thumb|320 px|alt1=refer to caption|Global mean surface-temperature change from 1880 to 2016, relative to the 1951–1980 mean. The black line is the global annual mean, and the red line is the five-year local regression line. The blue uncertainty bars show a 95% confidence interval. Global warming, also referred to as climate change, is the observed century-scale rise in the average temperature of the Earth's climate system and its related effects. Multiple lines of scientific evidence show that the climate system is warming. Many of the observed changes since the 1950s are unprecedented in the instrumental temperature record which extends back to the mid-19th century, and in paleoclimate proxy records covering thousands of years. In 2013, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded that "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." The largest human influence has been the emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide. Climate model projections summarized in the report indicated that during the 21st century, the global surface temperature is likely to rise a further in the lowest emissions scenario, and in the highest emissions scenario. These findings have been recognized by the national science academies of the major industrialized nations and are not disputed by any scientific body of national or international standing. Future climate change and associated impacts will differ from region to region.Solomon et al., Technical Summary,
Section TS.5.3: Regional-Scale Projections, in . Anticipated effects include increasing global temperatures, rising sea levels, changing precipitation, and expansion of deserts in the subtropics. Warming is expected to be greater over land than over the oceans and greatest in the Arctic, with the continuing retreat of glaciers, permafrost and sea ice. Other likely changes include more frequent extreme weather events such as heat waves, droughts, heavy rainfall with floods and heavy snowfall;On snowfall:
ocean acidification; and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the abandonment of populated areas due to rising sea levels. Because the climate system has a large "inertia" and greenhouse gases will remain in the atmosphere for a long time, many of these effects will persist for not only decades or centuries, but for tens of thousands of years to come. Possible societal responses to global warming include mitigation by emissions reduction, adaptation to its effects, building systems resilient to its effects, and possible future climate engineering. Most countries are parties to the United Nations Framework Convention on Climate Change (UNFCCC),. Most countries in the world are Parties to the United Nations Framework Convention on Climate Change (UNFCCC), which has adopted the limit. As of 25 November 2011, there are 195 parties (194 states and 1 regional economic integration organization (the European Union)) to the UNFCCC. whose ultimate objective is to prevent dangerous anthropogenic climate change. Parties to the UNFCCC have agreed that deep cuts in emissions are required "(...) deep cuts in global greenhouse gas emissions are required according to science, and as documented in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, with a view to reducing global greenhouse gas emissions so as to hold the increase in global average temperature below above preindustrial levels" and that global warming should be limited to well below compared to pre-industrial levels, with efforts made to limit warming to . thumb|upright=1.35|alt=The global map shows sea temperature rises of 0.5 to 1 degree Celsius; land temperature rises of 1 to 2 degree Celsius; and Arctic temperature rises of up to 4 degrees Celsius.| Average surface air temperatures from 2011 to 2020 compared to the 1951–1980 average
thumb|upright=1.35|alt=The graph from 1880 to 2020 shows natural drivers exhibiting fluctuations of about 0.3 degrees Celsius. Human drivers steadily increase by 0.3 degrees over 100 years to 1980, then steeply by 0.8 degrees more over the past 40 years. |Observed global average temperature change since the pre-industrial era. The main driver for increased global temperatures in the industrial era is human activity. Natural forces add relatively minor variability. Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known events in Earth's history. The main cause is the emission of greenhouse gases, mostly carbon dioxide () and methane. Burning fossil fuels for energy use creates most of these emissions. Agriculture, steelmaking, cement production, and forest loss are additional sources. Temperature rise is also affected by climate feedbacks such as the loss of sunlight-reflecting snow cover, and the release of carbon dioxide from drought-stricken forests. Collectively, these amplify global warming. On land, temperatures have risen about twice as fast as the global average. Deserts are expanding, while heat waves and wildfires are becoming more common.; Increased warming in the Arctic has contributed to melting permafrost, glacial retreat and sea ice loss. Higher temperatures are also causing more intense storms and other weather extremes. In places such as coral reefs, mountains, and the Arctic, many species are forced to relocate or become extinct, as their environment changes. Climate change threatens people with food and water scarcity, increased flooding, extreme heat, more disease, and economic loss. It can also drive human migration.; . The World Health Organization calls climate change the greatest threat to global health in the 21st century.; : "Climate change is the greatest threat to global health in the 21st century. Health professionals have a duty of care to current and future generations. You are on the front line in protecting people from climate impacts – from more heat-waves and other extreme weather events; from outbreaks of infectious diseases such as malaria, dengue and cholera; from the effects of malnutrition; as well as treating people that are affected by cancer, respiratory, cardiovascular and other non-communicable diseases caused by environmental pollution." Even if efforts to minimise future warming are successful, some effects will continue for centuries. These include sea level rise, and warmer, more acidic oceans. Many of these impacts are already felt at the current level of warming, which is about 1.2 °C (2 °F). The Intergovernmental Panel on Climate Change (IPCC) projects even greater impacts as warming continues to 1.5 °C and beyond. Additional warming also increases the risk of triggering tipping points, such as the melting of the Greenland ice sheet. Responding to these changes involves taking actions to limit the amount of warming, and adapting to them. Future warming can be reduced (mitigated) by lowering greenhouse gas emissions and removing them from the atmosphere. This will involve using more wind and solar energy, phasing out coal, and increasing energy efficiency.; . Switching to electric vehicles, and to heat pumps for homes and commercial buildings, will further limit emissions.; Prevention of deforestation and enhancing forests can help absorb . Some communities may adapt to climate change through better coastline protection, disaster management, and development of more resistant crops. By themselves, these efforts to adapt cannot avert the risk of severe, widespread and permanent impacts. Under the 2015 Paris Agreement, nations collectively agreed to keep warming "well under 2 °C" through mitigation efforts. However, with pledges made under the Agreement, global warming would still reach about 2.7 °C by the end of the century. Limiting warming to 1.5 °C would require halving emissions by 2030 and achieving net-zero emissions by 2050.; ; ;
Terminology
thumb|border|upright=1.35|Climate change is driven by rising greenhouse gas levels in the atmosphere. This strengthens the greenhouse effect which traps heat in Earth's climate system. Before the 1980s, it was unclear whether warming by greenhouse gases would dominate aerosol-induced cooling. Scientists then often used the term inadvertent climate modification to refer to the human impact on the climate. In the 1980s, the terms global warming and climate change were popularised. The former refers only to increased surface warming, the latter describes the full effect of greenhouse gases on the climate.. Global warming became the most popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. In the 2000s, the term climate change increased in popularity.. Global warming usually refers to human-induced warming of the Earth system, whereas climate change can refer to natural or anthropogenic change.: "when scientists or public leaders talk about global warming these days, they almost always mean human-caused warming"; : "Climate change refers to a change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings such as modulations of the solar cycles, volcanic eruptions and persistent anthropogenic changes in the composition of the atmosphere or in land use." The two terms are often used interchangeably.; : "'Climate change' and 'global warming' are often used interchangeably but have distinct meanings. ... Global warming refers to the upward temperature trend across the entire Earth since the early 20th century ... Climate change refers to a broad range of global phenomena ...[which] include the increased temperature trends described by global warming."; : "The terms global warming and climate change can be used interchangeably. Climate change is more accurate scientifically to describe the various effects of greenhouse gases on the world because it includes extreme weather, storms and changes in rainfall patterns, ocean acidification and sea level.". Various scientists, politicians and media figures have adopted the terms climate crisis or climate emergency to talk about climate change, and global heating instead of global warming.; The policy editor-in-chief of The Guardian said they included this language in their editorial guidelines "to ensure that we are being scientifically precise, while also communicating clearly with readers on this very important issue".; In 2019, Oxford Languages chose climate emergency as its word of the year, defining it as "a situation in which urgent action is required to reduce or halt climate change and avoid potentially irreversible environmental damage resulting from it".. Observed temperature rise
thumb|upright=1.35|Global surface temperature reconstruction over the last 2000 years using proxy data from tree rings, corals, and ice cores in blue.. Directly observed data is in red. Multiple independent instrumental datasets show that the climate system is warming. The 2011–2020 decade warmed to an average 1.09 °C [0.95–1.20 °C] compared to the pre-industrial baseline (1850–1900). Surface temperatures are rising by about 0.2 °C per decade,. with 2020 reaching a temperature of 1.2 °C above the pre-industrial era. Since 1950, the number of cold days and nights has decreased, and the number of warm days and nights has increased.. There was little net warming between the 18th century and the mid-19th century. Climate information for that period comes from climate proxies, such as trees and ice cores. They show that natural variations offset the early effects of the Industrial Revolution.; Thermometer records began to provide global coverage around 1850. Historical patterns of warming and cooling, like the Medieval Climate Anomaly and the Little Ice Age, did not occur at the same time across different regions. Temperatures may have reached as high as those of the late-20th century in a limited set of regions.; There have been prehistorical episodes of global warming, such as the Paleocene–Eocene Thermal Maximum. However, the modern observed rise in temperature and concentrations has been so rapid that even abrupt geophysical events in Earth's history do not approach current rates.. Evidence of warming from air temperature measurements are reinforced with a wide range of other observations.. Figure 2.5. There has been an increase in the frequency and intensity of heavy precipitation, melting of snow and land ice, and increased atmospheric humidity.; . Flora and fauna are also behaving in a manner consistent with warming; for instance, plants are flowering earlier in spring. Another key indicator is the cooling of the upper atmosphere, which demonstrates that greenhouse gases are trapping heat near the Earth's surface and preventing it from radiating into space. Regions warm at various rates. The pattern is independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet. Since the pre-industrial period, the average surface temperature over land regions has increased almost twice as fast as the global-average surface temperature. This is because of the larger heat capacity of oceans, and because oceans lose more heat by evaporation.. The thermal energy in the global climate system has grown with only brief pauses since at least 1970, and over 90% of this extra energy has been stored in the ocean.: "Ocean warming dominates the global energy change inventory. Warming of the ocean accounts for about 93% of the increase in the Earth's energy inventory between 1971 and 2010 (high confidence), with warming of the upper (0 to 700 m) ocean accounting for about 64% of the total. The rest has heated the atmosphere, melted ice, and warmed the continents. The Northern Hemisphere and the North Pole have warmed much faster than the South Pole and Southern Hemisphere. The Northern Hemisphere not only has much more land, but also more seasonal snow cover and sea ice. As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat.. Local black carbon deposits on snow and ice also contribute to Arctic warming. Arctic temperatures are increasing at over twice the rate of the rest of the world.; . Melting of glaciers and ice sheets in the Arctic disrupts ocean circulation, including a weakened Gulf Stream, further changing the climate.. Drivers of recent temperature rise
thumb|upright=1.35|left|Drivers of climate change from 1850–1900 to 2010–2019. There was no significant contribution from internal variability or solar and volcanic drivers. The climate system experiences various cycles on its own which can last for years (such as the El Niño–Southern Oscillation), decades or even centuries.; Other changes are caused by an imbalance of energy that is "external" to the climate system, but not always external to the Earth. Examples of external forcings 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, known internal climate variability and natural external forcings need to be ruled out. A key approach is to determine unique "fingerprints" for all potential causes, then compare these fingerprints with observed patterns of climate change.; For example, solar forcing can be ruled out as a major cause. Its fingerprint would be warming in the entire atmosphere. Yet, only the lower atmosphere has warmed, consistent with greenhouse gas forcing. Attribution of recent climate change shows that the main driver is elevated greenhouse gases, but that aerosols also have a strong effect. Greenhouse gases
The Earth absorbs sunlight, then radiates it as heat. Greenhouse gases in the atmosphere absorb and reemit infrared radiation, slowing the rate at which it can pass through the atmosphere and escape into space. 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.: "To emit 240 W m−2, a surface would have to have a temperature of around −19 °C. This is much colder than the conditions that actually exist at the Earth's surface (the global mean surface temperature is about 14 °C). While water vapour (~50%) and clouds (~25%) are the biggest contributors to the greenhouse effect, they increase as a function of temperature and are therefore feedbacks. On the other hand, concentrations of gases such as (~20%), tropospheric ozone,Ozone acts as a greenhouse gas in the lowest layer of the atmosphere, the troposphere (as opposed to the stratospheric ozone layer). CFCs and nitrous oxide are not temperature-dependent, and are therefore external forcings.;
thumb|upright=1.35| concentrations over the last 800,000 years as measured from ice cores (blue/green) and directly (black)
Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas),. has increased the amount of greenhouse gases in the atmosphere, resulting in a radiative imbalance. In 2019, the concentrations of and methane had increased by about 48% and 160%, respectively, since 1750.. These levels are higher than they have been at any time during the last 2 million years. Concentrations of methane are far higher than they were over the last 800,000 years. thumb|upright=1.35|The Global Carbon Project shows how additions to since 1880 have been caused by different sources ramping up one after another. Global anthropogenic greenhouse gas emissions in 2018, excluding those from land use change, were equivalent to 52 billion tonnes of . Of these emissions, 72% was , 19% was methane, 6% was nitrous oxide, and 3% was fluorinated gases. emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity. Additional emissions come from deforestation and industrial processes, which include the released by the chemical reactions for making cement, steel, aluminum, and fertiliser.; ; ; ; Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction.; Nitrous oxide emissions largely come from the microbial decomposition of fertiliser.; ; From a production standpoint, the primary sources of global greenhouse gas emissions are estimated as: electricity and heat (25%), agriculture and forestry (24%), industry and manufacturing (21%), transport (14%), and buildings (6%). Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for . Natural processes, such as carbon fixation in the soil and photosynthesis, more than offset the greenhouse gas contributions from deforestation. The land-surface sink is estimated to remove about 29% of annual global emissions. The ocean also serves as a significant carbon sink via a two-step process. First, dissolves in the surface water. Afterwards, the ocean's overturning circulation distributes it deep into the ocean's interior, where it accumulates over time as part of the carbon cycle. Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted .. Aerosols and clouds
Air pollution, in the form of aerosols, not only puts a large burden on human health, but also affects the climate on a large scale.; ; . From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed, a phenomenon popularly known as global dimming,. typically attributed to aerosols from biofuel and fossil fuel burning.; Globally, aerosols have been declining since 1990, meaning that they no longer mask greenhouse gas warming as much.; ; . Aerosols scatter and absorb solar radiation. They also have indirect effects on the Earth's radiation budget. Sulfate aerosols act as cloud condensation nuclei and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets.. They also reduce the growth of raindrops, which makes clouds more reflective to incoming sunlight.. Indirect effects of aerosols are the largest uncertainty in radiative forcing. While aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise.; . Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C by 2050. Changes of the land surface
thumb|left |The rate of global tree cover loss has approximately doubled since 2001, to an annual loss approaching an area the size of Italy. Humans change the Earth's surface mainly to create more agricultural land. Today, agriculture takes up 34% of Earth's land area, while 26% is forests, and 30% is uninhabitable (glaciers, deserts, etc.). The amount of forested land continues to decrease, largely due to conversion to cropland in the tropics.; . This deforestation is the most significant aspect of land surface change affecting global warming. The main causes of deforestation are: permanent land-use change from forest to agricultural land producing products such as beef and palm oil (27%), logging to produce forestry/forest products (26%), short term shifting cultivation (24%), and wildfires (23%). Land use changes not only affect greenhouse gas emissions. The type of vegetation in a region affects the local temperature. It impacts how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also affect temperatures by modifying the release of chemical compounds that influence clouds, and by changing wind patterns. In tropic and temperate areas the net effect is to produce significant warming, while at latitudes closer to the poles a gain of albedo (as forest is replaced by snow cover) leads to a cooling effect. Globally, these effects are estimated to have led to a slight cooling, dominated by an increase in surface albedo. Solar and volcanic activity
Physical climate models are unable to reproduce the rapid warming observed in recent decades when taking into account only variations in solar output and volcanic activity.; . 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. There has been no upward trend in the amount of the Sun's energy reaching the Earth. Further evidence for greenhouse gases causing global warming comes from measurements that show a warming of the lower atmosphere (the troposphere), coupled with a cooling of the upper atmosphere (the stratosphere).; . If solar variations were responsible for the observed warming, the troposphere and stratosphere would both warm.. Explosive volcanic eruptions represent the largest natural forcing over the industrial era. When the eruption is sufficiently strong (with sulfur dioxide reaching the stratosphere), sunlight can be partially blocked for a couple of years. The temperature signal lasts about twice as long. In the industrial era, volcanic activity has had negligible impacts on global temperature trends. Present-day volcanic CO2 emissions are equivalent to less than 1% of current anthropogenic CO2 emissions. Climate change feedback
thumb|Sea ice reflects 50% to 70% of incoming solar radiation while the dark ocean surface only reflects 6%, so melting sea ice is a self-reinforcing feedback. The response of the climate system to an initial forcing is modified by feedbacks: increased by self-reinforcing feedbacks and reduced by balancing feedbacks. The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and probably the net effect of clouds. The primary balancing mechanism is radiative cooling, as Earth's surface gives off more heat to space in response to rising temperature. In addition to temperature feedbacks, there are feedbacks in the carbon cycle, such as the fertilizing effect of on plant growth. Uncertainty over feedbacks is the major reason why different climate models project different magnitudes of warming for a given amount of emissions. As air gets warmer, it can hold more moisture. After initial warming due to emissions of greenhouse gases, the atmosphere will hold more water. Water vapour is a potent greenhouse gas, so this further heats the atmosphere. If cloud cover increases, more sunlight will be reflected back into space, cooling the planet. If clouds become higher and thinner, they act as an insulator, reflecting heat from below back downwards and warming the planet. Overall, the net cloud feedback over the industrial era has probably exacerbated temperature rise.. The reduction of snow cover and sea ice in the Arctic reduces the albedo of the Earth's surface.. More of the Sun's energy is now absorbed in these regions, contributing to amplification of Arctic temperature changes.. Arctic amplification is also melting permafrost, which releases methane and into the atmosphere. Around half of human-caused emissions have been absorbed by land plants and by the oceans. On land, elevated and an extended growing season have stimulated plant growth. Climate change increases droughts and heat waves that inhibit plant growth, which makes it uncertain whether this carbon sink will continue to grow in the future.. Soils contain large quantities of carbon and may release some when they heat up.: Our first-order estimate of a warming-induced loss of 190 Pg of soil carbon over the 21st century is equivalent to the past two decades of carbon emissions from fossil fuel burning. As more and heat are absorbed by the ocean, it acidifies, its circulation changes and phytoplankton takes up less carbon, decreasing the rate at which the ocean absorbs atmospheric carbon. Climate change can increase methane emissions from wetlands, marine and freshwater systems, and permafrost. Future warming and the carbon budget
upright=1.35|thumb|Projected global surface temperature changes relative to 1850–1900, based on CMIP6 multi-model mean changes. Future warming depends on the strengths of climate feedbacks and on emissions of greenhouse gases. The former are often estimated using climate models, developed by multiple scientific institutions. A climate model is a representation of the physical, chemical, and biological processes that affect the climate system.. Models include changes in the Earth's orbit, historical changes in the Sun's activity, and volcanic forcing. Computer models attempt to reproduce and predict the circulation of the oceans, the annual cycle of the seasons, and the flows of carbon between the land surface and the atmosphere. Models project different future temperature rises for given emissions of greenhouse gases; they do not fully agree on the strength of different feedbacks on climate sensitivity and magnitude of inertia of the climate system.. The physical realism of models is tested by examining their ability to simulate contemporary or past climates., FAQ 8.1. 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".. A subset of climate models add societal factors to a simple physical climate model. These models simulate how population, economic growth, and energy use affectand interact withthe 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 to generate climate change projections. In some scenarios emissions continue to rise over the century, while others have reduced emissions.; . Fossil fuel resources are too abundant for shortages to be relied on to limit carbon emissions in the 21st century.. Emissions scenarios can be combined with modelling of the carbon cycle to predict how atmospheric concentrations of greenhouse gases might change in the future. According to these combined models, by 2100 the atmospheric concentration of CO2 could be as low as 380 or as high as 1400 ppm, depending on the socioeconomic scenario and the mitigation scenario.; . The IPCC Sixth Assessment Report projects that global warming is very likely to reach 1.0 °C to 1.8 °C by the late 21st century under the very low GHG emissions scenario. In an intermediate scenario global warming would reach 2.1 °C to 3.5 °C, and 3.3 °C to 5.7 °C under the very high GHG emissions scenario. These projections are based on climate models in combination with observations. The remaining carbon budget is determined by modelling the carbon cycle and the climate sensitivity to greenhouse gases. According to the IPCC, global warming can be kept below 1.5 °C with a two-thirds chance if emissions after 2018 do not exceed 420 or 570 gigatonnes of . This corresponds to 10 to 13 years of current emissions. There are high uncertainties about the budget. For instance, it may be 100 gigatonnes of smaller due to methane release from permafrost and wetlands. Impacts
thumb|upright=1.35|The sixth IPCC Assessment Report projects changes in average soil moisture that can disrupt agriculture and ecosystems. A reduction in soil moisture by one standard deviation means that average soil moisture will approximately match the ninth driest year between 1850 and 1900 at that location. Physical environment
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.; . The rainfall rate and intensity of hurricanes and typhoons is likely increasing.. Frequency of tropical cyclones has not increased as a result of climate change. thumb|upright=1.35|Historical sea level reconstruction and projections up to 2100 published in 2017 by the U.S. Global Change Research Program. Global sea level is rising as a consequence of glacial melt, melt of the ice sheets in Greenland and Antarctica, and thermal expansion. Between 1993 and 2020, the rise increased over time, averaging 3.3 ± 0.3 mm per year.. Over the 21st century, the IPCC projects that in a very high emissions scenario the sea level could rise by 61–110 cm.: GMSL (global mean sea level, red) will rise between 0.43 m (0.29–0.59 m, likely range) (RCP2.6) and 0.84 m (0.61–1.10 m, likely range) (RCP8.5) by 2100 (medium confidence) relative to 1986–2005. Increased ocean warmth is undermining and threatening to unplug Antarctic glacier outlets, risking a large melt of the ice sheet. and the possibility of a 2-meter sea level rise by 2100 under high emissions. Climate change has led to decades of shrinking and thinning of the Arctic sea ice. While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur once every three to ten years at a warming level of 2 °C. Higher atmospheric concentrations have led to changes in ocean chemistry. An increase in dissolved is causing oceans to acidify.. In addition, oxygen levels are decreasing as oxygen is less soluble in warmer water. Dead zones in the ocean, regions with very little oxygen, are expanding too.;
Tipping points and long-term impacts
The greater the amount of global warming, the greater the risk of passing through ‘tipping points’, thresholds beyond which certain impacts can no longer be avoided even if temperatures are reduced.. An example is the collapse of West Antarctic and Greenland ice sheets, where a temperature rise of 1.5 to 2 °C may commit the ice sheets to melt, although the time scale of melt is uncertain and depends on future warming. Some large-scale changes could occur over a short time period, such as a collapse of the Atlantic Meridional Overturning Circulation,. which would trigger major climate changes in the North Atlantic, Europe, and North America.. The long-term effects of climate change include further ice melt, ocean warming, sea level rise, and ocean acidification. On the timescale of centuries to millennia, the magnitude of climate change will be determined primarily by anthropogenic emissions. This is due to 's long atmospheric lifetime. Oceanic uptake is slow enough that ocean acidification will continue for hundreds to thousands of years. These emissions are estimated to have prolonged the current interglacial period by at least 100,000 years. Sea level rise will continue over many centuries, with an estimated rise of after 2000 years.;
Nature and wildlife
Recent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes.. Higher atmospheric levels and an extended growing season have resulted in global greening. However, heatwaves and drought have reduced ecosystem productivity in some regions. The future balance of these opposing effects is unclear. Climate change has contributed to the expansion of drier climate zones, such as the expansion of deserts in the subtropics.; . The size and speed of global warming is making abrupt changes in ecosystems more likely. Overall, it is expected that climate change will result in the extinction of many species. The oceans have heated more slowly than the land, but plants and animals in the ocean have migrated towards the colder poles faster than species on land.; Just as on land, heat waves in the ocean occur more frequently due to climate change, harming a wide range of organisms such as corals, kelp, and seabirds. Ocean acidification makes it harder for 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. + Climate change impacts on the environment
Humans
thumb|upright=1.35 |The IPCC Sixth Assessment Report (2021) projects that extreme weather will be progressively more common as the Earth warms. The effects of climate change on humans, mostly due to warming and shifts in precipitation, have been detected worldwide. Impacts are now observable on all continents and across ocean regions, with low-latitude, less developed areas facing the greatest risk.. Continued warming has potentially “severe, pervasive and irreversible impacts” for people and ecosystems. The risks are unevenly distributed, but are generally greater for disadvantaged people in developing and developed countries. Food and health
Health impacts include both the direct effects of extreme weather, leading to injury and loss of life, and indirect effects such as undernutrition brought on by crop failures.; ; Various infectious diseases are more easily transmitted in a warmer climate, such as dengue fever, which affects children most severely, and malaria. Young children are the most vulnerable to food shortages, and together with older people, to extreme heat. The World Health Organization (WHO) has estimated that between 2030 and 2050, climate change is expected to cause around 250,000 additional deaths per year from heat exposure in elderly people, increases in diarrheal disease, malaria, dengue, coastal flooding, and childhood undernutrition. Over 500,000 additional adult deaths are projected yearly by 2050 due to reductions in food availability and quality.; Other major health risks associated with climate change include air and water quality.; The WHO has classified human impacts from climate change as the greatest threat to global health in the 21st century. Climate change is affecting food security. It has caused reduction in global mean yields of maize, wheat, and soybeans between 1981 and 2010.. Future warming could further reduce global yields of major crops.; Crop production will probably be negatively affected in low-latitude countries, while effects at northern latitudes may be positive or negative. Up to an additional 183 million people worldwide, particularly those with lower incomes, are at risk of hunger as a consequence of these impacts. The effects of warming on the oceans impact fish stocks, with a global decline in the maximum catch potential. Only polar stocks are showing an increased potential. Regions dependent on glacier water, regions that are already dry, and small islands are at increased risk of water stress due to climate change.; . Livelihoods
Economic damages due to climate change may be severe and there is a probability of disastrous tail-risk events.; . Climate change has likely already increased global economic inequality, and this trend is projected to continue.; ; . Most of the severe impacts are expected in sub-Saharan Africa and South-East Asia, where existing poverty is already exacerbated. The World Bank estimates that climate change could drive over 120 million people into poverty by 2030. Current inequalities between men and women, between rich and poor, and between different ethnicities have been observed to worsen as a consequence of climate variability and 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, but that future warming will bring increasing risks. Low-lying islands and coastal communities are threatened through hazards posed by sea level rise, such as flooding and permanent submergence. This could lead to statelessness for populations in island nations, such as the Maldives and Tuvalu.. In some regions, rise in temperature and humidity may be too severe for humans to adapt to. With worst-case climate change, models project that almost one-third of humanity might live in extremely hot and uninhabitable climates, similar to the current climate found in the Sahara. These factors, plus weather extremes, can drive environmental migration, both within and between countries. Displacement of people is expected to increase as a consequence of more frequent extreme weather, sea level rise, and conflict arising 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
Responses
Mitigation
thumb|upright=1.35|left|Scenarios of global greenhouse gas emissions. If all countries achieve their current Paris Agreement pledges, average warming by 2100 would still significantly exceed the maximum 2 °C target set by the Agreement. Climate change can be mitigated by reducing greenhouse gas emissions and by enhancing sinks that absorb greenhouse gases from the atmosphere.. In order to limit global warming to less than 1.5 °C with a high likelihood of success, global greenhouse gas emissions needs to be net-zero by 2050, or by 2070 with a 2 °C target. This requires far-reaching, systemic changes on an unprecedented scale in energy, land, cities, transport, buildings, and industry. The United Nations Environment Programme estimates that countries need to triple their pledges under the Paris Agreement within the next decade to limit global warming to 2 °C. An even greater level of reduction is required to meet the 1.5 °C goal. With pledges made under the Agreement as of October 2021, global warming would still have a 66% chance of reaching about 2.7 °C (range: 2.2–3.2 °C) by the end of the century. Although there is no single pathway to limit global warming to 1.5 or 2 °C,. most scenarios and strategies see a major increase in the use of renewable energy in combination with increased energy efficiency measures to generate the needed greenhouse gas reductions. To reduce pressures on ecosystems and enhance their carbon sequestration capabilities, changes would also be necessary in agriculture and forestry, such as preventing deforestation and restoring natural ecosystems by reforestation. Other approaches to mitigating climate change have a higher level of risk. Scenarios that limit global warming to 1.5 °C typically project the large-scale use of carbon dioxide removal methods over the 21st century.; There are concerns, though, about over-reliance on these technologies, and environmental impacts.; Solar radiation management (SRM) is also a possible supplement to deep reductions in emissions. However, SRM would raise significant ethical and legal issues, and the risks are poorly understood. Clean energy
thumb|upright=1.35|Coal, oil, and natural gas remain the primary global energy sources even as renewables have begun rapidly increasing. thumb|upright=1.35|Economic sectors with more greenhouse gas contributions have a greater stake in climate change policies. Renewable energy is key to limiting climate change. Fossil fuels accounted for 80% of the world's energy in 2018. The remaining share was split between nuclear power and renewables (including solar and wind power, bioenergy, geothermal energy, and hydropower).. That mix is projected to change significantly over the next 30 years.. Solar and wind have seen substantial growth and progress over the last few years. Solar panels and onshore wind are the cheapest forms of adding new power generation capacity in most countries.; Renewables represented 75% of all new electricity generation installed in 2019, nearly all solar and wind.. Meanwhile, nuclear power share remains the same but costs are increasing. Nuclear power generation is now several times more expensive per megawatt-hour than wind and solar. 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. The use of electricity for heating and transport, would rise to the point where electricity becomes the largest form of energy.; . Investment in coal would be eliminated and coal use nearly phased out by 2050.; . In transport, scenarios envision sharp increases in the market share of electric vehicles, of public transport and of a switch to low-carbon fuel for other transportation modes like shipping.; Heating would be increasingly decarbonised with the use of technologies like heat pumps.;
There are obstacles to the continued rapid growth of renewables. For solar and wind power, a key challenge is their intermittency and seasonal variability. Traditionally, hydro dams with reservoirs and conventional power plants have been used when variable energy production is low. Intermittency is further countered by expanding battery storage and matching energy demand and supply. Long-distance transmission can smooth variability of renewable output across wider geographic areas.; ; There can be environmental and land use concerns with large solar and wind projects,. while bioenergy is often not carbon-neutral and may have negative consequences for food security.. Hydropower growth has been slowing and is set to decline further due to concerns about social and environmental impacts. Low-carbon energy improves human health by minimising climate change and has the near-term benefit of reducing air pollution deaths,; which were estimated at 7 million annually in 2016.; Meeting the Paris Agreement goals that limit warming to a 2 °C increase could save about a million of those lives per year by 2050, whereas limiting global warming to 1.5 °C could save millions and simultaneously increase energy security and reduce poverty.; ; : "Limiting warming to 1.5 °C can be achieved synergistically with poverty alleviation and improved energy security and can provide large public health benefits through improved air quality, preventing millions of premature deaths. However, specific mitigation measures, such as bioenergy, may result in trade-offs that require consideration."
Energy efficiency
Reducing energy demand is another major aspect of reducing emissions. If less energy is needed, there is more flexibility for clean energy development. It also makes it easier to manage the electricity grid, and minimises carbon-intensive infrastructure development.; Major increases in energy efficiency investment will be required to achieve climate goals, comparable to the level of investment in renewable energy. Several COVID-19 related changes in energy use patterns, energy efficiency investments, and funding have made forecasts for this decade more difficult and uncertain. Strategies to reduce energy demand vary by sector. In transport, 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 increasing the energy efficiency of 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 aiming for higher levels of energy efficiency in retrofitting. The use of technologies like heat pumps can also increase building energy efficiency.. Agriculture and industry
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. Steel and cement production, responsible for about 13% of industrial emissions, present particular challenges. In these industries, carbon-intensive materials such as coke and lime play an integral role in the production, so that reducing emissions requires research into alternative chemistries. Carbon sequestration
thumb|upright=1.35|Most 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 beyond naturally occurring levels.: . Reforestation and tree planting on non-forest lands are among the most mature sequestration techniques, although the latter raises food security concerns. Soil carbon sequestration and coastal carbon sequestration are less understood options. The feasibility of land-based negative emissions methods for mitigation are uncertain; the IPCC has described mitigation strategies based on them as risky. Where energy production or -intensive heavy industries continue to produce waste , the gas can be captured and stored instead of released to the atmosphere. Although its current use is limited in scale and expensive,; ; carbon capture and storage (CCS) may be able to play a significant role in limiting emissions by mid-century. This technique, in combination with bio-energy (BECCS) can result in net negative emissions: is drawn from the atmosphere.; . It remains highly uncertain whether carbon dioxide removal techniques, such as BECCS, will be able to play a large role in limiting warming to 1.5 °C. Policy decisions that rely on carbon dioxide removal increase the risk of global warming rising beyond international goals. Adaptation
Adaptation is "the process of adjustment to current or expected changes in climate and its effects". Without additional mitigation, adaptation cannot avert the risk of "severe, widespread and irreversible" impacts. More severe climate change requires more transformative adaptation, which can be prohibitively expensive. The capacity and potential for humans to adapt is unevenly distributed across different regions and populations, and developing countries generally have less.. The first two decades of the 21st century saw an increase in adaptive capacity in most low- and middle-income countries with improved access to basic sanitation and electricity, but progress is slow. Many countries have implemented adaptation policies. However, there is a considerable gap between necessary and available finance. Adaptation to sea level rise consists of avoiding at-risk areas, learning to live with increased flooding and protection. If that fails, managed retreat may be needed. There are economic barriers for tackling dangerous heat impact. Avoiding strenuous work or having air conditioning is not possible for everybody. In agriculture, adaptation options include a switch to more sustainable diets, diversification, erosion control and genetic improvements for increased tolerance to a changing climate. Insurance allows for risk-sharing, but is often difficult to get for people on lower incomes. Education, migration and early warning systems can reduce climate vulnerability. 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 directly moved. 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 and trade-offs between adaptation and mitigation. Adaptation often offer short-term benefits, whereas mitigation has longer-term benefits. Increased use of air conditioning allows people to better cope with heat, but increases energy demand. Compact urban development may lead to reduced emissions from transport and construction. At the same time, it may increase the urban heat island effect, leading to higher temperatures and increased exposure. Increased food productivity has large benefits for both adaptation and mitigation.. Policies and politics
thumb|upright=1.35|The Climate Change Performance Index ranks countries by greenhouse gas emissions (40% of score), renewable energy (20%), energy use (20%), and climate policy (20%). 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. Climate change is strongly linked to sustainable development. Limiting global warming makes it easier to achieve sustainable development goals, such as eradicating poverty and reducing inequalities. The connection is recognised in Sustainable Development Goal 13 which is to "[t]ake urgent action to combat climate change and its impacts".; United Nations (2017) Resolution adopted by the General Assembly on 6 July 2017, Work of the Statistical Commission pertaining to the 2030 Agenda for Sustainable Development (A/RES/71/313) The goals on food, clean water and ecosystem protection have synergies with climate mitigation. The geopolitics of climate change is complex. It has often been framed as a free-rider problem, in which all countries benefit from mitigation done by other countries, but individual countries would lose from switching to a low-carbon economy themselves. This framing has been challenged. For instance, the benefits of a coal phase-out to public health and local environments exceed the costs in almost all regions. Furthermore, net importers of fossil fuels win economically from switching to clean energy, causing net exporters to face stranded assets: fossil fuels they cannot sell. Policy options
A wide range of policies, regulations, and laws are being used to reduce emissions. As of 2019, carbon pricing covers about 20% of global greenhouse gas emissions. Carbon can be priced with carbon taxes and emissions trading systems.; . Direct global fossil fuel subsidies reached $319 billion in 2017, and $5.2 trillion when indirect costs such as air pollution are priced in. Ending these can cause a 28% reduction in global carbon emissions and a 46% reduction in air pollution deaths. 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.;
Policy designed through the lens of climate justice tries to address human rights issues and social inequality. For instance, wealthy nations responsible for the largest share of emissions would have to pay poorer countries to adapt. As the use of fossil fuels is reduced, jobs in the sector are being lost. To achieve a just transition, these people would need to be retrained for other jobs. Communities with many fossil fuel workers would need additional investments.. International climate agreements
thumb|upright=1.35|Since 2000, rising emissions in China and the rest of world have surpassed the output of the United States and Europe., Table 7. thumb|upright=1.35|Per person, the United States generates at a far faster rate than other primary regions. Nearly all countries in the world are parties to the 1994 United Nations Framework Convention on Climate Change (UNFCCC). The goal of the UNFCCC is to prevent dangerous human interference with the climate system.. As stated in the convention, this requires that greenhouse gas concentrations are stabilised in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can be sustained.. The UNFCCC does not itself restrict emissions but rather provides a framework for protocols that do. Global emissions have risen since the UNFCCC was signed.. Its yearly conferences are the stage of global negotiations. The 1997 Kyoto Protocol extended the UNFCCC and included legally binding commitments for most developed countries to limit their emissions.; . During the negotiations, the G77 (representing developing countries) pushed for a mandate requiring developed countries to "[take] the lead" in reducing their emissions,; . since developed countries contributed most to the accumulation of greenhouse gases in the atmosphere. Per-capita emissions were also still relatively low in developing countries and developing countries would need to emit more to meet their development needs.. The 2009 Copenhagen Accord has been widely portrayed as disappointing because of its low goals, and was rejected by poorer nations including the G77.; ; ; . Associated parties aimed to limit the global temperature rise to below 2 °C.. The Accord set the goal of sending $100 billion per year to developing countries for mitigation and adaptation by 2020, and proposed the founding of the Green Climate Fund. , the fund has failed to reach its expected target, and risks a shrinkage in its funding. 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 . 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.. , 194 states and the European Union have signed the treaty and 191 states and the EU have ratified or acceded to the agreement.; . The 1987 Montreal Protocol, an international agreement to stop emitting ozone-depleting gases, may have been more effective at curbing greenhouse gas emissions than the Kyoto Protocol specifically designed to do so. The 2016 Kigali Amendment to the Montreal Protocol aims to reduce the emissions of hydrofluorocarbons, a group of powerful greenhouse gases which served as a replacement for banned ozone-depleting gases. This made the Montreal Protocol a stronger agreement against climate change. National responses
In 2019, the United Kingdom parliament became the first national government to declare a climate emergency.; . Other countries and jurisdictions followed suit.. That same year, the European Parliament declared a "climate and environmental emergency". The European Commission presented its European Green Deal with the goal of making the EU carbon-neutral by 2050.. Major countries in Asia have made similar pledges: South Korea and Japan have committed to become carbon-neutral by 2050, and China by 2060. In 2021, the European Commission released its “Fit for 55” legislation package, which contains guidelines for the car industry; all new cars on the European market must be zero-emission vehicles from 2035. While India has strong incentives for renewables, it also plans a significant expansion of coal in the country. 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.;
Scientific consensus and society
Scientific consensus
thumb|upright=1.35 |Academic studies of scientific agreement on human-caused global warming among climate experts show consensus to be nearly unanimous, and have reflected that the level of consensus correlates with expertise in climate science. There is a near-complete scientific consensus that the climate is warming and that this is caused by human activities. Agreement in recent literature reached over 99%. Older surveys found 90% to 100% of climate scientists agreeing on humanity's role in causing climate change, based on the exact question and who responded.; No scientific body of national or international standing disagrees with this view.; ; Consensus has further developed that some form of action should be taken to protect people against the impacts of climate change. National science academies have called on world leaders to cut global emissions.Joint statement of the ; . Scientific discussion takes place in journal articles that are peer-reviewed. Scientists assess these every few years in the Intergovernmental Panel on Climate Change reports.. The 2021 IPCC Assessment Report stated that it is "unequivocal" that climate change is caused by humans. Denial and misinformation
thumb|upright=1.00| Data has been cherry picked from short periods to falsely assert that global temperatures are not rising. Blue trendlines show short periods that mask longer-term warming trends (red trendlines). Blue dots show the so-called global warming hiatus.|left
Public debate about climate change has been strongly affected by climate change denial and misinformation, which originated in the United States and has since spread to other countries, particularly Canada and Australia. The actors behind climate change denial form a well-funded and relatively coordinated coalition of fossil fuel companies, industry groups, conservative think tanks, and contrarian scientists.; Like the tobacco industry, the main strategy of these groups has been to manufacture doubt about scientific data and results.; Many who deny, dismiss, or hold unwarranted doubt about the scientific consensus on anthropogenic climate change are labelled as "climate change skeptics", which several scientists have noted is a misnomer.;
There are different variants of climate denial: some deny that warming takes place at all, some acknowledge warming but attribute it to natural influences, and some minimise the negative impacts of climate change. Manufacturing uncertainty about the science later developed into a manufactured controversy: creating the belief that there is significant uncertainty about climate change within the scientific community in order to delay policy changes.. Strategies to promote these ideas include criticism of scientific institutions,. and questioning the motives of individual scientists. An echo chamber of climate-denying blogs and media has further fomented misunderstanding of climate change. Public awareness and opinion
Climate change came to international public attention in the late 1980s. Due to confusing media coverage in the early 1990s, people often confounded climate change with other environmental issues like ozone depletion.; In popular culture, the first movie to reach a mass public on the topic was The Day After Tomorrow in 2004, followed a few years later by the Al Gore documentary An Inconvenient Truth. Books, stories and films about climate change fall under the genre of climate fiction. Significant regional, gender, age and political differences exist in both public concern for, and understanding of, climate change. More highly educated people, and in some countries, women and younger people, were more likely to see climate change as a serious threat.. Partisan gaps also exist in many countries,. and countries with high emissions tend to be less concerned.. Views on causes of climate change vary widely between countries.. Concern has increased over time, to the point where a majority of citizens in many countries now express a high level of worry about climate change, or view it as a global emergency.; . Higher levels of worry are associated with stronger public support for policies that address climate change.. Protests and lawsuits
thumb| Canadian residents protesting against global warming
Climate protests have risen in popularity in the 2010s. These protests demand that political leaders take action to prevent climate change. They can take the form of public demonstrations, fossil fuel divestment, lawsuits and other activities.. Prominent demonstrations include the School Strike for Climate. In this initiative, young people across the globe have been protesting since 2018 by skipping school on Fridays, inspired by Swedish teenager Greta Thunberg.; . Mass civil disobedience actions by groups like Extinction Rebellion have protested by disrupting roads and public transport.. Litigation is increasingly used as a tool to strengthen climate action from public institutions and companies. Activists also initiate lawsuits which target governments and demand that they take ambitious action or enforce existing laws on climate change. Lawsuits against fossil-fuel companies generally seek compensation for loss and damage.. Discovery
thumb|upright=1.35|Tyndall's ratio spectrophotometer (drawing from 1861) measured how much infrared radiation was absorbed and emitted by various gases filling its central tube. 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 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 the effect is even greater with carbon dioxide. She concluded that "An atmosphere of that gas would give to our earth a high temperature..." Starting in 1859,. John Tyndall established that nitrogen and oxygen—together totalling 99% of dry air—are transparent to radiated heat. However, water vapour and some gases (in particular methane and carbon dioxide) absorb radiated heat and re-radiate that heat within 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 concentration in air was influenced by long-term geological processes. At the end of an ice age, warming from increased levels would increase the amount of water vapour, amplifying warming in a feedback loop. In 1896, he published the first climate model of its kind, showing that halving of levels could have produced the drop in temperature initiating the ice age. Arrhenius calculated the temperature increase expected from doubling to be around 5–6 °C. Other scientists were initially sceptical and believed the greenhouse effect to be saturated so that adding more would make no difference. They thought climate would be self-regulating.; From 1938 onwards Guy Stewart Callendar published evidence that climate was warming and levels rising,; . but his calculations met the same objections. In the 1950s, Gilbert Plass created a detailed computer model that included different atmospheric layers and the infrared spectrum. This model predicted that increasing levels would cause warming. Around the same time, Hans Suess found evidence that levels had been rising, and Roger Revelle showed that the oceans would not absorb the increase. The two scientists subsequently helped Charles Keeling to begin a record of continued increase, which has been termed the "Keeling Curve". Scientists alerted the public, and the dangers were highlighted at James Hansen's 1988 Congressional testimony., "News reporters gave only a little attention ...". The Intergovernmental Panel on Climate Change, set up in 1988 to provide formal advice to the world's governments, spurred interdisciplinary research.. See also
2020s in environmental history
Anthropocene – proposed new geological time interval in which humans are having significant geological impact
Global cooling – minority view held by scientists in the 1970s that imminent cooling of the Earth would take place
References
Explanatory notes
Notes
Sources
IPCC reports
Fourth Assessment Report
Fifth Assessment report
. AR5 Climate Change 2013: The Physical Science Basis — IPCC
. Chapters 1–20, SPM, and Technical Summary. . Archived . Public reactions to global warming and concern about its effects are also increasing. A global 2015 Pew Research Center report showed that a median of 54% of all respondents asked consider it "a very serious problem". Significant regional differences exist, with Americans and Chinese (whose economies are responsible for the greatest annual CO2 emissions) among the least concerned. Observed temperature changes
320px|thumb|Annual (thin lines) and five-year lowess smooth (thick lines) for the temperature anomalies averaged over the Earth’s land area and sea surface temperature anomalies (blue line) averaged over the part of the ocean that is free of ice at all times (open ocean). 320px|thumb|Two millennia of mean surface temperatures according to different reconstructions from climate proxies, each smoothed on a decadal scale, with the instrumental temperature record overlaid in black. In the period from 1880 to 2012, the global average (land and ocean) surface temperature has increased by 0.85 [0.65 to 1.06] °C, multiple independently produced datasets confirm. In the period from 1906 to 2005, Earth's average surface temperature rose by . The rate of warming almost doubled in the last half of that period (, against ). Although the popular press often reports
the increase of the average near-surface atmospheric temperature as the measure of global warming, most of the additional energy stored in the climate system since 1970 has accumulated in the oceans. The rest has melted ice and warmed the continents and the atmosphere. Since 1979, the average temperature of the lower troposphere has increased between per decade, satellite temperature measurements confirm. Climate proxies show the temperature to have been relatively stable over the one or two thousand years before 1850, with regionally varying fluctuations such as the Medieval Warm Period and the Little Ice Age.Jansen et al., Ch. 6, Palaeoclimate, Section 6.6.1.1: What Do Reconstructions Based on Palaeoclimatic Proxies Show?, pp. 466–478 , in . The warming evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups. Examples include sea level rise, widespread melting of snow and land ice,, in increased heat content of the oceans, increased humidity, and the earlier timing of spring events,, in e.g., the flowering of plants., in The probability that these changes could have occurred by chance is virtually zero. Regional trends and short-term fluctuations
Temperature increases vary a lot across the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures ( against ).Trenberth et al., Chap 3, Observations: Atmospheric Surface and Climate Change, Executive Summary, p. 237, in . Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because oceans lose more heat by evaporation. Since the beginning of industrialisation in the eighteenth century, the temperature difference between the hemispheres has increased due to melting of sea ice and snow in the North. In the past one hundred years, average arctic temperatures have been increasing at almost twice the rate of the rest of the world; however, arctic temperatures are also highly variable.TS.3.1.2 Spatial Distribution of Changes in Temperature, Circulation and Related Variables – AR4 WGI Technical Summary Although more greenhouse gases are emitted in the Northern than in the Southern Hemisphere, this fact does not contribute to the difference in warming because the major greenhouse gases persist long enough to diffuse within as well as between the hemispheres.Ehhalt et al., Chapter 4: Atmospheric Chemistry and Greenhouse Gases, Section 4.2.3.1: Carbon monoxide (CO) and hydrogen (H2), p. 256, in . The thermal inertia of the oceans and the slow responses of other indirect effects occasion the climate to take centuries or longer to adjust to past changes in forcings. One climate commitment study concluded that if greenhouse gases were stabilized at year 2000 levels, surface temperatures would still increase by about one-half degree Celsius, and another found that if they were stabilized at 2005 levels, surface warming could exceed a whole degree Celsius. Some of this surface warming will be driven by past natural forcings which are still seeking equilibrium in the climate system. One study using a highly simplified climate model indicates these past natural forcings may account for as much as 64% of the committed 2050 surface warming and their influence will fade with time compared to the human contribution. Global temperature is subject to short-term fluctuations that overlay long-term trends and can temporarily mask them. The relative stability in surface temperature from 2002 to 2009, which has since been dubbed the global warming hiatus by the media and some scientists, is an example of such an episode. 2015 updates to account for differing methods of measuring ocean surface temperature measurements show a positive trend over the recent decade. Warmest years vs. overall trend
Sixteen of the seventeen warmest years on record have occurred since 2000."U.S. scientists officially declare 2016 the hottest year on record. That makes three in a row." While record-breaking years attract considerable public interest, individual years are less significant than the overall trend. Some climatologists have criticized the attention that the popular press gives to "warmest year" statistics. In particular, ocean oscillations such as the El Niño Southern Oscillation (ENSO) can cause temperatures of a given year to be abnormally warm or cold for reasons unrelated to the overall trend of climate change. Gavin Schmidt stated "the long-term trends or the expected sequence of records are far more important than whether any single year is a record or not."
Initial causes of temperature changes (external forcings)
By itself, the climate system may generate random changes in global temperatures for years to decades at a time, but long-term changes emanate only from so-called external forcings., p.2 These forcings are "external" to the climate system, but not necessarily external to Earth. Examples of external forcings include changes in the composition of the atmosphere (e.g., increased concentrations of greenhouse gases), solar luminosity, volcanic eruptions, and variations in Earth's orbit around the Sun.Hegerl et al., Chapter 9: Understanding and Attributing Climate Change, Section 9.4.1.5: The Influence of Other Anthropogenic and Natural Forcings, in . "Recent estimates indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the second half of the 20th century, with a small net cooling from the combined effects of solar and volcanic forcings." p. 690
Greenhouse gases
The greenhouse effect is the process by which absorption and emission of infrared radiation by gases in a planet's atmosphere warm its lower atmosphere and surface. It was proposed by Joseph Fourier in 1824, discovered in 1860 by John Tyndall, was first investigated quantitatively by Svante Arrhenius in 1896, and its scientific description was developed in the 1930s through 1960s by Guy Stewart Callendar.Callendar, G. S. (1938) "The artificial production of carbon dioxide and its influence on temperature", Quarterly Journal of the Royal Meteorological Society, doi: 10.1002/qj.49706427503The Callendar Effect: the life and work of Guy Stewart Callendar (1898–1964) Amer Meteor Soc., Boston. On Earth, an atmosphere containing naturally occurring amounts of greenhouse gases causes air temperature near the surface to be about warmer than it would be in their absence., p. 97, in : "To emit 240 W m–2, a surface would have to have a temperature of around −19 °C. This is much colder than the conditions that actually exist at the Earth's surface (the global mean surface temperature is about 14 °C). Instead, the necessary −19 °C is found at an altitude about 5 km above the surface." Without the Earth's atmosphere, the Earth's average temperature would be well below the freezing temperature of water. The major greenhouse gases are water vapour, which causes about 36–70% of the greenhouse effect; carbon dioxide (CO2), which causes 9–26%; methane (CH4), which causes 4–9%; and ozone (O3), which causes 3–7%. Clouds also affect the radiation balance through cloud forcings similar to greenhouse gases. Human activity since the Industrial Revolution has increased the amount of greenhouse gases in the atmosphere, leading to increased radiative forcing from CO2, methane, tropospheric ozone, CFCs and nitrous oxide. According to work published in 2007, the concentrations of CO2 and methane had increased by 36% and 148% respectively since 1750. These levels are much higher than at any time during the last 800,000 years, the period for which reliable data has been extracted from ice cores. Less direct geological evidence indicates that CO2 values higher than this were last seen about 20 million years ago. Fossil fuel burning has produced about three-quarters of the increase in CO2 from human activity over the past 20 years. The rest of this increase is caused mostly by changes in land-use, particularly deforestation.IPCC, Summary for Policymakers , Concentrations of atmospheric greenhouse gases ... , p. 7, in . Another significant non-fuel source of anthropogenic CO2 emissions is the calcination of limestone for clinker production, a chemical process which releases CO2.IPCC (2007) AR4. Climate Change 2007: Working Group III: Mitigation of Climate Change, section 7.4.5.1. https://www.ipcc.ch/publications_and_data/ar4/wg3/en/ch7s7-4-5.html Estimates of global CO2 emissions in 2011 from fossil fuel combustion, including cement production and gas flaring, was 34.8 billion tonnes (9.5 ± 0.5 PgC), an increase of 54% above emissions in 1990. Coal burning was responsible for 43% of the total emissions, oil 34%, gas 18%, cement 4.9% and gas flaring 0.7%. In May 2013, it was reported that readings for CO2 taken at the world's primary benchmark site in Mauna Loa surpassed 400 ppm. According to professor Brian Hoskins, this is likely the first time CO2 levels have been this high for about 4.5 million years. Monthly global CO2 concentrations exceeded 400 ppm in March 2015, probably for the first time in several million years. On 12 November 2015, NASA scientists reported that human-made carbon dioxide continues to increase above levels not seen in hundreds of thousands of years; currently, about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere. thumb|Global carbon dioxide emissions by country. Over the last three decades of the twentieth century, gross domestic product per capita and population growth were the main drivers of increases in greenhouse gas emissions.Rogner, H.-H., et al., Chap. 1, Introduction, Section 1.3.1.2: Intensities, in . CO2 emissions are continuing to rise due to the burning of fossil fuels and land-use change. Emissions can be attributed to different regions. Attributions of emissions due to land-use change are subject to considerable uncertainty.Banuri et al., Chapter 3: Equity and Social Considerations, Section 3.3.3: Patterns of greenhouse gas emissions, and Box 3.1, pp. 92–93 in . Emissions scenarios, estimates of changes in future emission levels of greenhouse gases, have been projected that depend upon uncertain economic, sociological, technological, and natural developments.Fisher et al., Chapter 3: Issues related to mitigation in the long-term context, Section 3.1: Emissions scenarios: Issues related to mitigation in the long term context in . In most scenarios, emissions continue to rise over the century, while in a few, emissions are reduced.Morita, Chapter 2: Greenhouse Gas Emission Mitigation Scenarios and Implications, Section 2.5.1.4: Emissions and Other Results of the SRES Scenarios, in .Rogner et al., Ch. 1: Introduction, Figure 1.7, in . Fossil fuel reserves are abundant, and will not limit carbon emissions in the 21st century.IPCC, Summary for Policymakers, Introduction, paragraph 6, in . Emission scenarios, combined with modelling of the carbon cycle, have been used to produce estimates of how atmospheric concentrations of greenhouse gases might change in the future. Using the six IPCC SRES "marker" scenarios, models suggest that by the year 2100, the atmospheric concentration of CO2 could range between 541 and 970 ppm.Prentence et al., Chapter 3: The Carbon Cycle and Atmospheric Carbon Dioxide Executive Summary , in . This is 90–250% above the concentration in the year 1750. The popular media and the public often confuse global warming with ozone depletion, i.e., the destruction of stratospheric ozone (e.g., the ozone layer) by chlorofluorocarbons.Newell, P.J., 2000: Climate for change: non-state actors and the global politics of greenhouse. Cambridge University Press, . Although there are a few areas of linkage, the relationship between the two is not strong. Reduced stratospheric ozone has had a slight cooling influence on surface temperatures, while increased tropospheric ozone has had a somewhat larger warming effect. Aerosols and soot
left|thumb|alt=Refer to caption|Ship tracks can be seen as lines in these clouds over the Atlantic Ocean on the East Coast of the United States. Atmospheric particles from these and other sources could have a large effect on climate through the aerosol indirect effect. Global dimming, a gradual reduction in the amount of global direct irradiance at the Earth's surface, was observed from 1961 until at least 1990. Solid and liquid particles known as aerosols, produced by volcanoes and human-made pollutants, are thought to be the main cause of this dimming. They exert a cooling effect by increasing the reflection of incoming sunlight. The effects of the products of fossil fuel combustion – CO2 and aerosols – have partially offset one another in recent decades, so that net warming has been due to the increase in non-CO2 greenhouse gases such as methane. Radiative forcing due to aerosols is temporally limited due to the processes that remove aerosols from the atmosphere. Removal by clouds and precipitation gives tropospheric aerosols an atmospheric lifetime of only about a week, while stratospheric aerosols can remain for a few years. Carbon dioxide has a lifetime of a century or more, and as such, changes in aerosols will only delay climate changes due to carbon dioxide. Black carbon is second only to carbon dioxide for its contribution to global warming (contribution being estimated at 17 to 20%, whereas carbon dioxide contributes 40 to 45% to global warmingStatement made by Mark Jacobson of the Amosphere Energy Program at Stanford University in the documentary "Sea Blind"Sea Blind).V. Ramanathan and G. Carmichael, supra note 1, at 221 (". . . emissions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions.") Numerous scientists also calculate that black carbon may be second only to CO2 in its contribution to climate change, including Tami C. Bond & Haolin Sun, Can Reducing Black Carbon Emissions Counteract Global Warming, ENVIRON. SCI. TECHN. (2005), at 5921 ("BC is the second or third largest individual warming agent, following carbon dioxide and methane."); and J. Hansen, A Brighter Future, 53 CLIMATE CHANGE 435 (2002), available at http://pubs.giss.nasa.gov/docs/2002/2002_Hansen_1.pdf (calculating the climate forcing of BC at 1.0±0.5 W/m2). In addition to their direct effect by scattering and absorbing solar radiation, aerosols have indirect effects on the Earth's radiation budget. Sulfate aerosols act as cloud condensation nuclei and thus lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets, a phenomenon known as the Twomey effect. This effect also causes droplets to be of more uniform size, which reduces growth of raindrops and makes the cloud more reflective to incoming sunlight, known as the Albrecht effect. Indirect effects are most noticeable in marine stratiform clouds, and have very little radiative effect on convective clouds. Indirect effects of aerosols represent the largest uncertainty in radiative forcing.IPCC, "Aerosols, their Direct and Indirect Effects", pp. 291–292 in . Soot may either cool or warm Earth's climate system, depending on whether it is airborne or deposited. Atmospheric soot directly absorbs solar radiation, which heats the atmosphere and cools the surface. In isolated areas with high soot production, such as rural India, as much as 50% of surface warming due to greenhouse gases may be masked by atmospheric brown clouds. When deposited, especially on glaciers or on ice in arctic regions, the lower surface albedo can also directly heat the surface. The influences of atmospheric particles, including black carbon, are most pronounced in the tropics and sub-tropics, particularly in Asia, while the effects of greenhouse gases are dominant in the extratropics and southern hemisphere. thumb|alt=Refer to caption and adjacent text|Changes in total solar irradiance (TSI) and monthly sunspot numbers since the mid-1970s. thumb|alt=Refer to caption|Contribution of natural factors and human activities to radiative forcing of climate change.IPCC, Summary for Policymakers, Human and Natural Drivers of Climate Change, Figure SPM.2, in . Radiative forcing values are for the year 2005, relative to the pre-industrial era (1750). The contribution of solar irradiance to radiative forcing is 5% the value of the combined radiative forcing due to increases in the atmospheric concentrations of carbon dioxide, methane and nitrous oxide. Solar activity
Since 1978, solar irradiance has been measured by satellites. These measurements indicate that the Sun's radiative output has not increased since then, so the warming that occurred in the past 40 years cannot be attributed to an increase in solar energy reaching the Earth. Climate models have been used to examine the role of the Sun in recent climate change.Hegerl, et al., Chapter 9: Understanding and Attributing Climate Change, Frequently Asked Question 9.2: Can the Warming of the 20th century be Explained by Natural Variability?, in . Models are unable to reproduce the rapid warming observed in recent decades when only taking into account variations in solar output and volcanic activity. Models are, however, able to simulate the observed 20th century changes in temperature when they include all of the most important external forcings, consisting of both human influences and natural forcings. Another line of evidence for the Sun's non-attributability is the differing temperature changes at different levels in the Earth's atmosphere. According to basic physical principles, the greenhouse effect produces warming of the lower atmosphere (the troposphere), but cooling of the upper atmosphere (the stratosphere).Hegerl et al., Chapter 9: Understanding and Attributing Climate Change, Frequently Asked Question 9.2: Can the Warming of the 20th century be Explained by Natural Variability?, in . If solar variations were responsible for the observed warming, warming of both the troposphere and the stratosphere would be expected. Variations in Earth's orbit
The tilt of the Earth’s axis and the shape of its orbit around the Sun vary slowly over tens of thousands of years. This changes climate by changing the seasonal and latitudinal distribution of incoming solar energy at Earth's surface. During the last few thousand years, this phenomenon contributed to a slow cooling trend at high latitudes of the Northern Hemisphere during summer, a trend that was reversed by greenhouse-gas-induced warming during the 20th century. Orbital cycles favorable for glaciation are not expected within the next 50,000 years. Feedback
thumb|The dark ocean surface reflects only 6 percent of incoming solar radiation, instead sea ice reflects 50 to 70 percent. The climate system includes a range of feedbacks, which alter the response of the system to changes in external forcings. Positive feedbacks increase the response of the climate system to an initial forcing, while negative feedbacks reduce it. There are a range of feedbacks in the climate system, including water vapour, changes in ice-albedo (snow and ice cover affect how much the Earth's surface absorbs or reflects incoming sunlight), clouds, and changes in the Earth's carbon cycle (e.g., the release of carbon from soil). The main negative feedback is the energy the Earth's surface radiates into space as infrared radiation., p.19 According to the Stefan-Boltzmann law, if the absolute temperature (as measured in kelvins) doubles, radiated energy increases by a factor of 16 (2 to the 4th power). Feedbacks are an important factor in determining the sensitivity of the climate system to increased atmospheric greenhouse gas concentrations. Other factors being equal, a higher climate sensitivity means that more warming will occur for a given increase in greenhouse gas forcing., pp.26–27 Uncertainty over the effect of feedbacks is a major reason why different climate models project different magnitudes of warming for a given forcing scenario. More research is needed to understand the role of clouds and carbon cycle feedbacks in climate projections. The IPCC projections previously mentioned span the "likely" range (greater than 66% probability, based on expert judgement) for the selected emissions scenarios. However, the IPCC's projections do not reflect the full range of uncertainty. The lower end of the "likely" range appears to be better constrained than the upper end. An observation based study on future climate change, on the soil carbon feedback, conducted since 1991 in Harvard, suggests release of about 190 petagrams of soil carbon, the equivalent of the past two decades of greenhouse gas emissions from fossil fuel burning, until 2100 from the top 1-meter of Earth's soils, due to changes in microbial communities under elevated temperatures. Climate models do not account for this possible feedback mechanism. Climate models
A climate model is a representation of the physical, chemical and biological processes that affect the climate system.IPCC, Glossary A-D: "Climate Model", in . Such models are based on scientific disciplines such as fluid dynamics and thermodynamics as well as physical processes such as radiative transfer. The models may be used to predict a range of variables such as local air movement, temperature, clouds, and other atmospheric properties; ocean temperature, salt content, and circulation; ice cover on land and sea; the transfer of heat and moisture from soil and vegetation to the atmosphere; and chemical and biological processes, among others. Although researchers attempt to include as many processes as possible, simplifications of the actual climate system are inevitable because of the constraints of available computer power and limitations in knowledge of the climate system. Results from models can also vary due to different greenhouse gas inputs and the model's climate sensitivity. For example, the uncertainty in IPCC's 2007 projections is caused by (1) the use of multiple models, in with differing sensitivity to greenhouse gas concentrations, (2) the use of differing estimates of humanity's future greenhouse gas emissions, (3) any additional emissions from climate feedbacks that were not included in the models IPCC used to prepare its report, i.e., greenhouse gas releases from permafrost. The models do not assume the climate will warm due to increasing levels of greenhouse gases. Instead the models predict how greenhouse gases will interact with radiative transfer and other physical processes. Warming or cooling is thus a result, not an assumption, of the models. Clouds and their effects are especially difficult to predict. Improving the models' representation of clouds is therefore an important topic in current research.Stocker et al., Chapter 7: Physical Climate Processes and Feedbacks, Section 7.2.2: Cloud Processes and Feedbacks, in . Another prominent research topic is expanding and improving representations of the carbon cycle. Models are also used to help investigate the causes of recent climate change by comparing the observed changes to those that the models project from various natural and human causes. Although these models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects, they do indicate that the warming since 1970 is dominated by anthropogenic greenhouse gas emissions. The physical realism of models is tested by examining their ability to simulate contemporary or past climates.Randall et al., Chapter 8, Climate Models and Their Evaluation, Sec. FAQ 8.1 in . Climate models produce a good match to observations of global temperature changes over the last century, but do not simulate all aspects of climate.IPCC, Technical Summary, p. 54, in . Not all effects of global warming are accurately predicted by the climate models used by the IPCC. Observed Arctic shrinkage has been faster than that predicted. Precipitation increased proportionally to atmospheric humidity, and hence significantly faster than global climate models predict. Since 1990, sea level has also risen considerably faster than models predicted it would. Observed and expected environmental effects
thumb|right|350px|alt=Refer to caption and adjacent text|Projections of global mean sea level rise by Parris and others. Probabilities have not been assigned to these projections.Executive Summary, in Therefore, none of these projections should be interpreted as a "best estimate" of future sea level rise. Image credit: NOAA.Anthropogenic forcing has likely contributed to some of the observed changes, including sea level rise, changes in climate extremes (such as the number of warm and cold days), declines in Arctic sea ice extent, glacier retreat, and greening of the Sahara., in
The average sea ice decline recorded from 1953 to 2006 is -7.8%±0.6%/decade, this is more than three times the size of the average forecast trend of -2.5%±0.2%/decade. Even the ‘worst case scenario’ models didn’t forecast the extent of the sea ice decline adequately. The quickest rate of sea ice decline from any of the models associated with the Intergovernmental Panel on Climate Change Fourth Assessment Report was -5.4%±0.4%/decade. Global warming has led to decades of shrinking and thinning in a warm climate that has put the Arctic sea ice in a precarious position, it is now vulnerable to atmospheric anomalies. Projections of declines in Arctic sea ice vary., in Recent projections suggest that Arctic summers could be ice-free (defined as ice extent less than 1 million square km) as early as 2025–2030. "Detection" is the process of demonstrating that climate has changed in some defined statistical sense, without providing a reason for that change. Detection does not imply attribution of the detected change to a particular cause. "Attribution" of causes of climate change is the process of establishing the most likely causes for the detected change with some defined level of confidence.IPCC, Glossary A-D: "Detection and attribution", in . See also Hegerl et al., Section 9.1.2: What are Climate Change Detection and Attribution?, in . Detection and attribution may also be applied to observed changes in physical, ecological and social systems.Rosenzweig et al., Chapter 1: Assessment of Observed Changes and Responses in Natural and Managed Systems Section 1.2 Methods of detection and attribution of observed changes, in . Extreme weather
Changes in regional climate are expected to include greater warming over land, with most warming at high northern latitudes, and least warming over the Southern Ocean and parts of the North Atlantic Ocean.IPCC, Synthesis Report Summary for Policymakers, Section 3: Projected climate change and its impacts, in . Future changes in precipitation are expected to follow existing trends, with reduced precipitation over subtropical land areas, and increased precipitation at subpolar latitudes and some equatorial regions., p.1. Revision 15 October 2008, 4:47:16 PM. Projections suggest a probable increase in the frequency and severity of some extreme weather events, such as heat waves., in
A 2015 study published in Nature Climate Change, states:
Data analysis of extreme events from 1960 until 2010 suggests that droughts and heat waves appear simultaneously with increased frequency. Extremely wet or dry events within the monsoon period have increased since 1980. Sea level rise
thumb|250px|Map of the Earth with a six-metre sea level rise represented in red. thumb|right|alt=refer to caption|250px|Sparse records indicate that glaciers have been retreating since the early 1800s. In the 1950s measurements began that allow the monitoring of glacial mass balance, reported to the World Glacier Monitoring Service (WGMS) and the National Snow and Ice Data Center (NSIDC). The sea level rise since 1993 has been estimated to have been on average 2.6 mm and 2.9 mm per year ± 0.4 mm. Additionally, sea level rise has accelerated from 1995 to 2015. Over the 21st century, the IPCC projects for a high emissions scenario, that global mean sea level could rise by 52–98 cm. The IPCC's projections are conservative, and may underestimate future sea level rise.PROJECTIONS OF FUTURE SEA LEVEL RISE, pp.243–244, in: Ch. 7. Sea Level Rise and the Coastal Environment, in Other estimates suggest that for the same period, global mean sea level could rise by 0.2 to 2.0 m (0.7–6.6 ft), relative to mean sea level in 1992.4. Global Mean Sea Level Rise Scenarios, in: Main Report, in
Widespread coastal flooding would be expected if several degrees of warming is sustained for millennia.BOX SYN-1: SUSTAINED WARMING COULD LEAD TO SEVERE IMPACTS, p.5, in: Synopsis, in For example, sustained global warming of more than 2 °C (relative to pre-industrial levels) could lead to eventual sea level rise of around 1 to 4 m due to thermal expansion of sea water and the melting of glaciers and small ice caps. Melting of the Greenland ice sheet could contribute an additional 4 to 7.5 m over many thousands of years. It has been estimated that we are already committed to a sea-level rise of approximately 2.3 metres for each degree of temperature rise within the next 2,000 years. Warming beyond the 2 °C target would potentially lead to rates of sea-level rise dominated by ice loss from Antarctica. Continued CO2 emissions from fossil sources could cause additional tens of metres of sea level rise, over the next millennia and eventually ultimately eliminate the entire Antarctic ice sheet, causing about 58 metres of sea level rise. Ecological systems
thumb|As the climate change melts sea ice, the U.S. Geological Survey projects that two-thirds of polar bears will disappear by 2050. In terrestrial ecosystems, the earlier timing of spring events, as well as poleward and upward shifts in plant and animal ranges, have been linked with high confidence to recent warming.IPCC, Synthesis Report Summary for Policymakers, Section 1: Observed changes in climate and their effects, in . Future climate change is expected to affect particular ecosystems, including tundra, mangroves, coral reefs, and caves. It is expected that most ecosystems will be affected by higher atmospheric CO2 levels, combined with higher global temperatures.Fischlin, et al., Chapter 4: Ecosystems, their Properties, Goods and Services,
Executive Summary, p. 213, in . Executive summary not present in on-line text; see pdf. Overall, it is expected that climate change will result in the extinction of many species and reduced diversity of ecosystems.Schneider et al., Chapter 19: Assessing Key Vulnerabilities and the Risk from Climate Change, Section 19.3.4: Ecosystems and biodiversity, in . Increases in atmospheric CO2 concentrations have led to an increase in ocean acidity.Ocean Acidification, in: Ch. 2. Our Changing Climate, in Dissolved CO2 increases ocean acidity, measured by lower pH values. Between 1750 and 2000, surface-ocean pH has decreased by ≈0.1, from ≈8.2 to ≈8.1.Introduction, in Surface-ocean pH has probably not been below ≈8.1 during the past 2 million years. Projections suggest that surface-ocean pH could decrease by an additional 0.3–0.4 units by 2100.Ocean acidification, in: Executive summary, in Future ocean acidification could threaten coral reefs, fisheries, protected species, and other natural resources of value to society. 5. Ocean acidification, in
Ocean deoxygenation is projected to increase hypoxia by 10%, and triple suboxic waters (oxygen concentrations 98% less than the mean surface concentrations), for each 1 °C of upper ocean warming. Long-term effects
On the timescale of centuries to millennia, the magnitude of global warming will be determined primarily by anthropogenic CO2 emissions. Summary, pp.14–19, in
FAQ 12.3, in: Chapter 12: Long-term Climate Change: Projections, Commitments and Irreversibility, in , pp.88–89 (pp.90–91 of PDF chapter) This is due to carbon dioxide's very long lifetime in the atmosphere. Stabilizing the global average temperature would require large reductions in CO2 emissions, as well as reductions in emissions of other greenhouse gases such as methane and nitrous oxide.BOX 2.1: STABILIZATION AND NON-CO2 GREENHOUSE GASES (p.65), in: Chapter 2: Emissions, Concentrations, and Related Factors, in Emissions of CO2 would need to be reduced by more than 80% relative to their peak level. Even if this were achieved, global average temperatures would remain close to their highest level for many centuries. As of 2016, emissions of CO2 from burning fossil fuels had stopped increasing, but The Guardian reports they need to be "reduced to have a real impact on climate change". Meanwhile, this greenhouse gas continues to accumulate in the atmosphere. In that context, the New York Times reported that scientific installations analyzing oceanic air detected the excess carbon dioxide in the atmosphere "rose at the highest rate on record in 2015 and 2016." It hs been suggested that this rise in CO2 levels is the result of changing absorption patterns of the ocean and land surface in that they may have reached the limit of their ability to absorb carbon dioxide. Also, CO2 is not the only factor driving climate change. Concentrations of atmospheric methane, another greenhouse gas, rose dramatically between 2006–2016 for unknown reasons. This undermines efforts to combat global warming and there is a risk of an uncontrollable runaway greenhouse effect.Rapid rise in methane emissions in 10 years surprises scientists The Guardian
Long-term effects also include a response from the Earth's crust, due to ice melting and deglaciation, in a process called post-glacial rebound, when land masses are no longer depressed by the weight of ice. This could lead to landslides and increased seismic and volcanic activities. Tsunamis could be generated by submarine landslides caused by warmer ocean water thawing ocean-floor permafrost or releasing gas hydrates. Some world regions, such as the French Alps, already show signs of an increase in landslide frequency. Large-scale and abrupt impacts
Climate change could result in global, large-scale changes in natural and social systems., in Examples include the possibility for the Atlantic Meridional Overturning Circulation to slow- or shutdown, which in the instance of a shutdown would change weather in Europe and North America considerably, ocean acidification caused by increased atmospheric concentrations of carbon dioxide, and the long-term melting of ice sheets, which contributes to sea level rise. Some large-scale changes could occur abruptly, i.e., over a short time period, and might also be irreversible. Examples of abrupt climate change are the rapid release of methane and carbon dioxide from permafrost, which would lead to amplified global warming, or the shutdown of thermohaline circulation., pp. 1–7. Report website Scientific understanding of abrupt climate change is generally poor., p.3. PDF of Report The probability of abrupt change for some climate related feedbacks may be low., in Factors that may increase the probability of abrupt climate change include higher magnitudes of global warming, warming that occurs more rapidly, and warming that is sustained over longer time periods. Observed and expected effects on social systems
The effects of climate change on human systems, mostly due to warming or shifts in precipitation patterns, or both, have been detected worldwide. Production of wheat and maize globally has been impacted by climate change. While crop production has increased in some mid-latitude regions such as the UK and Northeast China, economic losses due to extreme weather events have increased globally. There has been a shift from cold- to heat-related mortality in some regions as a result of warming. Livelihoods of indigenous peoples of the Arctic have been altered by climate change, and there is emerging evidence of climate change impacts on livelihoods of indigenous peoples in other regions. Regional impacts of climate change are now observable at more locations than before, on all continents and across ocean regions.Cramer, W., et al., Executive summary, in: Chapter 18: Detection and attribution of observed impacts (archived 8 July 2014), pp.3–4, in
The future social impacts of climate change will be uneven.FAQ 7 and 8, in: Volume-wide Frequently Asked Questions (FAQs) (archived 8 July 2014), pp.2–3, in Many risks are expected to increase with higher magnitudes of global warming.Oppenheimer, M., et al., Section 19.6.3: Updating Reasons for Concern, in: Chapter 19: Emergent risks and key vulnerabilities (archived 8 July 2014), pp.39–46, in All regions are at risk of experiencing negative impacts.Field, C., et al., B-3: Regional Risks and Potential for Adaptation, in: Technical Summary (archived 8 July 2014), pp.27–30, in Low-latitude, less developed areas face the greatest risk.Oppenheimer, M., et al., Section 19.6.3: Updating Reasons for Concern, in: Chapter 19: Emergent risks and key vulnerabilities (archived 8 July 2014), pp.42–43, in A study from 2015 concluded that economic growth (gross domestic product) of poorer countries is much more impaired with projected future climate warming, than previously thought. A meta-analysis of 56 studies concluded in 2014 that each degree of temperature rise will increase violence by up to 20%, which includes fist fights, violent crimes, civil unrest or wars. Examples of impacts include:
Food: Crop production will probably be negatively affected in low latitude countries, while effects at northern latitudes may be positive or negative.Porter, J.R., et al., Executive summary, in: Chapter 7: Food security and food production systems (archived 8 July 2014), p.3, in Global warming of around 4.6 °C relative to pre-industrial levels could pose a large risk to global and regional food security.Reference temperature period converted from late-20th century to pre-industrial times (approximated in the source as 1850–1900). Assessment Box SPM-1 (p.14) and B-2. Sectoral Risks and Potential for Adaptation: Food security and food production systems (p.18), in: Summary for Policymakers (archived 8 July 2014), in
Health: Generally impacts will be more negative than positive.Smith, K.R., et al., FAQ 11.2, in: Chapter 11: Human health: impacts, adaptation, and co-benefits (archived 8 July 2014), p.37, in Impacts include: the effects of extreme weather, leading to injury and loss of life;Smith, K.R., et al., Section 11.4: Direct Impacts of Climate and Weather on Health, in: Chapter 11: Human health: impacts, adaptation, and co-benefits (archived 8 July 2014), pp.10–13, in and indirect effects, such as undernutrition brought on by crop failures.Smith, K.R., et al., Section 11.6.1. Nutrition, in: Chapter 11: Human health: impacts, adaptation, and co-benefits (archived 8 July 2014), pp.10–13, in
Habitat inundation
In small islands and mega deltas, inundation as a result of sea level rise is expected to threaten vital infrastructure and human settlements. This could lead to issues of homelessness in countries with low-lying areas such as Bangladesh, as well as statelessness for populations in countries such as the Maldives and Tuvalu. Economy
Estimates based on the IPCC A1B emission scenario from additional CO2 and CH4 greenhouse gases released from permafrost, estimate associated impact damages by US$43 trillion. Infrastructure
Continued permafrost degradation will likely result in unstable infrastructure in Arctic regions, or Alaska before 2100. Thus, impacting roads, pipelines and buildings, as well as water distribution, and cause slope failures. Possible responses to global warming
Mitigation
thumb|300px|alt=Refer to caption and image description|The graph on the right shows three "pathways" to meet the UNFCCC's 2 °C target, labelled "global technology", "decentralized solutions", and "consumption change". Each pathway shows how various measures (e.g., improved energy efficiency, increased use of renewable energy) could contribute to emissions reductions. Image credit: PBL Netherlands Environmental Assessment Agency., p.177, Report no: 500062001. Report website. Mitigation of climate change are actions to reduce greenhouse gas emissions, or enhance the capacity of carbon sinks to absorb GHGs from the atmosphere.Mitigation, in There is a large potential for future reductions in emissions by a combination of activities, including energy conservation and increased energy efficiency; the use of low-carbon energy technologies, such as renewable energy, nuclear energy, and carbon capture and storage;IPCC, Synthesis Report Summary for Policymakers, Section 4: Adaptation and mitigation options, in .Edenhofer, O., et al., Table TS.3, in: Technical summary (archived 30 December 2014), in: and enhancing carbon sinks through, for example, reforestation and preventing deforestation. A 2015 report by Citibank concluded that transitioning to a low carbon economy would yield positive return on investments. Near- and long-term trends in the global energy system are inconsistent with limiting global warming at below 1.5 or 2 °C, relative to pre-industrial levels.Clarke, L., et al., Executive summary, in: Chapter 6: Assessing Transformation Pathways (archived 30 December 2014), in: SPM4.1: Long-term mitigation pathways, in: Summary for Policymakers (archived 27 December 2014), in: Pledges made as part of the Cancún agreements are broadly consistent with having a likely chance (66 to 100% probability) of limiting global warming (in the 21st century) at below 3 °C, relative to pre-industrial levels. In limiting warming at below 2 °C, more stringent emission reductions in the near-term would allow for less rapid reductions after 2030.Edenhofer, O., et al., TS.3.1.2: Short- and long-term requirements of mitigation pathways, in: Technical summary (archived 30 December 2014), in: Many integrated models are unable to meet the 2 °C target if pessimistic assumptions are made about the availability of mitigation technologies.Edenhofer, O., et al., TS.3.1.3: Costs, investments and burden sharing, in: Technical summary (archived 30 December 2014), in:
Adaptation
Other policy responses include adaptation to climate change. Adaptation to climate change may be planned, either in reaction to or anticipation of climate change, or spontaneous, i.e., without government intervention.Smit et al., Chapter 18: Adaptation to Climate Change in the Context of Sustainable Development and Equity, Section 18.2.3: Adaptation Types and Forms, in . Planned adaptation is already occurring on a limited basis. The barriers, limits, and costs of future adaptation are not fully understood. A concept related to adaptation is adaptive capacity, which is the ability of a system (human, natural or managed) to adjust to climate change (including climate variability and extremes) to moderate potential damages, to take advantage of opportunities, or to cope with consequences., in Unmitigated climate change (i.e., future climate change without efforts to limit greenhouse gas emissions) would, in the long term, be likely to exceed the capacity of natural, managed and human systems to adapt., in
Environmental organizations and public figures have emphasized changes in the climate and the risks they entail, while promoting adaptation to changes in infrastructural needs and emissions reductions. Climate engineering
Climate engineering (sometimes called geoengineering or climate intervention) is the deliberate modification of the climate. It has been investigated as a possible response to global warming, e.g. by NASA and the Royal Society. Techniques under research fall generally into the categories solar radiation management and carbon dioxide removal, although various other schemes have been suggested. A study from 2014 investigated the most common climate engineering methods and concluded they are either ineffective or have potentially severe side effects and cannot be stopped without causing rapid climate change. Discourse about global warming
Political discussion
thumb|alt=refer to caption|right|Article 2 of the UN Framework Convention refers explicitly to "stabilization of greenhouse gas concentrations."Quoted in , "Synthesis of Scientific-Technical Information Relevant to Interpreting Article 2 of the UN Framework Convention on Climate Change", paragraph 4.1, p. 8 (pdf p. 18.) To stabilize the atmospheric concentration of , emissions worldwide would need to be dramatically reduced from their present level. Most countries in the world are parties to the United Nations Framework Convention on Climate Change (UNFCCC). The ultimate objective of the Convention is to prevent dangerous human interference of the climate system. As stated in the Convention, this requires that GHG 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 proceed in a sustainable fashion.Rogner et al., Chapter 1: Introduction, Executive summary, in . The Framework Convention was agreed on in 1992, but global emissions have risen since then. During negotiations, the G77 (a lobbying group in the United Nations representing 133 developing nations) pushed for a mandate requiring developed countries to "[take] the lead" in reducing their emissions. This was justified on the basis that the developed world's emissions had contributed most to the cumulation of GHGs in the atmosphere, per-capita emissions (i.e., emissions per head of population) were still relatively low in developing countries, and the emissions of developing countries would grow to meet their development needs. This mandate was sustained in the Kyoto Protocol to the Framework Convention, which entered into legal effect in 2005. In ratifying the Kyoto Protocol, most developed countries accepted legally binding commitments to limit their emissions. These first-round commitments expired in 2012. United States President George W. Bush rejected the treaty on the basis that "it exempts 80% of the world, including major population centres such as China and India, from compliance, and would cause serious harm to the US economy."
At the 15th UNFCCC Conference of the Parties, held in 2009 at Copenhagen, several UNFCCC Parties produced the Copenhagen Accord. Parties associated with the Accord (140 countries, as of November 2010) This publication is also available in e-book format
aim to limit the future increase in global mean temperature to below . The 16th Conference of the Parties (COP16) was held at Cancún in 2010. It produced an agreement, not a binding treaty, that the Parties should take urgent action to reduce greenhouse gas emissions to meet a goal of limiting global warming to above pre-industrial temperatures. It also recognized the need to consider strengthening the goal to a global average rise of . Scientific discussion
The discussion continues in scientific articles that are peer-reviewed and assessed by scientists who
work in the relevant fields and participate in the Intergovernmental Panel on Climate Change. The scientific consensus as of 2013 stated in the IPCC Fifth Assessment Report is that it "is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century"., in . A 2008 report by the U.S. National Academy of Sciences stated that most scientists by then agreed that observed warming in recent decades was primarily caused by human activities increasing the amount of greenhouse gases in the atmosphere. In 2005 the Royal Society stated that while the overwhelming majority of scientists were in agreement on the main points, some individuals and organizations opposed to the consensus on urgent action needed to reduce greenhouse gas emissions had tried to undermine the science and work of the IPCC. This document is also available in PDF format National science academies have called on world leaders for policies to cut global emissions. In the scientific literature, there is a strong consensus that global surface temperatures have increased in recent decades and that the trend is caused mainly by human-induced emissions of greenhouse gases. No scientific body of national or international standing disagrees with this view. In November 2017, a second warning to humanity signed by 15,364 scientists from 184 countries stated that "the current trajectory of potentially catastrophic climate change due to rising GHGs from burning fossil fuels, deforestation, and agricultural production — particularly from farming ruminants for meat consumption" is "especially troubling". A July 2017 study published in Environmental Research Letters asserts that the most significant action individuals could make to mitigate their own carbon footprint is to have fewer children, followed by living vehicle free, forgoing air travel and adopting a plant-based diet. Discussion by the public and in popular media
thumbnail|upright|Global warming was the cover story in this 2007 issue of Ms. magazine
The global warming controversy refers to a variety of disputes, substantially more pronounced in the popular media than in the scientific literature, regarding the nature, causes, and consequences of global warming. The disputed issues include the causes of increased global average air temperature, especially since the mid-20th century, whether this warming trend is unprecedented or within normal climatic variations, whether humankind has contributed significantly to it, and whether the increase is completely or partially an artefact of poor measurements. Additional disputes concern estimates of climate sensitivity, predictions of additional warming, and what the consequences of global warming will be. By 1990, American conservative think tanks had begun challenging the legitimacy of global warming as a social problem. They challenged the scientific evidence, argued that global warming would have benefits, and asserted that proposed solutions would do more harm than good.Aaron M. McCright and Riley E. Dunlap, "Challenging Global Warming as a Social Problem: An Analysis of the Conservative Movement's Counter-Claims", Social Problems, November 2000, Vol. 47 Issue 4, pp 499–522 in JSTOR Some people dispute aspects of climate change science. Organizations such as the libertarian Competitive Enterprise Institute, conservative commentators, and some companies such as ExxonMobil have challenged IPCC climate change scenarios, funded scientists who disagree with the scientific consensus, and provided their own projections of the economic cost of stricter controls. On the other hand, some fossil fuel companies have scaled back their efforts in recent years, or even called for policies to reduce global warming. Global oil companies have begun to acknowledge climate change exists and is caused by human activities and the burning of fossil fuels. Surveys of public opinion
The global warming problem came to international public attention in the late 1980s. Polling groups began to track opinions on the subject, at first mainly in the United States. The longest consistent polling, by Gallup in the US, found relatively small deviations of 10% or so from 1998 to 2015 in opinion on the seriousness of global warming, but with increasing polarization between those concerned and those unconcerned. The first major worldwide poll, conducted by Gallup in 2008–2009 in 127 countries, found that some 62% of people worldwide said they knew about global warming. In the advanced countries of North America, Europe and Japan, 90% or more knew about it (97% in the U.S., 99% in Japan); in less developed countries, especially in Africa, fewer than a quarter knew about it, although many had noticed local weather changes. Among those who knew about global warming, there was a wide variation between nations in belief that the warming was a result of human activities. By 2010, with 111 countries surveyed, Gallup determined that there had been a substantial decrease since 2007–2008 in the number of Americans and Europeans who viewed global warming as a serious threat. In the US, just a little over half the population (53%) viewed it as a serious concern for either themselves or their families; this was 10 points below the 2008 poll (63%). Latin America had the biggest rise in concern: 73% said global warming was a serious threat to their families. This global poll also found that people were more likely to attribute global warming to human activities than to natural causes, except in the US where nearly half (47%) of the population attributed global warming to natural causes. A March–May 2013 survey by Pew Research Center for the People & the Press polled 39 countries about global threats. According to 54% of those questioned, global warming featured top of the perceived global threats. In a January 2013 survey, Pew found that 69% of Americans say there is solid evidence that the Earth's average temperature has gotten warmer over the past few decades, up six points since November 2011 and 12 points since 2009.Climate Change: Key Data Points from Pew Research | Pew Research Center
A 2010 survey of 14 industrialized countries found that skepticism about the danger of global warming was highest in Australia, Norway, New Zealand and the United States, in that order, correlating positively with per capita emissions of carbon dioxide. Etymology
In the 1950s, research suggested increasing temperatures, and a 1952 newspaper reported "climate change". This phrase next appeared in a November 1957 report in The Hammond Times which described Roger Revelle's research into the effects of increasing human-caused emissions on the greenhouse effect, "a large scale global warming, with radical climate changes may result". Both phrases were only used occasionally until 1975, when Wallace Smith Broecker published a scientific paper on the topic, "Climatic Change: Are We on the Brink of a Pronounced Global Warming?" The phrase began to come into common use, and in 1976 Mikhail Budyko's statement that "a global warming up has started" was widely reported., and footnote 27 Other studies, such as a 1971 MIT report, referred to the human impact as "inadvertent climate modification", but an influential 1979 National Academy of Sciences study headed by Jule Charney followed Broecker in using global warming for rising surface temperatures, while describing the wider effects of increased as climate change.Erik Conway. "What's in a Name? Global Warming vs. Climate Change", NASA, 5 December 2008
In 1986 and November 1987, NASA climate scientist James Hansen gave testimony to Congress on global warming. There were increasing heatwaves and drought problems in the summer of 1988, and when Hansen testified in the Senate on 23 June he sparked worldwide interest. He said, "global warming has reached a level such that we can ascribe with a high degree of confidence a cause and effect relationship between the greenhouse effect and the observed warming."U.S. Senate, Committee on Energy and Natural Resources, "Greenhouse Effect and Global Climate Change, part 2" 100th Cong., 1st sess., 23 June 1988, p. 44. Public attention increased over the summer, and global warming became the dominant popular term, commonly used both by the press and in public discourse. In a 2008 NASA article on usage, Erik M. Conway defined global warming as "the increase in Earth’s average surface temperature due to rising levels of greenhouse gases", while climate change was "a long-term change in the Earth’s climate, or of a region on Earth." As effects such as changing patterns of rainfall and rising sea levels would probably have more impact than temperatures alone, he considered global climate change a more scientifically accurate term, and like the Intergovernmental Panel on Climate Change, the NASA website would emphasize this wider context. See also
Anthropocene
Climate change and agriculture
Effects of global warming on oceans
Environmental impact of the coal industry
Geologic temperature record
Global cooling
Glossary of climate change
Greenhouse gas emissions accounting
History of climate change science
Holocene extinction
Index of climate change articles
Scientific opinion on climate change
Notes
Citations
References
, p. 14. Report website. , Secretariat: TWAS (the Academy of Sciences for the Developing World), Trieste, Italy. (pb: )
(pb: )
(pb: )
. Climate Change 2013 Working Group 1 website. . Archived
. Also available at mitigation2014.org. pdf. The "Full Report", consisting of "The IPCC Second Assessment Synthesis of Scientific-Technical Information Relevant to Interpreting Article 2 of the UN Framework Convention on Climate Change" and the Summaries for Policymakers of the three Working Groups. (pb: ) pdf. . Summary for Policymakers Summary for Policymakers. (pb: )
(pb: )
(pb: )
. Archived url. . Report website. . Report summary. Also available as PDF
. Further reading
Hausfather, Zeke. No 'Pause' in Global Warming: Oceans Heating Up and Sea Levels Rising at Alarming Pace (January 2017). "UC-Berkeley climate scientist Zeke Hausfather details the findings of a new report that confirms NOAA data about climate change."
(pb: )
. Paper at IDEAS. (see Chapter 8)
(online version requires registration)
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Understanding Climate Change – Frequently Asked Questions – UCAR
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The World Bank – Climate Change – A 4 Degree Warmer World – We must and can avoid it
A world with this much CO²: lessons from 4 million years ago (Video)
The 8 Minute Epoch: 65 million Years with James Hansen (Video)
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Global Sea Level Rise Map
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● Mongabay graphing WRI data from
Yale Climate Connections
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Result of total melting of Polar regions on World – National Geographic
Up-to-the-second assessment of human-induced global warming since the second half of the 19th century – Oxford University
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Highlight colors show which account likely added that new text: Femke