Present-day climate change encompasses both global warming—defined as the continuous rise in global average temperature—and its extensive repercussions across Earth's climatic system. More broadly, the concept of climate change also incorporates historical, long-term shifts in Earth's climate. The contemporary escalation in global temperatures primarily results from anthropogenic activities, particularly the combustion of fossil fuels (coal, oil, and natural gas) since the onset of the Industrial Revolution. The emission of greenhouse gases stems from the utilization of fossil fuels, deforestation, and specific agricultural and industrial processes. These gases effectively absorb a portion of the thermal energy radiated by Earth subsequent to solar warming, thereby elevating the temperature of the lower atmosphere. Currently, Earth's atmosphere contains approximately 50% more carbon dioxide, the principal gas contributing to global warming, than was present at the conclusion of the pre-industrial period, reaching concentrations unprecedented in millions of years.
The environmental consequences of climate change are progressively intensifying. Observations indicate desert expansion, alongside a rising frequency of heat waves and wildfires. Exacerbated warming in the Arctic region has led to permafrost degradation, glacial recession, and a reduction in sea ice extent. Elevated temperatures also precipitate more severe storms, prolonged droughts, and other extreme weather phenomena. Swift ecological transformations in mountainous regions, coral reef ecosystems, and the Arctic compel numerous species to migrate or face extinction. Even with successful mitigation efforts to curtail future warming, certain impacts, such as oceanic warming, ocean acidification, and sea level elevation, are projected to persist for centuries.
Climate change poses significant threats to human populations, manifesting as heightened flooding, extreme thermal conditions, exacerbated food and water insecurity, increased disease prevalence, and substantial economic losses. Furthermore, it can precipitate human displacement and societal conflicts. The World Health Organization identifies climate change as a paramount threat to global health in the current century. Without decisive action to restrict warming, both human societies and natural ecosystems will confront increasingly severe risks. While adaptive strategies, such as implementing flood control systems or cultivating drought-resistant crops, can partially mitigate climate change risks, certain limitations to adaptation have already become apparent. Disadvantaged communities, despite contributing minimally to global emissions, possess the lowest adaptive capacity and are consequently most susceptible to the impacts of climate change.
Numerous impacts of climate change have been documented during the initial decades of the 21st century, with 2024 recorded as the warmest year, registering an increase of +1.60 °C (2.88 °F) since systematic temperature monitoring commenced in 1850. Further warming is projected to intensify these impacts and could activate critical tipping points, such as the complete disintegration of the Greenland ice sheet. The 2015 Paris Agreement established a collective commitment among nations to restrict global warming to "well under 2 °C". Nevertheless, current pledges submitted under this Agreement indicate that global warming is still likely to approach approximately 2.8 °C (5.0 °F) by the close of the century.
Global consensus supports climate action, with the majority of nations committed to ceasing carbon dioxide emissions. The transition away from fossil fuels can be achieved by eliminating subsidies, implementing energy conservation measures, and adopting energy sources that do not generate substantial carbon pollution. Such alternative energy sources encompass wind, solar, hydroelectric, and nuclear power. Sustainably generated electricity offers a viable substitute for fossil fuels in powering transportation, heating infrastructure, and facilitating industrial operations. Atmospheric carbon can also be sequestered, for example, through reforestation initiatives and agricultural practices that enhance soil carbon storage.
Terminology
Prior to the 1980s, scientific understanding was uncertain regarding whether the warming influence of elevated greenhouse gas concentrations outweighed the cooling effect of atmospheric particulates from air pollution. During this period, scientists employed the phrase inadvertent climate modification to denote anthropogenic influences on the climate. By the 1980s, the terms global warming and climate change gained prominence, frequently being used synonymously. From a scientific perspective, global warming specifically denotes an increase in the global average surface temperature, whereas climate change encompasses both global warming and its broader impacts on Earth's climate system, including alterations in precipitation patterns.
The term climate change can also be interpreted more expansively to incorporate historical climatic shifts that have occurred throughout Earth's geological past due to natural phenomena. Occasionally, the designation anthropogenic climate change is utilized to specify climatic alterations originating from human endeavors.
Global warming, a term first employed as early as 1975, gained widespread recognition after NASA climate scientist James Hansen utilized it during his 1988 testimony before the U.S. Senate. Since the 2000s, the usage of climate change has become increasingly prevalent. Various scientists, politicians, and media outlets may alternatively employ the terms climate crisis or climate emergency to refer to climate change, and may substitute global heating for global warming.
Global Temperature Increase
Historical Temperatures Preceding Contemporary Global Warming
Over the past several million years, Earth's climate has undergone cyclical transitions, characterized by alternating ice ages. One notable warmer interval was the Last Interglacial period, approximately 125,000 years ago, during which temperatures were between 0.5 °C and 1.5 °C higher than the pre-industrial baseline. This period also saw sea levels elevated by 5 to 10 meters compared to current levels. Conversely, the most recent glacial maximum, occurring 20,000 years ago, was approximately 5–7 °C colder, with sea levels more than 125 meters (410 ft) lower than today.
Temperatures stabilized during the current interglacial period, which commenced 11,700 years ago, a time that also marked the emergence of agriculture. Historical patterns of warming and cooling, such as the Medieval Warm Period and the Little Ice Age, did not manifest synchronously across all regions. In a limited number of areas, temperatures during these periods might have reached levels comparable to those of the late 20th century. Climatic information for these epochs is derived from proxy records, including tree rings and ice cores.
Warming Trends Since the Industrial Revolution
Around 1850, thermometer records began to provide comprehensive global coverage. Between the 18th century and 1970, there was minimal net warming, as the warming effect of greenhouse gas emissions was largely counterbalanced by the cooling impact of sulfur dioxide emissions. While sulfur dioxide contributes to acid rain, it also generates sulfate aerosols in the atmosphere, which reflect solar radiation and induce global dimming. After 1970, the escalating accumulation of greenhouse gases and the implementation of controls on sulfur pollution led to a pronounced increase in global temperatures.
The ongoing climatic changes are unprecedented over several millennia. Multiple independent datasets consistently indicate a worldwide increase in surface temperature, progressing at an approximate rate of 0.2 °C per decade. The decade spanning 2014–2023 experienced an average warming of 1.19 °C [1.06–1.30 °C] compared to the pre-industrial baseline (1850–1900). It is important to note that not every single year registers warmer than the preceding one, as internal climate variability processes can cause any given year to be approximately 0.2 °C warmer or colder than the average. From 1998 to 2013, negative phases of two such processes, the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO), contributed to a temporary deceleration in warming, termed the "global warming hiatus." Following this "hiatus," the opposite trend emerged, with 2024 registering temperatures well above the recent average, exceeding +1.5 °C. Consequently, temperature change is typically defined using a 20-year average, which effectively reduces the influence of short-term fluctuations from individual hot or cold years and decadal climate patterns, thereby revealing the long-term warming signal.
A diverse array of additional observations reinforces the evidence of global warming. The upper atmosphere is experiencing cooling because greenhouse gases are trapping heat closer to Earth's surface, thereby reducing the amount of thermal energy radiating into space. Warming also leads to a reduction in average snow cover and compels the retreat of glaciers. Concurrently, elevated temperatures intensify oceanic evaporation, resulting in increased atmospheric humidity and a greater frequency of more intense precipitation events. Ecologically, plants are flowering earlier in spring, and thousands of animal species have permanently shifted to cooler geographical areas.
Regional Disparities in Warming
Different regions of the world are experiencing warming at varying rates. This spatial pattern is independent of the specific locations where greenhouse gases are emitted, as these gases persist sufficiently long to diffuse across the entire planet. Since the pre-industrial period, the average surface temperature over terrestrial regions has increased almost twice as rapidly as the global average surface temperature. This disparity is primarily due to oceans losing more heat through evaporation and their substantial capacity for heat storage. The total thermal energy within the global climate system has steadily grown, with only brief interruptions, since at least 1970, and over 90% of this additional energy has been absorbed by the ocean. The remaining energy has contributed to atmospheric heating, ice melt, and the warming of continental landmasses.
The Northern Hemisphere and the North Pole have experienced significantly more rapid warming than the Southern Hemisphere and the South Pole. The Northern Hemisphere possesses a greater landmass, alongside more extensive seasonal snow cover and sea ice. As these surfaces transition from highly reflective to absorptive upon ice melt, they enhance heat absorption. Local deposits of black carbon on snow and ice also contribute to Arctic warming. Arctic surface temperatures are increasing three to four times more rapidly than the global average. The melting of polar ice sheets attenuates both the Atlantic and Antarctic components of thermohaline circulation, thereby altering global heat and precipitation patterns.
Future Global Temperature Projections
The World Meteorological Organization projects a nearly 50% probability that the five-year average global temperature will surpass a +1.5 °C threshold between 2024 and 2028. The IPCC anticipates the 20-year mean to exceed +1.5 °C in the early 2030s.
The IPCC Sixth Assessment Report (2021) projected that by 2100, global warming is highly probable to attain 1.0–1.8 °C under a very low greenhouse gas emissions scenario, 2.1–3.5 °C under an intermediate emissions scenario, or 3.3–5.7 °C under a very high emissions scenario. This warming trend is anticipated to persist beyond 2100 in the intermediate and high emission scenarios, with future projections of global surface temperatures by year 2300 reaching levels comparable to those observed millions of years in the past.
The remaining carbon budget for limiting specific temperature rises is quantified through modeling the carbon cycle and climate sensitivity to greenhouse gases. According to UNEP, global warming could be constrained below 2.0 °C with a 50% probability, provided that post-2023 emissions do not surpass 900 gigatonnes of CO2. This carbon budget is equivalent to approximately 16 years of current emission rates.
Drivers of Recent Global Temperature Increase
The climate system exhibits intrinsic cycles spanning years, decades, or even centuries. For example, El Niño events induce transient increases in surface temperature, whereas La Niña events lead to temporary cooling. The differential occurrence of these phenomena can influence decadal global temperature trajectories. Additional alterations stem from energetic imbalances originating from external forcings. Such forcings encompass shifts in greenhouse gas concentrations, solar luminosity, volcanic activity, and orbital variations of the Earth.
Ascertaining anthropogenic contributions to climate change involves developing distinct "fingerprints" for all plausible causal factors and comparing them against observed patterns and established internal climate variability. For instance, solar forcing—characterized by a uniform atmospheric warming signature—is discounted given that warming has been confined primarily to the lower atmosphere. Atmospheric aerosols exert a comparatively minor cooling influence. Other drivers, such as changes in albedo, demonstrate reduced significance.
Greenhouse Gases
Greenhouse gases are transmissive to solar radiation, thereby enabling its passage through the atmosphere to warm the Earth's surface. Subsequently, the Earth emits this energy as thermal radiation, a fraction of which is absorbed by greenhouse gases. This absorptive process impedes the egress of heat into space, consequently retaining thermal energy near the Earth's surface and leading to its gradual warming.
While water vapor (≈50%) and clouds (≈25%) are the primary contributors to the natural greenhouse effect, they fluctuate predominantly as a function of temperature, thus largely categorized as feedbacks that modify climate sensitivity. Conversely, concentrations of gases such as CO2 (≈20%), tropospheric ozone, CFCs, and nitrous oxide are introduced or depleted irrespective of temperature variations, and are consequently classified as external forcings that influence global temperatures.
Before the Industrial Revolution, endogenous concentrations of greenhouse gases maintained surface air temperatures approximately 33 °C higher than they would have been without their presence. Post-Industrial Revolution anthropogenic activities, primarily involving the extraction and combustion of fossil fuels (coal, oil, and natural gas), have augmented atmospheric greenhouse gas concentrations. By 2022, concentrations of CO2 and methane had risen by approximately 50% and 164%, respectively, relative to 1750 levels. Current CO2 concentrations surpass any recorded levels over the past 14 million years. Methane concentrations are significantly elevated compared to any point in the last 800,000 years.
In 2019, anthropogenic greenhouse gas emissions globally reached an equivalent of 59 billion tonnes of CO2. Carbon dioxide (CO2) constituted 75% of these emissions, followed by methane at 18%, nitrous oxide at 4%, and fluorinated gases at 2%. The combustion of fossil fuels for energy generation in sectors such as transportation, manufacturing, heating, and electricity production represents the primary source of CO§45§ emissions. Further CO§67§ emissions originate from deforestation and various industrial activities, encompassing the CO§89§ liberated through chemical reactions involved in the production of cement, steel, aluminum, and fertilizers. Sources of methane emissions include livestock, manure management, rice cultivation, landfills, wastewater treatment, coal mining, and the extraction of oil and natural gas. Nitrous oxide emissions are predominantly generated by the microbial decomposition of fertilizers.
Methane persists in the atmosphere for an average duration of 12 years, whereas CO2 exhibits a significantly longer atmospheric residence time. Earth's surface assimilates CO2 as an integral component of the global carbon cycle. Although terrestrial and oceanic flora annually absorb the majority of surplus CO§45§ emissions, this CO§67§ is subsequently released back into the atmosphere through the processes of biological digestion, combustion, or decomposition. Terrestrial carbon sequestration mechanisms, including soil carbon fixation and photosynthesis, account for the removal of approximately 29% of annual global CO§89§ emissions. Over the past two decades, oceanic systems have absorbed between 20% and 30% of anthropogenic CO§1011§ emissions. Long-term atmospheric removal of CO§1213§ occurs exclusively when it is sequestered within the Earth's crust, a geological process spanning millions of years.
Alterations in Land Surface
Approximately 30% of Earth's terrestrial surface is largely unsuitable for human habitation (e.g., glaciers, deserts), while forests constitute 26%, shrublands 10%, and agricultural land 34%. Deforestation represents the primary land-use change contributing to global warming, given that the removal of trees releases CO2 and eliminates a vital carbon sink when not offset by reforestation. From 2001 to 2018, permanent land clearing for agricultural expansion, supporting crop and livestock production, accounted for 27% of deforestation. An additional 24% of forest loss resulted from temporary clearing associated with shifting cultivation agricultural practices. Logging for timber and related products contributed to 26% of deforestation, with wildfires responsible for the remaining 23%. Certain forest areas, though not entirely cleared, have experienced significant degradation due to these anthropogenic and natural disturbances. The restoration of such forests consequently reinstates their capacity to function as carbon sinks.
Local vegetation cover significantly influences surface albedo, determining the proportion of solar radiation reflected back into space, as well as the rate of heat loss through evapotranspiration. For example, the conversion of dark forest to grassland results in a lighter surface, thereby increasing solar reflectivity. Furthermore, deforestation can alter the emission of chemical compounds that affect cloud formation and modify regional wind patterns. In tropical and temperate regions, the cumulative impact of deforestation leads to substantial warming, whereas forest restoration can mitigate local temperatures. Conversely, at higher latitudes nearer the poles, the replacement of forests with snow-covered, more reflective plains induces a localized cooling effect. Globally, the observed increases in surface albedo have constituted the primary direct climatic influence stemming from land use alterations. Consequently, the overall impact of land use change to date is estimated to exert a minor cooling effect.
Additional Contributing Factors
Atmospheric Aerosols and Cloud Dynamics
Atmospheric pollution, specifically in the form of aerosols, exerts a significant influence on global climate patterns. Aerosols interact with solar radiation by both scattering and absorbing it. A progressive decrease in solar radiation reaching Earth's surface was documented between 1961 and 1990. This phenomenon, commonly referred to as global dimming, is predominantly ascribed to sulfate aerosols generated from the combustion of high-sulfur fossil fuels, such as coal and bunker fuel. Minor contributions also arise from black carbon, originating from the combustion of fossil fuels and biomass, as well as from atmospheric dust. Worldwide, aerosol concentrations have decreased since 1990, largely owing to pollution control measures, thereby reducing their masking effect on greenhouse gas-induced warming.
Aerosols additionally exert indirect influences on Earth's radiative energy balance. Sulfate aerosols function as cloud condensation nuclei, promoting the formation of clouds characterized by a greater number of smaller droplets. Such clouds exhibit enhanced efficiency in reflecting solar radiation compared to those composed of fewer, larger droplets. Furthermore, they impede the growth of raindrops, consequently increasing the reflectivity of clouds to incident solar radiation. The indirect effects of aerosols represent the most substantial source of uncertainty in calculations of radiative forcing.
Although aerosols generally mitigate global warming by reflecting solar radiation, black carbon, when deposited as soot on snow or ice, can exacerbate global warming. This phenomenon not only enhances the absorption of solar energy but also accelerates ice melt and contributes to sea-level rise. Mitigating new black carbon accumulation in the Arctic region has the potential to decrease global warming by 0.2 °C by the year 2050. Conversely, the reduction in sulfur content in marine fuel oil since 2020 is projected to result in an additional 0.05 °C increase in the global mean temperature by 2050.
Solar and Volcanic Activity
Given that the Sun constitutes Earth's principal energy source, variations in incident solar radiation directly influence the climate system. Direct satellite measurements of solar irradiance are available, complemented by indirect estimations extending back to the early 17th century. However, since 1880, no discernible upward trend has been observed in the solar energy reaching Earth, a finding that contrasts with the observed warming of the lower atmosphere, specifically the troposphere. Furthermore, if increased solar energy were responsible for global warming, the upper atmosphere (stratosphere) would also exhibit warming; instead, it has demonstrated a cooling trend. This observation aligns with the hypothesis that greenhouse gases are impeding the escape of heat from Earth's atmosphere.
Explosive volcanic eruptions can either release gases, dust, and ash that partially obstruct solar radiation, leading to temperature reductions, or they can inject water vapor into the atmosphere, thereby augmenting greenhouse gas concentrations and elevating temperatures. Such temperature impacts are typically transient, persisting for only a few years, due to the limited atmospheric residence time of both water vapor and other volcanic ejecta. While volcanic CO2 emissions exhibit greater persistence, their magnitude is less than 1% of contemporary anthropogenic CO2 emissions. Nonetheless, volcanic activity remains the most significant natural forcing influencing temperature during the industrial epoch. However, similar to other natural forcings, its overall influence on global temperature trends since the Industrial Revolution has been negligible.
Climate Change Feedbacks
The climate system's reaction to an initial forcing is modulated by feedback mechanisms, which either intensify or mitigate the resultant change. Specifically, self-reinforcing or positive feedbacks augment the response, whereas balancing or negative feedbacks diminish it. Key reinforcing feedbacks include the water-vapor feedback, the ice-albedo feedback, and the net cloud feedback. The principal balancing mechanism is radiative cooling, wherein Earth's surface emits increased heat into space in response to elevated temperatures. Beyond temperature-related feedbacks, the carbon cycle also exhibits feedback loops, exemplified by the fertilizing impact of CO§89§ on plant biomass production. As greenhouse gas emissions persist, feedbacks are projected to increasingly trend towards a positive direction, thereby enhancing climate sensitivity.
These aforementioned feedback processes significantly modify the rate of global warming. For example, warmer atmospheric conditions enable the retention of greater moisture as water vapor, which itself functions as a potent greenhouse gas. Elevated air temperatures can also lead to higher and thinner clouds, which possess increased insulating properties, consequently intensifying climate warming. A further significant feedback mechanism involves the diminution of snow cover and sea ice in the Arctic, which decreases the regional surface reflectivity of Earth and accelerates Arctic warming. This amplified warming further contributes to permafrost degradation, resulting in the atmospheric release of methane and CO2.
Approximately half of anthropogenic CO2 emissions have been sequestered by terrestrial vegetation and oceanic systems. This absorption fraction is dynamic; should future CO2 emissions decline, Earth's capacity to absorb carbon could increase to approximately 70%. Conversely, if emissions rise significantly, while the absolute amount of absorbed carbon may still increase, the overall fraction absorbed will diminish to below 40%. This reduction in fractional absorption is attributable to climate change-induced increases in droughts and heat waves, which ultimately impede terrestrial plant growth, and to warmer soils releasing more carbon from decaying organic matter. Furthermore, the oceanic absorption rate of atmospheric carbon will decrease as oceans become more acidic and undergo alterations in thermohaline circulation and phytoplankton distribution. The primary reason for discrepancies in projected warming magnitudes across various climate models for a given emission scenario stems from uncertainties surrounding feedback mechanisms, particularly those related to cloud cover.
Modelling
Climate models represent the complex physical, chemical, and biological processes that influence the Earth's climate system. These models integrate natural phenomena, including variations in Earth's orbit, historical solar activity changes, and volcanic forcing. They are employed to estimate the projected warming from future emissions, accounting for the strength of climate feedbacks. Additionally, these models forecast oceanic circulation, the annual seasonal cycle, and the carbon flux between the land surface and the atmosphere.
The physical realism of climate models is evaluated by their capacity to simulate current or past climates. Historically, models have underestimated the rate of Arctic shrinkage and the increase in precipitation. While older models underestimated sea level rise since 1990, more recent models align well with observations. The 2017 United States National Climate Assessment highlights that "climate models may still be underestimating or missing relevant feedback processes." Furthermore, climate models may struggle to adequately predict short-term regional climatic shifts.
A subset of climate models incorporates societal factors into physical climate models. These integrated models simulate how population dynamics, economic growth, and energy consumption influence and interact with the physical climate. Leveraging this information, these models generate scenarios for future greenhouse gas emissions. These scenarios then serve as inputs for physical climate models and carbon cycle models to project potential changes in atmospheric greenhouse gas concentrations. Depending on the socioeconomic and mitigation scenarios, models predict atmospheric CO2 concentrations that vary widely, ranging from 380 to 1400 ppm.
Impacts
Environmental effects
The environmental effects of climate change are extensive and far-reaching, impacting oceans, ice, and weather patterns. These changes can manifest gradually or rapidly. Evidence for these effects is drawn from paleoclimatology, climate modeling, and contemporary observations. Since the 1950s, droughts and heat waves have occurred with increasing frequency and simultaneity. Extreme wet or dry events during the monsoon period have intensified in India and East Asia. Monsoonal precipitation across the Northern Hemisphere has increased since 1980. The rainfall rate and intensity of hurricanes and typhoons are likely increasing, and their geographic range is probably expanding poleward in response to climate warming. Conversely, the frequency of tropical cyclones has not increased as a direct result of climate change.
Global sea level is rising due to thermal expansion and the melting of glaciers and ice sheets. The rate of sea level rise has accelerated over time, reaching 4.8 cm per decade between 2014 and 2023. For the 21st century, the IPCC projects a sea level rise of 32–62 cm under a low emission scenario, 44–76 cm under an intermediate scenario, and 65–101 cm under a very high emission scenario. Marine ice sheet instability processes in Antarctica could substantially increase these values, including the possibility of a 2-meter sea level rise by 2100 under high emissions.
Climate change has resulted in decades of shrinking and thinning Arctic sea ice. While ice-free summers are projected to be rare at 1.5 °C of warming, they are expected to occur every three to ten years at a 2 °C warming level. Elevated atmospheric CO2 concentrations lead to increased dissolution of CO2 in the oceans, thereby enhancing ocean acidification. Furthermore, as oxygen is less soluble in warmer water, its concentrations in the ocean are decreasing, contributing to the expansion of marine dead zones.
Tipping points and long-term impacts
Higher levels of global warming elevate the probability of exceeding "tipping points," which are critical thresholds where significant impacts become unavoidable, even if temperatures subsequently revert to prior levels. For example, the Greenland ice sheet is currently undergoing melting; however, if global warming attains temperatures between 1.7 °C and 2.3 °C, its disintegration will persist until complete disappearance. Even if warming is subsequently mitigated to 1.5 °C or below, the ice sheet would still experience substantially greater ice loss compared to a scenario where the threshold was never reached. While the melting of ice sheets typically spans millennia, other tipping points could manifest more rapidly, affording societies less time for adaptation. The disintegration of major ocean currents, such as the Atlantic Meridional Overturning Circulation (AMOC), and irreparable harm to vital ecosystems, including the Amazon rainforest and coral reefs, could materialize within decades. A collapse of the AMOC, for instance, would constitute a severe climatic catastrophe, leading to a cooling effect in the Northern Hemisphere.
The protracted consequences of climate change for oceanic systems encompass continued ice melt, thermal expansion, elevated sea levels, acidification, and deoxygenation. These long-term impacts are projected to unfold over centuries to millennia, primarily attributable to the extended atmospheric residence time of CO2. Consequently, an estimated total sea level rise of 2.3 meters per degree Celsius (4.2 ft/°F) is anticipated over a 2000-year period. The gradual absorption of CO2 by oceans implies that ocean acidification will also persist for hundreds to thousands of years. Furthermore, deep ocean regions (exceeding 2,000 meters (6,600 ft) in depth) are already predisposed to a reduction of over 10% in dissolved oxygen due to historical warming. The West Antarctic ice sheet, moreover, appears committed to a virtually irreversible melting process, which would contribute to a sea level increase of at least 3.3 m (10 ft 10 in) over approximately 2000 years.
Nature and Wildlife
Contemporary warming trends have compelled numerous terrestrial and freshwater species to migrate towards higher latitudes and altitudes. For example, the geographical distribution of hundreds of North American avian species has shifted northward at an average velocity of 1.5 km/year over the preceding 55 years. Elevated atmospheric CO2 concentrations and an extended growing season have contributed to a phenomenon of global greening. Conversely, episodes of heatwaves and drought have diminished ecosystem productivity in certain areas. The eventual equilibrium between these contrasting effects remains indeterminate. A concomitant phenomenon instigated by climate change is the encroachment of woody plants, impacting an estimated 500 million hectares worldwide. Climate change has also facilitated the expansion of arid climatic zones, exemplified by desertification in subtropical regions. The magnitude and rapidity of global warming are increasing the likelihood of sudden ecological transformations. Consequently, climate change is projected to precipitate the extinction of numerous species.
While oceanic warming has progressed at a slower rate than terrestrial warming, marine flora and fauna have exhibited a more rapid poleward migration towards colder regions compared to their terrestrial counterparts. Analogous to terrestrial environments, marine heatwaves are occurring with increased frequency due to climate change, adversely affecting a diverse array of organisms, including corals, kelp, and seabirds. Ocean acidification impedes the ability of marine calcifying organisms, such as mussels, barnacles, and corals, to form shells and skeletons, while heatwaves have induced coral bleaching. Furthermore, harmful algal blooms, exacerbated by climate change and eutrophication, lead to reduced oxygen levels, disrupt marine food webs, and result in substantial losses of marine biodiversity. Coastal ecosystems are experiencing pronounced stress, with nearly half of global wetlands having vanished due to climate change and other anthropogenic influences. Terrestrial plants are also experiencing heightened stress from insect-induced damage.
Human Populations
The ramifications of climate change are universally affecting human populations across the globe. Observable impacts span all continents and oceanic regions, with low-latitude, less developed areas confronting the most substantial risks. Persistent warming portends potentially "severe, pervasive, and irreversible impacts" for both human societies and natural ecosystems. While these risks are heterogeneously distributed, they disproportionately affect disadvantaged populations in both developing and developed nations.
Health and Food Security
The World Health Organization identifies climate change as a paramount threat to global health in the twenty-first century. Scientific consensus highlights the irreversible detrimental impacts associated with it. Public health, along with food and water security, is compromised by extreme weather phenomena. Elevated temperatures contribute to heightened morbidity and mortality rates. The intensity and recurrence of extreme weather events are exacerbated by climate change. Furthermore, it can influence the transmission dynamics of infectious diseases, including dengue fever and malaria. Projections from the World Economic Forum indicate an additional 14.5 million fatalities attributable to climate change by 2050. Currently, 30% of the global populace resides in regions where excessive heat and humidity are already correlated with elevated mortality. By 2100, this proportion is projected to increase to between 50% and 75% of the world's population.
Despite a half-century of agricultural advancements leading to overall increases in crop yields, climate change has already attenuated the rate of this growth. Fisheries across numerous regions have experienced adverse impacts. Although agricultural productivity has seen positive effects in certain high-latitude zones, mid- and low-latitude areas have suffered negative consequences. The World Economic Forum forecasts that an escalation of drought conditions in specific regions could result in 3.2 million malnutrition-related deaths and childhood stunting by 2050. A 2 °C increase in global temperature is predicted to reduce global livestock populations by 7–10% by 2050, primarily due to diminished availability of animal feed. Should emissions persist in increasing throughout the remainder of the century, annual climate-related fatalities could exceed 9 million by 2100.
Economic Implications, Livelihoods, and Disparity
Climate change is anticipated to inflict substantial economic damages, potentially leading to catastrophic outcomes. Particularly severe impacts are projected for Southeast Asia and sub-Saharan Africa, regions where a majority of the populace relies on natural and agricultural resources for sustenance. Heat stress can impede the capacity of outdoor laborers to perform their duties. A 4 °C rise in global temperature could diminish labor capacity in these regions by 30% to 50%. The World Bank estimates that, absent adequate adaptation measures, climate change could push more than 120 million individuals into extreme poverty between 2016 and 2030.
Climate change poses a significant threat to the sports economy, manifesting through disrupted seasons, damaged infrastructure, and diminished fan engagement, with football, winter sports, and outdoor events facing the most immediate risks.
Climate change has exacerbated existing disparities rooted in wealth and social standing. Marginalized populations, possessing limited control over resources, encounter substantial challenges in mitigating, adapting to, and recovering from climate-induced shocks. Indigenous communities, whose livelihoods are intrinsically linked to their land and ecosystems, face threats to their well-being and traditional lifestyles from climate change. An expert assessment determined that climate change's contribution to armed conflict has been minor when contrasted with factors such as socioeconomic inequality and state capacity.
Although women are not intrinsically more vulnerable to climate change and its shocks, their adaptive capacity and resilience are constrained by limitations on resources and discriminatory gender norms. For instance, during climate shocks like heat stress, women's work burdens, particularly hours dedicated to agriculture, tend to decrease less significantly than those of men.
Climate-Induced Migration
Low-lying islands and coastal communities face threats from rising sea levels, which intensify the frequency of urban flooding. In certain instances, land is permanently submerged by the sea. Such occurrences could result in statelessness for populations residing in island nations like the Maldives and Tuvalu. In specific regions, escalating temperatures and humidity levels may become too extreme for human adaptation. Under worst-case climate change scenarios, models project that regions currently inhabited by nearly one-third of the global population could transform into uninhabitable, extremely hot climates akin to the Sahara.
These converging factors can instigate climate or environmental migration, both internally within nations and across international borders. A greater number of individuals are anticipated to be displaced due to sea level rise, extreme weather events, and conflicts arising from intensified competition for natural resources. Furthermore, climate change can heighten vulnerability, creating "trapped populations" unable to relocate due to insufficient resources.
Emission Reduction and Sequestration
Mitigation of climate change involves both decreasing the atmospheric emission rate of greenhouse gases and accelerating the removal of carbon dioxide from the atmosphere. Achieving a global warming limit below 2 °C necessitates reaching net-zero global greenhouse gas emissions by 2070. This objective mandates extensive, systemic transformations across the energy sector, land use, urban environments, transportation, infrastructure, and industrial operations, on an unparalleled scale.
According to estimates from the United Nations Environment Programme, nations must triple their commitments under the Paris Agreement within the coming decade to restrict global warming to 2 °C. Based on current pledges made under the Paris Agreement as of 2024, there is a 66% probability that global warming will remain below 2.8 °C by the century's end, with projections ranging from 1.9–3.7 °C, contingent upon precise implementation and technological advancements. Solely considering existing policies, this projected warming increases to 3.1 °C. From a global perspective, constraining warming to 2 °C could yield greater economic advantages than associated costs.
While no singular trajectory exists for limiting global warming to 2 °C, the majority of projected scenarios and strategic frameworks emphasize a substantial expansion in renewable energy deployment, coupled with enhanced energy efficiency initiatives, to achieve requisite greenhouse gas reductions. Furthermore, to alleviate ecological pressures and augment carbon sequestration capacities, modifications within agricultural and forestry practices are imperative, including the prevention of deforestation and the restoration of natural ecosystems through reforestation efforts.
Alternative climate change mitigation strategies present elevated risk profiles. Projections for limiting global warming to 1.5 °C generally anticipate extensive implementation of carbon dioxide removal technologies throughout the 21st century. Nevertheless, significant concerns persist regarding potential over-reliance on these methods and their associated environmental consequences.
Solar radiation modification (SRM) represents a proposed method for attenuating global warming by redirecting a portion of solar radiation away from Earth and into space. As SRM does not diminish greenhouse gas concentrations, it would not ameliorate ocean acidification and is therefore not classified as a mitigation strategy. SRM ought to be regarded solely as a complementary measure to mitigation, rather than a substitute, given inherent risks such as abrupt warming if its application were to cease unexpectedly. Stratospheric aerosol injection constitutes the most extensively researched SRM technique. While SRM could partially mitigate global warming and some of its effects, it carries environmental hazards, including alterations to precipitation patterns, alongside complex political dilemmas concerning its governance and implementation.
Clean Energy
Renewable energy sources are pivotal for constraining climate change. Historically, fossil fuels have constituted approximately 80% of global energy consumption for several decades. The residual proportion has been divided between nuclear power and various renewable sources, encompassing hydropower, bioenergy, wind, solar, and geothermal energy. Absolute fossil fuel consumption is projected to reach its zenith before 2030, subsequently entering a decline, with coal utilization anticipated to undergo the most significant reductions. In 2023, renewables comprised 86% of all newly installed electricity generation capacity. While other clean energy modalities, such as nuclear and hydropower, currently contribute a larger segment to the overall energy supply, their projected future expansion appears comparatively constrained.
Although solar photovoltaic arrays and onshore wind turbines now represent some of the most cost-effective options for deploying new power generation capacity across numerous regions, robust green energy policies are indispensable for facilitating a swift transition from fossil fuels to renewables. Attaining carbon neutrality by 2050 would necessitate renewable energy becoming the predominant source of electricity generation, potentially reaching 85% or higher by 2050 in certain projections. Concurrently, investment in coal would cease, and coal consumption would be almost entirely phased out by 2050.
Furthermore, electricity derived from renewable sources must evolve into the primary energy input for both heating and transportation sectors. The transport sector can transition from internal combustion engine vehicles to electric vehicles, public transportation systems, and active modes of transport, such as cycling and walking. For maritime shipping and aviation, the adoption of low-carbon fuels would significantly mitigate emissions. Heating systems could undergo progressive decarbonization through technologies like heat pumps.
The sustained rapid expansion of clean energy, including renewables, faces several impediments. Wind and solar power generation is characterized by intermittency and seasonal variability. Historically, hydroelectric dams with reservoirs and fossil fuel power plants have compensated for periods of low variable energy production. Future strategies involve expanding battery storage, optimizing energy demand-supply matching, and utilizing long-distance transmission to mitigate renewable output variability. Bioenergy frequently lacks carbon neutrality and may pose adverse implications for food security. The proliferation of nuclear power is constrained by controversies surrounding radioactive waste management, nuclear weapon proliferation risks, and accident concerns. Hydropower growth is limited by the saturation of optimal sites and the increasing social and environmental opposition encountered by new projects.
Low-carbon energy significantly enhances human health by mitigating climate change and reducing air pollution-related mortalities, which were estimated at 7 million annually in 2016. Achieving the Paris Agreement's objective of limiting warming to a 2 °C increase could avert approximately one million lives annually by 2050, whereas restricting global warming to 1.5 °C could save millions of lives while concurrently enhancing energy security and alleviating poverty. Improvements in air quality also yield economic advantages potentially surpassing mitigation expenditures.
Energy Conservation
Reducing energy demand constitutes a critical component in emission reduction strategies. Lower energy requirements provide greater latitude for the expansion of clean energy initiatives, facilitate electricity grid management, and curtail the development of carbon-intensive infrastructure. Substantial increases in energy efficiency investments are imperative to achieve climate goals, commensurate with the scale of investment in renewable energy sources. Various shifts in energy consumption patterns, efficiency investments, and financial allocations, attributable to the COVID-19 pandemic, have introduced considerable complexity and uncertainty into projections for the current decade.
Strategies to curtail energy demand are sector-specific. In the transport sector, a transition to more efficient transportation modalities, such as public transit and rail, or the adoption of electric vehicles, is feasible for both passenger and freight movement. Industrial approaches to reduce energy demand encompass enhancements to heating systems and motors, the development of less energy-intensive products, and the extension of product lifespans. Within the building sector, emphasis is placed on superior new construction design and elevated energy efficiency standards in retrofitting projects. Furthermore, the deployment of technologies such as heat pumps can augment building energy efficiency.
Agriculture and Industry
Agriculture and forestry are confronted by a tripartite challenge: mitigating greenhouse gas emissions, preventing further deforestation for agricultural expansion, and satisfying escalating global food demand. A comprehensive suite of interventions has the potential to reduce agriculture and forestry-derived emissions by two-thirds relative to 2010 levels. Such measures involve moderating the growth in demand for food and other agricultural commodities, enhancing land productivity, conserving and rehabilitating forest ecosystems, and diminishing greenhouse gas emissions stemming from agricultural practices.
On the demand side, a pivotal strategy for emission reduction involves transitioning populations towards plant-based dietary patterns. Cessation of livestock production for meat and dairy could eliminate approximately three-quarters of all emissions originating from agriculture and other land uses. Furthermore, livestock utilize 37% of the Earth's ice-free land surface and consume feed derived from 12% of land allocated to crops, thereby contributing to deforestation and land degradation.
Steel and cement production collectively account for approximately 13% of industrial CO2 emissions. In these industries, carbon-intensive feedstocks like coke and lime are integral to their production processes, necessitating research into alternative chemical pathways for CO2 emission reduction. In instances where energy generation or CO§45§-intensive heavy industries persistently generate waste CO§67§, technological solutions can occasionally be employed to capture and sequester the majority of the gas, rather than releasing it into the atmosphere. This technology, known as carbon capture and storage (CCS), may play a crucial yet circumscribed role in emission mitigation. Its implementation is comparatively costly, and its current deployment scale only sequesters approximately 0.1% of annual global greenhouse gas emissions.
Carbon Dioxide Removal
Natural carbon sinks possess the capacity to be augmented, enabling them to sequester substantially greater quantities of CO2 than their inherent capacities. Reforestation and afforestation, which involves establishing forests in previously unwooded areas, represent some of the most developed sequestration methodologies, although afforestation specifically introduces concerns regarding food security. Agricultural practitioners can foster carbon sequestration in soils by implementing strategies such as cultivating winter cover crops, minimizing the intensity and frequency of tillage, and incorporating compost and manure as soil amendments. The restoration of forests and landscapes offers numerous climatic advantages, including the sequestration and reduction of greenhouse gas emissions. Furthermore, the rehabilitation or creation of coastal wetlands, prairie ecosystems, and seagrass meadows enhances carbon uptake into organic matter. However, carbon sequestered within soils and organic matter, such as trees, carries an inherent risk of subsequent re-emission into the atmosphere due to shifts in land use, incidence of fire, or other ecological transformations.
Employing bioenergy alongside carbon capture and storage (BECCS) has the potential to achieve net negative emissions by extracting CO2 directly from the atmosphere. Nevertheless, significant uncertainty persists regarding the extent to which carbon dioxide removal techniques can substantially contribute to restricting global warming to 1.5 °C. Policy frameworks that heavily depend on carbon dioxide removal strategies inherently elevate the risk of global warming surpassing established international targets.
Adaptation
Adaptation is defined as "the process of adjustment to current or anticipated alterations in climate and their associated consequences." Absent further mitigation efforts, adaptation alone cannot prevent the occurrence of "severe, widespread, and irreversible" impacts. Escalating climate change necessitates more profound and transformative adaptation measures, which can incur prohibitive costs. The human capacity and potential for adaptation are not uniformly distributed across diverse regions and populations, with developing nations typically possessing fewer resources. While the initial two decades of the 21st century witnessed an enhancement in adaptive capacity within most low- and middle-income countries, marked by improved access to fundamental sanitation and electricity, the overall pace of progress remains sluggish. Numerous nations have enacted adaptation policies; however, a substantial disparity exists between the required and available financial resources.
Strategies for adapting to sea level rise encompass avoiding vulnerable regions, developing resilience to increased inundation, and constructing flood control infrastructure. Should these measures prove insufficient, managed retreat may become imperative. Significant economic impediments exist in addressing the detrimental impacts of extreme heat, as avoiding strenuous labor or accessing air conditioning is not universally feasible. Within the agricultural sector, adaptation alternatives include transitioning to more sustainable dietary practices, diversifying crops, implementing erosion control, and pursuing genetic enhancements to bolster tolerance to evolving climatic conditions. While insurance facilitates risk-sharing, it frequently remains inaccessible to individuals with lower incomes. Educational initiatives, migration strategies, and early warning systems can collectively diminish climate vulnerability. Furthermore, the cultivation of mangroves or the promotion of other coastal vegetation can provide natural buffers against storm events.
Ecosystems inherently adapt to climatic shifts, a process that can be augmented through human intervention. Enhancing connectivity between ecosystems facilitates species migration towards more propitious climatic conditions. Additionally, species can be deliberately introduced into regions that develop a favorable climate. The conservation and rehabilitation of natural and semi-natural environments contribute to building ecological resilience, thereby simplifying ecosystem adaptation. Numerous measures that foster adaptation within ecosystems simultaneously aid human adaptation through ecosystem-based approaches. For example, reinstating natural fire regimes diminishes the likelihood of catastrophic wildfires and mitigates human exposure to such events. Allocating greater space to rivers enables enhanced water storage within natural systems, consequently reducing flood risks. While restored forests function as carbon sinks, the establishment of trees in unsuitable geographical areas can inadvertently intensify climate impacts.
Both synergistic relationships and inherent trade-offs exist between adaptation and mitigation strategies. An illustrative synergy is enhanced food productivity, which confers substantial advantages for both adaptation to and mitigation of climate change. Conversely, an example of a trade-off is the augmented reliance on air conditioning, which enables individuals to better manage heat stress but concurrently escalates energy consumption. Another instance of a trade-off involves more compact urban planning, which can diminish emissions from transportation and construction, yet potentially intensify the urban heat island effect, thereby exposing populations to elevated heat-related health risks.
Policies and Politics
Countries most susceptible to climate change have historically contributed minimally to global emissions, thereby raising significant concerns regarding justice and equity. Mitigating global warming substantially facilitates the attainment of the United Nations' Sustainable Development Goals, including the eradication of poverty and the reduction of disparities. This interrelationship is formally acknowledged in Sustainable Development Goal 13, which mandates "urgent action to combat climate change and its impacts". Furthermore, objectives related to food security, access to clean water, and ecosystem preservation exhibit synergistic benefits with climate change mitigation efforts.
The geopolitical dimensions of climate change are intricate, frequently conceptualized as a free-rider dilemma wherein nations collectively benefit from the mitigation efforts of others, yet individual states perceive economic disadvantages in transitioning to a low-carbon economy independently. Nevertheless, mitigation strategies can also yield localized advantages; for example, the public health and environmental benefits derived from phasing out coal often surpass the associated costs across most regions. Moreover, countries that are net importers of fossil fuels stand to gain economically from adopting clean energy sources, while net exporters may encounter stranded assets, referring to fossil fuel reserves that become economically unviable.
Policy options
A diverse array of policies, regulatory frameworks, and legislative measures are currently employed to curtail emissions. By 2019, carbon pricing mechanisms encompassed approximately 20% of worldwide greenhouse gas emissions, implemented through carbon taxes and emissions trading systems. In 2017, direct global subsidies for fossil fuels amounted to 319 billion, escalating to 5.2 trillion when accounting for indirect costs such as air pollution. Eliminating these subsidies could result in a 28% decrease in global carbon emissions and a 46% reduction in fatalities attributable to air pollution. Funds conserved from fossil fuel subsidies could alternatively be reallocated to facilitate the transition towards clean energy. Additional direct approaches for mitigating greenhouse gases encompass vehicle efficiency standards, renewable fuel standards, and stringent air pollution regulations targeting heavy industry. Numerous nations mandate that utility providers augment the proportion of renewable sources in their electricity generation. An Open Coalition on Compliance Carbon Markets, established at COP30 (2025) with the objective of creating a global cap-and-trade system, is projected by some analyses to enhance emissions reductions seven-fold compared to existing policies. This initiative could also generate 200 billion annually for clean energy and social programs, potentially bridging the disparity between current emissions trajectories and the objectives of the Paris Agreement.
Climate justice
Policies formulated with a climate justice perspective aim to address concerns related to human rights and social inequality. Advocates of climate justice contend that the financial burden of climate adaptation should be borne by those primarily responsible for climate change, with the recipients of such funding being those most severely affected by its impacts. A practical application of this principle involves affluent nations providing financial assistance to less developed countries for adaptation measures.
Research by Oxfam in 2023 indicated that the wealthiest 10% of the global population accounted for 50% of worldwide emissions, whereas the poorest 50% were responsible for merely 8%. An alternative perspective on responsibility considers the production of emissions, suggesting that the leading 21 fossil fuel companies would collectively owe 5.4 trillion in climate reparations between 2025 and 2050. Achieving a just transition necessitates the provision of alternative employment opportunities for individuals currently employed in the fossil fuel industry, alongside strategic investments in their communities.
International climate agreements
The vast majority of nations globally are signatories to the 1994 United Nations Framework Convention on Climate Change (UNFCCC). The primary objective of the UNFCCC is to avert hazardous anthropogenic interference with the climate system. As articulated within the convention, this entails stabilizing atmospheric greenhouse gas concentrations at a level that permits natural ecosystem adaptation to climate change, safeguards food production, and supports sustainable economic development. The UNFCCC itself does not impose emission limitations but rather establishes a foundational framework for subsequent protocols that do. Despite its establishment, global emissions have increased since the UNFCCC's inception, with its annual conferences serving as crucial platforms for international negotiations.
The 1997 Kyoto Protocol expanded upon the UNFCCC framework, establishing legally binding obligations for most developed countries to limit their emissions. During negotiations, the G77, representing developing nations, advocated for a directive compelling developed countries to "[take] the lead" in reducing their emissions, given their primary responsibility for the atmospheric accumulation of greenhouse gases. Furthermore, per-capita emissions remained comparatively low in developing countries, necessitating increased emissions to fulfill their developmental requirements.
The 2009 Copenhagen Accord has been frequently characterized as a disappointment due to its modest objectives and was met with rejection from less affluent nations, including the G77 bloc. Participating entities sought to restrict the global temperature rise to below 2 °C. The accord established an objective to provide $100 billion annually to developing countries for climate change mitigation and adaptation efforts by 2020, and proposed the founding of the Green Climate Fund. By 2020, only $83.3 billion had been disbursed, with the full target anticipated to be met only by 2023.
In 2015, all United Nations member states negotiated the Paris Agreement, which seeks to maintain global warming significantly below 2.0 °C and includes an ambitious objective to limit warming to 1.5 °C. This agreement superseded the Kyoto Protocol. Unlike its predecessor, the Paris Agreement did not establish binding emission reduction targets; rather, a framework of procedural obligations was rendered mandatory. Nations are required to periodically establish increasingly ambitious objectives and reassess these targets quinquennially. The Paris Agreement reaffirmed the necessity of financial assistance for developing nations. As of March 2025, 194 states and the European Union have either acceded to or formally ratified the agreement.
The 1987 Montreal Protocol, an international agreement designed to phase out the production of ozone-depleting gases, has yielded significant benefits for climate change mitigation efforts. Numerous ozone-depleting substances, such as chlorofluorocarbons, are potent greenhouse gases; consequently, the prohibition of their production and consumption is estimated to have averted a temperature rise of 0.5 °C–1.0 °C, and mitigated further warming by safeguarding vegetation from ultraviolet radiation damage. The Protocol is estimated to have been more efficacious in curtailing greenhouse gas emissions than the Kyoto Protocol, which was specifically formulated for this purpose. The most recent amendment to the Montreal Protocol, the 2016 Kigali Amendment, mandated a reduction in hydrofluorocarbon emissions, these substances having been introduced as substitutes for prohibited ozone-depleting gases and also possessing significant greenhouse gas properties. Compliance with this amendment is projected to prevent a global temperature increase of 0.3 °C–0.5 °C.
National responses
In 2019, the United Kingdom parliament was the inaugural national legislature to declare a climate emergency. Subsequently, other nations and administrative regions adopted similar declarations. Concurrently, the European Parliament formally declared a "climate and environmental emergency." The European Commission unveiled its European Green Deal, aiming for the EU to achieve carbon neutrality by 2050. In 2021, the European Commission introduced its "Fit for 55" legislative package, which includes directives for the automotive sector, mandating that all new vehicles sold within the European market be zero-emission by 2035.
Prominent Asian nations have articulated comparable commitments: specifically, South Korea and Japan have pledged carbon neutrality by 2050, with China targeting this by 2060. Despite robust incentives for renewable energy, India concurrently intends a substantial increase in its domestic coal utilization. Vietnam stands out as one of the few rapidly developing, coal-reliant nations that has committed to eliminating unabated coal power by the 2040s or expeditiously thereafter.
By 2021, an analysis of 48 national climate plans, encompassing 40% of the Paris Agreement signatories, projected a mere 0.5% reduction in total greenhouse gas emissions relative to 2010 levels. This figure falls significantly short of the 45% or 25% reduction targets necessary to restrict global warming to 1.5 °C or 2 °C, respectively.
Society and culture
Denial and misinformation
Public discourse regarding climate change has been significantly influenced by climate change denial and misinformation, which originated in the United States and subsequently disseminated to other nations, notably Canada and Australia. This phenomenon stemmed from fossil fuel companies, industry associations, conservative think tanks, and contrarian scientists. Analogous to the tobacco industry's tactics, the primary strategy employed by these entities has involved cultivating skepticism concerning scientific data and findings related to climate change. Individuals exhibiting unsubstantiated skepticism about climate change are occasionally referred to as climate change "skeptics," although "contrarians" or "deniers" are considered more accurate designations.
Various manifestations of climate change denial exist: certain perspectives reject the occurrence of global warming entirely; others concede warming but ascribe it to natural climatic variability; while a third group downplays the adverse consequences of climate change. The deliberate creation of scientific uncertainty subsequently evolved into a fabricated controversy, fostering the perception of substantial scientific disagreement within the scientific community with the objective of impeding policy reforms. Tactics employed to advance these narratives encompass critiques of scientific organizations and impugning the motivations of individual researchers. A reinforcing media environment, comprising climate-denying blogs and outlets, has exacerbated public misapprehension of climate change.
Public Perception and Awareness
Climate change gained international public prominence in the late 1980s. Early 1990s media portrayals frequently led to public conflation of climate change with distinct environmental concerns, such as stratospheric ozone depletion. Within popular culture, the climate fiction film The Day After Tomorrow (2004) and Al Gore's documentary An Inconvenient Truth (2006) prominently addressed the subject of climate change.
Pronounced disparities are evident across regional, gender, age, and political demographics regarding both public apprehension and comprehension of climate change. Individuals with higher educational attainment, alongside women and younger demographics in specific nations, demonstrated a greater propensity to perceive climate change as a substantial menace. Analysis of college biology textbooks from the 2010s revealed a reduction in climate change content compared to the prior decade, accompanied by a diminished focus on mitigation strategies. Partisan divisions are also prevalent in numerous nations, with countries characterized by elevated CO2 emissions often exhibiting lower levels of concern. Perspectives on the anthropogenic and natural drivers of climate change diverge significantly across national contexts. Media reporting associated with climate protests has influenced public sentiment and shaped the specific facets of climate change that receive attention. Elevated levels of public concern correlate with enhanced public endorsement for climate change mitigation policies. Over time, public concern has intensified; by 2021, a majority of citizens in 30 nations articulated significant apprehension regarding climate change, or characterized it as a global emergency. A comprehensive 2024 survey encompassing 125 countries indicated that 89% of the global populace advocated for augmented political intervention, yet consistently underestimated the willingness of others to engage in such action.
Climate Activism
Climate change protests advocate for political leaders to implement measures aimed at mitigating global warming. These actions manifest as public demonstrations, campaigns for fossil fuel divestment, legal challenges, and various other forms of activism. Notable examples of such demonstrations include the School Strike for Climate movement. This global initiative, commencing in 2018, involves young individuals engaging in Friday school strikes, drawing inspiration from the Swedish activist, then-teenager Greta Thunberg. Groups such as Extinction Rebellion have employed mass civil disobedience tactics, including the disruption of roadways and public transportation systems, as a form of protest.
Litigation is progressively being utilized as a mechanism to compel enhanced climate action from both governmental bodies and corporate entities. Activists additionally file lawsuits against governments, seeking to mandate ambitious climate initiatives or the rigorous enforcement of extant environmental legislation. Legal actions directed at fossil fuel corporations typically aim to secure recompense for incurred losses and damages. On July 23, 2025, the International Court of Justice of the United Nations rendered an advisory opinion, unequivocally stating that nations are obligated to take measures to halt climate change, and that failure to fulfill this duty could expose them to legal action from other states. This imperative encompasses the fulfillment of commitments stipulated in international agreements to which they are signatories, exemplified by the 2015 Paris Climate Accord.
Historical Context
Foundational Discoveries
Nineteenth-century scientists, including Alexander von Humboldt, initiated the recognition of potential climate change impacts. During the 1820s, Joseph Fourier introduced the concept of the greenhouse effect, positing it as the reason for Earth's temperature exceeding what solar energy alone could account for. The Earth's atmosphere permits the passage of sunlight, allowing it to reach the surface where it undergoes conversion into thermal energy. Conversely, the atmosphere impedes the escape of heat radiated from the surface, retaining a portion of this energy and consequently warming the planet. In 1856, Eunice Newton Foote experimentally showed that the Sun's warming influence is more pronounced in air containing water vapor compared to dry air, and significantly amplified in the presence of carbon dioxide (CO2). Her publication, "Circumstances Affecting the Heat of the Sun's Rays," concluded that "an atmosphere of that gas would give to our earth a high temperature."
Commencing in 1859, John Tyndall demonstrated that nitrogen and oxygen, which collectively constitute 99% of dry air, exhibit transparency to radiated thermal energy. Conversely, water vapor and specific gases, including methane and carbon dioxide, absorb and subsequently re-emit radiated heat into the atmosphere. Tyndall hypothesized that fluctuations in the atmospheric concentrations of these gases could have been responsible for historical climatic shifts, such as ice ages.
Svante Arrhenius observed that atmospheric water vapor levels fluctuated continuously, whereas the concentration of CO2 was primarily governed by long-term geological phenomena. He theorized that elevated CO2 levels would induce warming, which in turn would augment atmospheric water vapor, thereby intensifying the warming through a positive feedback mechanism. In 1896, Arrhenius introduced a pioneering climate model, which projected that a 50% reduction in CO§45§ concentrations could have resulted in a temperature decrease sufficient to trigger an ice age. He estimated that a doubling of CO§67§ would lead to an approximate temperature increase of 5–6 °C. Initially, other scientists expressed skepticism, contending that the greenhouse effect was already saturated, implying that further increases in CO§89§ would be inconsequential, and that the climate system possessed inherent self-regulatory capabilities. From 1938 onwards, Guy Stewart Callendar presented empirical data indicating both global warming and rising CO§1011§ levels; however, his findings encountered similar scientific reservations.
The Emergence of Scientific Consensus
During the 1950s, Gilbert Plass developed a sophisticated computer model incorporating various atmospheric layers and the infrared spectrum. This model projected that elevated concentrations of CO2 would lead to global warming. Concurrently, Hans Suess discovered evidence of increasing CO2 levels, while Roger Revelle demonstrated that oceanic absorption would be insufficient to mitigate this rise. These two researchers subsequently assisted Charles Keeling in initiating the continuous measurement record known as the "Keeling Curve," which contributed to ongoing scientific inquiry throughout the 1960s concerning the potential anthropogenic causes of global warming. Subsequent investigations, including the National Research Council's 1979 Charney Report, corroborated the reliability of climate models predicting substantial warming. The anthropogenic origin of observed global warming and the hazards associated with unmitigated warming were publicly articulated in James Hansen's 1988 testimony before a United States Senate committee. Established in 1988 to offer authoritative guidance to global governments, the Intergovernmental Panel on Climate Change (IPCC) stimulated interdisciplinary research efforts. Within the framework of IPCC reports, scientists systematically evaluate the scientific discourse presented in peer-reviewed academic literature.
A near-unanimous scientific consensus affirms that the Earth's climate is undergoing warming, primarily attributable to human activities. No national or international scientific organization of repute dissents from this perspective. By 2019, the level of agreement within contemporary scientific literature surpassed 99%. The 2021 IPCC Assessment Report unequivocally declared that climate change is anthropogenically driven. Furthermore, a consensus has emerged regarding the imperative for action to safeguard populations from the adverse effects of climate change. National science academies have urged global leaders to implement reductions in worldwide emissions.
Contemporary Developments
Extreme event attribution (EEA), also referred to as attribution science, emerged during the initial decades of the 21st century. This scientific discipline employs climate models to ascertain and quantify the influence of anthropogenic climate change on the frequency, intensity, duration, and consequences of particular extreme weather phenomena. Findings from attribution research enable scientists and communicators to articulate conclusions such as, "this meteorological event was rendered at least n times more probable due to human-induced climate change," or "this heatwave was m degrees warmer than it would have been in a world devoid of global warming," or "this event would have been virtually impossible without climate change."
Enhanced computational capabilities in the 2000s, coupled with significant conceptual advancements between the early and mid-2010s, facilitated the ability of attribution science to identify the impacts of climate change on certain events with substantial certainty. Researchers utilize established, peer-reviewed attribution methodologies and climate simulations, which permits the dissemination of "rapid attribution studies" within a typical "news cycle" following meteorological occurrences.
References
Sources
This article integrates material from a freely available work, licensed under CC BY-SA 3.0. The text is derived from The status of women in agrifood systems – Overview, published by FAO.
IPCC reports
Other peer-reviewed sources
Books, reports and legal documents
Non-technical sources
- Intergovernmental Panel on Climate Change: IPCC (IPCC)
- Met Office: Climate Guide (Met Office)
- Royal Society. Climate change: Evidence and causes (Royal Society)