Effects of climate change

For effects of changes in climate prior to the current period of global warming, see Historical climatology.

Some climate change effects, clockwise from top left: Wildfire caused by heat and dryness, bleached coral caused by ocean acidification and heating, coastal flooding caused by storms and sea level rise, and environmental migration caused by desertification

The primary causes and the wide-ranging impacts of climate change. Some effects act as feedbacks that intensify climate change.

The effects of climate change span the impacts on physical environment, ecosystems and human societies due to human-caused climate change. The future impact of climate change depends on how much nations reduce greenhouse gas emissions and adapt to climate change. Effects that scientists predicted in the past—loss of sea ice, accelerated sea level rise and longer, more intense heat waves—are now occurring. The changes in climate are not uniform across the Earth. In particular, most land areas have warmed faster than most ocean areas, and the Arctic is warming faster than most other regions. The regional changes vary: at high latitudes it is the average temperature that is increasing, while for the oceans and tropics it is in particular the rainfall and the water cycle where changes are observed. Global warming changes regional climate via the melting of ice, changes in the hydrological cycle (such as rainfall) and changing currents in the oceans.

Physical changes include extreme weather, glacier retreat, sea level rise, declines in Arctic sea ice, and changes in the timing of seasonal events (such as earlier spring flowering). Since 1970, the ocean has absorbed more than 90% of the excess heat in the climate system. Even if global surface temperature is stabilized, sea levels will continue to rise and the ocean will continue to absorb excess heat from the atmosphere for many centuries. The uptake of carbon dioxide from the atmosphere is leading to ocean acidification.

Climate change has degraded land by raising temperatures, drying soils and increasing wildfire risk. Recent warming has strongly affected natural biological systems. Species worldwide are migrating poleward to colder areas. On land, many species move to higher elevations, whereas marine species seek colder water at greater depths. Between 1% and 50% of species on land were assessed to be at substantially higher risk of extinction due to climate change. Coral reefs and shellfish are vulnerable to the combined threat of ocean warming and acidification. Species biodiversity in urban areas are at risk due to the effects of climate change. Urbanization and industrialization have been linked to various factors of climate change such as pollution and temperature changes. Sea level rise remains a major concern for cities are along coastlines, affecting human settlements and infrastructure. The cities with warmer temperatures tend to have more frequent and severe thunderstorms and lightning.

Food security and access to fresh water are at risk due to rising temperatures. Climate change has profound impacts on human health, directly via heat stress and indirectly via the spread of infectious diseases. The vulnerability and exposure of humans to climate change varies by economic sector and by country. Wealthy industrialised countries, which have emitted the most CO₂, have more resources and so are the least vulnerable to global warming. Economic sectors that are likely to be affected include agriculture, fisheries, forestry, energy, insurance, financial services, tourism, and recreation. Some groups may be particularly at risk from climate change, such as the poor, women, children and indigenous peoples. They also have much lower levels of capacity for coping with the effects of environmental change. Climate change can result in environmental migration, especially in developing countries where people are directly dependent on land for food.

Observed and future changes in temperature

Further information: Global surface temperature, Instrumental temperature record, Heat wave, Ocean temperature, and Marine heatwave

Average surface air temperatures from 2011 to 2021 compared to the 1956–1976 average. Source: NASA

Global warming affects all elements of Earth's climate system. Global surface temperatures have risen by 1 °C and are expected to rise further in the future. Night-time temperatures have increased faster than daytime temperatures. The impact on the environment, wildlife, society and humanity depends on how much more the Earth warms.

One of the methods scientists use to predict the effects of human-caused climate change is to investigate past natural changes in climate. To assess changes in Earth's past climate scientists have studied tree rings, ice cores, corals, and ocean and lake sediments. These show that recent warming has surpassed anything in the last 2,000 years. By the end of the 21st century, temperatures may increase to a level not experienced since the mid-Pliocene, around 3 million years ago. At that time, mean global temperatures were about 2–4 °C warmer than pre-industrial temperatures, and the global mean sea level was up to 25 meters higher than it is today.

Projected temperature and sea-level rise relative to the 2000–2019 mean for RCP climate change scenarios up to 2500.

How much the world warms depends on what humans do or not to limit GHG emissions, and how sensitive the climate is to greenhouse gases. Scientists are pretty sure that with double the amount of GHG in the atmosphere the world would warm by 2.5 °C to 4 °C; but how much more humans will emit is less certain. The projected magnitude of warming by 2100 is closely related to the level of cumulative emissions over the 21st century (total emissions between 2000 and 2100). The higher the cumulative emissions over this time period, the greater the level of warming is projected to occur.

If emissions of CO₂ were to be abruptly stopped and no negative emission technologies deployed, the Earth's climate would not start moving back to its pre-industrial state. Instead, temperatures would stay elevated at the same level for several centuries. After about a thousand years, 20% to 30% of human-emitted CO₂ will remain in the atmosphere, not taken up by the ocean or the land, committing the climate to a warmer state long after emissions have stopped.

Mitigation policies currently in place will result in about 2.7 °C (2.0–3.6 °C, depending on how sensitive the climate is to greenhouse gas emissions) warming above pre-industrial levels. If all unconditional pledges and targets made by governments are achieved the temperature will rise by around 2.4 °C. If additionally all the countries that adopted or are considering to adopt net-zero targets will achieve it the temperature will rise by a median of 1.8 °C. There is a substantial gap between national plans and commitments and actions so far taken by governments around the world.

Weather-related changes

See also: Extreme weather

A dry lakebed in California, which is in 2022 experiencing its most serious drought in 1,200 years, worsened by climate change.

For the most part, weather continues much as it has, except climate change makes many aspects more extreme, especially heat waves, drought, rain intensity, and storm size and intensity. That is, climate change does not create these events, it exacerbates them. Global warming leads to an increase in extreme weather events such as heat waves, droughts, cyclones, blizzards and rainstorms. Such events will continue to occur more often and with greater intensity. Some individual extreme weather events are made worse by climate change.

The lower and middle atmosphere, where nearly all of the weather occurs, are heating due to the enhanced greenhouse effect. Increased greenhouse gases cause the higher parts of the atmosphere, the stratosphere, to cool. The heated atmosphere contains more water vapour, which is also a greenhouse gas and acts as a self-reinforcing feedback.

As temperatures increase, so does evaporation and atmospheric moisture content that increases heating by trapping outgoing radiation. Excess water vapour gets caught up in storms and makes them more intense, larger, and potentially longer lasting, so that rain and snow events are stronger and increase risk of flooding. Extra drying worsens any natural dry spells and droughts, and increases risk of heat waves and wildfires.

Rain and snow

Main article: Effects of climate change on the water cycle

Warming by greenhouse gas forcing has increased contrasts in rainfall amounts between wet and dry seasons, meaning "wet seasons are getting wetter, dry seasons are getting drier". Over oceans, salty areas are getting saltier and other regions are becoming less saline. Warming has also resulted in a detectable increase in the precipitation of northern high latitudes.

Higher temperatures lead to increased evaporation and surface drying. As the air warms, its water-holding capacity also increases, particularly over the oceans. Air can hold 7% more water vapour for every degree Celsius it is warmed. Changes have already been observed in the amount, intensity, frequency, and type of precipitation. Widespread increases in heavy precipitation have occurred even in places where total rain amounts have decreased.

In the case of precipitation, the rising temperatures and extra heat will "intensify" the Earth's water cycle, which means it will increase evaporation. Increased atmospheric water vapour results in more frequent and intense downpours and causes stronger extended droughts in certain regions. As a result, storm-affected areas are likely to experience increases in precipitation and an increased risk of flooding. In contrast, areas far away from storm tracks are likely to experience less precipitation and an increased risk of drought. Overall, there is likely to be longer hot dry spells, broken by more intense heavy rainfalls (along the lines of the English proverb "it never rains but it pours!").

Changes in regional climate are expected to include greater temperature increases over land, with most warming at high northern latitudes, and least warming over the Southern Ocean and parts of the North Atlantic Ocean. 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.

Lightnings

Lightning strikes occur more frequently in hot weather. According to a study published in 2014, the number of lightning strikes will increase by about 12% for every degree of rise in global average air temperature. However, the impact of global warming on lightning rates is poorly constrained. The well developed cities exert its consequences or influences upon the climate and the pollution of the city which in return affects the frequency and the effects of the thunderstorms and the lightning. The mid developed cities were found to have less impact on the thunderstorm while the large cities had warmer temperatures which lead to increased severity of the thunderstorms. The studies show that the urban areas modify their climate in terms of temperature and the rainfall it receives. Convection is one of the ways that the urban areas are able to change their climate. Two cities larger in size had dramatic differences in terms of the thunderstorm and the lightning they received, the differences were due to the population that each city held. The city with the most population produced more convection and the results related to the formation of the thunderstorms. The cities which are mid sized produced almost the same amount of the influences to modify their climate but the results do not explicitly show the effects on the convection. In Atlanta, the thunderstorms were happening at much more higher frequency on the weekdays than on the weekends. The effects of the lightining are also crucial to the trees and the ecosystem. The study done in 2016, by Abatzpglou and Williams, the percentage of the fires caused by the lightning was 40% from 1992 to 2013 in the Western areas of the United States. The lightning affects the trees which are planted in the certain areas which receives the most lightning and affecting the carbon cycle of the trees. The study done in 2009 by Bell el al, shows that the level of the aerosol have increased by the middle of the week by the amount of the people travelling through transportation. The increase in transportation and the aerosol gives rise to the thunderstorms especially in the cities where the humidity level are high or the temperature which is higher due to infrastructure such as; buildings which capture the heat.

Lightning in the Oradea,Romania (August 17, 2005)

Heat waves and temperature extremes

Large increases in both the frequency and intensity of extreme weather events (for increasing degrees of global warming) are expected.

Map of increasing heatwave trends (frequency and cumulative intensity) over the midlatitudes and Europe, July–August 1979–2020.

Global heating boosts the probability of extreme weather events such as heat waves where the daily maximum temperature exceeds the average maximum temperature by 5 °C (9 °F) for more than five consecutive days. In the last 30–40 years, heat waves with high humidity have become more frequent and severe. Extremely hot nights have doubled in frequency. The area in which extremely hot summers are observed has increased 50–100 fold. Heat waves with high humidity pose a big risk to human health while heat waves with low humidity lead to dry conditions that increase wildfires. The mortality from extreme heat is larger than the mortality from hurricanes, lightning, tornadoes, floods, and earthquakes together.

It was estimated in 2013 that global warming had increased the probability of local record-breaking monthly temperatures worldwide by a factor of 5. This was compared to a baseline climate in which no global warming had occurred. Using a medium global warming scenario, they project that by 2040, the number of monthly heat records globally could be more than 12 times greater than that of a scenario with no long-term warming.

Study results indicate that limiting global warming to 1.5 °C would prevent most of the tropics from reaching the wet-bulb temperature of the human physiological limit of 35 °C.

Future climate change will include more very hot days and fewer very cold days. The frequency, length and intensity of heat waves will very likely increase over most land areas. Higher growth in anthropogenic GHG emissions would cause more frequent and severe temperature extremes. Globally, cold waves have decreased in frequency. There is some evidence climate change leads to a weakening of the polar vortex, which would make the jet stream more wavy. This would lead to outbursts of very cold winter weather across parts of Eurasia and North America, as well as very warm air incursions into the Arctic.

Frequency (vertical axis) of local June–July–August temperature anomalies (relative to 1951–1980 mean) for Northern Hemisphere land in units of local standard deviation (horizontal axis). The distribution of anomalies has shifted to the right due to global warming, meaning that unusually hot summers have become more common.

Tropical cyclones and storms

This section is an excerpt from Tropical cyclones and climate change.[edit]

North Atlantic tropical cyclone activity according to the Power Dissipation Index, 1949–2015. Sea surface temperature has been plotted alongside the PDI to show how they compare. The lines have been smoothed using a five-year weighted average, plotted at the middle year.

Climate change affects tropical cyclones in a variety of ways: an intensification of rainfall and wind speed, an increase in the frequency of very intense storms and a poleward extension of where the cyclones reach maximum intensity are among the consequences of human-induced climate change. Tropical cyclones use warm, moist air as their source of energy or fuel. As climate change is warming ocean temperatures, there is potentially more of this fuel available.

Extreme event attribution

This section is an excerpt from Extreme event attribution.[edit]

Extreme event attribution, also known as attribution science, is a relatively new field of study in meteorology and climate science that tries to measure how ongoing climate change directly affects extreme events (rare events), for example extreme weather events. Attribution science aims to determine which such recent events can be explained by or linked to a warming atmosphere and are not simply due to natural variations.

Weather-related impacts

Floods

High tide flooding is increasing due to sea level rise, land subsidence, and the loss of natural barriers.

High tide flooding, also called tidal flooding, has become much more common in the past seven decades.

Global warming makes bigger storm events more common due to an intensification of the water cycle. This increase in the frequency of large storm events would alter existing Intensity-Duration-Frequency curves (IDF curves) due to the change in frequency, but also by lifting and steepening the curves in the future. The urban areas are prone to receiving more rainfall. The enormous amount of rainfall produces the pluvial flooding. The rural areas do not receive such type of flooding due to their infrastructure and the amount of the roads which cover the areas. The urban areas have concrete roads and the amount of the surface which has the ability to absorb the water is less than the rural or non-urban areas. Due to the surface differences, the water builds up in the cities and causing floods which also damage the infrastructure and the mass density of the people residing in the cities. Salt Creek, Illinois face both the small and large floods, and there has been increase in the small floods by 200 percent and due to the frequency that the small floods occur in, the consequence can be same as the large floods. The data showed direct correlation between the increase in floods and increase in urbanization. In Maryland, the frequency of the moderate floods had increased from 1940 in which the state experienced the floods once or twice a year to 1990 in which the flood was experienced up to six times.

Droughts

Climate change affects multiple factors associated with droughts, such as how much rain falls and how fast the rain evaporates again. Warming over land drives an increase in atmospheric evaporative demand which will increase the severity and frequency of droughts around much of the world. Scientists predict that in some regions of the world, there will be less rain in future due to global warming. These regions will therefore be more prone to drought in future: subtropical regions like the Mediterranean, southern Africa, south-western Australia and south-western South America, as well as tropical Central America, western Africa and the Amazon basin.

Physics dictates that higher temperatures lead to increased evaporation. The effect of this is soil drying and increased plant stress which will have impacts on agriculture. For this reason, even those regions where large changes in precipitation are not expected (such as central and northern Europe) will experience soil drying. The latest prediction of scientists in 2022 is that "If emissions of greenhouse gases are not curtailed, about a third of global land areas are projected to suffer from at least moderate drought by 2100". When droughts occur they are likely to be more intense than in the past.

Due to limitations on how much data is available about drought in the past, it is often impossible to confidently attribute a specific drought to human-induced climate change. Some areas however, such as the Mediterranean and California, already show the impacts of human activities. Their impacts are made worse because of increased water demand, population growth, urban expansion, and environmental protection efforts in many areas.

The frequency and the duration of droughts have both increased: They increased by 29% from the year 2000 to 2022. The prediction is that by 2050 more than 75% of humanity will live in drought conditions. Land restoration, especially by agroforestry, can help reduce the impact of droughts.

In 2019 the Intergovernmental Panel on Climate Change issued a Special Report on Climate Change and Land. The main statements of the report include: Between 1960 and 2013 the area of drylands in drought increased by 1% per year. In 2015, around 500 million people lived in areas impacted by desertification between the 1980s and 2000s. People who live in areas affected by land degradation and desertification are "increasingly negatively affected by climate change".

In the past, there were some apparently conflicting results in the scientific literature about how drought is changing due to climate change. This was found to be mostly due to problems with collection and analysis of data, for example in the formulation of the Palmer Drought Severity Index (PDSI) and the data sets used to determine the evapotranspiration component. The accurate attribution of the causes of drought also requires accounting for natural variability, especially El Niño Southern Oscillation (ENSO) effects and better analysis of precipitation data.

Wildfires

Further information: Wildfire § Climate change effects

Average U.S. acreage burned annually by wildfires has almost tripled in three decades.

Globally, 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. That warmer climate conditions pose more risks of wildfire is consistent with evidence from Earth's past: there was more fire in warmer periods, and less in colder climatic periods. Climate change increases evaporation, which 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 make the fire season longer, the time period in which severe wildfires are most likely. In regions where snow is disappearing, the fire season may get particularly more extended.

Even though weather conditions are raising the risks of wildfires, the total area burnt by wildfires has decreased globally. This is mostly the result of the conversion of savanna into croplands, after which there is less forest area that can burn. Prescribed burning, an indigenous practice in the US and Australia, can reduce the area burnt too, and may form an adaptation to increased risk. The carbon released from wildfires can further increase greenhouse gas concentrations. This feedback is not yet fully integrated into climate models.

Oceans

Oceans have taken up over 90% of the excess heat accumulated on Earth due to global warming, reducing the amount of heat building up in the atmosphere.

Time series of seasonal (red dots) and annual average (black line) global upper ocean heat content for the 0-700m layer between 1955 and 2008. The graph shows that ocean heat content has increased over this time period.

This section is an excerpt from Effects of climate change on oceans.[edit]

There are many effects of climate change on oceans. One of the main ones is an increase in ocean temperatures. More frequent marine heatwaves are linked to this. The rising temperature contributes to a rise in sea levels due to melting ice sheets. Other effects on oceans include sea ice decline, reducing pH values and oxygen levels, as well as increased ocean stratification. All this can lead to changes of ocean currents, for example a weakening of the Atlantic meridional overturning circulation (AMOC). The main root cause of these changes are the emissions of greenhouse gases from human activities, mainly burning of fossil fuels. Carbon dioxide and methane are examples of greenhouse gases. The additional greenhouse effect leads to ocean warming because the ocean takes up most of the additional heat in the climate system. The ocean also absorbs some of the extra carbon dioxide that is in the atmosphere. This causes the pH value of the seawater to drop. Scientists estimate that the ocean absorbs about 25% of all human-caused CO₂ emissions.

The various layers of the oceans have different temperatures. For example, the water is colder towards the bottom of the ocean. This temperature stratification will increase as the ocean surface warms due to rising air temperatures. Connected to this is a decline in mixing of the ocean layers, so that warm water stabilises near the surface. A reduction of cold, deep water circulation follows. 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. At the same time, contrasts in salinity are increasing. Salty areas are becoming saltier and fresher areas less salty.

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. The ocean has already lost oxygen throughout its water column. Oxygen minimum zones are increasing in size worldwide.

These changes harm marine ecosystems, and this can lead to biodiversity loss or changes in species distribution. This in turn can affect fishing and coastal tourism. For example, rising water temperatures are harming tropical coral reefs. The direct effect is coral bleaching on these reefs, because they are sensitive to even minor temperature changes. So a small increase in water temperature could have a significant impact in these environments. Another example is loss of sea ice habitats due to warming. This will have severe impacts on polar bears and other animals that rely on it. The effects of climate change on oceans put additional pressures on ocean ecosystems which are already under pressure by other impacts from human activities.

A part of the Great Barrier Reef in Australia in 2016 after a coral bleaching event

This map shows the general location and direction of the warm surface (red) and cold deep water (blue) currents of the thermohaline circulation. Salinity is represented by color in units of the Practical Salinity Scale. Low values (blue) are less saline, while high values (orange) are more saline.

Ice and snow

See also: Special Report on the Ocean and Cryosphere in a Changing Climate

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. The rate of ice loss has risen by 57% since the 1990s−from 0.8 to 1.2 trillion tonnes per year.

The cryosphere, the area of the Earth covered by snow or ice, is extremely sensitive to changes in global climate. Northern Hemisphere average annual snow cover has declined in recent decades. This pattern is consistent with warmer global temperatures. Some of the largest declines have been observed in the spring and summer months. During the 21st century, snow cover is projected to continue its retreat in almost all regions.

Glaciers and ice sheets decline

Further information: Retreat of glaciers since 1850

Since the beginning of the twentieth century, there has been a widespread retreat of glaciers. 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, whereas Antarctic ice loss is driven by warm ocean water melting the outlet glaciers. Research on Antarctica published in 2022, including the first map of iceberg calving, doubles the previous estimates of loss from ice shelves.

Future melt of the West Antarctic ice sheet is potentially abrupt under a high emission scenario, as a consequence of a partial collapse. Part of the ice sheet is grounded on bedrock below sea level, making it possibly vulnerable to the self-enhancing process of marine ice sheet instability. A further hypothesis is that marine ice cliff instability would also contribute to a partial collapse, but limited evidence is available for its importance. 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 on a timescale between decades and millennia.

In contrast to the West Antarctic ice sheet, melt of the Greenland ice sheet is projected to be taking place more gradually over millennia. Sustained warming between 1 °C (low confidence) and 4 °C (medium confidence) would lead to a complete loss of the ice sheet, contributing 7 m to sea levels globally. The ice loss could become irreversible due to a further self-enhancing feedback: the elevation-surface mass balance feedback. When ice melts on top of the ice sheet, the elevation drops. As air temperature is higher at lower altitude, this promotes further melt.

Sea ice changes

Sea ice reflects 50% to 70% of the incoming solar radiation, while 6% of the incoming solar energy is reflected by the ocean. With less solar energy, the sea ice absorbs and holds the surface colder, which can be a positive feedback toward climate change. As the climate warms, snow cover and sea ice extent decrease. Large-scale measurements of sea-ice have only been possible since the satellite era. The age of the sea ice is an important feature of the state of the sea ice cover.

Arctic sea ice decline

Arctic sea ice began to decline at the beginning of the twentieth century but the rate is accelerating. Since 1979, satellite records indicate the decline in summer sea ice coverage has been about 13% per decade. The thickness of sea ice has also decreased by 66% or 2.0 m over the last six decades with a shift from permanent ice to largely seasonal ice cover. While ice-free summers are expected to be rare at 1.5 °C degrees of warming, they are set to occur at least once every decade at a warming level of 2.0 °C. The Arctic will likely become ice-free at the end of some summers before 2050.

Sea ice changes in Antarctica

Main article: Antarctic sea ice § Recent trends and climate change

The annual mean Antarctic sea ice area is not showing a clear downwards or upwards trend over the period of reliable satellite data starting in 1979. There are remaining uncertainties on how to interpret this data due to the limited observational records and discrepancies between modelled and observed results for the sea ice cover.

Increase in sea level can damage infrastructure and destroy homes in cities and low-lying coastal regions.

Low Lying Costal Region

Sea level rise is a growing issue for coastal areas. Due to low elevation and increasing temperatures, cities are at great risk of being flooded. The population, area, and tree species will be affected and consequently city infrastructure will face severe damage as well, which will result in failures and destruction of critical infrastructure, immobilization due to transportation system breakdowns, blackouts, and salinity increasing in water supplies. Cities are robust and have numerous important infrastructures and are known for their great buildings, however, due to inland flooding and high levels of precipitation can cause erosion and damage to the infrastructures. Furthermore, the continuing sea-level rise will cause the loss of soil storage capacity due to extreme flooding which can impact soil quality and tree health. "When the water level is high it allows the waves and the erosion process to act farther up on the beach profile, causing a readjustment and resulting in a net erosion of the beach."

Permafrost thawing

See also: Climate change in Russia § Permafrost, and Arctic methane emissions

The southern part of the Arctic region (home to 4 million people) has experienced a temperature rise of 1 °C to 3 °C (1.8 °F to 5.4 °F) over the last 50 years. Canada, Alaska and Russia are experiencing initial melting of permafrost. This may disrupt ecosystems and by increasing bacterial activity in the soil lead to these areas becoming carbon sources instead of carbon sinks. Eastern Siberia's permafrost is gradually disappearing in the southern regions, leading to the loss of nearly 11% of Siberia's nearly 11,000 lakes since 1971. At the same time, western Siberia is at the initial stage where melting permafrost is creating new lakes, which will eventually start disappearing as in the east. Furthermore, permafrost melting will eventually cause methane release from melting permafrost peat bogs.

Wildlife and nature

Main article: Effects of climate change on ecosystems

See also: Extinction risk from climate change

Recent warming has strongly affected natural biological systems. Species worldwide are moving poleward to colder areas. On land, species may move to higher elevations, whereas marine species find colder water at greater depths. Of the drivers with the biggest global impact on nature, climate change ranks third over the five decades before 2020, with only change in land use and sea use, and direct exploitation of organisms having a greater impact.

The impacts of climate change in nature and nature's contributions to humans are projected to become more pronounced in the next few decades. Examples of climatic disruptions include fire, drought, pest infestation, invasion of species, storms, and coral bleaching events. The stresses caused by climate change, added to other stresses on ecological systems (e.g. land conversion, land degradation, harvesting, and pollution), threaten substantial damage to or complete loss of some unique ecosystems, and extinction of some critically endangered species. Key interactions between species within ecosystems are often disrupted because species from one location do not move to colder habitats at the same rate, giving rise to rapid changes in the functioning of the ecosystem. Impacts include changes in regional rainfall patterns, earlier leafing of trees and plants over many regions; movements of species to higher latitudes and altitudes in the Northern Hemisphere; changes in bird migrations in Europe, North America and Australia; and shifting of the oceans' plankton and fish from cold- to warm-adapted communities.

The Arctic is heating up twice as fast as the global mean. Seas are on track to rise one to four feet higher by 2100, threatening coastal habitats.

Ecosystems on land

Further information: Effects of climate change on terrestrial animals and Effects of climate change on plant biodiversity

Climate change has been estimated to be a major driver of biodiversity loss in cool conifer forests, savannas, mediterranean-climate systems, tropical forests, and the Arctic tundra. In other ecosystems, land-use change may be a stronger driver of biodiversity loss, at least in the near-term. Beyond the year 2050, climate change may be the major driver for biodiversity loss globally. Climate change interacts with other pressures such as habitat modification, pollution and invasive species. Interacting with these pressures, climate change increases extinction risk for a large fraction of terrestrial and freshwater species. Between 1% and 50% of species in different groups were assessed to be at substantially higher risk of extinction due to climate change.

Urban development and population contributes to climate change through factors such as pollution, deforestation, habitat destruction, and spread of disease. Scientists have linked these changes to a decrease in biodiversity in urban regions as a result of human interference. Ecologists Limburg and Schmidt found that there is a higher water temperature and temperature change in urban environments compared to non urban environments. Moreover, most major cities are found along costal zones and are home to a number of diverse species. Urbanization through building structures and city design like flood defenses in turn impact biodiversity. Storm flooding and costal erosion in these regions can lead to more water pollution, such as finding metals and ammonia in stream water, can lead to a decline in aquatic biota. Climate change also affects the amount of precipitation annually and seasonally; a reduction in the amount of snowfall in the winter months affects the spring vegetation and overall health of plants.

Nest of western snowy plover in the sand. Without adequate sand dunes, this species will not be able to reproduce.

Research shows that the growing season is getting longer each year throughout Europe. Bird populations in London, such as the Grey Heron, have increased due to better water quality and more temperate winters. Migratory patterns of birds and insects in London such as the swallow and orange tip butterfly have been noticed earlier as well due to an increase in spring temperature. In water, wetland organisms sensitive to changes in river flow as a result of climate change have also changed migratory patterns southeast or northeast of England. In Florida, the lower keys marsh rabbit is endangered due to rising sea levels. This species is native to Florida's marshes however, rising sea levels have caused the rabbits to relocate inwards where urbanization has taken over. Due to the effects of rising sea level and urbanization, there is very little habitat remaining for the marsh rabbit to thrive. Similarly, the snowy plover exclusively reproduces in sand dunes yet, rising sea levels disrupts the natural breeding spot for this bird. Without having an adequate area to breed, the snowy plover also remains as one of Florida's threatened species.

While urbanization in New Zealand is thriving, researchers are noticing a negative effect on the island's biodiversity. Research done in Wellington, New Zealand showed that the effects of climate change in conjunction with their rapid growth is affecting plant and animal life. Natural habitats are getting smaller and smaller, reducing the opportunity for certain plants to survive. Alongside this, researchers are noticing that with an increase in temperature, predation and invasive species are becoming more common. Researchers advise introducing more pest-free urban wildlife sanctuaries as they have seen success with them on the island in the past. Doing this would ensure that highly important native animals, like the kererū and tūī, are conserved while keeping invasive species out, ultimately preserving New Zealand's biodiversity in the face of climate change.

Amazon rainforest

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

Rainfall that falls 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, exacerbated by climate change which brings more frequent droughts to the area. The higher frequency of droughts seen in the first two decades of the 21st century, as well as other data, signal that a tipping point from rainforest to savanna might be close. One study concluded that this ecosystem could enter a mode of a 50-years-long collapse to a savanna around 2021, after which it would become increasingly and disproportionally more difficult to prevent or reverse this shift.

Marine ecosystems

Main article: Effects of climate change on oceans § Impacts on marine life

Marine heatwaves have seen an increased frequency and have widespread impacts on life in the oceans, such as mass dying events and coral bleaching. Harmful algae blooms have increased in response to warming waters, loss of oxygen and eutrophication. Between one-quarter and one-third of our fossil fuel emissions are consumed by the earth's oceans, which are now 30 percent more acidic than they were in pre-industrial times. This acidification poses a serious threat to aquatic life, particularly creatures such as oysters, clams, and coral with calcified shells or skeletons. Melting sea ice destroys habitat, including for algae that grows on its underside. It is likely that the oceans warmed faster between 1993 and 2017 compared to the period starting in 1969.

Warm water coral reefs are very sensitive to global warming and ocean acidification. Coral reefs provide a habitat for thousands of species and 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. Coral reefs are not the only framework organisms, organisms that build physical structures that form habitats for other sea creatures, affected by climate change: mangroves and seagrass are considered to be at moderate risk for lower levels of global warming according to the Special Report on the Ocean and Cryosphere in a Changing Climate.

Urban planning and landscaping also increases levels of nitrates into water bodies, affecting organisms that occupy those ecosystems. Excess nitrate levels are found in fertilizer; once water becomes contaminated with nitrates and makes its way into a body of water. This provides an ideal environment for algal blooms to form. These blooms over consume oxygen and block sunlight, ultimately causing fish casualties.

Tipping points and irreversible impacts

Main articles: Tipping points in the climate system and Abrupt climate change

Self-reinforcing feedbacks amplify climate change. The climate system exhibits "threshold behaviour" or tipping points when these feedbacks lead parts of the Earth system into a new state, such as the runaway loss of ice sheets or the destruction of forests. Tipping points are studied using data from Earth's distant past and by physical modelling. There is already moderate risk of global tipping points at 1 °C above pre-industrial temperatures, and that risk becomes high at 2.5 °C.

Tipping points are "perhaps the most 'dangerous' aspect of future climate changes", leading to irreversible impacts on society. Many tipping points are interlinked, so that triggering one may lead to a cascade of effects, even well below 2 °C of warming. A 2018 study states that 45% of environmental problems, including those caused by climate change are interconnected and make the risk of a domino effect bigger.

There are a number of climate change impacts on the environment that may be irreversible, at least over the timescale of many human generations. These include the large-scale singularities such as the melting of the Greenland and West Antarctic ice sheets, and changes to the Atlantic Meridional Overturning Circulation. In biological systems, the extinction of species would be an irreversible impact. In social systems, unique cultures may be lost or the survival of endangered languages may be exacerbated due to climate change. For example, humans living on atoll islands face risks due to sea level rise, sea surface warming, and increased frequency and intensity of extreme weather events.

Health, food security and water security

Simplified conceptual causal loop diagram of cascading global climate failure, related to the concept of One Health

Health

This section is an excerpt from Effects of climate change on human health.[edit]

The effects of climate change on human health are profound and increase the likelihood of many diseases and conditions. There is widespread agreement among researchers, health professionals and organizations that climate change is the biggest global health threat of the 21st century.

Rising temperatures and changes in weather patterns are increasing the severity of heat waves, extreme weather and other causes of illness, injury or death. Heat waves and extreme weather events have a big impact on health both directly and indirectly. When people are exposed to higher temperatures for longer time periods they might experience heat illness and heat-related death.

Effects of Climate Change on Mental Health

According to Deutchs Arzteblatt International many studies have highlighted the risk of mental illness being higher in cities than in rural areas. The world is already facing the effects of climate change and is said to continue to experience the various impacts of climate change on mental health causing mental health to be a growing concern. Physical health impacts such as air quality and respiratory illness, injury from extreme weather conditions, spread of vector borne disease s are due to the effects of climate change. These health impacts are burdened mostly on low-income or vulnerable populations. Furthermore, extreme weather conditions cause interferences in social, economic, and environmental determinants, and cause distress about the future all leading to health and mental health problems. The rising temperature can lead to an increase in sea levels and an increase in natural disasters leading resulting in cities and communities being heavily impacted. The responses during these events are acute traumatic stress which is alleviated after conditions are stable and safe, but also many face Post traumatic stress disorder that can affect and trigger depression, anxiety, and fear their whole life causing health problems. Some studies have also explained how sea level rising, heavy precipitation, and coastal flooding can cause gastrointestinal illness. A research on community effected by Hurricane Katrina showed high rates of depression, domestic violence, suicide attempts, and cases of PTSD. Due to displacement, loss of employment, and infrastructure damage many experienced stress increasing cases of abuse and violence on both adults and children.

Increase in seasonal allergies due to Climate change

The genus Ambrosia that consists of A artemisiifolia and A trifida which causes allergic rhinitis.

Urban areas are also a hotspot for the impacts of climate change has caused temperatures and CO2 levels to increase. A highly controlled experiment by Zika and Caulfield illustrated the increase of CO2 causing an increase in photosynthesis, vegetative growth, and pollen production. The genus Ambrosia that consists of A artemisiifolia and A trifida which causes allergic rhinitis increasing seasonal allergies. During various experiments done to find the correlation between climate change in urban areas, the growth response of ragweed occurred 3–4 days earlier in urban sites and above ground biomass increased by 8%-10% at semi-rural sites, 61%-66% in the suburban sites in 2000-2001 and by 189% at the urban site in 2001. Subsequently, earlier pollen shed at urbanized sites. Climate change caused varying production rates of pollen in different areas. In cities rising temperatures and CO2 levels caused to show a relation between climate change and exposure to pollen due to increased biomass of ragweed plants that cause allergies.

Food security

Main articles: Effects of climate change on agriculture and Effects of climate change on fisheries

Climate change will impact agriculture and food production around the world due to the effects of elevated CO₂ in the atmosphere; higher temperatures; altered precipitation and transpiration regimes; increased frequency of extreme events; and modified weed, pest, and pathogen pressure. Droughts result in crop failures and the loss of pasture for livestock. Loss and poor growth of livestock cause milk yield and meat production to decrease. 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 makes this type of land degradation and desertification worse.

Climate change is projected to negatively affect all four pillars of food security: not only how much food is available, but also how easy food is to access (prices), food quality and how stable the food system is. For example, climate change is already affecting the productivity of wheat and other key staples. The availability, quality and stability of wines are impacted by shifts in temperature affecting the traditional range and practices of viniculture, and by smoke taint from extreme fire events.

In many areas, fisheries have already seen their catch decrease because of global warming and changes in biochemical cycles. In combination with overfishing, warming waters decrease the maximum catch potential. Global catch potential is projected to reduce further in 2050 by less than 4% if emissions are reduced strongly, and by about 8% for very high future emissions, with growth in the Arctic Ocean.

Water security

Between 1.5 and 2.5 billion people live in areas with regular water security issues. If global warming would reach 4 °C, water insecurity would affect about twice as many people. Water resources are projected to decrease in most dry subtropical regions and mid-latitudes, but increase in high latitudes. However, as streamflow becomes more variable, even regions with increased water resources can experience additional short-term shortages. The arid regions of India, China, the US and Africa are already seeing dry spells and drought impact water availability.

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: pollutants can be transported into water bodies by the 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: warm water contains less oxygen.

This section is an excerpt from Water security § Climate change.[edit]

Impacts of climate change that are tied to water, affect people's water security on a daily basis. They include more frequent and intense heavy precipitation which affects the frequency, size and timing of floods. Also droughts can alter the total amount of freshwater and cause a decline in groundwater storage, and reduction in groundwater recharge. Reduction in water quality due to extreme events can also occur.^: 558 Faster melting of glaciers can also occur.

Global climate change will probably make it more complex and expensive to ensure water security. It creates new threats and adaptation challenges. This is because climate change leads to increased hydrological variability and extremes. Climate change has many impacts on the water cycle. These result in higher climatic and hydrological variability, which can threaten water security. Changes in the water cycle threaten existing and future water infrastructure. It will be harder to plan investments for future water infrastructure as there are so many uncertainties about future variability for the water cycle. This makes societies more exposed to risks of extreme events linked to water and therefore reduces water security.

Economic impacts

Main article: Economic impacts of climate change

The distribution of warming impacts from emitters has been unequal, with high-income, high-emitting countries benefitting while harming low-income, low-emitting countries.

Economic forecasts of the impact of global warming vary considerably. Researchers have warned that current economic modelling may seriously underestimate the impact of potentially catastrophic climate change, and point to the need for new models that give a more accurate picture of potential damages. Nevertheless, one 2018 study found that potential global economic gains if countries implement mitigation strategies to comply with the 2 °C target set at the Paris Agreement are in the vicinity of US$17 trillion per year up to 2100 compared to a very high emission scenario.

Global losses reveal rapidly rising costs due to extreme weather events since the 1970s. Socio-economic factors have contributed to the observed trend of global losses, such as population growth and increased wealth. Part of the growth is also related to regional climatic factors, e.g., 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. The trend does, however, suggest increasing vulnerability of social systems to climate change.

Economic inequality

Business activities affected by climate changed as found in the European Investment Bank Investment Survey 2020

Climate change has contributed towards global economic inequality. Wealthy countries in colder regions have either felt little overall economic impact from climate change, or possibly benefited, whereas poor hotter countries very likely grew less than if global warming had not occurred.

The total economic impacts from climate change are difficult to estimate, but increase for higher temperature changes. For instance, total damages are estimated to be 90% less if global warming is limited to 1.5 °C compared to 3.66 °C, a warming level chosen to represent no mitigation. One study found a 3.5% reduction in global GDP by the end of the century if warming is limited to 3 °C, excluding the potential effect of tipping points. Another study noted that global economic impact is underestimated by a factor of two to eight when tipping points are excluded from consideration. In the Oxford Economics high emission scenario, a temperature rise of 2 degrees by 2050 would reduce global GDP by 2.5% – 7.5%. By the year 2100 in this case, the temperature would rise by 4 degrees, which could reduce the global GDP by 30% in the worst case.

Most affected sectors apart from agriculture and fisheries

Thermal power stations (fossil fuel plants and nuclear power plants) depend on water to cool them. Not only is there increased demand for fresh water, but climate change can increase the likelihood of drought and fresh water shortages. Another impact for thermal power plants, is that increasing the temperatures in which they operate reduces their efficiency and hence their output. Changes in the amount of river flow correlate with the amount of energy produced by a dam. The result of diminished river flow can be a power shortage in areas that depend heavily on hydroelectric power. Brazil in particular, is vulnerable due to its having reliance on hydroelectricity as increasing temperatures, lower water flow, and alterations in the rainfall regime, could reduce total energy production by 7% annually by the end of the century.

Oil and natural gas infrastructure is affected by the effects of climate change and the increased risk of disasters such as storm, cyclones, flooding and rising sea levels.

New Orleans submerged after Hurricane Katrina, September 2005

Insurance is an important tool to manage risks, but 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. In 2019, Munich Re noted that climate change could cause home insurance to become unaffordable for households at or below average incomes.

Roads, airport runways, railway lines and pipelines, (including oil pipelines, sewers, water mains etc.) may require increased maintenance and renewal as they become subject to greater temperature variation. Regions already adversely affected include areas of permafrost, which are subject to high levels of subsidence, resulting in buckling roads, sunken foundations, and severely cracked runways.

Impacts on societies

Climate change impacts health, the availability of drinking water and food, inequality and economic growth. The effects of climate change are often interlinked and can exacerbate each other as well as existing vulnerabilities. The impacts are often exacerbated by related environmental disruptions and pressures such as pollution and biodiversity loss. Some areas may become too hot for humans to live in. People in some areas may experience internal or long-distance displacement (and thus become climate refugees) triggered by climate change related changes or disasters.

The effects of climate change, in combination with the sustained increases in greenhouse gas emissions, have led scientists to characterize it as a "climate emergency" or "climate crisis". Some climate researchers and activists have called it an "existential threat to civilization".

Displacement and migration

Further information: § Human settlement, and Climate migrant

Overlap between future population distribution and extreme heat

Climate change affects displacement of people in several ways. Firstly, involuntary displacement may increase through the increased number and severity of weather-related disasters which destroy homes and habitats. Effects of climate change such as desertification and rising sea levels gradually erode livelihood and force communities to abandon traditional homelands for more accommodating environments. On the other hand, some households may fall (further) into poverty due to climate change, limiting their ability to move to areas less affected.

According to the Internal Displacement Monitoring Centre in 2020 approximately 30 million people were displaced by extreme weather events while approximately 10 million by violence and wars and climate change significantly contributed to this. The United Nations says there are already 64 million migrants in the world fleeing wars, hunger, persecution and the effects of global warming. In 2018, the World Bank estimated that climate change will cause internal migration of between 31 and 143 million people as they escape crop failures, water scarcity, and sea level rise. The study only included Sub-Saharan Africa, South Asia, and Latin America.

Sea level rise at the Marshall Islands, reaching the edge of a village (from the documentary One Word)

Asia and the Pacific is the global area most prone to natural disasters, both in terms of the absolute number of disasters and of populations affected. It is highly exposed to climate impacts, and is home to highly vulnerable population groups, who are disproportionately poor and marginalized. A 2015 Asian Development Bank report highlights "environmental hot spots" that are particular risk of flooding, cyclones, typhoons, and water stress.

Gradual but pervasive environmental change and sudden natural disasters both influence the nature and extent of human migration but in different ways. United Nations High Commissioner for Refugees stated that climate change increases mass displacement, in many regions, including Sahel, East Africa, South Asia, the "drought corridor" in Latin America. 90% of refugees comes from "climate vulnerable hotspots".

Some Pacific Ocean island nations, such as Tuvalu, Kiribati, and the Maldives, are considering the eventual possibility of evacuation, as flood defense may become economically unrealistic.

The two broad sets of potential interventions are climate change mitigation and building "greater capacity within vulnerable populations so that they may adapt through means that do not lead to distress migration or conflict". There are various reasons for why, especially large-scale- or distant-source-, migration is often widely undesired and opposed in both (or either) host and origin countries, such as shortage of housing, cultural identity or cohesion or sovereignty, and economics-related reasons.

Governments have considered various approaches to reduce migration compelled by environmental conditions in at-risk communities, including programs of social protection, livelihoods development, basic urban infrastructure development, and disaster risk management. Some experts support migration as an appropriate way for people to cope with environmental changes. However, this is controversial because migrants – particularly low-skilled ones – are among the most vulnerable people in society and are often denied basic protections and access to services.

Slow-onset disasters and gradual environmental erosion such as desertification, reduction of soil fertility, coastal erosion and sea-level rise are likely to induce long-term migration. Migration related to desertification and reduced soil fertility is likely to be predominantly from rural areas in developing countries to towns and cities.

Conflict

Main article: Climate security

Overlap between state fragility, extreme heat, and nuclear and biological catastrophic hazards

Climate change can worsen conflicts by exacerbating tensions over limited resources like drinking water (in the case of water conflicts). Climate change also has the potential to cause large population dislocations and migration, which can also lead to increased tensions. However, factors other than climate change are judged to be substantially more important in affecting conflict. These factors include intergroup inequality and low socio-economic development. In some cases, climate change can even lead to more peaceful relationships between groups, as environmental problems requires common policy to be developed.

Global warming has been described as a "threat multiplier". Certain conditions make it more likely that climate change impacts conflict: ethnic exclusion, an economy dependent on agriculture, insufficient infrastructure, poor local governance, and low levels of development. 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.

Social impacts on vulnerable groups

The impacts of climate change on humans are not distributed uniformly within communities. Individual and social factors such as gender, age, education, ethnicity, geography and language lead to differential vulnerability and capacity to adapt to the effects of climate change. The following more vulnerable groups have been identified:

• 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 the increased exposure and vulnerability. 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.
• Women: Climate change increases gender inequality, reduces women's ability to be financially independent, and has an overall negative impact on the social and political rights of women, especially in economies that are heavily based on agriculture.
• Indigenous peoples: Indigenous communities geographically tend to be located in regions more vulnerable to climate change such as native rainforests, the Arctic, and coastal areas. Indigenous communities across the globe generally have economic disadvantages that are not as prevalent in non-indigenous communities due to the ongoing oppression they have experienced. These disadvantages include lower education levels and higher rates of poverty and unemployment, which add to their vulnerability to climate change.
• Children: The Lancet review on health and climate change lists children as the worst-affected category by climate change. Children are also 14–44 percent more likely to die from environmental factors, again leaving them the most vulnerable. Those in urban areas will be affected by lower air quality and overcrowding, and will struggle the most to better their situation.
• Racial minorities: The environmental justice (EJ) movement and climate justice (CJ) movement address environmental racism in bringing attention and enacting change so that marginalized populations are not disproportionately vulnerable to climate change and pollution.

Human settlements

Further information: Sea level rise and Climate change and cities

A major challenge for human settlements is sea level rise, indicated by ongoing observation and research of rapid declines in ice-mass balance from both Greenland and Antarctica. Estimates for 2100 are at least twice as large as previously estimated by IPCC AR4, with an upper limit of about two meters. Depending on regional changes, increased precipitation patterns can cause more flooding or extended drought stresses water resources.

A 2020 study projects that regions inhabited by a third of the human population could become as hot as the hottest parts of the Sahara within 50 years without a change in patterns of population growth and without migration, unless greenhouse gas emissions are reduced. The projected annual average temperature of above 29 °C for these regions would be outside the "human temperature niche" – a suggested range for climate biologically suitable for humans based on historical data of mean annual temperatures (MAT) – and the most affected regions have little adaptive capacity as of 2020. The cities that are on the low-lying coastal regions in Asia, the rate at which their population is increasing is 140,000 per day with the prediction of the weather which will increase to 4 degree Celsius by the end of the century and sea levels which would rise by 1 meter by 2100.

In small islands and megadeltas, inundation as a result of sea level rise is expected to threaten vital infrastructure and human settlements. This could lead to issues of statelessness for populations in countries such as the Maldives and Tuvalu and homelessness in countries with low-lying areas such as Bangladesh. In 1991, 140,000 people died and the 10 million became homeless when the floods hit Bangladesh. In Myanmar, the storm killed 146,000 people which was hit in 2007.

Projections for cities in 2050

In 2019 the Crowther Lab from ETH Zürich paired the climatic conditions of 520 major cities worldwide with the predicted climatic conditions of cities in 2050. 22% of the major cities are predicted to have climatic conditions that do not exist in any city today. 2050 London will have a climate similar to 2019 Melbourne, Athens and Madrid like Fez, Morocco, Nairobi like Maputo. The Indian city Pune will be like Bamako in Mali, Bamako will be like Niamey in Niger. Brasilia will be like Goiania.

Increased extreme heat exposure from both climate change and the urban heat island effect threatens urban settlements.

Especially affected regions

The Arctic, Africa, small islands, Asian megadeltas and the Middle East are regions that are likely to be especially affected by climate change. Low-latitude, less-developed regions are at most risk of experiencing negative impacts due to climate change.

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, however, ASEAN's climate mitigation efforts are not commensurate with the climate change threats the region faces. Africa is one of the most vulnerable continents to climate variability and change because of multiple existing stresses and low adaptive capacity. Climate change is projected to decrease freshwater availability in central, south, east and southeast Asia, particularly in large river basins. With population growth and increasing demand from higher standards of living, this decrease could adversely affect more than a billion people by the 2050s. Small islands, whether located in the tropics or higher latitudes, are already exposed to extreme weather events and changes in sea level. This existing exposure will likely make these areas sensitive to the effects of climate change.

Developed countries are also vulnerable to climate change, and have already been negatively affected by increases in the severity and frequency of some extreme weather events, such as heat waves, floods, wildfires, and tropical cyclones.

Low-lying coastal regions

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

For historical reasons to do with trade, many of the world's largest and most prosperous cities are on the coast. In developing countries, the poorest often live on floodplains, because it is the only available space, or fertile agricultural land. These settlements often lack infrastructure such as dykes and early warning systems. Poorer communities also tend to lack the insurance, savings, or access to credit needed to recover from disasters.

Socioeconomic impacts of climate change in coastal and low-lying areas will be overwhelmingly adverse. The following impacts were projected in 2007 with very high confidence:

• Coastal and low-lying areas would be exposed to increasing risks including coastal erosion due to climate change and sea level rise.
• By the 2080s, millions of people would experience floods every year due to sea level rise. The numbers affected were projected to be largest in the densely populated and low-lying mega-deltas of Asia and Africa; and smaller islands were judged to be especially vulnerable.

Given high coastal population density, estimates of the number of people at risk of coastal flooding from climate-driven sea-level rise varies from 190 million, to 300 million or even 640 million in a worst-case scenario related to the instability of the Antarctic ice sheet. The most people affected are in the densely-populated and low-lying megadeltas of Asia and Africa.

The Greenland ice sheet is estimated to have reached a point of no return, continuing to melt even if warming stopped. Over time that would submerge many of the world's coastal cities including low-lying islands, especially combined with storm surges and high tides.

Small islands

Further information: Effects of climate change on island nations

Small islands developing states are especially vulnerable to the effects of climate change, especially sea level rise. They are expected to experience more intense storm surges, salt water intrusion, and coastal destruction. Low-lying small islands in the Pacific, Indian, and Caribbean regions are at risk of permanent inundation and population displacement. On the islands of Fiji, Tonga and western Samoa, concentrations of migrants from outer islands inhabit low and unsafe areas along the coasts.

Atoll nations, which include countries that are composed entirely of the smallest form of islands, called motus, are at risk of entire population displacement. These nations include Kiribati, Maldives, the Marshall Islands, Tokelau, and Tuvalu. Vulnerability is increased by small size, isolation from other land, low financial resources, and lack of protective infrastructure.

A study that engaged the experiences of residents in atoll communities found that the cultural identities of these populations are strongly tied to these lands. Human rights activists argue that the potential loss of entire atoll countries, and consequently the loss of national sovereignty, self-determination, cultures, and indigenous lifestyles cannot be compensated for financially. Some researchers suggest that the focus of international dialogues on these issues should shift from ways to relocate entire communities to strategies that instead allow for these communities to remain on their lands.

Possibility of societal collapse

Further information: Global catastrophe scenarios § Climate change

Main articles: Climate apocalypse and Climate endgame

Several researchers have suggested that collapse of the current societal organization – the contemporary global, interconnected civilization – could occur at 3 degrees of warming, especially when considering that climate change is not the only environmental pressure and challenge humanity faces.

In 2022, researchers around the Centre for the Study of Existential Risk reported that the risk of climate change (indirectly) resulting in worldwide societal collapse, or possibly eventual human extinction, is a "dangerously underexplored" global topic, despite there being indications of such being possible as worst-case scenarios and that "integrated catastrophe assessment" is missing.

Human impacts as rationale for mitigation

There is a misconception that climate change mitigation primarily is about conservation of nature (e.g. due to "love of nature") or the protection of the planet (which has experienced several mass extinction events) or an external environment – instead the primary rationale or intended effects and purpose of climate change mitigation is suggested to be protection of humans (from suffering, reduced quality of life and earlier death) and of sustained human civilization (e.g. national security) or, broadly, to enable a just future for all on a thriving planet which humans not only often value but also depend upon. It has been described as protection of humanity rather than protection of the climate.

See also

• Anthropocene
• Effects of climate change on developing countries
• Global catastrophic risk
• Politics of climate change

References

Sources

• IPCC AR4 WG1 (2007), Solomon, S.; Qin, D.; Manning, M.; Chen, Z.; Marquis, M.; Averyt, K.B.; Tignor, M.; Miller, H.L. (eds.), Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, ISBN 978-0-521-88009-1{{citation}}: CS1 maint: numeric names: authors list (link) (pb: 978-0-521-70596-7).
• IPCC AR4 WG2 (2007), Parry, M.L.; Canziani, O.F.; Palutikof, J.P.; van der Linden, P.J.; Hanson, C.E. (eds.), Climate Change 2007: Impacts, Adaptation and Vulnerability, Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, ISBN 978-0-521-88010-7{{citation}}: CS1 maint: numeric names: authors list (link) (pb: 978-0-521-70597-4).

• IPCC AR4 SYR (2007), Core Writing Team; Pachauri, R.K; Reisinger, A. (eds.), Climate Change 2007: Synthesis Report, Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Geneva, Switzerland: IPCC, ISBN 978-92-9169-122-7{{citation}}: CS1 maint: numeric names: authors list (link).
• IPCC SREX (2012), Field, C.B.; et al. (eds.), Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX), Cambridge University Press, archived from the original on 19 December 2012. Summary for Policymakers available in Arabic, Chinese, French, Russian, and Spanish.

• IPCC AR5 WG1 (2013), Stocker, T.F.; et al. (eds.), Climate Change 2013: The Physical Science Basis. Working Group 1 (WG1) Contribution to the Intergovernmental Panel on Climate Change (IPCC) 5th Assessment Report (AR5), Cambridge University Press{{citation}}: CS1 maint: numeric names: authors list (link). Climate Change 2013 Working Group 1 website.

• IPCC AR5 WG2 A (2014), Field, C.B.; et al. (eds.), Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II (WG2) to the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), Cambridge University Press, archived from the original on 16 April 2014{{citation}}: CS1 maint: numeric names: authors list (link). Archived

• IPCC (2018). Masson-Delmotte, V.; Zhai, P.; Pörtner, H. O.; Roberts, D.; et al. (eds.). Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty (PDF). Intergovernmental Panel on Climate Change.

• IPCC (2019). Pörtner, H.-O.; Roberts, D.C.; Masson-Delmotte, V.; Zhai, P.; et al. (eds.). IPCC Special Report on the Ocean and Cryosphere in a Changing Climate (PDF). IPCC.

• IPCC (2019). Shukla, P.R.; Skea, J.; Calvo Biendia, E.; Masson-Delmotte, V.; et al. (eds.). Climate Change and Land. An IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems (PDF). In press.

• IPCC (2019). "Summary for Policymakers" (PDF). IPCC SRCCL 2019. pp. 3–34.

•  This article incorporates public domain material from Kennedy, C.H. (10 July 2012). ClimateWatch Magazine » State of the Climate in 2011: Highlights. NOAA. Archived from the original on 10 May 2013. Retrieved 20 March 2013.

•  This article incorporates public domain material from Glossary of Climate Change Terms: Climate Change: US EPA. US Environmental Protection Agency (EPA) Climate Change Division. 14 June 2012.

External links

• IPCC Working Group I (WG I). Intergovernmental Panel on Climate Change group which assesses the physical scientific aspects of the climate system and climate change.
• Climate from the World Meteorological Organization
• Climate change UN Department of Economic and Social Affairs Sustainable Development
• Effects of climate change from the Met Office
• United Nations Environment Programme and climate change