Effects of climate change

Some climate change effects: wildfire caused by heat and dryness, bleached coral caused by ocean acidification and heating, environmental migration caused by desertification, and coastal flooding caused by storms and sea level rise.

Effects of climate change are well documented and growing for Earth's natural environment and human societies. Changes to the climate system include an overall warming trend, changes to precipitation patterns, and more extreme weather. As the climate changes it impacts the natural environment with effects such as more intense forest fires, thawing permafrost, and desertification. These changes impact ecosystems and societies, and can become irreversible once tipping points are crossed. Climate activists are engaged in a range of activities around the world that seek to ameliorate these issues or prevent them from happening.^[1]

The effects of climate change vary in timing and location. Up until now the Arctic has warmed faster than most other regions due to climate change feedbacks.^[2] Surface air temperatures over land have also increased at about twice the rate they do over the ocean, causing intense heat waves. These temperatures would stabilize if greenhouse gas emissions were brought under control. Ice sheets and oceans absorb the vast majority of excess heat in the atmosphere, delaying effects there but causing them to accelerate and then continue after surface temperatures stabilize. Sea level rise is a particular long term concern as a result. The effects of ocean warming also include marine heatwaves, ocean stratification, deoxygenation, and changes to ocean currents.^[3]: 10 The ocean is also acidifying as it absorbs carbon dioxide from the atmosphere.^[4]

The ecosystems most immediately threatened by climate change are in the mountains, coral reefs, and the Arctic. Excess heat is causing environmental changes in those locations that exceed the ability of animals to adapt.^[9] Species are escaping heat by migrating towards the poles and to higher ground when they can.^[10] Sea level rise threatens coastal wetlands with flooding. Decreases in soil moisture in certain locations can cause desertification and damage ecosystems like the Amazon Rainforest.^[11]: 9 At 2 °C (3.6 °F) of warming, around 10% of species on land would become critically endangered.^[12]: 259

Humans are vulnerable to climate change in many ways. Sources of food and fresh water can be threatened by environmental changes. Human health can be impacted by weather extremes or by ripple effects like the spread of infectious diseases. Economic impacts include changes to agriculture, fisheries, and forestry. Higher temperatures will increasingly prevent outdoor labor in tropical latitudes due to heat stress. Island nations and coastal cities may be inundated by rising sea levels. Some groups of people may be particularly at risk from climate change, such as the poor, children, and indigenous peoples. Industrialised countries, which have emitted the vast majority of CO₂, have more resources to adapt to global warming than developing nations do.^[13] Cumulative effects and extreme weather events can lead to displacement and migration.^[14]

Global warming affects all parts of Earth's climate system.^[16] Global surface temperatures have risen by 1.1 °C (2.0 °F). Scientists say they will rise further in the future.^[17][18] 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.^[2] Night-time temperatures have increased faster than daytime temperatures.^[19] The impact on nature and people depends on how much more the Earth warms.^[20]: 787

Scientists use several methods to predict the effects of human-caused climate change. One is to investigate past natural changes in climate.^[21] To assess changes in Earth's past climate scientists have studied tree rings, ice cores, corals, and ocean and lake sediments.^[22] These show that recent temperatures have surpassed anything in the last 2,000 years.^[23] 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.^[24]: 322 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 metres (82 ft) higher than it is today.^[25]: 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.^[26]: 54

How much the world warms depends on human greenhouse gas emissions and on how sensitive the climate is to greenhouse gases.^[27] 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).^[28] 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.^[29]

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 by 2.4 °C (4.3 °F) if governments achieved all their unconditional pledges and targets. 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.^[30]

Large increases in both the frequency and intensity of extreme weather events (for increasing degrees of global warming) are expected.^[31]: 18 Extreme heat events are forecast to be among the most affected by global warming.

Climate Central's review of climate attribution studies covered almost 750 extreme weather events and trends, of various event types.^[32] The review found that climate change made almost all studied event types substantially more likely or more severe—with cold/snow/ice events being the exception.^[32]

The lower and middle atmosphere, where nearly all weather occurs, are heating due to the greenhouse effect.^[33] Evaporation and atmospheric moisture content increase as temperatures rise.^[34] Water vapour is a greenhouse gas, so this process is a self-reinforcing feedback.^[35]

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.^[34] 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 using a process called 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.^[36] In addition, the time shifts of the season onsets, changes in the length of the season durations have been reported in many regions of the world.^{[37][38][39][40][41]} As a result of changes in climatic patterns and rising global temperatures, extreme weather events like heatwaves and heavy precipitation are occurring more frequently and with increasing severity.^[42]

New high temperature records have outpaced new low temperature records on a growing portion of Earth's surface.^[43]

Map of increasing heatwave trends (frequency and cumulative intensity) over the midlatitudes and Europe, July–August 1979–2020^[44]

US heat waves have increased in frequency, average duration, and intensity.^[45]

Also, heat wave seasons have grown in length.^[45]

Over decades, the average number of days spent in heat waves in the U.S. annually has increased, based on increases in both the average annual number of heat waves and on their average durations.^[45]

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.^[46] Climate change will lead to more very hot days and fewer very cold days.^[47]: 7 There are fewer cold waves.^[31]: 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).^[48]

Heat stress is related to temperature.^[49] 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.^[50][51]

There is some evidence climate change is leading to a weakening of the polar vortex. This would make the jet stream more wavy.^[52] This would lead to outbursts of very cold winter weather across parts of Eurasia^[53] and North America and incursions of very warm air into the Arctic.^[54][55][56] Some studies found a weakening of the AMOC by about 15% since 1950, causing cooling in the North Atlantic and warming in the Gulf Stream region.^[57] Climate change is expected to weaken AMOC in all emissions scenarios^[58] and, in some high emissions scenarios, can bring it to collapse. This can result in cooling of some parts of Europe by up to 30 degrees and warming in the southern hemisphere.^[59]

Warming increases global average precipitation. Precipitation is when water vapour condenses out of clouds, such as rain and snow.^[60]: 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.^[60]: 1057 Scientists have observed changes in the amount, intensity, frequency, and type of precipitation.^[61] Overall, climate change is causing longer hot dry spells, broken by more intense rainfall.^{[62]: 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.^[60]: 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.^[60]: 1058

New Orleans submerged after Hurricane Katrina, September 2005

Water temperature increases caused by climate change intensified peak wind speeds in all 2024 Atlantic hurricanes.^[63]

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.^[64] Furthermore, tropical cyclones and storm tracks are moving towards the poles. This means some regions will see large changes in maximum wind speeds.^[64][65] Scientists expect there will be fewer tropical cyclones, but they expect their strength to increase.^[65] There has probably been an increase in the number of tropical cyclones that intensify rapidly.^[64] Meteorological and seismological data indicate a widespread increase in wind-driven global ocean wave energy in recent decades that has been attributed to an increase in storm intensity over the oceans due to climate change.^[66][67][68] Atmospheric turbulence dangerous for aviation (hard to predict or that cannot be avoided by flying higher) probably increases due to climate change.^[69]

The sixth IPCC Assessment Report included projections of changes in average soil moisture.

A dry lakebed in California In 2022, the state was experiencing its most serious drought in 1,200 years, worsened by climate change.^[70]

Due to an increase in heavy rainfall events, floods are likely to become more severe when they do occur.^[60]: 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.^[60]: 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.^[60]: 1155

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.^{[71][60]: 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.^[60]: 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.^[60]: 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.^[60]: 1157 Due to global warming droughts are more frequent and intense than in the past.^[72]

Several social factors may worsen the impact of droughts. These are increased water demand, population growth and urban expansion in many areas.^[73] Land restoration techniques, such as agroforestry, can help reduce the impact of droughts.^[74]

Wildfire disasters (those claiming at least 10 lives or affecting over 100 people) have increased substantially in recent decades.^[75] Climate change intensifies heatwaves and droughts that dry vegetation, which in turn fuels wildfires.^[75]

Globally, wildfires and deforestation have reduced forests' net absorption of greenhouse gases, reducing their effectiveness at mitigating climate change.^[76] Global warming increases forest fires that release more greenhouse gases, creating a feedback loop that causes more warming.^[77]

Over recent decades, "forest disturbance" (damage) by fire has increased in most of the planet's forest zones.^[78] The increase in area, frequency, and severity of forest fires creates a positive feedback that increases global warming.^[78]

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.^[79] Climate change increases evapotranspiration. This can cause vegetation and soils 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.^[80]

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 is an indigenous practice in the US and Australia. It can reduce wildfire burning.^[80]

The carbon released from wildfires adds to carbon dioxide in Earth's atmosphere and therefore contributes to the greenhouse effect. Climate models do not yet fully reflect this climate change feedback.^[31]: 20

In regions sensitive to climate change the frequency and intensity of eruptions will change as global warming increases. Glacier retreat and stronger precipitation can increase the chances for an eruption. As of 2024, government agencies are already addressing these changes and scientists are working to map the volcanoes most sensitive to climate change. The concerns regions are where glaciers are melting fast, and there are volcanoes heavily affected by precipitation. 716 volcanoes worldwide, may be affected by more extreme precipitation. Melting ice and extreme rainfall also increase secondary hazards, particularly lahars and disturb eruption forecasting by inducing ground displacements.^[81]

Earthquakes can be triggered by changes in the amount of stress on a fault in the Earth's crust. Strong rain, snow, drought and more pumping of groundwater by humans during droughts, can do it by increasing or reducing the weight of water on some pieces of the Earth's crust. So, as climate change will cause more extreme weather, it can induce more earthquakes. Glacier retreat reduce stress loads on Earth's crust underneath, creating glacial earthquakes. Glacial earthquakes in Greenland for example, peak in frequency in the summer months and are increasing over time, possibly in response to global warming.^[82][83]

Sea level rise can also create pressure on tectonic faults, increasing risk for earthquakes.^[84][85]

In Greenland, melting glaciers triggered a landslide, which caused a mega-tsunami in September 2023. Earthquake sensors around the world detected the resulting vibration, but the scale and duration of the event was unprecedented, so at first scientists failed to understand it. Further investigation revealed that the cause was the collapse of a 1,200-metre-high mountain peak into the remote Dickson Fjord on September 16, 2023, after the glacier below the mountain melted to a sufficient degree. The collapse into the fjord, in turn, launched a wave 200 metres high, which caused repeated movement of water back and forth in the fjord, generating seismic waves that were detectable worldwide for nine days.^[86]

The cryosphere, the area of the Earth covered by snow or ice, is extremely sensitive to changes in global climate.^[109] There has been an extensive loss of snow on land since 1981. Some of the largest declines have been observed in the spring.^[110] During the 21st century, snow cover is projected to continue its retreat in almost all regions.^{[111]: 39–69}

Since the beginning of the twentieth century, there has been a widespread retreat of glaciers.^{[112]: 1215} Those glaciers that are not associa