂ emissions. Volcanic activity still represents the single largest natural impact (forcing) on temperature in the industrial era. Yet, like the other natural forcings, it has had negligible impacts on global temperature trends since the Industrial Revolution.

Climate change feedbacks

Main articles: Climate change feedbacks and Climate sensitivity

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 climate system's response to an initial forcing is shaped by feedbacks, which either amplify or dampen the change. Self-reinforcing or positive feedbacks increase the response, while balancing or negative feedbacks reduce it. The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and the net cloud feedback. 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. Feedbacks are expected to trend in a positive direction as greenhouse gas emissions continue, raising climate sensitivity.

These feedback processes alter the pace of global warming. For instance, warmer air can hold more moisture in the form of water vapour, which is itself a potent greenhouse gas. Warmer air can also make clouds higher and thinner, and therefore more insulating, increasing climate warming. The reduction of snow cover and sea ice in the Arctic is another major feedback, this reduces the reflectivity of the Earth's surface in the region and accelerates Arctic warming. This additional warming also contributes to permafrost thawing, which releases methane and CO₂ into the atmosphere.

Around half of human-caused CO₂ emissions have been absorbed by land plants and by the oceans. This fraction is not static and if future CO₂ emissions decrease, the Earth will be able to absorb up to around 70%. If they increase substantially, it'll still absorb more carbon than now, but the overall fraction will decrease to below 40%. This is because climate change increases droughts and heat waves that eventually inhibit plant growth on land, and soils will release more carbon from dead plants when they are warmer. The rate at which oceans absorb atmospheric carbon will be lowered as they become more acidic and experience changes in thermohaline circulation and phytoplankton distribution. Uncertainty over feedbacks, particularly cloud cover, is the major reason why different climate models project different magnitudes of warming for a given amount of emissions.

Modelling

Further information: Climate model and Climate change scenario

Energy flows between space, the atmosphere, and Earth's surface. Most sunlight passes through the atmosphere to heat the Earth's surface, then greenhouse gases absorb most of the heat the Earth radiates in response. Adding to greenhouse gases increases this insulating effect, causing an energy imbalance that heats the planet up.

A climate model is a representation of the physical, chemical and biological processes that affect the climate system. Models 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. Models also 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 current 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.

A subset of climate models add societal factors to a 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.

Impacts

Main article: Effects of climate change

In virtually all countries and territories around the world, scientists in the field of extreme event attribution have concluded that human-caused global warming has increased the number of days of extreme heat events over long-term norms.

Environmental effects

Further information: Effects of climate change on oceans and Effects of climate change on the water cycle

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. The 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 thermal expansion and the melting of glaciers and ice sheets. Sea level rise has increased over time, reaching 4.8 cm per decade between 2014 and 2023. Over the 21st century, the IPCC projects 32–62 cm of sea level rise under a low emission scenario, 44–76 cm under an intermediate one and 65–101 cm under a very high emission scenario. Marine ice sheet instability processes in Antarctica may add substantially to these values, including 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 cause more CO₂ to dissolve in the oceans, which is making them more acidic. Because oxygen is less soluble in warmer water, its concentrations in the ocean are decreasing, and dead zones are expanding.

Tipping points and long-term impacts

Main article: Tipping points in the climate system

Different levels of global warming may cause different parts of Earth's climate system to reach tipping points that cause transitions to different states.

Greater degrees of global warming increase the risk of passing through 'tipping points'—thresholds beyond which certain major impacts can no longer be avoided even if temperatures return to their previous state. For instance, the Greenland ice sheet is already melting, but if global warming reaches levels between 1.7 °C and 2.3 °C, its melting will continue until it fully disappears. If the warming is later reduced to 1.5 °C or less, it will still lose a lot more ice than if the warming was never allowed to reach the threshold in the first place. While the ice sheets would melt over millennia, other tipping points would occur faster and give societies less time to respond. The collapse of major ocean currents like the Atlantic meridional overturning circulation (AMOC), and irreversible damage to key ecosystems like the Amazon rainforest and coral reefs can unfold in a matter of decades. The collapse of the AMOC would be a severe climate catastrophe, resulting in a cooling of the Northern Hemisphere.

The long-term effects of climate change on oceans include further ice melt, ocean warming, sea level rise, ocean acidification and ocean deoxygenation. The timescale of long-term impacts are centuries to millennia due to CO₂'s long atmospheric lifetime. The result is an estimated total sea level rise of 2.3 metres per degree Celsius (4.2 ft/°F) after 2000 years. Oceanic CO₂ uptake is slow enough that ocean acidification will also continue for hundreds to thousands of years. Deep oceans (below 2,000 metres (6,600 ft)) are also already committed to losing over 10% of their dissolved oxygen by the warming which occurred to date. Further, the West Antarctic ice sheet appears committed to practically irreversible melting, which would increase the sea levels by at least 3.3 m (10 ft 10 in) over approximately 2000 years.

Nature and wildlife

Further information: Effects of climate change on oceans and Effects of climate change on biomes

Recent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes. For instance, the range of hundreds of North American birds has shifted northward at an average rate of 1.5 km/year over the past 55 years. 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. A related phenomenon driven by climate change is woody plant encroachment, affecting up to 500 million hectares globally. 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. Plants have come under increased stress from damage by insects.

Climate change impacts on the environment

Ecological collapse. Coral bleaching from thermal stress has damaged the Great Barrier Reef and threatens coral reefs worldwide.   Extreme weather. Drought and high temperatures worsened the 2020 bushfires in Australia.   Arctic warming. Permafrost thaws undermine infrastructure and release methane, a greenhouse gas.   Habitat destruction. Many arctic animals rely on sea ice, which has been disappearing in a warming Arctic.   Pest propagation. Mild winters allow more pine beetles to survive to kill large swaths of forest.

Humans

Main article: Effects of climate change

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.

Health and food

Main articles: Effects of climate change on agriculture § Global food security and undernutrition, and Effects of climate change on human health

The World Health Organization calls climate change one of the biggest threats to global health in the 21st century. Scientists have warned about the irreversible harms it poses. Extreme weather events affect public health, and food and water security. Temperature extremes lead to increased illness and death. Climate change increases the intensity and frequency of extreme weather events. It can affect transmission of infectious diseases, such as dengue fever and malaria. According to the World Economic Forum, 14.5 million more deaths are expected due to climate change by 2050. 30% of the global population currently live in areas where extreme heat and humidity are already associated with excess deaths. By 2100, 50% to 75% of the global population would live in such areas.

While total crop yields have been increasing in the past 50 years due to agricultural improvements, climate change has already decreased the rate of yield growth. Fisheries have been negatively affected in multiple regions. While agricultural productivity has been positively affected in some high latitude areas, mid- and low-latitude areas have been negatively affected. According to the World Economic Forum, an increase in drought in certain regions could cause 3.2 million deaths from malnutrition by 2050 and stunting in children. With 2 °C warming, global livestock headcounts could decline by 7–10% by 2050, as less animal feed will be available. If the emissions continue to increase for the rest of century, then over 9 million climate-related deaths would occur annually by 2100.

Livelihoods and inequality

Further information: Economic analysis of climate change and Climate security

Economic damages due to climate change may be severe and there is a chance of disastrous consequences. Severe impacts are expected in South-East Asia and sub-Saharan Africa, where most of the local inhabitants are dependent upon natural and agricultural resources. Heat stress can prevent outdoor labourers from working. If warming reaches 4 °C then labour capacity in those regions could be reduced by 30 to 50%. The World Bank estimates that between 2016 and 2030, climate change could drive over 120 million people into extreme poverty without adaptation.

Inequalities based on wealth and social status have worsened due to climate change. Major difficulties in mitigating, adapting to, and recovering from 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

Main article: Climate migration

Low-lying islands and coastal communities are threatened by sea level rise, which makes urban 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 areas almost one-third of humanity live in might become Sahara-like uninhabitable and extremely hot climates.

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

Environmental migration. Sparser rainfall leads to desertification that harms agriculture and can displace populations. Shown: Telly, Mali (2008).   Agricultural changes. Droughts, rising temperatures, and extreme weather negatively impact agriculture. Shown: Texas, US (2013).   Tidal flooding. Sea-level rise increases flooding in low-lying coastal regions. Shown: Venice, Italy (2004).   Storm intensification. Bangladesh after Cyclone Sidr (2007) is an example of catastrophic flooding from increased rainfall.   Heat wave intensification. Events like the 2022 Southern Cone heat wave are becoming more common.

Reducing and recapturing emissions

Further information: Climate change mitigation

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. To limit global warming to less than 2 °C global greenhouse gas emissions need to be net-zero by 2070. 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. With pledges made under the Paris Agreement as of 2024, there would be a 66% chance that global warming is kept under 2.8 °C by the end of the century (range: 1.9–3.7 °C, depending on exact implementation and technological progress). When only considering current policies, this raises to 3.1 °C. 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 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 a proposal for reducing global warming by reflecting some sunlight away from Earth and back into space. Because it does not reduce greenhouse gas concentrations, it would not address ocean acidification and is not considered mitigation. SRM should be considered only as a supplement to mitigation, not a replacement for it, due to risks such as rapid warming if it were abruptly stopped and not restarted. The most-studied approach is stratospheric aerosol injection. SRM could reduce global warming and some of its impacts, though imperfectly. It poses environmental risks, such as changes to rainfall patterns, as well as political challenges, such as who would decide whether to use it.

Clean energy

Main articles: Sustainable energy and Sustainable transport

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). Fossil fuel use is expected to peak in absolute terms prior to 2030 and then to decline, with coal use experiencing the sharpest reductions. Renewables represented 86% of all new electricity generation installed in 2023. 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.

While solar panels and onshore wind are now among the cheapest forms of adding new power generation capacity in many locations, green energy policies are needed to achieve a rapid transition from fossil fuels to renewables. 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 decarbonized with technologies like heat pumps.

There are obstacles to the continued rapid growth of clean energy, including renewables. Wind and solar produce energy intermittently and with seasonal variability. Traditionally, hydro dams with reservoirs and fossil fuel 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 minimizing climate change as well as 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

Main articles: Efficient energy use and 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 minimizes 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

See also: Sustainable agriculture and Green industrial policy

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. Where energy production or CO₂-intensive heavy industries continue to produce waste CO₂, technology can sometimes be used to capture and store most of the gas instead of releasing it to the atmosphere. This technology, carbon capture and storage (CCS), could have a critical but limited role in reducing emissions. It is relatively expensive and has been deployed only to an extent that removes around 0.1% of annual greenhouse gas emissions.

Carbon dioxide removal

Main articles: Carbon dioxide removal and 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 afforestation (planting forests where there were none before) 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. 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.

The use of bioenergy in conjunction with carbon capture and storage (BECCS) can result in net negative emissions as 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

Main article: Climate change 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 building flood controls. 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 favourable 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. An example of a trade-off is that increased use of air conditioning allows people to better cope with heat, but increases energy demand. Another trade-off example is that more compact urban development may reduce emissions from transport and construction, but may also increase the urban heat island effect, exposing people to heat-related health risks.

Examples of adaptation methods

Mangrove planting and other habitat conservation can reduce coastal flooding.   Seawalls to protect against storm surge worsened by sea level rise   Green roofs to provide cooling in cities   Selective breeding for drought-resistant crops

Policies and politics

See also: Politics of climate change and Climate change mitigation § Policies

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

No data

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 the UN's Sustainable Development Goals, such as eradicating poverty and reducing inequalities. The connection is recognized 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. Sometimes mitigation also has localized benefits though. 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

Further information: Climate policy

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. An Open Coalition on Compliance Carbon Markets with the aim of creating a global cap and trade system was established at COP30 (2025). According to some calculations it can increase emissions reduction seven-fold over current policies, deliver $200 billion per year for clean-energy and social programs and even close the gap between current emissions trajectory and the goals of the Paris agreement.

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 of emissions is another way to look at responsibility: under that approach, 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

Further information: United Nations Framework Convention on Climate Change

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 stabilized 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 March 2025, 194 states and the European Union have acceded to or ratified the agreement.

The 1987 Montreal Protocol, an international agreement to phase out production of ozone-depleting gases, has had benefits for climate change mitigation. Several ozone-depleting gases like chlorofluorocarbons are powerful greenhouse gases, so banning their production and usage may have avoided a temperature rise of 0.5 °C–1.0 °C, as well as additional warming by preventing damage to vegetation from ultraviolet radiation. It is estimated that the agreement has been more effective at curbing greenhouse gas emissions than the Kyoto Protocol specifically designed to do so. The most recent amendment to the Montreal Protocol, the 2016 Kigali Amendment, committed to reducing the emissions of hydrofluorocarbons, which served as a replacement for banned ozone-depleting gases and are also potent greenhouse gases. Should countries comply with the amendment, a warming of 0.3 °C–0.5 °C is estimated to be avoided.

National responses

Annual CO₂ emissions by region. This measures fossil fuel and industry emissions. Land use change is not included.

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. 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.

Major countries in Asia have made similar pledges: South Korea and Japan have committed to become carbon-neutral by 2050, and China by 2060. 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 and culture

Denial and misinformation

Further information: Climate change denial and Fossil fuels lobby

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 rectangle with blue dots shows the so-called global warming hiatus.

Public debate about climate change has been strongly affected by climate change denial and misinformation, which first emerged in the United States and has since spread to other countries, particularly Canada and Australia. It originated from 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 climate-change related scientific data and results. People who hold unwarranted doubt about climate change are sometimes called climate change "skeptics", although "contrarians" or "deniers" are more appropriate terms.

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 minimize 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 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

Further information: Climate communication, Media coverage of climate change, and Public opinion on climate change

The public substantially underestimates the degree of scientific consensus that humans are causing climate change (2022 data). 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. College biology textbooks from the 2010s featured less content on climate change compared to those from the preceding decade, with decreasing emphasis on solutions. 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. Media coverage linked to protests has had impacts on public sentiment as well as on which aspects of climate change are focused upon. Higher levels of worry are associated with stronger public support for policies that address climate change. Concern has increased over time, and in 2021 a majority of citizens in 30 countries expressed a high level of worry about climate change, or view it as a global emergency. A 2024 survey across 125 countries found that 89% of the global population demanded intensified political action, but systematically underestimated other peoples' willingness to act.

Climate movement

Main articles: Climate movement and Climate change litigation

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 activist and then-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. On 23 July 2025, the UN's International Court of Justice issued its advisory opinion, saying explicitly that states must act to stop climate change, and if they fail to accomplish that duty, other states can sue them. This obligation includes implementing their commitments in international agreements they are parties to, such as the 2015 Paris Climate Accord.

History

For broader coverage of this topic, see History of climate change science.

Early discoveries

Eunice Newton Foote showed carbon dioxide's heat-capturing effect in 1856, foreseeing its implications for the planet. (Carbon dioxide was called "carbonic acid gas".)

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). In "Circumstances Affecting the Heat of the Sun's Rays" she concluded that "[a]n atmosphere of that gas would give to our earth a high temperature".

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

Starting in 1859, John Tyndall established that nitrogen and oxygen—together totalling 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 sceptical 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

See also: Scientific consensus on climate change

Scientific consensus on causation: Academic studies of scientific agreement on human-caused global warming among climate experts (2010–2015) reflect that the level of consensus correlates with expertise in climate science. A 2019 study found scientific consensus to be at 100%, and a 2021 study concluded that consensus exceeded 99%. Another 2021 study found that 98.7% of climate experts indicated that the Earth is getting warmer mostly because of human activity.

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—the "Keeling Curve"—which was part of continued scientific investigation through the 1960s into possible human causation of global warming. Studies such as the National Research Council's 1979 Charney Report supported the accuracy of climate models that forecast significant warming. Human causation of observed global warming and dangers of unmitigated warming were publicly presented in James Hansen's 1988 testimony before a US Senate committee. 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 nearly unanimous scientific consensus that the climate is warming and that this is caused by human activities. No scientific body of national or international standing disagrees with this view. As of 2019, agreement in recent literature reached over 99%. The 2021 IPCC Assessment Report stated that it is "unequivocal" that climate change is caused by humans. Consensus has further developed that 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.

Recent developments

Extreme event attribution (EEA), also known as attribution science, was developed in the early decades of the 21st century. EEA uses climate models to identify and quantify the role that human-caused climate change plays in the frequency, intensity, duration, and impacts of specific individual extreme weather events. Results of attribution studies allow scientists and journalists to make statements such as, "this weather event was made at least n times more likely by human-caused climate change" or "this heatwave was made m degrees hotter than it would have been in a world without global warming" or "this event was effectively impossible without climate change". Greater computing power in the 2000s and conceptual breakthroughs in the early to mid 2010s enabled attribution science to detect the effects of climate change on some events with high confidence. Scientists use attribution methods and climate simulations that have already been peer reviewed, allowing "rapid attribution studies" to be published within a "news cycle" time frame after weather events.

Sustainability

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Sustainability

Three visual representations of sustainability and its three dimensions. The left image shows sustainability as three intersecting circles. The top right is a nested approach where social and economic sustainability are contained within environmental sustainability. The bottom right shows pillars with the different components holding up sustainability.

Sustainability (from the latin sustinere - hold up, hold upright; furnish with means of support; bear, undergo, endure) is the ability to continue over a long period of time. In modern usage it generally refers to a state in which the environment, economy, and society will continue to exist over a long period of time. Many definitions emphasize the environmental dimension. This can include addressing key environmental problems, such as climate change and biodiversity loss. The idea of sustainability can guide decisions at the global, national, organizational, and individual levels. A related concept is that of sustainable development, and the terms are often used to mean the same thing. UNESCO distinguishes the two like this: "Sustainability is often thought of as a long-term goal (i.e. a more sustainable world), while sustainable development refers to the many processes and pathways to achieve it."

Details around the economic dimension of sustainability are controversial. Scholars have discussed this under the concept of weak and strong sustainability. For example, there will always be tension between the ideas of "welfare and prosperity for all" and environmental conservation, so trade-offs are necessary. It would be desirable to find ways that separate economic growth from harming the environment. This means using fewer resources per unit of output even while growing the economy. This decoupling reduces the environmental impact of economic growth, such as pollution. Doing this is difficult.

It is challenging to measure sustainability as the concept is complex, contextual, and dynamic. Indicators have been developed to cover the environment, society, or the economy but there is no fixed definition of sustainability indicators. The metrics are evolving and include indicators, benchmarks, and audits. They include sustainability standards and certification systems, like Fairtrade and Organic. They also involve indices and accounting systems, such as corporate sustainability reporting and triple Bottom Line accounting.

It is necessary to address many barriers to sustainability to achieve a sustainability transition or sustainability transformation. Some barriers arise from nature and its complexity while others are extrinsic to the concept of sustainability. For example, they can result from the dominant institutional frameworks in countries.

Global issues of sustainability are difficult to tackle because they need global solutions. Existing global organizations such as the UN and WTO are seen as inefficient in enforcing current global regulations. One reason for this is the lack of suitable sanctioning mechanisms. Governments are not the only sources of action for sustainability. For example, business groups have tried to integrate ecological concerns with economic activity, seeking sustainable business. Religious leaders have stressed the need for caring for nature and environmental stability. Individuals can also choose to live more sustainably.

Some people have criticized the idea of sustainability. One point of criticism is that the concept is vague and only a buzzword. Another is that sustainability might be an impossible goal. Some experts have pointed out that "no country is delivering what its citizens need without transgressing the biophysical planetary boundaries".

Some would say that sustainability is not a movement, it’s a way of life. It extends past saving the planet into saving yourself. To give your family and community a life that is sustainable for the next generation. A great example of this are the Kibbutzim in Israel that are self sustainable farm communities. The Amish also live a sustainable life. While some have chosen Homesteading (in modern times this terms usually refers to one buying a piece of land and living a self sufficient lifestyle including a self sufficient electric and water system).

Definitions

Current usage

Sustainability is regarded as a "normative concept". This means it is based on what people value or find desirable: "The quest for sustainability involves connecting what is known through scientific study to applications in pursuit of what people want for the future."

The 1983 UN Commission on Environment and Development (Brundtland Commission) had a big influence on the use of the term sustainability today. The commission's 1987 Brundtland Report provided a definition of sustainable development. The report, Our Common Future, defines it as development that "meets the needs of the present without compromising the ability of future generations to meet their own needs". The report helped bring sustainability into the mainstream of policy discussions. It also popularized the concept of sustainable development.

Some other key concepts to illustrate the meaning of sustainability include:

• It may be a fuzzy concept, but in a positive sense: the goals are more important than the approaches or means applied.
• It connects with other essential concepts, such as resilience, adaptive capacity, and vulnerability.
• Choices matter: "it is not possible to sustain everything, everywhere, forever".
• Scale matters in both space and time, and place matters.
• Limits exist (see planetary boundaries).

In everyday usage, sustainability often focuses on the environmental dimension.

Specific definitions

A single specific definition of sustainability may never be possible, but the concept is still useful. There have been attempts to define it, for example:

• "Sustainability can be defined as the capacity to maintain or improve the state and availability of desirable materials or conditions over the long term."
• "Sustainability [is] the long-term viability of a community, set of social institutions, or societal practice. In general, sustainability is understood as a form of intergenerational ethics in which the environmental and economic actions taken by present persons do not diminish the opportunities of future persons to enjoy similar levels of wealth, utility, or welfare."
• "Sustainability means meeting our own needs without compromising the ability of future generations to meet their own needs. In addition to natural resources, we also need social and economic resources. Sustainability is not just environmentalism. Embedded in most definitions of sustainability we also find concerns for social equity and economic development."

Some definitions focus on the environmental dimension. The Oxford Dictionary of English defines sustainability as: "the property of being environmentally sustainable; the degree to which a process or enterprise is able to be maintained or continued while avoiding the long-term depletion of natural resources".

Historical usage

Further information: Sustainable development § Development of the concept

The term sustainability is derived from the Latin word sustinere. "To sustain" can mean to maintain, support, uphold, or endure. So sustainability is the ability to continue over a long period of time.

In the past, sustainability referred to environmental sustainability. It meant using natural resources so that people in the future could continue to rely on them in the long term. The concept of sustainability, or Nachhaltigkeit in German, goes back to Hans Carl von Carlowitz (1645–1714), and applied to forestry. The term for this now would be sustainable forest management. He used this term to mean the long-term responsible use of a natural resource. In his 1713 work Silvicultura oeconomica, he wrote that "the highest art/science/industriousness [...] will consist in such a conservation and replanting of timber that there can be a continuous, ongoing and sustainable use". The shift in use of "sustainability" from preservation of forests (for future wood production) to broader preservation of environmental resources (to sustain the world for future generations) traces to a 1972 book by Ernst Basler, based on a series of lectures at M.I.T.

The idea itself goes back a long time: Communities have always worried about the capacity of their environment to sustain them in the long term. Many ancient cultures, traditional societies, and indigenous peoples have restricted the use of natural resources.

Comparison to sustainable development

Further information: Sustainable development

The terms sustainability and sustainable development are closely related. In fact, they are often used to mean the same thing. Both terms are linked with the "three dimensions of sustainability" concept. One distinction is that sustainability is a general concept, while sustainable development can be a policy or organizing principle. Scholars say sustainability is a broader concept because sustainable development focuses mainly on human well-being.

Sustainable development has two linked goals. It aims to meet human development goals. It also aims to enable natural systems to provide the natural resources and ecosystem services needed for economies and society. The concept of sustainable development has come to focus on economic development, social development and environmental protection for future generations.

Dimensions

Development of three dimensions

Sustainability Venn diagram, where sustainability is thought of as the area where the three dimensions overlap

Scholars usually distinguish three different areas of sustainability. These are the environmental, the social, and the economic. Several terms are in use for this concept. Authors may speak of three pillars, dimensions, components, aspects, perspectives, factors, or goals. All mean the same thing in this context. The three dimensions paradigm has few theoretical foundations.

The popular three intersecting circles, or Venn diagram, representing sustainability first appeared in a 1987 article by the economist Edward Barbier.

Scholars rarely question the distinction itself. The idea of sustainability with three dimensions is a dominant interpretation in the literature.

In the Brundtland Report, the environment and development are inseparable and go together in the search for sustainability. It described sustainable development as a global concept linking environmental and social issues. It added sustainable development is important for both developing countries and industrialized countries:

The 'environment' is where we all live; and 'development' is what we all do in attempting to improve our lot within that abode. The two are inseparable. [...] We came to see that a new development path was required, one that sustained human progress not just in a few pieces for a few years, but for the entire planet into the distant future. Thus 'sustainable development' becomes a goal not just for the 'developing' nations, but for industrial ones as well.

— Our Common Future (also known as the Brundtland Report)

The Rio Declaration from 1992 is seen as "the foundational instrument in the move towards sustainability". It includes specific references to ecosystem integrity. The plan associated with carrying out the Rio Declaration also discusses sustainability in this way. The plan, Agenda 21, talks about economic, social, and environmental dimensions:

Countries could develop systems for monitoring and evaluation of progress towards achieving sustainable development by adopting indicators that measure changes across economic, social and environmental dimensions.

— United Nations Conference on Environment & Development – Earth Summit (1992)

Agenda 2030 from 2015 also viewed sustainability in this way. It sees the 17 Sustainable Development Goals (SDGs) with their 169 targets as balancing "the three dimensions of sustainable development, the economic, social and environmental".

Hierarchy

The diagram with three nested ellipses indicates a hierarchy among the three dimensions of sustainability: both economy and society are constrained by environmental limits.

The wedding cake model for the sustainable development goals is similar to the nested ellipses diagram, where the environmental dimension or system is the basis for the other two dimensions.

Scholars have discussed how to rank the three dimensions of sustainability. Many publications state that the environmental dimension is the most important. (Planetary integrity or ecological integrity are other terms for the environmental dimension.)

Protecting ecological integrity is the core of sustainability according to many experts. If this is the case then its environmental dimension sets limits to economic and social development.

The diagram with three nested ellipses is one way of showing the three dimensions of sustainability together with a hierarchy: It gives the environmental dimension a special status. In this diagram, the environment includes society, and society includes economic conditions. Thus it stresses a hierarchy.

This nested hierarchy has led some scholars and Indigenous thinkers to call for decentering the human in sustainability discourse, arguing that ecological systems should not merely be valued for their utility to humans but as interdependent life systems with intrinsic worth.

Another model shows the three dimensions in a similar way: In this SDG wedding cake model, the economy is a smaller subset of the societal system. And the societal system in turn is a smaller subset of the biosphere system.

In 2022 an assessment examined the political impacts of the Sustainable Development Goals. The assessment found that the "integrity of the earth's life-support systems" was essential for sustainability. The authors said that "the SDGs fail to recognize that planetary, people and prosperity concerns are all part of one earth system, and that the protection of planetary integrity should not be a means to an end, but an end in itself". The aspect of environmental protection is not an explicit priority for the SDGs. This causes problems as it could encourage countries to give the environment less weight in their developmental plans. The authors state that "sustainability on a planetary scale is only achievable under an overarching Planetary Integrity Goal that recognizes the biophysical limits of the planet".

Other frameworks bypass the compartmentalization of sustainability into separate dimensions completely.

Environmental sustainability

See also: Human impact on the environment and Environmentalism

A circular economy can improve aspects of environmental sustainability (left: the 'take, make, waste' linear approach; right: the circular economy approach).

The environmental dimension is central to the overall concept of sustainability. People became more and more aware of environmental pollution in the 1960s and 1970s. This led to discussions on sustainability and sustainable development. This process began in the 1970s with concern for environmental issues. These included natural ecosystems or natural resources and the human environment. It later extended to all systems that support life on Earth, including human society.Reducing these negative impacts on the environment would improve environmental sustainability.

Environmental pollution is not a new phenomenon. But it has been only a local or regional concern for most of human history. Awareness of global environmental issues increased in the 20th century. The harmful effects and global spread of pesticides like DDT came under scrutiny in the 1960s. In the 1970s it emerged that chlorofluorocarbons (CFCs) were depleting the ozone layer. This led to the de facto ban of CFCs with the Montreal Protocol in 1987.

In the early 20th century, Arrhenius discussed the effect of greenhouse gases on the climate (see also: history of climate change science). Climate change due to human activity became an academic and political topic several decades later. This led to the establishment of the IPCC in 1988 and the UNFCCC in 1992.

In 1972, the UN Conference on the Human Environment took place. It was the first UN conference on environmental issues. It stated it was important to protect and improve the human environment. It emphasized the need to protect wildlife and natural habitats:

The natural resources of the earth, including the air, water, land, flora and fauna and [...] natural ecosystems must be safeguarded for the benefit of present and future generations through careful planning or management, as appropriate.

— UN Conference on the Human Environment

In 2000, the UN launched eight Millennium Development Goals. The aim was for the global community to achieve them by 2015. Goal 7 was to "ensure environmental sustainability". But this goal did not mention the concepts of social or economic sustainability.

Specific problems often dominate public discussion of the environmental dimension of sustainability: In the 21st century these problems have included climate change, biodiversity and pollution. Other global problems are loss of ecosystem services, land degradation, environmental impacts of animal agriculture and air and water pollution, including marine plastic pollution and ocean acidification. Many people worry about human impacts on the environment. These include impacts on the atmosphere, land, and water resources.

Human activities now have an impact on Earth's geology and ecosystems. This led Paul Crutzen to call the current geological epoch the Anthropocene.

The importance of citizens in accomplishing climate change adaptation, mitigation, and more general sustainable development objectives is being emphasized more and more by urban climate change governance (Hegger, Mees, & Wamsler, 2022). The Sustainable Development Goals and the Glasgow Climate Pact are two recent international agreements that acknowledge that sustainability transformations depend on both individual and social attitudes, values, and behaviors in addition to technical solutions (IPCC, 2022; Wamsler et al., 2021). Through their roles as voters, activists, consumers, and community members—particularly in decision-making, information co-production, and localized self-governance initiatives—citizens are seen as crucial change agents (Mees et al., 2016; Wamsler, 2017).

Economic sustainability

See also: Fiscal sustainability and Debt Sustainability Analysis

The economic dimension of sustainability is controversial. This is because the term development within sustainable development can be interpreted in different ways. Some may take it to mean only economic development and growth. This can promote an economic system that is bad for the environment. Others focus more on the trade-offs between environmental conservation and achieving welfare goals for basic needs (food, water, health, and shelter).

Economic development can indeed reduce hunger or energy poverty, especially in the least developed countries. That is why Sustainable Development Goal 8 calls for economic growth to drive social progress and well-being, where indicators include real GDP per capita growth. However, the challenge is to expand economic activities while reducing their environmental impact. In other words, humanity will have to find ways how societal progress (potentially by economic development) can be reached without excess strain on the environment.

The Brundtland report says poverty causes environmental problems. Poverty also results from them. So addressing environmental problems requires understanding the factors behind world poverty and inequality. The report demands a new development path for sustained human progress. It highlights that this is a goal for both developing and industrialized nations.

UNEP and UNDP launched the Poverty-Environment Initiative in 2005 which has three goals. These are reducing extreme poverty, greenhouse gas emissions, and net natural asset loss. This guide to structural reform will enable countries to achieve the SDGs. It should also show how to address the trade-offs between ecological footprint and economic development.

The government debt increases of many countries were found unsustainable in the long-term.

Social sustainability

Social justice is just one part of social sustainability.

See also: Dependency ratio and Generational accounting

The social dimension of sustainability is not well defined. One definition states that a society is sustainable in social terms if people do not face structural obstacles in key areas. These key areas are health, influence, competence, impartiality and meaning-making.

Some scholars place social issues at the very center of discussions. They suggest that all the domains of sustainability are social. These include ecological, economic, political, and cultural sustainability. These domains all depend on the relationship between the social and the natural. The ecological domain is defined as human embeddedness in the environment. From this perspective, social sustainability encompasses all human activities. It goes beyond the intersection of economics, the environment, and the social.

There are many broad strategies for more sustainable social systems. They include improved education and the political empowerment of women. This is especially the case in developing countries. They include greater regard for social justice. This involves equity between rich and poor both within and between countries. And it includes intergenerational equity. Providing more social safety nets to vulnerable populations would contribute to social sustainability. Current pension systems are financially unsustainable in some countries.

A society with a high degree of social sustainability would lead to livable communities with a good quality of life (being fair, diverse, connected and democratic).

Indigenous communities might have a focus on particular aspects of sustainability, for example spiritual aspects, community-based governance and an emphasis on place and locality.

Another aspect of social sustainability would be gender equity. According to reports from the United Nations and various research studies, women are disproportionately affected by climate related issues and sustainability efforts than men are. To name a few, natural disasters, carbon taxes, and public transportation expansions have all reportedly had unequal consequences on women and other marginalized groups by making it harder for them to afford different goods and services or newer transit routes (longer car rides equate to more gas purchases), as well as putting them at risk of becoming targets of violence.

These issues often go unaddressed and unheard, as women do not have the ability to voice these concerns due to the little to nonexistent presence of women in environmental policymaking. Despite the contrast in ability, women are often given the responsibility of solving the issues of climate change more than men are, due to the stereotypical feminine aspect of caring for the planet. For this reason, scholars urge the need for more female representation and leadership in environmental politics and policymaking. They also highlight the link between environmental and social sustainability and the importance of addressing the two together so that actual progress can be made, as policymakers often categorize and handle them separately. By improving healthcare, education, and representation in government, women will be empowered to have a voice in policy making.

Proposed additional dimensions

Some experts have proposed further dimensions. These could cover institutional, cultural, political, and technical dimensions.

Cultural sustainability

Further information: Cultural sustainability

Some scholars have argued for a fourth dimension. They say the traditional three dimensions do not reflect the complexity of contemporary society. For example, Agenda 21 for culture and the United Cities and Local Governments argue that sustainable development should include a solid cultural policy. They also advocate for a cultural dimension in all public policies. Another example was the Circles of Sustainability approach, which included cultural sustainability.

Interactions between dimensions

Environmental and economic dimensions

Further information: Weak and strong sustainability

See also: Sustainable city

People often debate the relationship between the environmental and economic dimensions of sustainability. In academia, this is discussed under the term weak and strong sustainability. In that model, the weak sustainability concept states that capital made by humans could replace most of the natural capital. Natural capital is a way of describing environmental resources. People may refer to it as nature. An example for this is the use of environmental technologies to reduce pollution.

The opposite concept in that model is strong sustainability. This assumes that nature provides functions that technology cannot replace. Thus, strong sustainability acknowledges the need to preserve ecological integrity. The loss of those functions makes it impossible to recover or repair many resources and ecosystem services. Biodiversity, along with pollination and fertile soils, are examples. Others are clean air, clean water, and regulation of climate systems.

Weak sustainability has come under criticism. It may be popular with governments and business but does not ensure the preservation of the earth's ecological integrity. This is why the environmental dimension is so important.

The World Economic Forum illustrated this in 2020. It found that $44 trillion of economic value generation depends on nature. This value, more than half of the world's GDP, is thus vulnerable to nature loss. Three large economic sectors are highly dependent on nature: construction, agriculture, and food and beverages. Nature loss results from many factors. They include land use change, sea use change and climate change. Other examples are natural resource use, pollution, and invasive alien species.

Trade-offs

Trade-offs between different dimensions of sustainability are a common topic for debate. Balancing the environmental, social, and economic dimensions of sustainability is difficult. This is because there is often disagreement about the relative importance of each. To resolve this, there is a need to integrate, balance, and reconcile the dimensions. For example, humans can choose to make ecological integrity a priority or to compromise it.

Some even argue the Sustainable Development Goals are unrealistic. Their aim of universal human well-being conflicts with the physical limits of Earth and its ecosystems.

Measurement tools

Further information: Sustainability metrics and indices

Urban sustainability analysis of the greater urban area of the city of São Paulo using the 'Circles of Sustainability' method of the UN and Metropolis Association

Sustainability measurement is a set of frameworks or indicators used to measure how sustainable something is. This includes processes, products, services and businesses. Sustainability is difficult to quantify and it may even be impossible to measure as there is no fixed definition. To measure sustainability, frameworks and indicators consider environmental, social and economic domains. The metrics vary by use case and are still evolving. They include indicators, benchmarks and audits. They include sustainability standards and certification systems like Fairtrade and Organic. They also involve indices and accounting. They can include assessment, appraisal and other reporting systems. The metrics are used over a wide range of spatial and temporal scales.

Environmental impacts of humans

Further information: Planetary boundaries and Ecological footprint

There are several methods to measure or describe human impacts on Earth. They include the ecological footprint, ecological debt, carrying capacity, and sustainable yield. The idea of planetary boundaries is that there are limits to the carrying capacity of the Earth. It is important not to cross these thresholds to prevent irreversible harm to the Earth. These planetary boundaries involve several environmental issues. These include climate change and biodiversity loss. They also include types of pollution. These are biogeochemical (nitrogen and phosphorus), ocean acidification, land use, freshwater, ozone depletion, atmospheric aerosols, and chemical pollution. (Since 2015 some experts refer to biodiversity loss as change in biosphere integrity. They refer to chemical pollution as introduction of novel entities.)

The IPAT formula measures the environmental impact of humans. It emerged in the 1970s. It states this impact is proportional to human population, affluence and technology. This implies various ways to increase environmental sustainability. One would be human population control. Another would be to reduce consumption and affluence such as energy consumption. Another would be to develop innovative or green technologies such as renewable energy.

The Millennium Ecosystem Assessment from 2005 measured 24 ecosystem services. It concluded that only four have improved over the last 50 years. It found 15 are in serious decline and five are in a precarious condition.

Economic costs

The doughnut model, with indicators to what extent the ecological ceilings are overshot and social foundations are not met yet

Experts in environmental economics have calculated the cost of using public natural resources. One project calculated the damage to ecosystems and biodiversity loss. This was the Economics of Ecosystems and Biodiversity project from 2007 to 2011.

An entity that creates environmental and social costs often does not pay for them. The market price also does not reflect those costs. In the end, government policy is usually required to resolve this problem.

Decision-making can take future costs and benefits into account. The tool for this is the social discount rate. The bigger the concern for future generations, the lower the social discount rate should be. Another approach is to put an economic value on ecosystem services. This allows us to assess environmental damage against perceived short-term welfare benefits. One calculation is that, "for every dollar spent on ecosystem restoration, between three and 75 dollars of economic benefits from ecosystem goods and services can be expected".

In recent years, economist Kate Raworth has developed the concept of doughnut economics. This aims to integrate social and environmental sustainability into economic thinking. The social dimension acts as a minimum standard to which a society should aspire. The carrying capacity of the planet acts an outer limit.

Barriers

There are many reasons why sustainability is so difficult to achieve. These reasons have the name sustainability barriers. Before addressing these barriers it is important to analyze and understand them. Some barriers arise from nature and its complexity ("everything is related"). Others arise from the human condition. One example is the value-action gap. This reflects the fact that people often do not act according to their convictions. Experts describe these barriers as intrinsic to the concept of sustainability.

Other barriers are extrinsic to the concept of sustainability. This means it is possible to overcome them. One way would be to put a price tag on the consumption of public goods. Some extrinsic barriers relate to the nature of dominant institutional frameworks. Examples would be where market mechanisms fail for public goods. Existing societies, economies, and cultures encourage increased consumption. There is a structural imperative for growth in competitive market economies. This inhibits necessary societal change.

Furthermore, there are several barriers related to the difficulties of implementing sustainability policies. There are trade-offs between the goals of environmental policies and economic development. Environmental goals include nature conservation. Development may focus on poverty reduction. There are also trade-offs between short-term profit and long-term viability. Political pressures generally favor the short term over the long term. So they form a barrier to actions oriented toward improving sustainability.

Barriers to sustainability may also reflect current trends. These could include consumerism and short-termism.

Conflicts, lack of international cooperation are also considered as a barrier to achieve sustainability. 61 scientists, including Michael Meeropol, Don Trent Jacobs and 24 organizations including Scientist Rebellion endorsed an appeal saying we can not stop the ecological crisis without stopping overconsumption and this is impossible as wars continue because GDP is directly linked to military potential.

Transition

Characteristics

Sustainability transformation (or transition), though not universally defined, refers to a deep, system-wide change affecting technology, economy, society, values, and goals. It is a complex and multi-layered process that must happen at all scales, from local communities to global governance institutions. However, it is often politically debated, as different stakeholders may disagree on both the goals and the methods of change. Additionally, such transformations can challenge existing power structures and resource distribution.

A sustainability transition requires major change in societies. They must change their fundamental values and organizing principles. These new values would emphasize "the quality of life and material sufficiency, human solidarity and global equity, and affinity with nature and environmental sustainability". A transition may only work if far-reaching lifestyle changes accompany technological advances.

Scientists have pointed out that: "Sustainability transitions come about in diverse ways, and all require civil-society pressure and evidence-based advocacy, political leadership, and a solid understanding of policy instruments, markets, and other drivers."

There are four possible overlapping processes of transformation. They each have different political dynamics. Technology, markets, government, or citizens can lead these processes.

The European Environment Agency defines a sustainability transition as "a fundamental and wide-ranging transformation of a socio-technical system towards a more sustainable configuration that helps alleviate persistent problems such as climate change, pollution, biodiversity loss or resource scarcities." The concept of sustainability transitions is similar to the concept of energy transitions.

One expert argues a sustainability transition must be "supported by a new kind of culture, a new kind of collaboration, [and] a new kind of leadership". It requires a large investment in "new and greener capital goods, while simultaneously shifting capital away from unsustainable systems".

In 2024 an interdisciplinary group of experts including Chip Fletcher, William J. Ripple, Phoebe Barnard, Kamanamaikalani Beamer, Christopher Field, David Karl, David King, Michael E. Mann and Naomi Oreskes advocated for a paradigm shift toward genuine sustainability and resource regeneration. They said that "such a transformation is imperative to reverse the tide of biodiversity loss due to overconsumption and to reinstate the security of food and water supplies, which are foundational for the survival of global populations."

Principles

It is possible to divide action principles to make societies more sustainable into four types. These are nature-related, personal, society-related and systems-related principles.

• Nature-related principles: decarbonize; reduce human environmental impact by efficiency, sufficiency and consistency; be net-positive – build up environmental and societal capital; prefer local, seasonal, plant-based and labor-intensive; polluter-pays principle; precautionary principle; and appreciate and celebrate the beauty of nature.
• Personal principles: practise contemplation, apply policies with caution, celebrate frugality.
• Society-related principles: grant the least privileged the greatest support; seek mutual understanding, trust and many wins; strengthen social cohesion and collaboration; engage stakeholders; foster education – share knowledge and collaborate.
• Systems-related principles: apply systems thinking; foster diversity; make what is relevant to the public more transparent; maintain or increase option diversity.

Example steps

There are many approaches that people can take to transition to environmental sustainability. These include maintaining ecosystem services, protecting and co-creating common resources, reducing food waste, and promoting dietary shifts towards plant-based foods. Another is reducing population growth by cutting fertility rates. Others are promoting new green technologies, and adopting renewable energy sources while phasing out subsidies to fossil fuels.

In 2017 scientists published an update to the 1992 World Scientists' Warning to Humanity. It showed how to move towards environmental sustainability. It proposed steps in three areas:

• Reduced consumption: reducing food waste, promoting dietary shifts towards mostly plant-based foods.
• Reducing the number of consumers: further reducing fertility rates and thus population growth.
• Technology and nature conservation: there are several related approaches. One is to maintain nature's ecosystem services. Another is promote new green technologies. Another is changing energy use. One aspect of this is to adopt renewable energy sources. At the same time it is necessary to end subsidies to energy production through fossil fuels.

Agenda 2030 for the Sustainable Development Goals

United Nations Sustainable Development Goals

In 2015, the United Nations agreed the Sustainable Development Goals (SDGs). Their official name is Agenda 2030 for the Sustainable Development Goals. The UN described this programme as a very ambitious and transformational vision. It said the SDGs were of unprecedented scope and significance.

The UN said: "We are determined to take the bold and transformative steps which are urgently needed to shift the world on to a sustainable and resilient path."

The 17 goals and targets lay out transformative steps. For example, the SDGs aim to protect the future of planet Earth. The UN pledged to "protect the planet from degradation, including through sustainable consumption and production, sustainably managing its natural resources and taking urgent action on climate change, so that it can support the needs of the present and future generations".

Options for overcoming barriers

Further information: Sustainable development § Pathways

Issues around economic growth

Further information: Eco-economic decoupling, Degrowth, and Steady-state economy

Example of decoupling: Countries that managed to reduce their greenhouse gas emissions (working towards a low-carbon economy) while still growing their economy

Eco-economic decoupling is an idea to resolve tradeoffs between economic growth and environmental conservation. The idea is to "decouple environmental bads from economic goods as a path towards sustainability". This would mean "using less resources per unit of economic output and reducing the environmental impact of any resources that are used or economic activities that are undertaken". The intensity of pollutants emitted makes it possible to measure pressure on the environment. This in turn makes it possible to measure decoupling. This involves following changes in the emission intensity associated with economic output. Examples of absolute long-term decoupling are rare. But some industrialized countries have decoupled GDP growth from production- and consumption-based CO₂ emissions. Yet, even in this example, decoupling alone is not enough. It is necessary to accompany it with "sufficiency-oriented strategies and strict enforcement of absolute reduction targets".

One study in 2020 found no evidence of necessary decoupling. This was a meta-analysis of 180 scientific studies. It found that there is "no evidence of the kind of decoupling needed for ecological sustainability" and that "in the absence of robust evidence, the goal of decoupling rests partly on faith". Some experts have questioned the possibilities for decoupling and thus the feasibility of green growth. Some have argued that decoupling on its own will not be enough to reduce environmental pressures. They say it would need to include the issue of economic growth. There are several reasons why adequate decoupling is currently not taking place. These are rising energy expenditure, rebound effects, problem shifting, the underestimated impact of services, the limited potential of recycling, insufficient and inappropriate technological change, and cost-shifting.

The decoupling of economic growth from environmental deterioration is difficult. This is because the entity that causes environmental and social costs does not generally pay for them. So the market price does not express such costs. For example, the cost of packaging into the price of a product. may factor in the cost of packaging. But it may omit the cost of disposing of that packaging. Economics describes such factors as externalities, in this case a negative externality. Usually, it is up to government action or local governance to deal with externalities.

For highly developed nations, sustainable practices and climate policies "often lead to conflicts between short-term economic interests and long-term environmental goals." However, for developing countries, efforts to address climate change are limited by their financial resources. To effectively advance sustainability, solutions need to focus on "fostering political commitment, enhancing inter-agency coordination, securing adequate funding, and engaging diverse stakeholders to overcome these challenges."

There are various ways to incorporate environmental and social costs and benefits into economic activities. Examples include: taxing the activity (the polluter pays); subsidizing activities with positive effects (rewarding stewardship); and outlawing particular levels of damaging practices (legal limits on pollution).

Government action and local governance

A textbook on natural resources and environmental economics stated in 2011: "Nobody who has seriously studied the issues believes that the economy's relationship to the natural environment can be left entirely to market forces." This means natural resources will be over-exploited and destroyed in the long run without government action.

Elinor Ostrom (winner of the 2009 Nobel Prize in Economics) expanded on this. She stated that local governance (or self-governance) can be a third option besides the market or the national government. She studied how people in small, local communities manage shared natural resources. She showed that communities using natural resources can establish rules their for use and maintenance. These are resources such as pastures, fishing waters, and forests. This leads to both economic and ecological sustainability. Successful self-governance needs groups with frequent communication among participants. In this case, groups can manage the usage of common goods without overexploitation. Based on Ostrom's work, some have argued that: "Common-pool resources today are overcultivated because the different agents do not know each other and cannot directly communicate with one another."

Global governance

See also: Global governance

Launch of the UN Sustainable Development Solutions Network (SDSN) Chapter, Indonesia

Questions of global concern are difficult to tackle. That is because global issues need global solutions. But existing global organizations (UN, WTO, and others) do not have sufficient means. For example, they lack sanctioning mechanisms to enforce existing global regulations. Some institutions do not enjoy universal acceptance. An example is the International Criminal Court. Their agendas are not aligned (for example UNEP, UNDP, and WTO) And some accuse them of nepotism and mismanagement.

Multilateral international agreements, treaties, and intergovernmental organizations (IGOs) face further challenges. These result in barriers to sustainability. Often these arrangements rely on voluntary commitments. An example is Nationally Determined Contributions for climate action. There can be a lack of enforcement of existing national or international regulation. And there can be gaps in regulation for international actors such as multi-national enterprises. Critics of some global organizations say they lack legitimacy and democracy. Institutions facing such criticism include the WTO, IMF, World Bank, UNFCCC, G7, G8 and OECD.

Responses by nongovernmental stakeholders

Businesses

See also: Environmental, social, and corporate governance

The Forest Stewardship Council (FSC) seal for wood products is meant to indicate sustainable production of wood (in a forest in Germany).

Sustainable business practices integrate ecological concerns with social and economic ones. One accounting framework for this approach uses the phrase "people, planet, and profit". The name of this approach is the triple bottom line. The circular economy is a related concept. Its goal is to decouple environmental pressure from economic growth.

Growing attention towards sustainability has led to the formation of many organizations. These include the Sustainability Consortium of the Society for Organizational Learning, the Sustainable Business Institute, and the World Business Council for Sustainable Development. Supply chain sustainability looks at the environmental and human impacts of products in the supply chain. It considers how they move from raw materials sourcing to production, storage, and delivery, and every transportation link on the way.

Religious communities

Further information: Religion and environmentalism

Religious leaders have stressed the importance of caring for nature and environmental sustainability. In 2015 over 150 leaders from various faiths issued a joint statement to the UN Climate Summit in Paris 2015. They reiterated a statement made in the Interfaith Summit in New York in 2014:

As representatives from different faith and religious traditions, we stand together to express deep concern for the consequences of climate change on the earth and its people, all entrusted, as our faiths reveal, to our common care. Climate change is indeed a threat to life, a precious gift we have received and that we need to care for.

Individuals

Further information: Sustainable living

Individuals can also live in a more sustainable way. They can change their lifestyles, practise ethical consumerism, and embrace frugality. These sustainable living approaches can also make cities more sustainable. They do this by altering the built environment. Such approaches include sustainable transport, sustainable architecture, and zero emission housing. Research can identify the main issues to focus on. These include flying, meat and dairy products, car driving, and household sufficiency. Research can show how to create cultures of sufficiency, care, solidarity, and simplicity.

Some young people are using activism, litigation, and on-the-ground efforts to advance sustainability. This is particularly the case in the area of climate action.

Assessments and reactions

Impossible to reach

Scholars have criticized the concepts of sustainability and sustainable development from different angles. One was Dennis Meadows, one of the authors of the first report to the Club of Rome, called "The Limits to Growth". He argued many people deceive themselves by using the Brundtland definition of sustainability. This is because the needs of the present generation are actually not met today. Instead, economic activities to meet present needs will shrink the options of future generations. Another criticism is that the paradigm of sustainability is no longer suitable as a guide for transformation. This is because societies are "socially and ecologically self-destructive consumer societies".

Some scholars have even proclaimed the end of the concept of sustainability. This is because humans now have a significant impact on Earth's climate system and ecosystems. It might become impossible to pursue sustainability because of these complex, radical, and dynamic issues. Others have called sustainability a utopian ideal: "We need to keep sustainability as an ideal; an ideal which we might never reach, which might be utopian, but still a necessary one."

Vagueness

The term is often hijacked and thus can lose its meaning. People use it for all sorts of things, such as saving the planet to recycling your rubbish. A specific definition may never be possible. This is because sustainability is a concept that provides a normative structure. That describes what human society regards as good or desirable.

But some argue that while sustainability is vague and contested it is not meaningless. Although lacking in a singular definition, this concept is still useful. Scholars have argued that its fuzziness can actually be liberating. This is because it means that "the basic goal of sustainability (maintaining or improving desirable conditions [...]) can be pursued with more flexibility".

Confusion and greenwashing

Sustainability has a reputation as a buzzword. People may use the terms sustainability and sustainable development in ways that are different to how they are usually understood. This can result in confusion and mistrust. So a clear explanation of how the terms are being used in a particular situation is important.

Greenwashing is a practice of deceptive marketing. It is when a company or organization provides misleading information about the sustainability of a product, policy, or other activity. Investors are wary of this issue as it exposes them to risk. The reliability of eco-labels is also doubtful in some cases. Ecolabelling is a voluntary method of environmental performance certification and labelling for food and consumer products. The most credible eco-labels are those developed with close participation from all relevant stakeholders.