Climate change

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For a discussion of climate trends throughout Earth's history, see Climate variability and change. Climate change_sentence_0

For other uses, see Climate change (disambiguation). Climate change_sentence_1

"Global warming" redirects here. Climate change_sentence_2

For other uses, see Global warming (disambiguation). Climate change_sentence_3

Climate change includes both the global warming driven by human emissions of greenhouse gases, and the resulting large-scale shifts in weather patterns. Climate change_sentence_4

Though there have been previous periods of climatic change, since the mid-20th century, humans have had unprecedented impact on Earth's climate system and caused change on a global scale. Climate change_sentence_5

The largest driver of warming is the emission of greenhouse gases, of which more than 90% are carbon dioxide (CO 2) and methane. Climate change_sentence_6

Fossil fuel burning for energy consumption is the main source of these emissions, with additional contributions from agriculture, deforestation, and industrial processes. Climate change_sentence_7

The human cause of climate change is not disputed by any scientific body of national or international standing. Climate change_sentence_8

Temperature rise is accelerated or tempered by climate feedbacks, such as loss of sunlight-reflecting snow and ice cover, increased water vapour (a greenhouse gas itself), and changes to land and ocean carbon sinks. Climate change_sentence_9

Because land surfaces heat faster than ocean surfaces, deserts are expanding and heat waves and wildfires are more common. Climate change_sentence_10

Surface temperature rise is greatest in the Arctic, where it has contributed to melting permafrost which releases more greenhouse gases and the retreat of glaciers and sea ice, causing the land and ocean to absorb more heat. Climate change_sentence_11

Increasing atmospheric energy and rates of evaporation cause more intense storms and weather extremes, which damage infrastructure and agriculture. Climate change_sentence_12

Rising temperatures are limiting ocean productivity and harming fish stocks in most parts of the globe. Climate change_sentence_13

Current and anticipated effects from undernutrition, heat stress and disease have led the World Health Organization to declare climate change the greatest threat to global health in the 21st century. Climate change_sentence_14

Environmental effects include the extinction or relocation of many species as their ecosystems change, most immediately in coral reefs, mountains, and the Arctic. Climate change_sentence_15

Even if efforts to minimize future warming are successful, some effects will continue for centuries, including rising sea levels, rising ocean temperatures, and ocean acidification. Climate change_sentence_16

Many of these effects are already observed at the current level of warming, which is about 1.1 °C (2.0 °F). Climate change_sentence_17

The Intergovernmental Panel on Climate Change (IPCC) has issued a series of reports that project significant increases in these impacts as warming continues to 1.5 °C (2.7 °F) and beyond. Climate change_sentence_18

Under the Paris Agreement, nations agreed to keep warming "well under 2.0 °C (3.6 °F)" by reducing greenhouse gas emissions. Climate change_sentence_19

However, under those pledges, global warming would reach about 2.8 °C (5.0 °F) by the end of the century, and current policies will result in about 3.0 °C (5.4 °F) of warming. Climate change_sentence_20

Limiting warming to 1.5 °C (2.7 °F) would require halving emissions by 2030, then reaching near-zero emissions by 2050. Climate change_sentence_21

Mitigation efforts include the development and deployment of low-carbon energy technologies, enhanced energy efficiency, phase-out of coal, reforestation, and forest preservation. Climate change_sentence_22

Climate engineering techniques, most prominently solar radiation management and carbon dioxide removal, have substantial limitations and carry large uncertainties. Climate change_sentence_23

Societies are also working to adapt to current and future global-warming effects through improved coastline protection, better disaster management, and the development of more resistant crops. Climate change_sentence_24

Observed temperature rise Climate change_section_0

Main articles: Temperature record of the last 2,000 years and Instrumental temperature record Climate change_sentence_25

Multiple independently produced instrumental datasets show that the climate system is warming, with the 2009–2018 decade being 0.93 ± 0.07 °C (1.67 ± 0.13 °F) warmer than the pre-industrial baseline (1850–1900). Climate change_sentence_26

Currently, surface temperatures are rising by about 0.2 °C (0.36 °F) per decade. Climate change_sentence_27

Since 1950, the number of cold days and nights has decreased, and the number of warm days and nights has increased. Climate change_sentence_28

Historical patterns of warming and cooling, like the Medieval Climate Anomaly and the Little Ice Age, did not occur at the same time across regions, but may have reached temperatures as high as those of the late-20th century in a limited set of regions. Climate change_sentence_29

There have been prehistorical episodes of global warming, such as the Paleocene–Eocene Thermal Maximum. Climate change_sentence_30

However, the modern observed rise in temperature and CO 2 concentrations has been so rapid that even abrupt geophysical events that took place in Earth's history do not approach current rates. Climate change_sentence_31

There was little net warming between the 18th century and the mid-19th century. Climate change_sentence_32

Climate proxies, sources of climate information from natural archives such as trees and ice cores, show that natural variations offset the early effects of the Industrial Revolution. Climate change_sentence_33

The Intergovernmental Panel on Climate Change (IPCC) has adopted the baseline reference period 1850–1900 as an approximation of pre-industrial global mean surface temperature, when thermometer records began to provide global coverage. Climate change_sentence_34

Evidence of warming from air temperature measurements are reinforced with a wide range of other observations. Climate change_sentence_35

There has been an increase in the frequency and intensity of heavy precipitation, melting of snow and land ice, and increased atmospheric humidity. Climate change_sentence_36

Flora and fauna are also behaving in a manner consistent with warming; for instance, plants are flowering earlier in spring. Climate change_sentence_37

Another key indicator is the cooling of the upper atmosphere, which demonstrates that greenhouse gases are trapping heat near the Earth's surface and preventing it from radiating into space. Climate change_sentence_38

Although record-breaking years attract considerable media attention, individual years are less significant than the longer global temperature trend. Climate change_sentence_39

An example of a shorter episode is the slower rate of surface temperature increase from 1998 to 2012, which was labeled the "global warming hiatus". Climate change_sentence_40

Throughout this period, ocean heat storage continued to progress steadily upwards, and in subsequent years, surface temperatures have spiked upwards. Climate change_sentence_41

The slower pace of warming can be attributed to a combination of natural temperature variability, reduced solar activity, and increased reflection of sunlight by particles from volcanic eruptions. Climate change_sentence_42

Regional variation Climate change_section_1

See also: Climate variability and change § Variability between regions Climate change_sentence_43

Global warming refers to global averages, with the amount of warming varying by region. Climate change_sentence_44

Patterns of warming are independent of where greenhouse gases are emitted, because the gases persist long enough to diffuse across the planet; however, localized black carbon deposits on snow and ice do contribute to Arctic warming. Climate change_sentence_45

Since the pre-industrial period, global average land temperatures have increased almost twice as fast as global average surface temperatures. Climate change_sentence_46

This is because of the larger heat capacity of oceans, and because oceans lose more heat by evaporation. Climate change_sentence_47

Over 90% of the additional energy in the climate system over the last 50 years has been stored in the ocean, warming it. Climate change_sentence_48

The remainder of the additional energy has melted ice and warmed the continents and the atmosphere. Climate change_sentence_49

The Northern Hemisphere and North Pole have warmed much faster than the South Pole and Southern Hemisphere. Climate change_sentence_50

The Northern Hemisphere not only has much more land, but also more snow area and sea ice, because of how the land masses are arranged around the Arctic Ocean. Climate change_sentence_51

As these surfaces flip from reflecting a lot of light to being dark after the ice has melted, they start absorbing more heat. Climate change_sentence_52

The Southern Hemisphere already had little sea ice in summer before it started warming. Climate change_sentence_53

Arctic temperatures have increased and are predicted to continue to increase during this century at over twice the rate of the rest of the world. Climate change_sentence_54

Melting of glaciers and ice sheets in the Arctic disrupts ocean circulation, including a weakened Gulf Stream, causing increased warming in some areas. Climate change_sentence_55

Physical drivers of recent climate change Climate change_section_2

Main article: Attribution of recent climate change Climate change_sentence_56

By itself, the climate system experiences various cycles which can last for years (such as the El Niño–Southern Oscillation) to decades or centuries. Climate change_sentence_57

Other changes are caused by an imbalance of energy that is "external" to the climate system, but not always external to the Earth. Climate change_sentence_58

Examples of external forcings include changes in the composition of the atmosphere (e.g. increased concentrations of greenhouse gases), solar luminosity, volcanic eruptions, and variations in the Earth's orbit around the Sun. Climate change_sentence_59

The attribution of climate change is the effort to scientifically show which mechanisms are responsible for observed changes in Earth's climate. Climate change_sentence_60

To determine the human contribution, known internal climate variability and natural external forcings need to be ruled out. Climate change_sentence_61

A key approach is to use computer modelling of the climate system to determine unique "fingerprints" for all potential causes. Climate change_sentence_62

By comparing these fingerprints with observed patterns and evolution of climate change, and the observed history of the forcings, the causes of the changes can be determined. Climate change_sentence_63

For example, solar forcing can be ruled out as major cause because its fingerprint is warming in the entire atmosphere, and only the lower atmosphere has warmed, as expected from greenhouse gases (which trap heat energy radiating from the surface). Climate change_sentence_64

Attribution of recent climate change shows that the primary driver is elevated greenhouse gases, but that aerosols also have a strong effect. Climate change_sentence_65

Greenhouse gases Climate change_section_3

Main articles: Greenhouse gas, Greenhouse effect, and Carbon dioxide in Earth's atmosphere Climate change_sentence_66

See also: Illustrative model of greenhouse effect on climate change Climate change_sentence_67

The Earth absorbs sunlight, then radiates it as heat. Climate change_sentence_68

Some of this infrared radiation is absorbed by greenhouse gases in the atmosphere, and because they re-emit it in all directions part of the heat is trapped on Earth instead of escaping into space. Climate change_sentence_69

Before the Industrial Revolution, naturally-occurring amounts of greenhouse gases caused the air near the surface to be about 33 °C (59 °F) warmer than it would have been in their absence. Climate change_sentence_70

Without the Earth's atmosphere, the Earth's average temperature would be well below the freezing point of water. Climate change_sentence_71

While water vapour (~50%) and clouds (~25%) are the biggest contributors to the greenhouse effect, they increase as a function of temperature and are therefore considered feedbacks. Climate change_sentence_72

On the other hand, concentrations of gases such as CO 2 (~20%), ozone and nitrous oxide are not temperature-dependent, and are hence considered external forcings. Climate change_sentence_73

Ozone acts as a greenhouse gas in the lowest layer of the atmosphere, the troposphere (as opposed to the stratospheric ozone layer). Climate change_sentence_74

Furthermore, ozone is highly reactive and interacts with other greenhouse gases and aerosols. Climate change_sentence_75

Human activity since the Industrial Revolution, mainly extracting and burning fossil fuels (coal, oil, and natural gas), has increased the amount of greenhouse gases in the atmosphere. Climate change_sentence_76

These elevated levels of gases such as CO 2, methane, tropospheric ozone, CFCs, and nitrous oxide drive up temperatures via radiative forcing. Climate change_sentence_77

In 2018, the concentrations of CO 2 and methane had increased by about 45% and 160%, respectively, since 1750. Climate change_sentence_78

In 2013, CO2 readings taken at the world's primary benchmark site in Mauna Loa surpassed 400 ppm for the first time (normal pre-industrial levels were ~270ppm). Climate change_sentence_79

These CO 2 levels are much higher than they have been at any time during the last 800,000 years, the period for which reliable data have been collected from air trapped in ice cores. Climate change_sentence_80

Less direct geological evidence indicates that CO 2 values have not been this high for millions of years. Climate change_sentence_81

Global anthropogenic greenhouse gas emissions in 2018, excluding those from land use change, were equivalent to 52 billion tonnes of CO 2. Climate change_sentence_82

Of these emissions, 72% was CO 2, 19% was methane, 6% was nitrous oxide, and 3% was fluorinated gases. Climate change_sentence_83

CO 2 emissions primarily come from burning fossil fuels to provide usable light and heat energy for transport, manufacturing, heating, and electricity. Climate change_sentence_84

Additional CO 2 emissions come from deforestation and industrial processes, which include the CO 2 released by the chemical reactions for making cement, steel, aluminum, and fertilizer. Climate change_sentence_85

Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, coal mining, as well as oil and gas extraction. Climate change_sentence_86

Nitrous oxide emissions largely come from the microbial decomposition of inorganic and organic fertilizer. Climate change_sentence_87

From a consumption standpoint, the dominant sources of global 2010 emissions were: food and human waste (34%), thermal comfort, washing, and lighting (26%); freight, travel, commuting, and communication (25%); and building construction (15%). Climate change_sentence_88

These emissions take into account the embodied fossil fuel energy in manufacturing materials including metals (e.g. steel, aluminum), concrete, glass, and plastic, which are largely used in buildings, infrastructure, and transportation. Climate change_sentence_89

From a production standpoint, the primary sources of global greenhouse gas emissions are estimated as: electricity and heat (25%), agriculture and forestry (24%), industry and manufacturing (21%), transport (14%), and buildings (6%). Climate change_sentence_90

Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for CO 2. Climate change_sentence_91

Natural processes, such as carbon fixation in the soil and photosynthesis, more than offset the greenhouse gas contributions from deforestation. Climate change_sentence_92

The land-surface sink is estimated to remove about 11 billion tonnes of CO 2 annually from the atmosphere, or about 29% of global CO 2 emissions. Climate change_sentence_93

The ocean also serves as a significant carbon sink via a two-step process. Climate change_sentence_94

First, CO 2 dissolves in the surface water. Climate change_sentence_95

Afterwards, the ocean's overturning circulation distributes it deep into the ocean's interior, where it accumulates over time as part of the carbon cycle. Climate change_sentence_96

Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted CO 2. Climate change_sentence_97

The strength of both the land and ocean sinks increases as CO 2 levels in the atmosphere rise. Climate change_sentence_98

Land surface change Climate change_section_4

Humans change the Earth's surface mainly to create more agricultural land. Climate change_sentence_99

Today, agriculture takes up 34% of Earth's land area, while 26% is forests, and 30% is uninhabitable (glaciers, deserts, etc.). Climate change_sentence_100

The amount of forested land continues to decrease, largely due to conversion to cropland in the tropics. Climate change_sentence_101

This deforestation is the most significant aspect of land surface change affecting global warming. Climate change_sentence_102

The main causes of deforestation are: permanent land-use change from forest to agricultural land producing products such as beef and palm oil (27%), logging to produce forestry/forest products (26%), short term shifting cultivation (24%), and wildfires (23%). Climate change_sentence_103

In addition to affecting greenhouse gas concentrations, land-use changes affect global warming through a variety of other chemical and physical mechanisms. Climate change_sentence_104

Changing the type of vegetation in a region affects the local temperature, by changing how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. Climate change_sentence_105

For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Climate change_sentence_106

Deforestation can also contribute to changing temperatures by affecting the release of aerosols and other chemical compounds that influence clouds, and by changing wind patterns (when the land surface presents different obstructions to wind). Climate change_sentence_107

In tropic and temperate areas the net effect is to produce a significant warming, while at latitudes closer to the poles a gain of albedo (as forest is replaced by snow cover) leads to an overall cooling effect. Climate change_sentence_108

Globally, these effects are estimated to have led to a slight cooling, dominated by an increase in surface albedo. Climate change_sentence_109

Aerosols and clouds Climate change_section_5

Air pollution, in the form of aerosols, not only puts a large burden on human health, but also affects the climate on a large scale. Climate change_sentence_110

From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed, a phenomenon popularly known as global dimming, typically attributed to aerosols from biofuel and fossil fuel burning. Climate change_sentence_111

Aerosol removal by precipitation gives tropospheric aerosols an atmospheric lifetime of only about a week, while stratospheric aerosols can remain in the atmosphere for a few years. Climate change_sentence_112

Globally, aerosols have been declining since 1990, meaning that they no longer mask greenhouse gas warming as much. Climate change_sentence_113

In addition to their direct effects (scattering and absorbing solar radiation), aerosols have indirect effects on the Earth's radiation budget. Climate change_sentence_114

Sulfate aerosols act as cloud condensation nuclei and thus lead to clouds that have more and smaller cloud droplets. Climate change_sentence_115

These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets. Climate change_sentence_116

This effect also causes droplets to be more uniform in size, which reduces the growth of raindrops and makes clouds more reflective to incoming sunlight. Climate change_sentence_117

Indirect effects of aerosols are the largest uncertainty in radiative forcing. Climate change_sentence_118

While aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Climate change_sentence_119

Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise. Climate change_sentence_120

Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C (0.36 °F) by 2050. Climate change_sentence_121

Natural forcings Climate change_section_6

Further information: Solar activity and climate Climate change_sentence_122

As the Sun is the Earth's primary energy source, changes in incoming sunlight directly affect the climate system. Climate change_sentence_123

Solar irradiance has been measured directly by satellites, and indirect measurements are available from the early 1600s. Climate change_sentence_124

There has been no upward trend in the amount of the Sun's energy reaching the Earth. Climate change_sentence_125

Explosive volcanic eruptions represent the largest natural forcing over the industrial era. Climate change_sentence_126

When the eruption is sufficiently strong (with sulfur dioxide reaching the stratosphere) sunlight can be partially blocked for a couple of years, with a temperature signal lasting about twice as long. Climate change_sentence_127

In the industrial era, volcanic activity has had negligible impacts on global temperature change trends. Climate change_sentence_128

Present-day volcanic CO2 emissions are equivalent to less than 1% of current anthropogenic CO2 emissions. Climate change_sentence_129

Physical climate models are unable to reproduce the rapid warming observed in recent decades when taking into account only variations in solar output and volcanic activity. Climate change_sentence_130

Further evidence for greenhouse gases being the cause of recent climate change come from measurements showing the warming of the lower atmosphere (the troposphere), coupled with the cooling of the upper atmosphere (the stratosphere). Climate change_sentence_131

If solar variations were responsible for the observed warming, warming of both the troposphere and the stratosphere would be expected, but that has not been the case. Climate change_sentence_132

Climate change feedback Climate change_section_7

Main articles: Climate change feedback and Climate sensitivity Climate change_sentence_133

The response of the climate system to an initial forcing is modified by feedbacks: increased by self-reinforcing feedbacks and reduced by balancing feedbacks. Climate change_sentence_134

The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and probably the net effect of clouds. Climate change_sentence_135

The primary balancing feedback to global temperature change is radiative cooling to space as infrared radiation in response to rising surface temperature. Climate change_sentence_136

Uncertainty over feedbacks is the major reason why different climate models project different magnitudes of warming for a given amount of emissions. Climate change_sentence_137

As air gets warmer, it can hold more moisture. Climate change_sentence_138

After an initial warming due to emissions of greenhouse gases, the atmosphere will hold more water. Climate change_sentence_139

As water vapour is a potent greenhouse gas, this further heats the atmosphere. Climate change_sentence_140

If cloud cover increases, more sunlight will be reflected back into space, cooling the planet. Climate change_sentence_141

If clouds become more high and thin, they act as an insulator, reflecting heat from below back downwards and warming the planet. Climate change_sentence_142

Overall, the net cloud feedback over the industrial era has probably exacerbated temperature rise. Climate change_sentence_143

The reduction of snow cover and sea ice in the Arctic reduces the albedo of the Earth's surface. Climate change_sentence_144

More of the Sun's energy is now absorbed in these regions, contributing to Arctic amplification, which has caused Arctic temperatures to increase at more than twice the rate of the rest of the world. Climate change_sentence_145

Arctic amplification is also melting permafrost, which releases methane and CO 2 into the atmosphere as another self-reinforcing feedback. Climate change_sentence_146

Barely half of human-caused CO 2 emissions have been absorbed by land plants and by the oceans. Climate change_sentence_147

On land, elevated CO 2 and an extended growing season have stimulated plant growth. Climate change_sentence_148

Climate change also increases droughts and heat waves that inhibit plant growth, which makes it uncertain that this balancing feedback will persist in the future. Climate change_sentence_149

Soils contain large quantities of carbon and may release some when they heat up. Climate change_sentence_150

As more CO 2 and heat are absorbed by the ocean, it acidifies, its circulation changes and phytoplankton takes up less carbon, decreasing the rate at which the ocean absorbs atmospheric carbon. Climate change_sentence_151

Climate change can also increase methane emissions from wetlands, marine and freshwater systems, and permafrost. Climate change_sentence_152

Future warming and the carbon budget Climate change_section_8

Further information: Carbon budget and Climate model Climate change_sentence_153

Future warming depends on the strengths of climate feedbacks and on emissions of greenhouse gases. Climate change_sentence_154

The former are often estimated using climate models. Climate change_sentence_155

A climate model is a representation of the physical, chemical, and biological processes that affect the climate system. Climate change_sentence_156

Models also include changes in the Earth's orbit, historical changes in the Sun's activity, and volcanic forcing. Climate change_sentence_157

Computer models attempt to reproduce and predict the circulation of the oceans, the annual cycle of the seasons, and the flows of carbon between the land surface and the atmosphere. Climate change_sentence_158

There are more than two dozen scientific institutions that develop major climate models. Climate change_sentence_159

Models project different future temperature rises for given emissions of greenhouse gases; they also do not fully agree on the strength of different feedbacks on climate sensitivity and magnitude of inertia of the climate system. Climate change_sentence_160

The physical realism of models is tested by examining their ability to simulate contemporary or past climates. Climate change_sentence_161

Past models have underestimated the rate of Arctic shrinkage and underestimated the rate of precipitation increase. Climate change_sentence_162

Sea level rise since 1990 was underestimated in older models, but more recent models agree well with observations. Climate change_sentence_163

The 2017 United States-published National Climate Assessment notes that "climate models may still be underestimating or missing relevant feedback processes". Climate change_sentence_164

Four Representative Concentration Pathways (RCPs) are used as input for climate models: "a stringent mitigation scenario (RCP2.6), two intermediate scenarios (RCP4.5 and RCP6.0) and one scenario with very high [greenhouse gas] emissions (RCP8.5)". Climate change_sentence_165

RCPs only look at concentrations of greenhouse gases, and so does not include the response of the carbon cycle. Climate change_sentence_166

Climate model projections summarized in the IPCC Fifth Assessment Report indicate that, during the 21st century, the global surface temperature is likely to rise a further 0.3 to 1.7 °C (0.5 to 3.1 °F) in a moderate scenario, or as much as 2.6 to 4.8 °C (4.7 to 8.6 °F) in an extreme scenario, depending on the rate of future greenhouse gas emissions and on climate feedback effects. Climate change_sentence_167

A subset of climate models add societal factors to a simple physical climate model. Climate change_sentence_168

These models simulate how population, economic growth, and energy use affect—and interact with—the physical climate. Climate change_sentence_169

With this information, these models can produce scenarios of how greenhouse gas emissions may vary in the future. Climate change_sentence_170

This output is then used as input for physical climate models to generate climate change projections. Climate change_sentence_171

In some scenarios emissions continue to rise over the century, while others have reduced emissions. Climate change_sentence_172

Fossil fuel resources are too abundant for shortages to be relied on to limit carbon emissions in the 21st century. Climate change_sentence_173

Emissions scenarios can be combined with modelling of the carbon cycle to predict how atmospheric concentrations of greenhouse gases might change in the future. Climate change_sentence_174

According to these combined models, by 2100 the atmospheric concentration of CO2 could be as low as 380 or as high as 1400 ppm, depending on the socioeconomic scenario and the mitigation scenario. Climate change_sentence_175

The remaining carbon emissions budget is determined by modelling the carbon cycle and the climate sensitivity to greenhouse gases. Climate change_sentence_176

According to the IPCC, global warming can be kept below 1.5 °C (2.7 °F) with a two-thirds chance if emissions after 2018 do not exceed 420 or 570 gigatonnes of CO 2, depending on exactly how the global temperature is defined. Climate change_sentence_177

This amount corresponds to ten to thirteen years of current emissions. Climate change_sentence_178

There are high uncertainties about the budget; for instance, it may be 100 gigatonnes of CO 2 smaller due to methane release from permafrost and wetlands. Climate change_sentence_179

Effects Climate change_section_9

Main article: Effects of climate change Climate change_sentence_180

Physical environment Climate change_section_10

Main article: Physical impacts of climate change Climate change_sentence_181

The environmental effects of climate change are broad and far-reaching, affecting oceans, ice, and weather. Climate change_sentence_182

Changes may occur gradually or rapidly. Climate change_sentence_183

Evidence for these effects comes from studying climate change in the past, from modelling, and from modern observations. Climate change_sentence_184

Since the 1950s, droughts and heat waves have appeared simultaneously with increasing frequency. Climate change_sentence_185

Extremely wet or dry events within the monsoon period have increased in India and East Asia. Climate change_sentence_186

The maximum rainfall and wind speed from hurricanes and typhoons is likely increasing. Climate change_sentence_187

Climate change has led to decades of shrinking and thinning of the Arctic sea ice, making it vulnerable to atmospheric anomalies. Climate change_sentence_188

Projections of declines in Arctic sea ice vary. Climate change_sentence_189

While ice-free summers are expected to be rare at 1.5 °C (2.7 °F) degrees of warming, they are set to occur once every three to ten years at a warming level of 2.0 °C (3.6 °F), increasing ice–albedo feedback. Climate change_sentence_190

Global sea level is rising as a consequence of glacial melt, melt of the ice sheets in Greenland and Antarctica, and thermal expansion. Climate change_sentence_191

Between 1993 and 2017, the rise increased over time, averaging 3.1 ± 0.3 mm per year. Climate change_sentence_192

Over the 21st century, the IPCC projects that in a very high emissions scenario the sea level could rise by 61–110 cm. Climate change_sentence_193

Increased ocean warmth is undermining and threatening to unplug Antarctic glacier outlets, risking a large melt of the ice sheet and the possibility of a 2-meter sea level rise by 2100 under high emissions. Climate change_sentence_194

Higher atmospheric CO 2 concentrations have also led to changes in ocean chemistry. Climate change_sentence_195

An increase in dissolved CO 2 is causing ocean acidification, which is making it more difficult for calcinate shells to form. Climate change_sentence_196

In addition, oxygen levels are decreasing as oxygen is less soluble in warmer water, with hypoxic dead zones expanding as a result of algal blooms stimulated by higher temperatures, higher CO 2 levels, ocean deoxygenation, and eutrophication. Climate change_sentence_197

Tipping points and long-term impacts Climate change_section_11

The greater the amount of global warming, the greater the risk of passing through ‘tipping points’, thresholds beyond which certain impacts can no longer be avoided even if temperatures are reduced. Climate change_sentence_198

An example is the collapse of West Antarctic and Greenland ice sheets, where a certain temperature rise commits an ice sheet to melt, although the time scale required is uncertain and depends on future warming. Climate change_sentence_199

Some large-scale changes could occur over a short time period, such as a collapse of the Atlantic Meridional Overturning Circulation, which would trigger major climate changes in the North Atlantic, Europe, and North America. Climate change_sentence_200

The long-term effects of climate change include further ice melt, ocean warming, sea level rise, and ocean acidification. Climate change_sentence_201

On the timescale of centuries to millennia, the magnitude of climate change will be determined primarily by anthropogenic CO 2 emissions. Climate change_sentence_202

This is due to CO 2's long atmospheric lifetime. Climate change_sentence_203

Oceanic CO 2 uptake is slow enough that ocean acidification will continue for hundreds to thousands of years. Climate change_sentence_204

These emissions are estimated to have prolonged the current interglacial period by at least 100,000 years. Climate change_sentence_205

Sea level rise will continue over many centuries, with an estimated rise of 2.3 metres per degree Celsius (4.2 ft/°F) after 2000 years. Climate change_sentence_206

Nature and wildlife Climate change_section_12

Main article: Climate change and ecosystems Climate change_sentence_207

Recent warming has driven many terrestrial and freshwater species poleward and towards higher altitudes. Climate change_sentence_208

Higher atmospheric CO 2 levels and an extended growing season have resulted in global greening, whereas heatwaves and drought have reduced ecosystem productivity in some regions. Climate change_sentence_209

The future balance of these opposing effects is unclear. Climate change_sentence_210

Climate change has contributed to the expansion of drier climate zones, such as the expansion of deserts in the subtropics. Climate change_sentence_211

The size and speed of global warming is making abrupt changes in ecosystems more likely. Climate change_sentence_212

Overall, it is expected that climate change will result in the extinction of many species. Climate change_sentence_213

The oceans have heated more slowly than the land, but plants and animals in the ocean have migrated towards the colder poles faster than species on land. Climate change_sentence_214

Just as on land, heat waves in the ocean occur more frequently due to climate change, with harmful effects found on a wide range of organisms such as corals, kelp, and seabirds. Climate change_sentence_215

Ocean acidification threatens damage to coral reefs, fisheries, protected species, and other natural resources of value to society. Climate change_sentence_216

Harmful algae bloom enhanced by climate change and eutrophication cause anoxia, disruption of food webs and massive large-scale mortality of marine life. Climate change_sentence_217

Coastal ecosystems are under particular stress, with almost half of wetlands having disappeared as a consequence of climate change and other human impacts. Climate change_sentence_218

Humans Climate change_section_13

Further information: Effects of climate change on human health, Climate security, Economics of climate change, and Climate change and agriculture Climate change_sentence_219

The effects of climate change on humans, mostly due to warming and shifts in precipitation, have been detected worldwide. Climate change_sentence_220

Regional impacts of climate change are now observable on all continents and across ocean regions, with low-latitude, less developed areas facing the greatest risk. Climate change_sentence_221

The Arctic, Africa, small islands, and Asian megadeltas are likely to be especially affected by future climate change. Climate change_sentence_222

Health impacts include both the direct effects of extreme weather, leading to injury and loss of life, as well as indirect effects, such as undernutrition brought on by crop failures. Climate change_sentence_223

Various infectious diseases are more easily transmitted in a warmer climate, such as dengue fever, which affects children most severely, and malaria. Climate change_sentence_224

Young children are the most vulnerable to food shortages, and together with older people, to extreme heat. Climate change_sentence_225

The World Health Organization (WHO) has estimated that between 2030 and 2050, climate change is expected to cause approximately 250,000 additional deaths per year from heat exposure in elderly people, increases in diarrheal disease, malaria, dengue, coastal flooding, and childhood undernutrition. Climate change_sentence_226

Over 500,000 additional adult deaths are projected yearly by 2050 due to reductions in food availability and quality. Climate change_sentence_227

Other major health risks associated with climate change include air and water quality. Climate change_sentence_228

The WHO has classified human health impacts from climate change as the greatest threat to global health in the 21st century. Climate change_sentence_229

Climate change is affecting food security and has caused reduction in global mean yields of maize, wheat, and soybeans between 1981 and 2010. Climate change_sentence_230

Future warming could further reduce global yields of major crops. Climate change_sentence_231

Crop production will probably be negatively affected in low-latitude countries, while effects at northern latitudes may be positive or negative. Climate change_sentence_232

Up to an additional 183 million people worldwide, particularly those with lower incomes, are at risk of hunger as a consequence of these impacts. Climate change_sentence_233

The effects of warming on the oceans also impact fish stocks, with a global decline in the maximum catch potential. Climate change_sentence_234

Only polar stocks are showing an increased potential. Climate change_sentence_235

Regions dependent on glacier water, regions that are already dry, and small islands are also at increased risk of water stress due to climate change. Climate change_sentence_236

Economic damages due to climate change have been underestimated, and may be severe, with the probability of disastrous tail-risk events being nontrivial. Climate change_sentence_237

Climate change has likely already increased global economic inequality, and is projected to continue doing so. Climate change_sentence_238

Most of the severe impacts are expected in sub-Saharan Africa and South-East Asia, where existing poverty is already exacerbated. Climate change_sentence_239

The World Bank estimates that climate change could drive over 120 million people into poverty by 2030. Climate change_sentence_240

Current inequalities between men and women, between rich and poor, and between different ethnicities have been observed to worsen as a consequence of climate variability and climate change. Climate change_sentence_241

Low-lying islands and coastal communities are threatened through hazards posed by sea level rise, such as flooding and permanent submergence. Climate change_sentence_242

This could lead to statelessness for populations in island nations, such as the Maldives and Tuvalu. Climate change_sentence_243

In some regions, rise in temperature and humidity may also be too severe for humans to adapt to. Climate change_sentence_244

In the next 50 years, 1 to 3 billion people are projected to be left outside the historically favourable climate conditions. Climate change_sentence_245

These factors, plus weather extremes, can drive environmental migration, both within and between countries. Climate change_sentence_246

Up to 1 billion people could be displaced due to climate change by 2050, with 200 million being the most repeated prediction; however, these numbers have been described as an upper bound. Climate change_sentence_247

Responses Climate change_section_14

The two conventional responses are mitigation (preventing as much additional warming as possible by reducing greenhouse gas emissions) and adaptation (adjusting society to compensate for unavoidable warming). Climate change_sentence_248

Many of the countries that have contributed least to global greenhouse gas emissions are among the most vulnerable to climate change, which raises questions about justice and fairness with regard to mitigation and adaptation. Climate change_sentence_249

A third option is climate engineering, which refers to direct interventions in the Earth's climate system. Climate change_sentence_250

Mitigation Climate change_section_15

Main article: Climate change mitigation Climate change_sentence_251

The IPCC has stressed the need to keep global warming below 1.5 °C (2.7 °F) compared to pre-industrial levels in order to avoid some irreversible impacts. Climate change_sentence_252

Climate change impacts can be mitigated by reducing greenhouse gas emissions and by enhancing the capacity of Earth's surface to absorb greenhouse gases from the atmosphere. Climate change_sentence_253

In order to limit global warming to less than 1.5 °C with a high likelihood of success, the IPCC estimates that global greenhouse gas emissions will need to be net zero by 2050, or by 2070 with a 2 °C target. Climate change_sentence_254

This will require far-reaching, systemic changes on an unprecedented scale in energy, land, cities, transport, buildings, and industry. Climate change_sentence_255

To make progress towards a goal of limiting warming to 1.5 °C, the United Nations Environment Programme estimates that, within the next decade, countries will need to triple the amount of reductions they have committed to in their current Paris Agreements. Climate change_sentence_256

Changing sources of energy Climate change_section_16

Long-term scenarios point to rapid and significant investment in renewable energy and energy efficiency as key to reducing GHG emissions. Climate change_sentence_257

Fossil fuels accounted for 80% of the world's energy in 2018, while the remaining share of power production was split between nuclear power, hydropower, and non-hydro renewables; that mix is expected to change significantly over the next 30 years. Climate change_sentence_258

Renewable energy technologies include solar and wind power, bioenergy, geothermal energy, and hydropower. Climate change_sentence_259

Photovoltaic solar and wind, in particular, have seen substantial growth and progress over the last few years, such that they are currently among the cheapest sources of new power generation. Climate change_sentence_260

Renewables represented 75% of all new electricity generation installed in 2019, with solar and wind constituting nearly all of that amount. Climate change_sentence_261

There are obstacles to the continued rapid development of renewable energy. Climate change_sentence_262

Environmental and land use concerns are sometimes associated with large solar, wind and hydropower projects. Climate change_sentence_263

Solar and wind power also require energy storage systems and other modifications to the electricity grid to operate effectively, although several storage technologies are now emerging to supplement the traditional use of pumped-storage hydropower. Climate change_sentence_264

The use of rare-earth metals and other hazardous materials has also been raised as a concern with solar power. Climate change_sentence_265

The use of bioenergy is often not carbon neutral, and may have negative consequences for food security, largely due to the amount of land required compared to other renewable energy options. Climate change_sentence_266

Hydropower growth has been slowing and is set to decline further due to concerns about social and environmental impacts. Climate change_sentence_267

While not renewable, nuclear energy has continued to be a significant low-carbon part of the global energy mix. Climate change_sentence_268

However, nuclear power costs are increasing amidst stagnant power share, so that nuclear power generation is now several times more expensive per megawatt hour than wind and solar. Climate change_sentence_269

Carbon capture and sequestration Climate change_section_17

Where energy production or CO 2-intensive heavy industries continue to produce waste CO 2, the gas can be captured and stored instead of being released to the atmosphere. Climate change_sentence_270

Although costly, carbon capture and storage (CCS) may be able to play a significant role in limiting CO 2 emissions by mid-century. Climate change_sentence_271

Earth's natural carbon sinks can be enhanced to sequester significantly larger amounts of CO 2 beyond naturally occurring levels. Climate change_sentence_272

Forest preservation, reforestation and tree planting on non-forest lands are considered the most effective, although they raise food security concerns. Climate change_sentence_273

Soil management on croplands and grasslands is another effective mitigation technique. Climate change_sentence_274

As models disagree on the feasibility of land-based negative emissions methods for mitigation, strategies based on them are risky. Climate change_sentence_275

Decarbonization pathways Climate change_section_18

Although there is no single pathway to limit global warming to 1.5 or 2.0 °C (2.7 or 3.6 °F), most scenarios and strategies see a major increase in the use of renewable energy in combination with increased energy efficiency measures to generate the needed greenhouse gas reductions. Climate change_sentence_276

To reduce pressures on ecosystems and enhance their carbon sequestration capabilities, changes would also be necessary in forestry and agriculture. Climate change_sentence_277

Scenarios that limit global warming to 1.5 °C generally project the large scale use of CO 2 removal methods in addition to greenhouse gas reduction approaches. Climate change_sentence_278

To achieve carbon neutrality by 2050, renewable energy would become the dominant form of electricity generation, rising to 85% or more by 2050 in some scenarios. Climate change_sentence_279

The use of electricity for other needs, such as heating, would rise to the point where electricity becomes the largest form of overall energy supply by 2050. Climate change_sentence_280

Investment in coal would be eliminated and coal use nearly phased out by 2050. Climate change_sentence_281

In transport, scenarios envision sharp increases in the market share of electric vehicles, low carbon fuel substitution for other transportation modes like shipping, and changes in transportation patterns that increase efficiency, for example increased public transport. Climate change_sentence_282

Buildings will see additional electrification with the use of technologies like heat pumps, as well as continued energy efficiency improvements achieved via low energy building codes. Climate change_sentence_283

Industrial efforts will focus on increasing the energy efficiency of production processes, such as the use of cleaner technology for cement production, designing and creating less energy intensive products, increasing product lifetimes, and developing incentives to reduce product demand. Climate change_sentence_284

The agriculture and forestry sector faces a triple challenge of limiting greenhouse gas emissions, preventing further conversion of forests to agricultural land, and meeting increases in world food demand. Climate change_sentence_285

A suite of actions could reduce agriculture/forestry based greenhouse gas emissions by 66% from 2010 levels by reducing growth in demand for food and other agricultural products, increasing land productivity, protecting and restoring forests, and reducing greenhouse gas emissions from agricultural production. Climate change_sentence_286

Policies and measures Climate change_section_19

A wide range of policies, regulations and laws are being used to reduce greenhouse gases. Climate change_sentence_287

Carbon pricing mechanisms include carbon taxes and emissions trading systems. Climate change_sentence_288

As of 2019, carbon pricing covers about 20% of global greenhouse gas emissions. Climate change_sentence_289

Renewable portfolio standards have been enacted in several countries requiring utilities to increase the percentage of electricity they generate from renewable sources. Climate change_sentence_290

Phasing out of fossil fuel subsidies, currently estimated at $300 billion globally (about twice the level of renewable energy subsidies), could reduce greenhouse gas emissions by 6%. Climate change_sentence_291

Subsidies could also be redirected to support the transition to clean energy. Climate change_sentence_292

More prescriptive methods that can reduce greenhouse gases include vehicle efficiency standards, renewable fuel standards, and air pollution regulations on heavy industry. Climate change_sentence_293

Reducing air pollution from the burning of fossil fuels will have significant co-benefits in terms of human health. Climate change_sentence_294

For instance, the WHO estimates that ambient air pollution currently causes 4.2 million deaths per year due to stroke, heart disease, lung cancer, and respiratory diseases. Climate change_sentence_295

Meeting Paris Agreement goals could save about a million of those lives per year worldwide from reduced pollution by 2050. Climate change_sentence_296

As the use of fossil fuels is reduced, there are Just Transition considerations involving the social and economic challenges that arise. Climate change_sentence_297

An example is the employment of workers in the affected industries, along with the well-being of the broader communities involved. Climate change_sentence_298

Climate justice considerations, such as those facing indigenous populations in the Arctic, are another important aspect of mitigation policies. Climate change_sentence_299

Adaptation Climate change_section_20

Main article: Climate change adaptation Climate change_sentence_300

Adaptation is "the process of adjustment to current or expected changes in climate and its effects". Climate change_sentence_301

As climate change effects vary across regions, so do adaptation strategies. Climate change_sentence_302

While some adaptation responses call for trade-offs, others bring synergies and co-benefits. Climate change_sentence_303

Increased use of air conditioning allows people to better cope with heat, but also increases energy demand. Climate change_sentence_304

Other examples of adaptation include improved coastline protection, better disaster management, and the development of more resistant crops. Climate change_sentence_305

Adaptation is especially important in developing countries since they are predicted to bear the brunt of the effects of climate change. Climate change_sentence_306

The capacity and potential for humans to adapt, called adaptive capacity, is unevenly distributed across different regions and populations, and developing countries generally have less. Climate change_sentence_307

There are limits to adaptation and more severe climate change requires more transformative adaptation, which can be prohibitively expensive. Climate change_sentence_308

The public sector, private sector, and communities are all gaining experience with adaptation, and adaptation is becoming embedded within their planning processes. Climate change_sentence_309

Climate engineering Climate change_section_21

Main article: Climate engineering Climate change_sentence_310

Geoengineering or climate engineering is the deliberate large-scale modification of the climate, considered a potential future method for counteracting climate change. Climate change_sentence_311

Techniques fall generally into the categories of solar radiation management and carbon dioxide removal, although various other schemes have been suggested. Climate change_sentence_312

A 2018 review paper concluded that although geoengineering is physically possible, all the techniques are in early stages of development, carry large risks and uncertainties and raise significant ethical and legal issues. Climate change_sentence_313

Society and culture Climate change_section_22

Political response Climate change_section_23

Main article: Politics of climate change Climate change_sentence_314

The geopolitics of climate change is complex and has often been framed as a free-rider problem, in which all countries benefit from mitigation done by other countries, but individual countries would lose from investing in a transition to a low-carbon economy themselves. Climate change_sentence_315

However, net importers of fossil fuels win economically from transitioning, causing net exporters to face stranded assets: fossil fuels they cannot sell, if they choose not to transition. Climate change_sentence_316

Furthermore, the benefits in terms of public health and local environmental improvements of coal phase out exceed the costs in almost all regions, potentially further eliminating the free-rider problem. Climate change_sentence_317

The geopolitics are further complicated by the supply chain of rare earth metals necessary to produce many clean technologies. Climate change_sentence_318

United Nations Framework Convention Climate change_section_24

Further information: United Nations Framework Convention on Climate Change Climate change_sentence_319

Nearly all countries in the world are parties to the United Nations Framework Convention on Climate Change (UNFCCC). Climate change_sentence_320

The objective of the UNFCCC is to prevent dangerous human interference with the climate system. Climate change_sentence_321

As stated in the convention, this requires that greenhouse gas concentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally to climate change, food production is not threatened, and economic development can be sustained. Climate change_sentence_322

Global emissions have risen since signing of the UNFCCC, as it does not actually restrict emissions but rather provides a framework for protocols that do. Climate change_sentence_323

Its yearly conferences are the stage of global negotiations. Climate change_sentence_324

The United Nations Framework Convention on Climate Change is mentioned in a target of the Sustainable Development Goal 13 which is to "Take urgent action to combat climate change and its impacts". Climate change_sentence_325

This target calls for developed countries to implement the commitments of mobilizing $100 billion per year to address the needs of developing countries, and make sure the Green Climate Fund becomes operational as soon as possible. Climate change_sentence_326

Other climate change treaties include the 1997 Kyoto Protocol, which extended UNFCCC and in which most developed countries accepted legally binding commitments to limit their emissions, and the 2009 Copenhagen Accord. Climate change_sentence_327

During Kyoto Protocol negotiations, the G77 (representing developing countries) pushed for a mandate requiring developed countries to "[take] the lead" in reducing their emissions, since developed countries contributed most to the accumulation of greenhouse gases in the atmosphere, and since per-capita emissions were still relatively low in developing countries. Climate change_sentence_328

(and emissions of developing countries would grow to meet their development needs.) Climate change_sentence_329

Copenhagen Accord has been widely portrayed as disappointing because of its low goals, and has been rejected by poorer nations including the G77. Climate change_sentence_330

Nations associated with the Accord aimed to limit the future increase in global mean temperature to below 2.0 °C (3.6 °F). Climate change_sentence_331

In 2015 all UN countries negotiated the Paris Agreement, which aims to keep global warming well below 1.5 °C (2.7 °F) and contains an aspirational goal of keeping warming under 1.5 °C. Climate change_sentence_332

The agreement replaced the Kyoto Protocol. Climate change_sentence_333

Unlike Kyoto, no binding emission targets were set in the Paris Agreement. Climate change_sentence_334

Instead, the procedure of regularly setting ever more ambitious goals and reevaluating these goals every five years has been made binding. Climate change_sentence_335

The Paris Agreement reiterated that developing countries must be financially supported. Climate change_sentence_336

As of December 2020, 193 states and the European Union have signed the treaty and 188 states and the EU have ratified or acceded to the agreement. Climate change_sentence_337

In November 2020 the United States withdrew from the Paris Agreement. Climate change_sentence_338

Other policy Climate change_section_25

In 2019, the British Parliament became the first national government in the world to officially declare a climate emergency. Climate change_sentence_339

Other countries and jurisdictions followed suit. Climate change_sentence_340

In November 2019 the European Parliament declared a "climate and environmental emergency", and the European Commission presented its European Green Deal with the goal of making the EU carbon-neutral by 2050. Climate change_sentence_341

Major countries in Asia have made similar pledges: South Korea and Japan have committed to become carbon neutral by 2050, and China by 2060. Climate change_sentence_342

While ozone depletion and global warming are considered separate problems, the solution to the former has significantly mitigated global warming. Climate change_sentence_343

The greenhouse gas emission mitigation of the Montreal Protocol, an international agreement to stop emitting ozone-depleting gases, is estimated to have been more effective than that of the Kyoto Protocol, which was specifically designed to curb greenhouse gas emissions. Climate change_sentence_344

It has been argued that the Montreal Protocol may have done more than any other measure, as of 2017, to mitigate global warming as those substances were also powerful greenhouse gases. Climate change_sentence_345

Scientific consensus Climate change_section_26

Main article: Scientific consensus on climate change Climate change_sentence_346

There is an overwhelming scientific consensus that global surface temperatures have increased in recent decades and that the trend is caused mainly by human-induced emissions of greenhouse gases, with 97% or more of actively publishing climate scientists agreeing. Climate change_sentence_347

The consensus has grown to 100% among research scientists on anthropogenic global warming as of 2019. Climate change_sentence_348

No scientific body of national or international standing disagrees with this view. Climate change_sentence_349

Consensus has further developed that some form of action should be taken to protect people against the impacts of climate change, and national science academies have called on world leaders to cut global emissions. Climate change_sentence_350

Scientific discussion takes place in journal articles that are peer-reviewed, which scientists subject to assessment every couple of years in the Intergovernmental Panel on Climate Change reports. Climate change_sentence_351

In 2013, the IPCC Fifth Assessment Report stated that "is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century". Climate change_sentence_352

Their 2018 report expressed the scientific consensus as: "human influence on climate has been the dominant cause of observed warming since the mid-20th century". Climate change_sentence_353

Scientists have issues two warnings to humanity, in 2017 and 2019, expressing concern about the current trajectory of potentially catastrophic climate change, and about untold human suffering as a consequence. Climate change_sentence_354

The public Climate change_section_27

Further information: Climate communication, Media coverage of climate change, and Public opinion on climate change Climate change_sentence_355

Climate change came to international public attention in the late 1980s. Climate change_sentence_356

Due to confusing media coverage in the early 1990s, understanding was often confounded by conflation with other environmental issues like ozone depletion. Climate change_sentence_357

In popular culture, the first movie to reach a mass public on the topic was The Day After Tomorrow in 2004, followed a few years later by the Al Gore documentary An Inconvenient Truth. Climate change_sentence_358

Books, stories and films about climate change fall under the genre of climate fiction. Climate change_sentence_359

Significant regional differences exist in both public concern for and public understanding of climate change. Climate change_sentence_360

In 2015 a median of 54% of respondents considered it "a very serious problem", but Americans and Chinese (whose economies are responsible for the greatest annual CO2 emissions) were among the least concerned. Climate change_sentence_361

A 2020 Pew research study finds that in the US the issue is also highly partisan, with belief that humans are contributing a great deal to climate change believed by 72% of Democrats and only 22% of Republicans, while belief that government should do more to reduce its effects supported by 89% of Democrats and only 35% of Republicans. Climate change_sentence_362

Denial and misinformation Climate change_section_28

See also: Fossil fuels lobby and Climate change denial Climate change_sentence_363

Public debate about climate change has been strongly affected by climate change denial and misinformation, which originated in the United States and has since spread to other countries, particularly Canada and Australia. Climate change_sentence_364

The actors behind climate change denial form a well-funded and relatively coordinated coalition of fossil fuel companies, industry groups, conservative think tanks, and contrarian scientists. Climate change_sentence_365

Like the tobacco industry before, the main strategy of these groups has been to manufacture doubt about scientific data and results. Climate change_sentence_366

Many who deny, dismiss, or hold unwarranted doubt about the scientific consensus on anthropogenic climate change are labelled as "climate change skeptics", which several scientists have noted is a misnomer. Climate change_sentence_367

There are different variants of climate denial: some deny that warming takes place at all, some acknowledge warming but attribute it to natural influences, and some minimize the negative impacts of climate change. Climate change_sentence_368

Manufacturing uncertainty about the science later developed into a manufacturing controversy: creating the belief that there is significant uncertainty about climate change within the scientific community in order to delay policy changes. Climate change_sentence_369

Strategies to promote these ideas include criticism of scientific institutions, and questioning the motives of individual scientists. Climate change_sentence_370

An "echo chamber" of climate-denying blogs and media has further fomented misunderstanding of climate change. Climate change_sentence_371

Protest and litigation Climate change_section_29

Main article: Climate movement Climate change_sentence_372

Climate protests have risen in popularity in the 2010s in such forms as public demonstrations, fossil fuel divestment, and lawsuits. Climate change_sentence_373

Prominent recent demonstrations include the school strike for climate, and civil disobedience. Climate change_sentence_374

In the school strike, youth across the globe have protested by skipping school, inspired by Swedish teenager Greta Thunberg. Climate change_sentence_375

Mass civil disobedience actions by groups like Extinction Rebellion have protested by causing disruption. Climate change_sentence_376

Litigation is increasingly used as a tool to strengthen climate action, with many lawsuits targeting governments to demand that they take ambitious action or enforce existing laws regarding climate change. Climate change_sentence_377

Lawsuits against fossil-fuel companies, from activists, shareholders and investors, generally seek compensation for loss and damage. Climate change_sentence_378

Discovery Climate change_section_30

For broader coverage of this topic, see History of climate change science. Climate change_sentence_379

In 1824 Joseph Fourier proposed a version of the greenhouse effect; transparent atmosphere lets through visible light, which warms the surface. Climate change_sentence_380

The warmed surface emits infrared radiation, but the atmosphere is relatively opaque to infrared and slows the emission of energy, warming the planet. Climate change_sentence_381

Starting in 1859, John Tyndall established that nitrogen and oxygen (99% of dry air) are transparent to infrared, but water vapour and traces of some gases (significantly methane and carbon dioxide) both absorb infrared and, when warmed, emit infrared radiation. Climate change_sentence_382

Changing concentrations of these gases could have caused "all the mutations of climate which the researches of geologists reveal" including ice ages. Climate change_sentence_383

Svante Arrhenius noted that water vapour in air continuously varied, but carbon dioxide (CO 2) was determined by long term geological processes. Climate change_sentence_384

At the end of an ice age, warming from increased CO 2 would increase the amount of water vapour, amplifying its effect in a feedback process. Climate change_sentence_385

In 1896, he published the first climate model of its kind, showing that halving of CO 2 could have produced the drop in temperature initiating the ice age. Climate change_sentence_386

Arrhenius calculated the temperature increase expected from doubling CO 2 to be around 5–6 °C (9.0–10.8 °F). Climate change_sentence_387

Other scientists were initially sceptical and believed the greenhouse effect to be saturated so that adding more CO 2 would make no difference. Climate change_sentence_388

Experts thought climate would be self-regulating. Climate change_sentence_389

From 1938 Guy Stewart Callendar published evidence that climate was warming and CO 2 levels increasing, but his calculations met the same objections. Climate change_sentence_390

Early calculations treated the atmosphere as a single layer but in the 1950s, Gilbert Plass used digital computers to model the different layers and found added CO 2 would cause warming. Climate change_sentence_391

In the same decade Hans Suess found evidence CO 2 levels had been rising, Roger Revelle showed the oceans would not absorb the increase, and together they helped Charles Keeling to begin a record of continued increase, the Keeling Curve. Climate change_sentence_392

Scientists alerted the public, and the dangers were highlighted at James Hansen's 1988 Congressional testimony. Climate change_sentence_393

The Intergovernmental Panel on Climate Change, set up in 1988 to provide formal advice to the world's governments, spurred interdisciplinary research. Climate change_sentence_394

Terminology Climate change_section_31

Before the 1980s, when it was unclear whether warming by greenhouse gases would dominate aerosol-induced cooling, scientists often used the term inadvertent climate modification to refer to humankind's impact on the climate. Climate change_sentence_395

In the 1980s, the terms global warming and climate change were introduced, the former referring only to increased surface warming, while the latter describes the full effect of greenhouse gases on the climate. Climate change_sentence_396

Global warming became the most popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Climate change_sentence_397 Senate. Climate change_sentence_398

In the 2000s, the term climate change increased in popularity. Climate change_sentence_399

Global warming usually refers to human-induced warming of the Earth system, whereas climate change can refer to natural as well as anthropogenic change. Climate change_sentence_400

The two terms are often used interchangeably. Climate change_sentence_401

Various scientists, politicians and media figures have adopted the terms climate crisis or climate emergency to talk about climate change, while using global heating instead of global warming. Climate change_sentence_402

The policy editor-in-chief of The Guardian explained that they included this language in their editorial guidelines "to ensure that we are being scientifically precise, while also communicating clearly with readers on this very important issue". Climate change_sentence_403

Oxford Dictionary chose climate emergency as its word of the year in 2019 and defines the term as "a situation in which urgent action is required to reduce or halt climate change and avoid potentially irreversible environmental damage resulting from it". Climate change_sentence_404

See also Climate change_section_32

Climate change_unordered_list_0

  • Anthropocene – proposed new geological time interval in which humans are having significant geological impactClimate change_item_0_0
  • Global cooling – minority view held by scientists in the 1970s that imminent cooling of the Earth would take placeClimate change_item_0_1
  • Milankovitch cyclesClimate change_item_0_2

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: change.