GLOBAL WARMING, also referred to as CLIMATE CHANGE, is the observed
century-scale rise in the average temperature of the
In 2013, the Intergovernmental Panel on
Future climate change and associated impacts will differ from region to region around the globe. Anticipated effects include warming global temperature, rising sea levels , changing precipitation , and expansion of deserts in the subtropics . Warming is expected to be greater over land than over the oceans and greatest in the Arctic , with the continuing retreat of glaciers , permafrost and sea ice . Other likely changes include more frequent extreme weather events such as heat waves , droughts , heavy rainfall with floods and heavy snowfall ; ocean acidification ; and species extinctions due to shifting temperature regimes. Effects significant to humans include the threat to food security from decreasing crop yields and the abandonment of populated areas due to rising sea levels . Because the climate system has a large "inertia " and greenhouse gases will remain in the atmosphere for a long time, many of these effects will persist for not only decades or centuries, but for tens of thousands of years to come.
Possible societal responses to global warming include mitigation by
emissions reduction, adaptation to its effects, building systems
resilient to its effects, and possible future climate engineering .
Most countries are parties to the United Nations Framework Convention
Public reactions to global warming and concern about its effects are
also increasing. A global 2015
Pew Research Center
* 1 Observed temperature changes
* 1.1 Regional trends and short-term fluctuations * 1.2 Warmest years vs overall trend
* 2 Initial causes of temperature changes (external forcings)
* 2.1 Greenhouse gases * 2.2 Aerosols and soot * 2.3 Solar activity * 2.4 Variations in Earth\'s orbit
* 5 Observed and expected environmental effects
* 6 Observed and expected effects on social systems
* 6.1 Habitat inundation * 6.2 Economy * 6.3 Infrastructure
* 7 Possible responses to global warming
* 7.1 Mitigation
* 7.2 Adaptation
* 8 Discourse about global warming
* 8.1 Political discussion * 8.2 Scientific discussion
* 8.3 Discussion by the public and in popular media
* 8.3.1 Surveys of public opinion
* 9 Etymology * 10 See also * 11 Notes * 12 Citations * 13 References * 14 Further reading
* 15 External links
* 15.1 Research * 15.2 Educational
OBSERVED TEMPERATURE CHANGES
Instrumental temperature record World map
showing surface temperature trends (°C per decade) between 1950 and
2014. Two millennia of mean surface temperatures according to
different reconstructions from climate proxies , each smoothed on a
decadal scale, with the instrumental temperature record overlaid in
In the period from 1880 to 2012, the global average (land and ocean) surface temperature has increased by 0.85 °C, multiple independently produced datasets confirm. In the period from 1906 to 2005, Earth\'s average surface temperature rose by 7002273890000000000♠0.74±0.18 °C. The rate of warming almost doubled in the last half of that period (7002273279999999999♠0.13±0.03 °C per decade, against 7002273219999999999♠0.07±0.02 °C per decade). Although the popular press often reports the increase of the average near-surface atmospheric temperature as the measure of global warming, most of the additional energy stored in the climate system since 1970 has gone into the oceans. The rest has melted ice and warmed the continents and the atmosphere .
Since 1979, the average temperature of the lower troposphere has
increased between 0.12 and 0.135 °C (0.216 and 0.243 °F) per decade,
satellite temperature measurements confirm.
The warming evident in the instrumental temperature record is consistent with a wide range of observations, as documented by many independent scientific groups. Examples include sea level rise , widespread melting of snow and land ice, increased heat content of the oceans , increased humidity , and the earlier timing of spring events, e.g., the flowering of plants. The probability that these changes could have occurred by chance is virtually zero.
REGIONAL TRENDS AND SHORT-TERM FLUCTUATIONS
Play media Temperature anomalies arranged by country 1900 - 2016. Deviation from the 1951-1980 mean temperature. Visualization based on GISTEMP data.
Temperature increases vary a lot across the globe. Since 1979, land temperatures have increased about twice as fast as ocean temperatures (7002273399999999999♠0.25 °C per decade against 7002273279999999999♠0.13 °C per decade). Ocean temperatures increase more slowly than land temperatures because of the larger effective heat capacity of the oceans and because oceans lose more heat by evaporation. Since the beginning of industrialisation in the eighteenth century, the temperature difference between the hemispheres has increased due to melting of sea ice and snow in the North. In the past one hundred years, average arctic temperatures have been increasing at almost twice the rate of the rest of the world; however, arctic temperatures are also highly variable. Although more greenhouse gases are emitted in the Northern than in the Southern Hemisphere, this fact does not contribute to the difference in warming because the major greenhouse gases persist long enough to diffuse within as well as between the hemispheres.
The thermal inertia of the oceans and the slow responses of other indirect effects occasion the climate to take centuries or longer to adjust to past changes in forcings. One climate commitment study concluded that if greenhouse gases were stabilized at year 2000 levels, surface temperatures would still increase by about one-half degree Celsius, and another found that if they were stabilized at 2005 levels, surface warming could exceed a whole degree Celsius. Some of this surface warming will be driven by past natural forcings which are still seeking equilibrium in the climate system . One study using a highly simplified climate model indicates these past natural forcings may account for as much as 64% of the committed 2050 surface warming and their influence will fade with time compared to the human contribution.
Global temperature is subject to short-term fluctuations that overlay long-term trends and can temporarily mask them. The relative stability in surface temperature from 2002 to 2009, which has since been dubbed the global warming hiatus by the media and some scientists, is an example of such an episode. 2015 updates to account for differing methods of measuring ocean surface temperature measurements show a positive trend over the recent decade.
WARMEST YEARS VS OVERALL TREND
Sixteen of the seventeen warmest years on record have occurred since 2000. While record-breaking years attract considerable public interest, individual years are less significant than the overall trend. Some climatologists have criticized the attention that the popular press gives to "warmest year" statistics. In particular, ocean oscillations such as the El Niño Southern Oscillation (ENSO) can cause temperatures of a given year to be abnormally warm or cold for reasons unrelated to the overall trend of climate change. Gavin Schmidt stated "the long-term trends or the expected sequence of records are far more important than whether any single year is a record or not."
INITIAL CAUSES OF TEMPERATURE CHANGES (EXTERNAL FORCINGS)
CO2 concentrations over the last 400,000 years. Greenhouse effect schematic showing energy flows between space, the atmosphere, and Earth's surface. Energy exchanges are expressed in watts per square metre (W/m2). Main article: Attribution of recent climate change
The climate system can spontaneously generate changes in global temperature for years to decades at a time but long-term changes in global temperature require external forcings. These forcings are "external" to the climate system but not necessarily external to Earth. Examples of external forcings include changes in atmospheric composition (e.g., increased concentrations of greenhouse gases ), solar luminosity , volcanic eruptions, and variations in Earth\'s orbit around the Sun.
The greenhouse effect is the process by which absorption and emission of infrared radiation by gases in a planet's atmosphere warm its lower atmosphere and surface. It was proposed by Joseph Fourier in 1824, discovered in 1860 by John Tyndall , was first investigated quantitatively by Svante Arrhenius in 1896, and its scientific description was developed in the 1930s through 1960s by Guy Stewart Callendar . Annual world greenhouse gas emissions, in 2010, by sector. Percentage share of global cumulative energy-related CO2 emissions between 1751 and 2012 across different regions.
On Earth, an atmosphere containing naturally occurring amounts of greenhouse gases causes air temperature near the surface to be about 33 °C (59 °F) warmer than it would be in their absence. Without the Earth's atmosphere, the Earth's average temperature would be well below the freezing temperature of water. The major greenhouse gases are water vapour , which causes about 36–70% of the greenhouse effect; carbon dioxide (CO2), which causes 9–26%; methane (CH4), which causes 4–9%; and ozone (O3), which causes 3–7%. Clouds also affect the radiation balance through cloud forcings similar to greenhouse gases.
Human activity since the
In May 2013, it was reported that readings for CO2 taken at the world's primary benchmark site in Mauna Loa surpassed 400 ppm . According to professor Brian Hoskins , this is likely the first time CO2 levels have been this high for about 4.5 million years. Monthly global CO2 concentrations exceeded 400 ppm in March 2015, probably for the first time in several million years. On 12 November 2015, NASA scientists reported that human-made carbon dioxide continues to increase above levels not seen in hundreds of thousands of years: currently, about half of the carbon dioxide released from the burning of fossil fuels is not absorbed by vegetation and the oceans and remains in the atmosphere. Global carbon dioxide emissions by country.
Over the last three decades of the twentieth century, gross domestic product per capita and population growth were the main drivers of increases in greenhouse gas emissions. CO2 emissions are continuing to rise due to the burning of fossil fuels and land-use change. :71 Emissions can be attributed to different regions . Attributions of emissions due to land-use change are subject to considerable uncertainty. :289
Emissions scenarios , estimates of changes in future emission levels
of greenhouse gases, have been projected that depend upon uncertain
economic, sociological , technological , and natural developments. In
most scenarios, emissions continue to rise over the century, while in
a few, emissions are reduced.
The popular media and the public often confuse global warming with ozone depletion , i.e., the destruction of stratospheric ozone (e.g., the ozone layer) by chlorofluorocarbons . Although there are a few areas of linkage , the relationship between the two is not strong. Reduced stratospheric ozone has had a slight cooling influence on surface temperatures, while increased tropospheric ozone has had a somewhat larger warming effect.
AEROSOLS AND SOOT
Ship tracks can be seen as lines in these clouds over the Atlantic Ocean on the east coast of the United States. Atmospheric particles from these and other sources could have a large effect on climate through the aerosol indirect effect.
Global dimming , a gradual reduction in the amount of global direct
irradiance at the Earth's surface, was observed from 1961 until at
least 1990. Solid and liquid particles known as aerosols, produced by
volcanoes and human-made pollutants , are thought to be the main cause
of this dimming. They exert a cooling effect by increasing the
reflection of incoming sunlight. The effects of the products of fossil
fuel combustion – CO2 and aerosols – have partially offset one
another in recent decades, so that net warming has been due to the
increase in non-CO2 greenhouse gases such as methane. Radiative
forcing due to aerosols is temporally limited due to the processes
that remove aerosols from the atmosphere. Removal by clouds and
precipitation gives tropospheric aerosols an atmospheric lifetime of
only about a week, while stratospheric aerosols can remain for a few
In addition to their direct effect by scattering and absorbing solar radiation, aerosols have indirect effects on the Earth\'s radiation budget . Sulfate aerosols act as cloud condensation nuclei and thus lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets, a phenomenon known as the Twomey effect . This effect also causes droplets to be of more uniform size, which reduces growth of raindrops and makes the cloud more reflective to incoming sunlight, known as the Albrecht effect . Indirect effects are most noticeable in marine stratiform clouds, and have very little radiative effect on convective clouds. Indirect effects of aerosols represent the largest uncertainty in radiative forcing.
Soot may either cool or warm Earth's climate system , depending on
whether it is airborne or deposited. Atmospheric soot directly absorbs
solar radiation, which heats the atmosphere and cools the surface. In
isolated areas with high soot production, such as rural India, as much
as 50% of surface warming due to greenhouse gases may be masked by
atmospheric brown clouds . When deposited, especially on glaciers or
on ice in arctic regions, the lower surface albedo can also directly
heat the surface. The influences of atmospheric particles, including
black carbon, are most pronounced in the tropics and sub-tropics,
particularly in Asia, while the effects of greenhouse gases are
dominant in the extratropics and southern hemisphere. Changes in
total solar irradiance (TSI) and monthly sunspot numbers since the
mid-1970s. Contribution of natural factors and human activities
to radiative forcing of climate change.
Main article: Solar activity and climate
Since 1978, solar irradiance has been measured by satellites . These measurements indicate that the Sun's radiative output has not increased since then, so the warming that occurred in the past 40 years cannot be attributed to an increase in solar energy reaching the Earth.
Another line of evidence for the Sun's non-attributability is the differing temperature changes at different levels in the Earth's atmosphere. According to basic physical principles, the greenhouse effect produces warming of the lower atmosphere (the troposphere), but cooling of the upper atmosphere (the stratosphere). If solar variations were responsible for the observed warming, warming of both the troposphere and the stratosphere would be expected.
VARIATIONS IN EARTH\'S ORBIT
Main article: Milankovitch cycles
The tilt of the Earth’s axis and the shape of its orbit around the Sun vary slowly over tens of thousands of years. This changes climate by changing the seasonal and latitudinal distribution of incoming solar energy at Earth's surface. During the last few thousand years, this phenomenon contributed to a slow cooling trend at high latitudes of the Northern Hemisphere during summer, a trend that was reversed by greenhouse-gas-induced warming during the 20th century. Orbital cycles favorable for glaciation are not expected within the next 50,000 years.
Climate change feedback and
The climate system includes a range of feedbacks , which alter the response of the system to changes in external forcings. Positive feedbacks increase the response of the climate system to an initial forcing, while negative feedbacks reduce it.
There are a range of feedbacks in the climate system, including water
vapour , changes in ice-albedo (snow and ice cover affect how much the
Earth's surface absorbs or reflects incoming sunlight), clouds, and
changes in the Earth's carbon cycle (e.g., the release of carbon from
soil ). The main negative feedback is the energy the Earth's surface
radiates into space as infrared radiation . According to the
Feedbacks are an important factor in determining the sensitivity of the climate system to increased atmospheric greenhouse gas concentrations. Other factors being equal, a higher climate sensitivity means that more warming will occur for a given increase in greenhouse gas forcing. Uncertainty over the effect of feedbacks is a major reason why different climate models project different magnitudes of warming for a given forcing scenario. More research is needed to understand the role of clouds and carbon cycle feedbacks in climate projections.
The IPCC projections previously mentioned span the "likely" range (greater than 66% probability, based on expert judgement) for the selected emissions scenarios. However, the IPCC's projections do not reflect the full range of uncertainty. The lower end of the "likely" range appears to be better constrained than the upper end.
Calculations of global warming prepared in or before 2001 from a
range of climate models under the SRES A2 emissions scenario, which
assumes no action is taken to reduce emissions and regionally divided
economic development. Projected change in annual mean surface air
temperature from the late 20th century to the middle 21st century,
based on a medium emissions scenario (SRES A1B). This scenario
assumes that no future policies are adopted to limit greenhouse gas
emissions. Image credit:
A climate model is a representation of the physical, chemical and biological processes that affect the climate system. Such models are based on scientific disciplines such as fluid dynamics and thermodynamics as well as physical processes such as radiative transfer . The models may be used to predict a range of variables such as local air movement, temperature, clouds, and other atmospheric properties; ocean temperature, salt content , and circulation ; ice cover on land and sea; the transfer of heat and moisture from soil and vegetation to the atmosphere; and chemical and biological processes, among others.
Although researchers attempt to include as many processes as possible, simplifications of the actual climate system are inevitable because of the constraints of available computer power and limitations in knowledge of the climate system. Results from models can also vary due to different greenhouse gas inputs and the model's climate sensitivity. For example, the uncertainty in IPCC's 2007 projections is caused by (1) the use of multiple models with differing sensitivity to greenhouse gas concentrations, (2) the use of differing estimates of humanity's future greenhouse gas emissions, (3) any additional emissions from climate feedbacks that were not included in the models IPCC used to prepare its report, i.e., greenhouse gas releases from permafrost.
The models do not assume the climate will warm due to increasing levels of greenhouse gases. Instead the models predict how greenhouse gases will interact with radiative transfer and other physical processes. Warming or cooling is thus a result, not an assumption, of the models.
Clouds and their effects are especially difficult to predict. Improving the models' representation of clouds is therefore an important topic in current research. Another prominent research topic is expanding and improving representations of the carbon cycle.
Models are also used to help investigate the causes of recent climate change by comparing the observed changes to those that the models project from various natural and human causes. Although these models do not unambiguously attribute the warming that occurred from approximately 1910 to 1945 to either natural variation or human effects, they do indicate that the warming since 1970 is dominated by anthropogenic greenhouse gas emissions.
The physical realism of models is tested by examining their ability
to simulate contemporary or past climates.
OBSERVED AND EXPECTED ENVIRONMENTAL EFFECTS
Main article: Effects of global warming Projections of global mean sea level rise by Parris and others. Probabilities have not been assigned to these projections. Therefore, none of these projections should be interpreted as a "best estimate" of future sea level rise. Image credit: NOAA.
Anthropogenic forcing has likely contributed to some of the observed changes, including sea level rise, changes in climate extremes (such as the number of warm and cold days), declines in Arctic sea ice extent, glacier retreat , and greening of the Sahara .
During the 21st century, glaciers and snow cover are projected to continue their widespread retreat. Projections of declines in Arctic sea ice vary. Recent projections suggest that Arctic summers could be ice-free (defined as ice extent less than 1 million square km ) as early as 2025–2030.
"Detection" is the process of demonstrating that climate has changed in some defined statistical sense, without providing a reason for that change. Detection does not imply attribution of the detected change to a particular cause. "Attribution" of causes of climate change is the process of establishing the most likely causes for the detected change with some defined level of confidence. Detection and attribution may also be applied to observed changes in physical, ecological and social systems.
Changes in regional climate are expected to include greater warming
over land, with most warming at high northern latitudes , and least
warming over the
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. Projections suggest a probable increase in the frequency and severity of some extreme weather events, such as heat waves .
A 2015 study published in Nature
About 18% of the moderate daily precipitation extremes over land are attributable to the observed temperature increase since pre-industrial times, which in turn primarily results from human influence. For 2 °C of warming the fraction of precipitation extremes attributable to human influence rises to about 40%. Likewise, today about 75% of the moderate daily hot extremes over land are attributable to warming. It is the most rare and extreme events for which the largest fraction is anthropogenic, and that contribution increases nonlinearly with further warming.
Data analysis of extreme events from 1960 until 2010 suggests that droughts and heat waves appear simultaneously with increased frequency. Extremely wet or dry events within the monsoon period have increased since 1980.
SEA LEVEL RISE
Map of the
The sea level rise since 1993 has been estimated to have been on average 2.6 mm and 2.9 mm per year ± 0.4 mm. Additionally, sea level rise has accelerated from 1995 to 2015. Over the 21st century, the IPCC projects for a high emissions scenario, that global mean sea level could rise by 52–98 cm. The IPCC's projections are conservative, and may underestimate future sea level rise. Other estimates suggest that for the same period, global mean sea level could rise by 0.2 to 2.0 m (0.7–6.6 ft), relative to mean sea level in 1992.
Widespread coastal flooding would be expected if several degrees of
warming is sustained for millennia. For example, sustained global
warming of more than 2 °C (relative to pre-industrial levels) could
lead to eventual sea level rise of around 1 to 4 m due to thermal
expansion of sea water and the melting of glaciers and small ice caps
. Melting of the
Greenland ice sheet
Warming beyond the 2 °C target would potentially lead to rates of
sea-level rise dominated by ice loss from
Main article: Climate change and ecosystems
In terrestrial ecosystems , the earlier timing of spring events, as well as poleward and upward shifts in plant and animal ranges, have been linked with high confidence to recent warming. Future climate change is expected to affect particular ecosystems, including tundra , mangroves , coral reefs , and caves . It is expected that most ecosystems will be affected by higher atmospheric CO2 levels, combined with higher global temperatures. Overall, it is expected that climate change will result in the extinction of many species and reduced diversity of ecosystems.
Increases in atmospheric CO2 concentrations have led to an increase in ocean acidity . Dissolved CO2 increases ocean acidity, measured by lower pH values. Between 1750 and 2000, surface-ocean pH has decreased by ≈0.1, from ≈8.2 to ≈8.1. Surface-ocean pH has probably not been below ≈8.1 during the past 2 million years. Projections suggest that surface-ocean pH could decrease by an additional 0.3–0.4 units by 2100. Future ocean acidification could threaten coral reefs , fisheries , protected species , and other natural resources of value to society.
Ocean deoxygenation is projected to increase hypoxia by 10%, and triple suboxic waters (oxygen concentrations 98% less than the mean surface concentrations), for each 1 °C of upper ocean warming.
On the timescale of centuries to millennia, the magnitude of global warming will be determined primarily by anthropogenic CO2 emissions. This is due to carbon dioxide's very long lifetime in the atmosphere.
Stabilizing the global average temperature would require large
reductions in CO2 emissions, as well as reductions in emissions of
other greenhouse gases such as methane and nitrous oxide. Emissions
of CO2 would need to be reduced by more than 80% relative to their
peak level. Even if this were achieved, global average temperatures
would remain close to their highest level for many centuries. As of
2016, emissions of CO2 from burning fossil fuels had stopped
Also, CO2 is not the only factor driving climate change. Concentrations of atmospheric methane, another greenhouse gas, rose dramatically between 2006–2016 for unknown reasons. This undermines efforts to combat global warming and there is a risk of an uncontrollable runaway greenhouse effect .
Long-term effects also include a response from the Earth's crust, due to ice melting and deglaciation, in a process called post-glacial rebound , when land masses are no longer depressed by the weight of ice. This could lead to landslides and increased seismic and volcanic activities. Tsunamis could be generated by submarine landslides caused by warmer ocean water thawing ocean-floor permafrost or releasing gas hydrates . Some world regions, such as the French Alps, already show signs of an increase in landslide frequency.
LARGE-SCALE AND ABRUPT IMPACTS
Main article: Abrupt climate change See also: Cold blob (North Atlantic)
Climate change could result in global, large-scale changes in natural and social systems . Examples include the possibility for the Atlantic Meridional Overturning Circulation to slow- or shutdown, which in the instance of a shutdown would change weather in Europe and North America considerably, ocean acidification caused by increased atmospheric concentrations of carbon dioxide, and the long-term melting of ice sheets , which contributes to sea level rise.
Some large-scale changes could occur abruptly , i.e., over a short time period, and might also be irreversible . Examples of abrupt climate change are the rapid release of methane and carbon dioxide from permafrost , which would lead to amplified global warming, or the shutdown of thermohaline circulation . Scientific understanding of abrupt climate change is generally poor. The probability of abrupt change for some climate related feedbacks may be low. Factors that may increase the probability of abrupt climate change include higher magnitudes of global warming, warming that occurs more rapidly, and warming that is sustained over longer time periods.
OBSERVED AND EXPECTED EFFECTS ON SOCIAL SYSTEMS
The effects of climate change on human systems , mostly due to warming or shifts in precipitation patterns, or both, have been detected worldwide. Production of wheat and maize globally has been impacted by climate change. While crop production has increased in some mid-latitude regions such as the UK and Northeast China, economic losses due to extreme weather events have increased globally. There has been a shift from cold- to heat-related mortality in some regions as a result of warming. Livelihoods of indigenous peoples of the Arctic have been altered by climate change, and there is emerging evidence of climate change impacts on livelihoods of indigenous peoples in other regions. Regional impacts of climate change are now observable at more locations than before, on all continents and across ocean regions.
The future social impacts of climate change will be uneven. Many risks are expected to increase with higher magnitudes of global warming. All regions are at risk of experiencing negative impacts. Low-latitude, less developed areas face the greatest risk. A study from 2015 concluded that economic growth (gross domestic product) of poorer countries is much more impaired with projected future climate warming, than previously thought.
A meta-analysis of 56 studies concluded in 2014 that each degree of temperature rise will increase violence by up to 20%, which includes fist fights, violent crimes, civil unrest or wars.
Examples of impacts include:
* Food : Crop production will probably be negatively affected in low
latitude countries, while effects at northern latitudes may be
positive or negative.
In small islands and mega deltas , inundation as a result of sea
level rise is expected to threaten vital infrastructure and human
settlements. This could lead to issues of homelessness in countries
with low-lying areas such as
Estimates based on the IPCC A1B emission scenario from additional CO2 and CH4 greenhouse gases released from permafrost, estimate associated impact damages by US$43 trillion.
Continued permafrost degradation will likely result in unstable infrastructure in Arctic regions, or Alaska before 2100. Thus, impacting roads, pipelines and buildings, as well as water distribution, and cause slope failures .
POSSIBLE RESPONSES TO GLOBAL WARMING
Main article: Climate change mitigation The graph on the right shows three "pathways" to meet the UNFCCC's 2 °C target, labelled "global technology", "decentralized solutions", and "consumption change". Each pathway shows how various measures (e.g., improved energy efficiency, increased use of renewable energy) could contribute to emissions reductions. Image credit: PBL Netherlands Environmental Assessment Agency .
Mitigation of climate change are actions to reduce greenhouse gas
emissions, or enhance the capacity of carbon sinks to absorb GHGs from
the atmosphere. There is a large potential for future reductions in
emissions by a combination of activities, including energy
conservation and increased energy efficiency ; the use of low-carbon
energy technologies, such as renewable energy , nuclear energy , and
carbon capture and storage ; and enhancing carbon sinks through, for
example, reforestation and preventing deforestation . A 2015 report
Near- and long-term trends in the global energy system are
inconsistent with limiting global warming at below 1.5 or 2 °C,
relative to pre-industrial levels. Pledges made as part of the
In limiting warming at below 2 °C, more stringent emission reductions in the near-term would allow for less rapid reductions after 2030. Many integrated models are unable to meet the 2 °C target if pessimistic assumptions are made about the availability of mitigation technologies.
Main article: Adaptation to global warming
Other policy responses include adaptation to climate change. Adaptation to climate change may be planned, either in reaction to or anticipation of climate change, or spontaneous, i.e., without government intervention. Planned adaptation is already occurring on a limited basis. The barriers, limits, and costs of future adaptation are not fully understood.
A concept related to adaptation is adaptive capacity , which is the ability of a system (human, natural or managed) to adjust to climate change (including climate variability and extremes) to moderate potential damages, to take advantage of opportunities, or to cope with consequences. Unmitigated climate change (i.e., future climate change without efforts to limit greenhouse gas emissions) would, in the long term, be likely to exceed the capacity of natural, managed and human systems to adapt.
Environmental organizations and public figures have emphasized changes in the climate and the risks they entail, while promoting adaptation to changes in infrastructural needs and emissions reductions.
DISCOURSE ABOUT GLOBAL WARMING
Politics of global warming
Most countries in the world are parties to the United Nations
Framework Convention on
During negotiations, the G77 (a lobbying group in the United Nations representing 133 developing nations) :4 pushed for a mandate requiring developed countries to " the lead" in reducing their emissions. This was justified on the basis that: the developed world's emissions had contributed most to the cumulation of GHGs in the atmosphere; per-capita emissions (i.e., emissions per head of population) were still relatively low in developing countries; and the emissions of developing countries would grow to meet their development needs. :290
This mandate was sustained in the
Kyoto Protocol to the Framework
Convention, :290 which entered into legal effect in 2005. In
ratifying the Kyoto Protocol, most developed countries accepted
legally binding commitments to limit their emissions. These
first-round commitments expired in 2012. United States President
George W. Bush
At the 15th UNFCCC Conference of the Parties , held in 2009 at
See also: Scientific opinion on climate change and Surveys of scientists\' views on climate change
The discussion continues in scientific articles that are
peer-reviewed and assessed by scientists who work in the relevant
fields and participate in the Intergovernmental Panel on Climate
Change . The scientific consensus as of 2013 stated in the IPCC Fifth
Assessment Report is that it "is extremely likely that human influence
has been the dominant cause of the observed warming since the mid-20th
century". A 2008 report by the U.S. National Academy of Sciences
stated that most scientists by then agreed that observed warming in
recent decades was primarily caused by human activities increasing the
amount of greenhouse gases in the atmosphere. In 2005 the Royal
In the scientific literature, there is a strong consensus that global surface temperatures have increased in recent decades and that the trend is caused mainly by human-induced emissions of greenhouse gases. No scientific body of national or international standing disagrees with this view .
DISCUSSION BY THE PUBLIC AND IN POPULAR MEDIA
The global warming controversy refers to a variety of disputes, substantially more pronounced in the popular media than in the scientific literature, regarding the nature, causes, and consequences of global warming. The disputed issues include the causes of increased global average air temperature , especially since the mid-20th century, whether this warming trend is unprecedented or within normal climatic variations, whether humankind has contributed significantly to it, and whether the increase is completely or partially an artefact of poor measurements. Additional disputes concern estimates of climate sensitivity, predictions of additional warming, and what the consequences of global warming will be.
By 1990, American conservative think tanks had begun challenging the
legitimacy of global warming as a social problem. They challenged the
scientific evidence , argued that global warming would have benefits ,
and asserted that proposed solutions would do more harm than good.
Some people dispute aspects of climate change science. Organizations
such as the libertarian
Competitive Enterprise Institute
Surveys Of Public Opinion
Main article: Public opinion on climate change
The global warming problem came to international public attention in the late 1980s. Polling groups began to track opinions on the subject, at first mainly in the United States. The longest consistent polling, by Gallup in the US, found relatively small deviations of 10% or so from 1998 to 2015 in opinion on the seriousness of global warming, but with increasing polarization between those concerned and those unconcerned.
The first major worldwide poll, conducted by Gallup in 2008–2009 in 127 countries, found that some 62% of people worldwide said they knew about global warming. In the advanced countries of North America, Europe and Japan, 90% or more knew about it (97% in the U.S., 99% in Japan); in less developed countries, especially in Africa, fewer than a quarter knew about it, although many had noticed local weather changes. Among those who knew about global warming, there was a wide variation between nations in belief that the warming was a result of human activities.
By 2010, with 111 countries surveyed, Gallup determined that there
had been a substantial decrease since 2007–2008 in the number of
A March–May 2013 survey by
Pew Research Center
Climate change and agriculture
Effects of global warming on oceans
Environmental impact of the coal industry
Geologic temperature record
Glossary of climate change
* ^ The 2001 joint statement was signed by the national academies
of science of Australia, Belgium, Brazil, Canada, the Caribbean, the
People's Republic of China, France, Germany, India, Indonesia,
Ireland, Italy, Malaysia, New Zealand, Sweden, and the UK. The 2005
statement added Japan, Russia, and the U.S. The 2007 statement added
Mexico and South Africa. The
Network of African Science Academies ,
Polish Academy of Sciences
* ^ Gillis, Justin (2015-11-28). "Short Answers to Hard Questions
* ^ On snowfall:
* Christopher Joyce (15 February 2010). "Get This: Warming Planet
Can Mean More Snow". NPR.
* ^ Battisti, David S.; Naylor, Rosamond L. (2009-01-09).
"Historical Warnings of Future Food Insecurity with Unprecedented
Seasonal Heat". Science. 323 (5911): 240–244. ISSN 0036-8075 . PMID
19131626 . doi :10.1126/science.1164363 .
* ^ US NRC 2012 , p. 26
* ^ Peter, U.; et al. "Clark et al. 2016 Consequences of
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