The primary causes[1] and the wide-ranging impacts[2][3][4]: 3–36 of climate change. Some effects act as positive feedbacks that intensify climate change.[5]
Climate change affects the physical environment, ecosystems and human societies. Changes in the climate system include an overall warming trend, more extreme weather and rising sea levels. These in turn impact nature and wildlife, as well as human settlements and societies.[6] The effects of human-caused climate change are broad and far-reaching. This is especially so if there is no significant climate action. Experts sometimes describe the projected and observed negative impacts of climate change as the climate crisis.
Recent warming has had a big effect on natural biological systems.[9] It has degraded land by raising temperatures, drying soils and increasing wildfire risk.[10]: 9 Species all over the world are migrating towards the poles to colder areas. On land, many species move to higher ground, whereas marine species seek colder water at greater depths.[11] At 2 °C (3.6 °F) of warming, around 10% of species on land would become critically endangered.[12]: 259
Food security and access to fresh water are at risk due to rising temperatures. Climate change has profound impacts on human health. These can be direct impacts via heat stress. They can be indirect changes via the spread of infectious diseases. Humans are vulnerable and exposed to climate change in different ways. This varies by economic sector and by country. Wealthy industrialised countries, which have emitted the most CO2, have more resources. So they are the least vulnerable to global warming.[13] Climate change affects many economic sectors. They include agriculture, fisheries, forestry, energy, insurance, and tourism. Some groups may be particularly at risk from climate change, such as the poor, women, children and indigenous peoples.[14][15] Climate change can lead to displacement and changes in migration flows.[16]
Average surface air temperatures from 2011 to 2021 compared to the 1956–1976 average. Source: NASA
Global warming affects all parts of Earth's climate system.[17] Global surface temperatures have risen by 1.1 °C (2.0 °F). Scientists say they will rise further in the future.[18][19] The changes in climate are not uniform across the Earth. In particular, most land areas have warmed faster than most ocean areas. The Arctic is warming faster than most other regions.[7] Night-time temperatures have increased faster than daytime temperatures.[20] The impact on nature and people depends on how much more the Earth warms.[21]
Scientists use several methods to predict the effects of human-caused climate change. One is to investigate past natural changes in climate.[22] To assess changes in Earth's past climate scientists have studied tree rings, ice cores, corals, and ocean and lake sediments.[23] These show that recent temperatures have surpassed anything in the last 2,000 years.[24] By the end of the 21st century, temperatures may increase to a level last seen in the mid-Pliocene. This was around 3 million years ago.[25] At that time, mean global temperatures were about 2–4 °C (3.6–7.2 °F) warmer than pre-industrial temperatures. The global mean sea level was up to 25 meters higher than it is today.[26]: 323 The modern observed rise in temperature and CO2 concentrations has been rapid. even abrupt geophysical events in Earth's history do not approach current rates.[27]: 54
How much the world warms depends on human greenhouse gas emissions and how sensitive the climate is to greenhouse gases.[28] The more carbon dioxide (CO2) is emitted in the 21st century the hotter the world will be by 2100. For a doubling of greenhouse gas concentrations, the global mean temperature would rise by about 2.5–4 °C (4.5–7.2 °F).[29] What would happen if emissions of CO2 stopped abruptly and there was no use of negative emission technologies? The Earth's climate would not start moving back to its pre-industrial state. Temperatures would stay at the same high level for several centuries. After about a thousand years, 20% to 30% of human-emitted CO2 would remain in the atmosphere. The ocean and land would not have taken them. This would commit the climate to a warmer state long after emissions have stopped.[30]
With current mitigation policies the temperature will be about 2.7 °C (2.0–3.6 °C) above pre-industrial levels by 2100. It would rise to 2.4 °C (4.3 °F) if governments achieve all unconditional pledges and targets they have made. If all the countries that have set or are considering net-zero targets achieve them, the temperature will rise by around 1.8 °C (3.2 °F). There is a big gap between national plans and commitments and the actions that governments have taken around the world.[31]
Weather
The lower and middle atmosphere, where nearly all weather occurs, are heating due to the greenhouse effect.[32] Evaporation and atmospheric moisture content increase as temperatures rise.[33]Water vapour is a greenhouse gas, so this process is a self-reinforcing feedback.[34]
The excess water vapour also gets caught up in storms. This makes them more intense, larger, and potentially longer-lasting. This in turn causes rain and snow events to become stronger and leads to increased risk of flooding. Extra drying worsens natural dry spells and droughts. This increases risk of heat waves and wildfires.[33] Scientists have identified human activities as the cause of recent climate trends. They are now able to estimate the impact of climate change on extreme weather events. They call this process extreme event attribution. For instance such research can look at historical data for a region and conclude that a specific heat wave was more intense due to climate change.[35] In addition , the time shifts of the season onsets, changes in the lenght of the saeson durations have been reported in many regions of the world[36][37][38][39][40]. As a result of this, the timing of the extreme weather events such as heavy precipitaions and heat waves is changing in parallel with season shifting.
New high temperature records have outpaced new low temperature records on a growing portion of Earth's surface.[41]
Large increases in both the frequency and intensity of extreme weather events (for increasing degrees of global warming) are expected.[42]: 18
Map of increasing heatwave trends (frequency and cumulative intensity) over the midlatitudes and Europe, July–August 1979–2020[43]
Heatwaves over land have become more frequent and more intense in almost all world regions since the 1950s, due to climate change. Heat waves are more likely to occur simultaneously with droughts. Marine heatwaves are twice as likely as they were in 1980.[44] Climate change will lead to more very hot days and fewer very cold days.[45]: 7 There are fewer cold waves.[42]: 8
Experts can often attribute the intensity of individual heat waves to global warming. Some extreme events would have been nearly impossible without human influence on the climate system. A heatwave that would occur once every ten years before global warming started now occurs 2.8 times as often. Under further warming, heatwaves are set to become more frequent. An event that would occur every ten years would occur every other year if global warming reaches 2 °C (3.6 °F).[46]
Heat stress is related to temperature. It also increases if humidity is higher. The wet-bulb temperature measures both temperature and humidity. Humans cannot adapt to a wet-bulb temperature above 35 °C (95 °F). This heat stress can kill people. If global warming is kept below 1.5 or 2 °C (2.7 or 3.6 °F), it will probably be possible to avoid this deadly heat and humidity in most of the tropics. But there may still be negative health impacts.[47][48]
There is some evidence climate change is leading to a weakening of the polar vortex. This would make the jet stream more wavy.[49] This would lead to outbursts of very cold winter weather across parts of Eurasia[50] and North America and incursions of very warm air into the Arctic.[51][52][53]
Warming increases global average precipitation. Precipitation is when water vapour condenses out of clouds, such as rain and snow.[54]: 1057 Higher temperatures increase evaporation and surface drying. As the air warms it can hold more water. For every degree Celsius it can hold 7% more water vapour.[54]: 1057 Scientists have observed changes in the amount, intensity, frequency, and type of precipitation.[55] Overall, climate change is causing longer hot dry spells, broken by more intense rainfall.[56]: 151, 154
Climate change has increased contrasts in rainfall amounts between wet and dry seasons. Wet seasons are getting wetter and dry seasons are getting drier. In the northern high latitudes, warming has also caused an increase in the amount of snow and rain.[54]: 1057 In the Southern Hemisphere, the rain associated with the storm tracks has shifted south. Changes in monsoons vary a lot. More monsoon systems are becoming wetter than drier. In Asia summer monsoons are getting wetter. The West African monsoon is getting wetter over the central Sahel, and drier in the far western Sahel.[54]: 1058
Storms become wetter under climate change. These include tropical cyclones and extratropical cyclones. Both the maximum and mean rainfall rates increase. This more extreme rainfall is also true for thunderstorms in some regions.[57] Furthermore, tropical cyclones and storm tracks are moving towards the poles. This means some regions will see large changes in maximum wind speeds.[57][58] Scientists expect there will be fewer tropical cyclones. But they expect their strength to increase.[58] There has probably been an increase in the number of tropical cyclones that intensify rapidly.[57]
Impacts on land
Floods
The global average sea level has risen about 250 millimetres (9.8 in) since 1880,[59] increasing the elevation on top of which other types of flooding (high-tide flooding, storm surge) occur.
Long-term sea level rise occurs in addition to intermittent tidal flooding. NOAA predicts different levels of sea level rise for coastlines within a single country.[60]
Due to an increase in heavy rainfall events, floods are likely to become more severe when they do occur.[54]: 1155 The interactions between rainfall and flooding are complex. There are some regions in which flooding is expected to become rarer. This depends on several factors. These include changes in rain and snowmelt, but also soil moisture.[54]: 1156 Climate change leaves soils drier in some areas, so they may absorb rainfall more quickly. This leads to less flooding. Dry soils can also become harder. In this case heavy rainfall runs off into rivers and lakes. This increases risks of flooding.[54]: 1155
Droughts
A dry lakebed in California. In 2022, the state was experiencing its most serious drought in 1,200 years, worsened by climate change.[61]
Climate change affects many factors associated with droughts. These include how much rain falls and how fast the rain evaporates again. Warming over land increases the severity and frequency of droughts around much of the world.[62][54]: 1057 In some tropical and subtropical regions of the world, there will probably be less rain due to global warming. This will make them more prone to drought. Droughts are set to worsen in many regions of the world. These include Central America, the Amazon and south-western South America. They also include West and Southern Africa. The Mediterranean and south-western Australia are also some of these regions.[54]: 1157
Higher temperatures increase evaporation. This dries the soil and increases plant stress. Agriculture suffers as a result. This means even regions where overall rainfall is expected to remain relatively stable will experience these impacts.[54]: 1157 These regions include central and northern Europe. Without climate change mitigation, around one third of land areas are likely to experience moderate or more severe drought by 2100.[54]: 1157 Due to global warming droughts are more frequent and intense than in the past.[63]
Several impacts make their impacts worse. These are increased water demand, population growth and urban expansion in many areas.[64]Land restoration can help reduce the impact of droughts. One example of this is agroforestry.[65]
Wildfire disasters (those claiming at least 10 lives or affecting over 100 people) have increased substantially in recent decades.[66] Climate change intensifies heatwaves and droughts that dry vegetation, which in turn fuels wildfires.[66]
Climate change promotes the type of weather that makes wildfires more likely. In some areas, an increase of wildfires has been attributed directly to climate change. Evidence from Earth's past also shows more fire in warmer periods.[67]Climate change increases evaporation. This can cause vegetation to dry out. When a fire starts in an area with very dry vegetation, it can spread rapidly. Higher temperatures can also lengthen the fire season. This is the time of year in which severe wildfires are most likely, particularly in regions where snow is disappearing.[68]
Weather conditions are raising the risks of wildfires. But the total area burnt by wildfires has decreased. This is mostly because savanna has been converted to cropland, so there are fewer trees to burn. Prescribed burning isan indigenous practice in the US and Australia. It can reduce wildfire burning.[68] The carbon released from wildfires can add to greenhouse gas concentrations. Climate models do not yet full reflect this feedback.[42]: 20
Oceans
Oceans have taken up almost 90% of the excess heat accumulated on Earth due to global warming.[69]Part of the Great Barrier Reef in Australia in 2016 after a coral bleaching event
Ocean temperature stratification is the difference in temperature between the various layers of the ocean. It increases as the ocean surface warms due to rising air temperatures.[73]: 471 The decline in mixing of the ocean layers stabilizes warm water near the surface. It also reduces cold, deep water circulation. The reduced vertical mixing makes it harder for the ocean to absorb heat. So a larger share of future warming goes into the atmosphere and land. One result is an increase in the amount of energy available for tropical cyclones and other storms. Another result is a decrease in nutrients for fish in the upper ocean layers. These changes also reduce the ocean's capacity to store carbon.[74] At the same time, contrasts in salinity are increasing. Salty areas are becoming saltier and fresher areas less salty.[75]
Warmer water cannot contain the same amount of oxygen as cold water. As a result, oxygen from the oceans moves to the atmosphere. Increased thermal stratification may reduce the supply of oxygen from surface waters to deeper waters. This lowers the water's oxygen content even more.[76] The ocean has already lost oxygen throughout its water column. Oxygen minimum zones are expanding worldwide.[73]: 471
Sea level rise
Between 1901 and 2018, the average global sea level rose by 15–25 cm (6–10 in), or an average of 1–2 mm per year.[77] This rate accelerated to 4.62 mm/yr for the decade 2013–2022.[78]Climate change due to human activities is the main cause. Between 1993 and 2018, thermal expansion of water accounted for 42% of sea level rise. Melting temperate glaciers accounted for 21%, with Greenland accounting for 15% and Antarctica 8%.[79]: 1576 Sea level rise lags changes in the Earth's temperature. So sea level rise will continue to accelerate between now and 2050 in response to warming that is already happening.[80] What happens after that will depend on what happens with human greenhouse gas emissions. Sea level rise may slow down between 2050 and 2100 if there are deep cuts in emissions. It could then reach a little over 30 cm (1 ft) from now by 2100. With high emissions it may accelerate. It could rise by 1 m (3+1⁄2 ft) or even 2 m (6+1⁄2 ft) by then.[81][82] In the long run, sea level rise would amount to 2–3 m (7–10 ft) over the next 2000 years if warming amounts to 1.5 °C (2.7 °F). It would be 19–22 metres (62–72 ft) if warming peaks at 5 °C (9.0 °F).[81]: 21
Rising seas ultimately impact every coastal and island population on Earth.[83][84] This can be through flooding, higher storm surges, king tides, and tsunamis. These have many knock-on effects. They lead to loss of coastal ecosystems like mangroves. Crop production falls because of salinization of irrigation water and damage to ports disrupts sea trade.[85][86][87] The sea level rise projected by 2050 will expose places currently inhabited by tens of millions of people to annual flooding. Without a sharp reduction in greenhouse gas emissions, this may increase to hundreds of millions in the latter decades of the century.[88] Areas not directly exposed to rising sea levels could be affected by large scale migrations and economic disruption.
Earth lost 28 trillion tonnes of ice between 1994 and 2017, with melting grounded ice (ice sheets and glaciers) raising the global sea level by 34.6 ±3.1 mm.[89] The rate of ice loss has risen by 57% since the 1990s−from 0.8 to 1.2 trillion tonnes per year.[89]Melting of glacial mass is approximately linearly related to temperature rise.[90]Shrinkage of snow cover duration in the Alps, starting ca. end of the 19th century, highlighting climate change adaptation needs[91]
The cryosphere, the area of the Earth covered by snow or ice, is extremely sensitive to changes in global climate.[92] There has been an extensive loss of snow on land since 1981. Some of the largest declines have been observed in the spring.[93] During the 21st century, snow cover is projected to continue its retreat in almost all regions.[94]: 39–69
Since the beginning of the twentieth century, there has been a widespread retreat of glaciers.[95]: 1215 Those glaciers that are not associated with the polar ice sheets lost around 8% of their mass between 1971 and 2019.[95]: 1275 In the Andes in South America and in the Himalayas in Asia, the retreat of glaciers could impact water supply.[96][97] The melting of those glaciers could also cause landslides or glacial lake outburst floods.[98]
The melting of the Greenland and West Antarctic ice sheets will continue to contribute to sea level rise over long time-scales. The Greenland ice sheet loss is mainly driven by melt from the top. Antarctic ice loss is driven by warm ocean water melting the outlet glaciers.[95]: 1215
Future melt of the West Antarctic ice sheet is potentially abrupt under a high emission scenario, as a consequence of a partial collapse.[99]: 595–596 Part of the ice sheet is grounded on bedrock below sea level. This makes it possibly vulnerable to the self-enhancing process of marine ice sheet instability. Marine ice cliff instability could also contribute to a partial collapse. But there is limited evidence for its importance.[95]: 1269–1270 A partial collapse of the ice sheet would lead to rapid sea level rise and a local decrease in ocean salinity. It would be irreversible for decades and possibly even millennia.[99]: 595–596 The complete loss of the West Antarctic ice sheet would cause over 5 metres (16 ft) of sea level rise.[100]
In contrast to the West Antarctic ice sheet, melt of the Greenland ice sheet is projected to take place more gradually over millennia.[99]: 595–596 Sustained warming between 1 °C (1.8 °F) (low confidence) and 4 °C (7.2 °F) (medium confidence) would lead to a complete loss of the ice sheet. This would contribute 7 m (23 ft) to sea levels globally.[26]: 363 The ice loss could become irreversible due to a further self-enhancing feedback. This is called the elevation-surface mass balance feedback. When ice melts on top of the ice sheet, the elevation drops. Air temperature is higher at lower altitudes, so this promotes further melting.[26]: 362
Reporting the reduction in Antarctic sea ice extent in mid 2023, researchers concluded that a "regime shift" may be taking place "in which previously important relationships no longer dominate sea ice variability".[101]
Sea ice reflects 50% to 70% of the incoming solar radiation back into space. Only 6% of incoming solar energy is reflected by the ocean.[102] As the climate warms, the area covered by snow or sea ice decreases. After sea ice melts, more energy is absorbed by the ocean, so it warms up. This ice-albedo feedback is a self-reinforcing feedback of climate change.[103] Large-scale measurements of sea ice have only been possible since we have been using satellites.[104]
Sea ice in the Arctic has declined in recent decades in area and volume due to climate change. It has been melting more in summer than it refreezes in winter. The decline of sea ice in the Arctic has been accelerating during the early twenty-first century. It has a rate of decline of 4.7% per decade. It has declined over 50% since the first satellite records.[105][106][107] Ice-free summers are expected to be rare at 1.5 °C (2.7 °F) degrees of warming. They are set to occur at least once every decade with a warming level of 2 °C (3.6 °F).[108]: 8 The Arctic will likely become ice-free at the end of some summers before 2050.[95]: 9
Sea ice extent in Antarctica varies a lot year by year. This makes it difficult to determine a trend, and record highs and record lows have been observed between 2013 and 2023. The general trend since 1979, the start of the satellite measurements, has been roughly flat. Between 2015 and 2023, there has been a decline in sea ice, but due to the high variability, this does not correspond to a significant trend.[109]
Globally, permafrost warmed by about 0.3 °C between 2007 and 2016. The extent of permafrost has been falling for decades. More decline is expected in the future.[95]: 1280 Permafrost thaw makes the ground weaker and unstable. The thaw can seriously damage human infrastructure in permafrost areas such as railways, settlements and pipelines.[110]: 236 Thawing soil can also release methane and CO2 from decomposing microbes. This can generate a strong feedback loop to global warming.[111][112] Some scientists believe that carbon storage in permafrost globally is approximately 1600 gigatons. This is twice the atmospheric pool.[113]
Recent warming has had a big effect on natural biological systems.[9]Species worldwide are moving poleward to colder areas. On land, species may move to higher elevations. Marine species find colder water at greater depths.[11] Climate change had the third biggest impact on nature out of various factors in the five decades up to 2020. Only change in land use and sea use and direct exploitation of organisms had a bigger impact.[114]
The impacts of climate change on nature are likely to become bigger in the next few decades.[115] The stresses caused by climate change, combine with other stresses on ecological systems such as land conversion, land degradation, harvesting, and pollution. They threaten substantial damage to unique ecosystems. They can even result in their complete loss and the extinction of species.[116][117] This can disrupt key interactions between species within ecosystems. This is because species from one location do not leave the warming habitat at the same rate. The result is rapid changes in the way the ecosystem functions.[11] Impacts include changes in regional rainfall patterns. Another is earlier leafing of trees and plants over many regions. Movements of species to higher latitudes and altitudes,[118] changes in bird migrations, and shifting of the oceans' plankton and fish from cold- to warm-adapted communities are other impacts.[119]
These changes of land and ocean ecosystems have direct effects on human well-being.[120][121] For instance, ocean ecosystems help with coastal protection and provide food.[121] Freshwater and land ecosystems can provide water for human consumption. Furthermore, these ecosystems can store carbon. This helps to stabilize the climate system.[120]
Climate change is a major driver of biodiversity loss in different land types. These include cool conifer forests, savannas, mediterranean-climate systems, tropical forests, and the Arctic tundra.[122] In other ecosystems, land-use change may be a stronger driver of biodiversity loss, at least in the near term.[122] Beyond 2050, climate change may be the major cause of biodiversity loss globally.[122] Climate change interacts with other pressures. These include habitat modification, pollution and invasive species. Through this interaction, climate change increases the risk of extinction for many terrestrial and freshwater species.[123] At 1.2 °C (2.2 °F) of warming (around 2023[124]) some ecosystems are threatened by mass die-offs of trees and from heatwaves.[125] At 2 °C (3.6 °F) of warming, around 10% of species on land would become critically endangered. This differs by group. For instance insects and salamanders are more vulnerable.[12]: 259
The rate of global tree cover loss has approximately doubled since 2001, to an annual loss approaching an area the size of Italy.[126]
Rainfall on the Amazon rainforest is recycled when it evaporates back into the atmosphere instead of running off away from the rainforest. This water is essential for sustaining the rainforest. Due to deforestation the rainforest is losing this ability. This effect is even worse because climate change brings more frequent droughts to the area. The higher frequency of droughts in the first two decades of the 21st century and other data signal that a tipping point from rainforest to savanna might be close. A 2019 study concluded that this ecosystem could begin a 50-year-long collapse to a savanna around 2021. After that it would become increasingly and disproportionally more difficult to prevent or reverse this shift.[127][128][129]
Marine heatwaves are happening more often. They have widespread impacts on life in the oceans. These include mass dying events and coral bleaching.[130]Harmful algae blooms have increased. This is in response to warming waters, loss of oxygen and eutrophication.[131]: 451 Melting sea ice destroys habitat, including for algae that grows on its underside.[132]
Ocean acidification can harm marine organisms in various ways. Shell-forming organisms like oysters are particularly vulnerable. Some phytoplankton and seagrass species may benefit. However, some of these are toxic to fish phytoplankton species. Their spread poses risks to fisheries and aquaculture. Fighting pollution can reduce the impact of acidification.[133]
Warm-water coral reefs are very sensitive to global warming and ocean acidification. Coral reefs provide a habitat for thousands of species. They provide ecosystem services such as coastal protection and food. The resilience of reefs can be improved by curbing local pollution and overfishing. But 70–90% of today's warm-water coral reefs will disappear even if warming is kept to 1.5 °C (2.7 °F).[134]: 179 Coral reefs are framework organisms. They build physical structures that form habitats for other sea creatures. Other framework organisms are also at risk from climate change. Mangroves and seagrass are considered to be at moderate risk from lower levels of global warming.[134]: 225
Possible tipping elements in the climate systemExamples of some effects of global warming that can amplify (positive feedbacks) or reduce (negative feedbacks) global warming[135][136] Observations and modeling studies indicate that there is a net positive feedback to Earth's current global warming.[137] Positive feedbacks can propel the climate system toward tipping points.
Feedbacks that reinforce themselves can make climate change worse.[138] The climate system exhibits "threshold behaviour" or tipping points when these feedbacks lead parts of the Earth system into a new state. Examples are the runaway loss of ice sheets or the dieback of forests.[139][140] Tipping behaviour is found in all parts of the climate system. These include ecosystems, ice sheets, and the circulation of the ocean and atmosphere.[141] Tipping points are studied using data from Earth's distant past and by physical modelling.[139] There is already moderate risk of global tipping points at 1 °C (1.8 °F) above pre-industrial temperatures. That becomes a high risk at 2.5 °C (4.5 °F).[134]: 254, 258 It is possible that some tipping points are close or have already been crossed. Examples are the West Antarctic and Greenland ice sheets, the Amazon rainforest and warm-water coral reefs.[142]
Tipping points are perhaps the most dangerous aspect of future climate change. They would lead to irreversible impacts on society.[143] A collapse of the Atlantic meridional overturning circulation would likely halve rainfall in India. It would probably lead to severe drops in temperature in Northern Europe.[144] Many tipping points are interlinked. This means triggering one may lead to a cascade of effects.[145] This could happen even well below 2 °C (3.6 °F) of warming.[146] A 2018 study states that 45% of environmental problems, including those caused by climate change, are interconnected. This makes the risk of a domino effect bigger.[147][148]
Further impacts may be irreversible, at least over the timescale of many human generations.[149] This includes warming of the deep ocean and acidification. These are set to continue even when global temperatures stop rising.[150] In biological systems, the extinction of species would be an irreversible impact.[149] In social systems, unique cultures may be lost.[149] Climate change could make it more likely that endangered languages disappear.[151]
Health, food security and water security
Humans have a climate niche. This is a certain range of temperatures in which they flourish. Outside that niche, conditions are less favourable. This leads to negative effects on health, food security and more. This niche is a mean annual temperature above 29ºC. As of May 2023, 60 million people lived outside this niche. With every additional 0.1 degree of warming, 140 million people will be pushed out of it.[152]
Health
The effects of climate change on human health are increasingly well studied and quantified.[153][154] Rising temperatures and changes in weather patterns are increasing the frequency and severity of heat waves, wildfires, droughts, floods, landslides, hurricanes, and other causes of injury and illness. Heat waves and extreme weather events have a big impact on health both directly and indirectly. Direct effects of exposure to high and extended temperatures include illness, reduced labour capacity for outdoor workers, and heat-related mortality.[155]
In addition to direct impacts, climate change and extreme weather events cause changes in the biosphere. Climate-sensitive pathogens and vector-borne diseases may increase in some regions. Changes in temperature are creating conditions favorable to mosquito-borne diseases such as dengue fever, and waterborne diseases including diarrhoeal disease.[155][156] Climate change will impact where infectious diseases are able to spread in the future. Many infectious diseases will spread to new geographic areas where people have not previously been exposed or developed immunity.[157][158]
Changes in climate can cause decreasing yields for some crops and regions, resulting in higher food costs, food insecurity, and undernutrition. Water insecurity is also a concern. Increases in poverty, displacement, migration, violent conflict, and negative effects on mental health are all occurring.[159][160][155]
The effects of climate change on mental health and wellbeing are documented. This is especially the case for vulnerable populations and those with pre-existing serious mental illness.[161] There are three broad pathways by which these effects can take place: directly, indirectly or via awareness.[162] The direct pathway includes stress-related conditions caused by exposure to extreme weather events. These include post-traumatic stress disorder (PTSD). Scientific studies have linked mental health to several climate-related exposures. These include heat, humidity, rainfall, drought, wildfires and floods.[163] The indirect pathway can be disruption to economic and social activities. An example is when an area of farmland is less able to produce food.[163] The third pathway can be of mere awareness of the climate change threat, even by individuals who are not otherwise affected by it.[162]
An additional aspect to consider is the detrimental impact climate change can have on green or blue natural spaces, which in themselves have been proven to have beneficial impact on mental health.[164][165] Impacts of anthropogenic climate change, such as freshwater pollution or deforestation, degrade these landscapes and reduce public access.[166] Even when the green and blue spaces are intact, access to them is not equal across society, which is an issue of environmental justice and economic inequality.[167]
Climate change will affect agriculture and food production around the world. The reasons include the effects of elevated CO2 in the atmosphere. Higher temperatures and altered precipitation and transpiration regimes are also factors. Increased frequency of extreme events and modified weed, pest, and pathogen pressure are other factors.[168] Droughts result in crop failures and the loss of pasture for livestock.[169] Loss and poor growth of livestock cause milk yield and meat production to decrease.[170] The rate of soil erosion is 10–20 times higher than the rate of soil accumulation in agricultural areas that use no-till farming. In areas with tilling it is 100 times higher. Climate change worsens this type of land degradation and desertification.[10]: 5
Climate change is projected to negatively affect all four pillars of food security. It will affect how much food is available. It will also affect how easy food is to access through prices, food quality, and how stable the food system is.[171] Climate change is already affecting the productivity of wheat and other staples.[172][173]
In many areas, fishery catches are already decreasing because of global warming and changes in biochemical cycles. In combination with overfishing, warming waters decrease the amount of fish in the ocean.[4]: 12 Per degree of warming, ocean biomass is expected to decrease by about 5%. Tropical and subtropical oceans are most affected, while there may be more fish in polar waters.[174]
Water security
Water resources can be affected by climate change in various ways. The total amount of freshwater available can change, for instance due to dry spells or droughts. Heavy rainfall and flooding can have an impact on water quality. They can transport pollutants into water bodies through increased surface runoff. In coastal regions, more salt may find its way into water resources due to higher sea levels and more intense storms. Higher temperatures also directly degrade water quality. This is because warm water contains less oxygen.[175] Changes in the water cycle threaten existing and future water infrastructure. It will be harder to plan investments for water infrastructure. This is because there are significant uncertainties about future variability of the water cycle.[176]
Between 1.5 and 2.5 billion people live in areas with regular water security issues. If global warming reaches 4 °C (7.2 °F), water insecurity would affect about twice as many people.[175] Water resources are likely to decrease in most dry subtropical regions and mid-latitudes. But they will increase in high latitudes. However, variable streamflow means even regions with increased water resources can experience additional short-term shortages.[177]: 251 In the arid regions of India, China, the US and Africa dry spells and drought are already affecting water availability.[175]
Human settlement
Climate change is particularly likely to affect the Arctic, Africa, small islands, Asian megadeltas and the Middle East regions.[178][179] Low-latitude, less-developed regions are most at risk of experiencing negative climate change impacts.[14] The ten countries of the Association of Southeast Asian Nations (ASEAN) are among the most vulnerable in the world to the negative effects of climate change. ASEAN's climate mitigation efforts are not in proportion to the climate change threats the region faces.[180]
Overlap between future population distribution and extreme heat in a high emission scenario[181]
Regions inhabited by a third of the human population could become as hot as the hottest parts of the Sahara within 50 years. This would happen if greenhouse gas emissions continue to grow rapdily without a change in patterns of population growth and without migration. The projected average temperature of above 29 °C (84 °F) for these regions would be outside the "human temperature niche". This is a range for climate that is biologically suitable for humans. It is based on historical data of mean annual temperatures. The most affected regions have little adaptive capacity.[182][183]
Increased extreme heat exposure from climate change and the urban heat island effect threatens urban settlements.[184] This is made worse by the loss of shade from urban trees that cannot withstand the heat stress.[185]
In 2019, the Crowther Lab from ETH Zurich paired the climatic conditions of 520 major cities worldwide with the predicted climatic conditions of cities in 2050. It found that 22% of the major cities would have climatic conditions that do not exist in any city today. For instance, 2050 London would have a climate similar to 2019 Melbourne in Australia. Athens and Madrid would be like Fez in Morocco. Nairobi in Kenya would be like Maputo in Mozambique. The Indian city Pune would be like Bamako in Mali and Bamako would be like Niamey in Niger. Brasilia would be like Goiania, both in Brazil.[186][187]
Low-lying cities and other settlements near the sea face multiple simultaneous risks from climate change. They face flooding risks from sea level rise. In addition they may face impacts from more severe storms, ocean acidification, and salt intrusion into the groundwater. Changes like continued development in exposed areas increase the risks that these regions face.[188]
Floodplains and low-lying coastal areas will flood more frequently due to climate change, like this area of Myanmar which was submerged by Cyclone Nargis.
Population density on the coasts is high. Estimates of the number of people at risk of coastal flooding from climate-driven sea level rise vary. Estimates range from 190 million[189] to 300 million. It could even be 640 million in a worst-case scenario related to the instability of the Antarctic ice sheet.[190][191] People are most affected in the densely-populated low-lying megadeltas of Asia and Africa.[192]
Small island developing states are especially vulnerable. They are likely to experience more intense storm surges, salt water intrusion and coastal destruction.[193] Low-lying small islands in the Pacific, Indian, and Caribbean regions even risk permanent inundation. This would displace their population.[194][195][196] On the islands of Fiji, Tonga and western Samoa, migrants from outer islands inhabit low and unsafe areas along the coasts.[196] The entire populations of small atoll nations such as Kiribati, Maldives, the Marshall Islands, and Tuvalu are at risk of being displaced.[197][194] This could raise issues of statelessness.[198] Several factors increase their vulnerability. These are small size, isolation from other land, low financial resources, and lack of protective infrastructure.[194]
Impacts on societies
Climate change has many impacts on society. It affects health, the availability of drinking water and food, inequality and economic growth. The effects of climate change are often interlinked. They can exacerbate each other as well as existing vulnerabilities.[199][200][201] Some areas may become too hot for humans to live in.[202][203] Climate-related changes or disasters may lead people in some areas to move to other parts of the country or to other countries.
Some scientists describe the effects of climate change, with continuing increases in greenhouse gas emissions, as a "climate emergency" or "climate crisis".[204][205] Some researchers[206][207] and activists[208] describe them as an existential threat to civilization. Some define these threats under climate security. The consequences of climate change, and the failure to address it, can distract people from tackling its root causes. This leads to what some researchers have termed a "climate doom loop".[209]
Displacement is when people move within a country. Migration is when they move to another country. Some people use the terms interchangeably. Climate change affects displacement in several ways. More frequent and severe weather-related disasters may increase involuntary displacement. These destroy homes and habitats. Climate impacts such as desertification and rising sea levels gradually erode livelihoods. They force communities to abandon traditional homelands. Other forms of migration are adaptive and voluntary. They are based on individual or household decisions.[210]: 1079 On the other hand, some households may fall into poverty or get poorer due to climate change. This limits their ability to move to less affected areas.[211]
Migration due to climate and weather is usually within countries. But it is long-distance. Slow-onset disasters such as droughts and heat are more likely to cause long-term migration than weather disasters like floods.[211] Migration due to desertification and reduced soil fertility is typically from rural areas in developing countries to towns and cities.[212]: 109
According to the Internal Displacement Monitoring Centre, extreme weather events displaced approximately 30 million people in 2020. Violence and wars displaced approximately 10 million in the same year. There may have been a contribution of climate change to these conflicts.[213][214] In 2018, the World Bank estimated that climate change will cause internal migration of between 31 and 143 million people by 2050. This would be as they escape crop failures, water scarcity, and sea level rise. The study covered only Sub-Saharan Africa, South Asia, and Latin America.[215][216]
Sea level rise at the Marshall Islands, reaching the edge of a village (from the documentary One Word)
Overlap between state fragility, extreme heat, and nuclear and biological catastrophic hazards[181]
Climate change can worsen conflicts over water and other resources. Climate change can also cause large population dislocations and migration. This can lead to increased tensions.[217][218] At the micro level, climate change has also been found to lead to spikes in violent crime.[219] Scientists have found that factors other than climate change were more important in affecting conflict over the last century. One such factor is inequality between groups. Another is low socio-economic development.[220] In some cases, climate change can lead to more peaceful relationships between groups. This is because environmental problems need common policies.[221]
Global warming has been described as a "threat multiplier".[222] Conditions in certain places make it more likely that climate change will have an impact on conflict. These include ethnic exclusion, economies dependent on agriculture, insufficient infrastructure, poor local governance, and low levels of development.[221] A spike in wheat prices following crop losses from a period of drought may have contributed to the onset of the "Arab Spring" protests and revolutions in 2010.[223][221]
Business activities affected by climate changed as found in the European Investment Bank Investment Survey 2020
Economic forecasts of the impact of global warming vary considerably. The impacts are worse if there is insufficient adaptation.[224] Economic modelling may underrate the impact of catastrophic climatic changes. When estimating losses, economists choose a discount rate. This determines how much one prefers to have goods or cash now compared to at a future date. Using a high discount rate may understate economic losses. This is because losses for future generations weigh less heavily.[225]
Economic impacts are bigger the more the temperature rises.[226] Scientists have compared impacts with warming of 1.5 ºC (2.7 ºF) and a level of 3.66 ºC (6.59 ºF). They use this higher figure to represent no efforts to stop emissions. They found that total damages at 1.5 ºC were 90% less than at 3.66 ºC. [134]: 256 One study found that global GDP at the end of the century would be 3.5% less if warming is limited to 3 °C (5.4 °F). This study excludes the potential effect of tipping points. Another study found that excluding tipping points underestimates the global economic impact by a factor of two to eight.[134]: 256 Another study found that a temperature rise of 2 °C (3.6 °F) by 2050 would reduce global GDP by 2.5%–7.5%. By 2100 in this scenario the temperature would rise by 4 °C (7.2 °F). This could reduce global GDP by 30% in the worst case.[227]
Global losses reveal rapidly rising costs due to extreme weather events since the 1970s.[228] Socio-economic factors have contributed to the observed trend of global losses. These factors include population growth and increased wealth.[229] Regional climatic factors also play a role. These include changes in precipitation and flooding events. It is difficult to quantify the relative impact of socio-economic factors and climate change on the observed trend.[230] The trend does suggest social systems are increasing vulnerable to climate change.[230]
Economic inequality
Rich nations have done the most to fuel climate change.[231]
Climate change has contributed to global economic inequality. Wealthy countries in colder regions have felt little overall economic impact from climate change or may have benefited. Poor hotter countries probably grew less than if there had been no global warming.[232][233]
Highly affected sectors
Climate change has a bigger impact on economic sectors directly affected by weather than on other sectors.[234] It heavily affects agriculture, fisheries and forestry.[235] It also affects the tourism and energy sectors.[234] Agriculture and forestry have suffered economic losses due to droughts and extreme heat.[236] If global warming goes over 1.5 ºC, there may be limits to how much tourism and outdoor work can adapt.[237]
In the energy sector, thermal power plants depend on water to cool them. Climate change can increase the likelihood of drought and fresh water shortages. Higher operating temperatures make them less efficient. This reduces their output.[238] Hydropower is affected by changes in the water cycle such as river flows. Diminished river flows can cause power shortages in areas that depend on hydroelectric power. Brazil relies on hydroelectricity. So it is particularly vulnerable. Rising temperatures, lower water flow, and changes in rainfall could reduce total energy production by 7% annually by the end of the century.[238] Climate change affects oil and natural gas infrastructure. This is also vulnerable to the increased risk of disasters such as storms, cyclones, flooding and rising sea levels.[239]
Global warming affects the insurance and financial services sectors.[134]: 212–213, 228, 252 Insurance is an important tool to manage risks. But it is often unavailable to poorer households. Due to climate change, premiums are going up for certain types of insurance, such as flood insurance. Poor adaptation to climate change further widens the gap between what people can afford and the costs of insurance, as risks increase.[240] In 2019 Munich Re said climate change could make home insurance unaffordable for households at or below average incomes.[241]
Social impacts on vulnerable groups
Climate change does not affect people within communities in the same way. It can have a bigger impact on vulnerable groups such as women, the elderly, religious minorities and refugees than on others.[242]
People living in poverty: Climate change disproportionally affects poor people in low-income communities and developing countries around the world. Those in poverty have a higher chance of experiencing the ill-effects of climate change, due to their increased exposure and vulnerability.[243] A 2020 World Bank paper estimated that between 32 million to 132 million additional people will be pushed into extreme poverty by 2030 due to climate change.[244]
Women: Climate change increases gender inequality.[245] It reduces women's ability to be financially independent,[246] and has an overall negative impact on the social and political rights of women. This is especially the case in economies that are heavily based on agriculture.[245]
Indigenous peoples: Indigenous communities tend to rely more on the environment for food and other necessities. This makes them more vulnerable to disturbances in ecosystems.[247] Indigenous communities across the globe generally have bigger economic disadvantages than non-indigenous communities. This is due to the oppression they have experienced. These disadvantages include less access to education and jobs and higher rates of poverty. All this makes them more vulnerable to climate change.[248]
Children: The Lancet review on health and climate change lists children among the worst-affected by global warming.[249] Children are 14–44 percent more likely to die from environmental factors.[250]
Climate change has long been described as a severe risk to humans. Climate change as an existential threat has emerged as a key theme in the climate movement. People from small island nations also use this theme. There has not been extensive research in this topic. Existential risks are threats that could cause the extinction of humanity or destroy the potential of intelligent life on Earth.[251] Key risks of climate change do not fit that definition. However, some key climate risks do have an impact people's ability to survive. For instance, areas may become too hot to survive, or sea level rise may make it impossible to live at a specific location.[252][253][251]
Long-term scenarios (up to 2500)
In 2021, researchers found that projecting effects of greenhouse gas emissions only for up to 2100, as widely practiced in research and policy-making, is short-sighted. They then modeled RCPs, climate change scenarios and their effects for up to 2500.[254][255]
Projections for crop suitability to 2100 and 2500 under the moderate–high RCP6.0 emission scenario
Global mean near-surface air temperature and thermosteric sea-level rise anomalies relative to the 2000–2019 mean for RCP scenarios
Mean number of months per year where heat stress exceeds 38°C (UTCI scale) in present (2020) and future climates
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