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Global warming is the current temperature rise in Earth's atmosphere and oceans.
The evidence for this temperature rise is unequivocal[2]and, with greater than 90%
certainty, scientists have determined that most of it is caused by human activities
that increase concentrations of greenhouse gases in the atmosphere, such asdeforestation and burning of fossil fuels.[3][4][5][6]This finding is recognized by the
national science academies of all the major industrialized countries and is not
disputed by any scientific body of national or international standing.[7][8][A]
The instrumental temperature record shows that the average global surface
temperature increased by 0.74 C (1.33 F)during the 20th century.[9] Climate
model projections are summarized in the 2007 Fourth Assessment Report (AR4) by
the Intergovernmental Panel on Climate Change (IPCC). They indicate that during
the 21st century the global surface temperature is likely to rise a further 1.5 to 1.9 C(2.7 to 3.4 F) for their lowest emissions scenario and 3.4 to 6.1 C (6.1 to 11 F) for
their highest.[10]The ranges of these estimates arise from the use of models with
differing sensitivity to greenhouse gas concentrations.[11][12]
An increase in global temperature will cause sea levels to rise and will change the
amount and pattern of precipitation, and a probable expansion
of subtropical deserts.[13]Warming is expected to be strongest in the Arctic and
would be associated with continuing retreat of glaciers, permafrost and sea ice.
Other likely effects of the warming include more frequent occurrence of extremeweather events including heatwaves, droughts and heavy rainfall events, species
extinctions due to shifting temperature regimes, and changes in agricultural yields.
Warming and related changes will vary from region to region around the globe,
though the nature of these regional changes is uncertain.[14]In a 4 C world, the
limits for human adaptation are likely to be exceeded in many parts of the world,
while the limits for adaptation for natural systems would largely be exceeded
throughout the world. Hence, the ecosystem services upon which human livelihoods
depend would not be preserved.[15]
Proposed responses to global warming include mitigation to reduce
emissions, adaptation to the effects of global warming, and geoengineering to
remove greenhouse gases from the atmosphere or reflect incoming solar radiation
back to space. The main international mitigation effort is the Kyoto Protocol, which
seeks to stabilize greenhouse gas concentration to prevent a "dangerous
anthropogenic interference".[16]As of May 2010, 192 states had ratified the
protocol.[17]The only members of the UNFCCC that were asked to sign the treaty but
have not yet ratified it are the USA and Afghanistan.
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_sensitivityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-9http://en.wikipedia.org/wiki/Special_Report_on_Emissions_Scenarioshttp://en.wikipedia.org/wiki/Intergovernmental_Panel_on_Climate_Changehttp://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Reporthttp://en.wikipedia.org/wiki/Climate_modelhttp://en.wikipedia.org/wiki/Climate_modelhttp://en.wikipedia.org/wiki/Global_warming#cite_note-grida7-8http://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Global_warming#cnote_Ahttp://en.wikipedia.org/wiki/Global_warming#cite_note-6http://en.wikipedia.org/wiki/Global_warming#cite_note-6http://en.wikipedia.org/wiki/Global_warming#cite_note-4http://en.wikipedia.org/wiki/Global_warming#cite_note-4http://en.wikipedia.org/wiki/Global_warming#cite_note-2http://en.wikipedia.org/wiki/Global_warming#cite_note-2http://en.wikipedia.org/wiki/Global_warming#cite_note-AR4_SYR_1.1-1 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Greenhouse gases
Main articles:Greenhouse gas, Greenhouse effect, Radiative forcing, andCarbon
dioxide in Earth's atmosphere
The greenhouse effect is the process by
which absorption and emission of infrared radiation by gases in the atmospherewarm
a planet's lower atmosphere and surface. It was proposed by Joseph Fourier in 1824
and was first investigated quantitatively by Svante Arrhenius in 1896.[37]
Naturally occurring amounts of greenhouse gases have a mean warming effect of
about 33 C (59 F).[38][C]The major greenhouse gases are water vapor, which
causes about 3670 percent of the greenhouse effect; carbon dioxide (CO2), which
causes 926 percent; methane (CH4), which causes 49 percent; and ozone (O3),
which causes 37 percent.[39][40][41]Clouds also affect the radiation balance
through cloud forcings similar to greenhouse gases.
Human activity since the Industrial Revolution has increased the amount of
greenhouse gases in the atmosphere, leading to increased radiative forcing from
CO2, methane, tropospheric ozone, CFCs and nitrous oxide. The concentrations of
CO2 and methane have increased by 36% and 148% respectively since
1750.[42]These levels are much higher than at any time during the last 800,000
years, the period for which reliable data has been extracted from ice
cores.[43][44][45][46]Less direct geological evidence indicates that CO2 values higher
than this were last seen about 20 million years ago.[47] Fossil fuelburning has
produced about three-quarters of the increase in CO2 from human activity over the
past 20 years. The rest of this increase is caused mostly by changes in land-use,
particularly deforestation.[48]
Per capita greenhouse gas emissions in 2005, including land-use change.
Total greenhouse gas emissions in 2005, including land-use change.
Over the last three decades of the 20th century, gross domestic product per capita
and population growth were the main drivers of increases in greenhouse gas
emissions.[49]CO2 emissions are continuing to rise due to the burning of fossil fuels
and land-use change.[50][51]:71 Emissions can be attributed to different regions. The
two figures opposite show annual greenhouse gas emissions for the year 2005,
including land-use change. Attribution of emissions due to land-use change is a
controversial issue.[52][53]:289
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wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_WG1_AR4_Ch1-37http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_WG1_AR4_Ch1-37http://en.wikipedia.org/wiki/Global_warming#cite_note-36http://en.wikipedia.org/wiki/Svante_Arrheniushttp://en.wikipedia.org/wiki/Joseph_Fourierhttp://en.wikipedia.org/wiki/Planethttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Emission_spectrumhttp://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmospherehttp://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_atmospherehttp://en.wikipedia.org/wiki/Radiative_forcinghttp://en.wikipedia.org/wiki/Greenhouse_effecthttp://en.wikipedia.org/wiki/Greenhouse_gas 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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.[54]In most
scenarios, emissions continue to rise over the century, while in a few, emissions are
reduced.[55][56]Fossil fuel reserves are abundant, and will not limit carbon emissions
in the 21st century.[57]Emission scenarios, combined with modelling of the carbon
cycle, have been used to produce estimates of how atmospheric concentrations of
greenhouse gases might change in the future. Using the six IPCC SRES "marker"
scenarios, models suggest that by the year 2100, the atmospheric concentration of
CO2 could range between 541 and 970 ppm.[58]This is an increase of 90250%
above the concentration in the year 1750.
The popular media and the public often confuse global warming with the ozone hole,
i.e., the destruction of stratosphericozone by chlorofluorocarbons.[59][60]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.[61]
Particulates and soot
Ship tracks over the Atlantic Ocean on the east coast of the United States. The
climatic impacts from particulate forcing could have a large effect on climate through
the indirect effect.
Global dimming, a gradual reduction in the amount of global direct irradiance at the
Earth's surface, has partially counteracted global warming from 1960 to the
present.[62]The main cause of this dimming is particulates produced by volcanoes
and human made pollutants, which exerts a cooling effect by increasing the
reflection of incoming sunlight. The effects of the products of fossil fuel combustion
CO2 and aerosolshave largely offset one another in recent decades, so that net
warming has been due to the increase in non-CO2 greenhouse gases such as
methane.[63]Radiative forcing due to particulates is temporally limited due to wet
deposition which causes them to have anatmospheric lifetime of one week. Carbon
dioxide has a lifetime of a century or more, and as such, changes in particulate
concentrations will only delay climate changes due to carbon dioxide.[64]
In addition to their direct effect by scattering and absorbing solar radiation,
particulates have indirect effects on the radiation budget.[65]Sulfates act as cloud
condensation nuclei and thus lead to clouds that have more and smaller cloud
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observed changes in clouds or to be a significant contributor to present-day climate
change.[81]
Studies in 2011 have indicated that solar activity may be slowing, and that the next
solar cycle could be delayed. To what extent is not yet clear; Solar Cycle 25 is due tostart in 2020, but may be delayed to 2022 or even longer. It is even possible that Sol
could be heading towards another Maunder Minimum. While there is not yet a
definitive link between solar sunspot activity and global temperatures, the scientists
conducting the solar activity study believe that global greenhouse gas emissions
would prevent any possible cold snap.[82]
Feedback
Main article:Climate change feedback
Feedback is a process in which changing one quantity changes a second quantity,
and the change in the second quantity in turn changes the first. Positive
feedback increases the change in the first quantity while negative feedback reduces
it. Feedback is important in the study of global warming because it may amplify or
diminish the effect of a particular process.
The main positive feedback in the climate system is the water vapor feedback. The
main negative feedback is radiative cooling through the StefanBoltzmann law,
which increases as the fourth power of temperature. Positive and negativefeedbacks are not imposed as assumptions in the models, but are instead emergent
properties that result from the interactions of basic dynamical and thermodynamic
processes.
Imperfect understanding of feedbacks is a major cause of uncertainty and concern
about global warming.[citation needed] A wide range of potential feedback process exist,
such as Arctic methane release and ice-albedo feedback. Consequentially,
potential tipping points may exist, which may have the potential to cause abrupt
climate change.[83]
For example, the "emission scenarios" used by IPCC in its 2007 report primarily
examined greenhouse gas emissions from human sources. In 2011, a joint study
by NSIDC-(US) and NOAA-(US) calculated the additional greenhouse gas emissions
that would emanate from melted and decomposing permafrost, even if policymakers
attempt to reduce human emissions from the currently-unfolding A1FI scenario to the
A1B scenario.[84]The team found that even at the much lower level of human
emissions, permafrost thawing and decomposition would still result in 190 64 Gt C
of permafrost carbon being added to the atmosphere on top of the human sources.
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Importantly, the team made three extremely conservative assumptions: (1) that
policymakers will embrace the A1B scenario instead of the currently-unfolding A1FI
scenario, (2) that all of the carbon would be released as carbon dioxide instead of
methane, which is more likely and over a 20 year lifetime has 72x the greenhouse
warming power of CO2, and (3) their model did not project additional temperature
rise caused by the release of these additional gases.[84][85]These very conservative
permafrost carbon dioxide emissions are equivalent to about 1/2 of all carbon
released from fossil fuel burning since the dawn of the Industrial Age,[86]and is
enough to raise atmospheric concentrations by an additional 87 29 ppm, beyond
human emissions. Once initiated, permafrost carbon forcing (PCF) is irreversible, is
strong compared to other global sources and sinks of atmospheric CO2, and due to
thermal inertia will continue for many years even if atmospheric warming stops.[84]A
great deal of this permafrost carbon is actually being released as highly flammable
methane instead of carbon dioxide.[87]IPCC 2007's temperature projections did not
take any of the permafrost carbon emissions into account and therefore
underestimate the degree of expected climate change.[84][85]
Other research published in 2011 found that increased emissions of methane could
instigate significant feedbacks that amplify the warming attributable to the methane
alone. The researchers found that a 2.5-fold increase in methane emissions would
cause indirect effects that increase the warming 250% above that of the methane
alone. For a 5.2-fold increase, the indirect effects would be 400% of the warming
from the methane alone.[88]
Climate models
Main article:Global climate model
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.
The geographic distribution of surface warming during the 21st century calculated by
the HadCM3 climate model if a business as usual scenario is assumed for economic
growth and greenhouse gas emissions. In this figure, the globally averaged warming
corresponds to 3.0 C (5.4 F).
A climate model is a computerized representation of the five components of
the climate system: Atmosphere,hydrosphere, cryosphere, land surface,
and biosphere.[89]Such models are based on physical principles including fluid
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dynamics, thermodynamics and radiative transfer. There can be components which
represent 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; chemical
and biological processes; and others.[90]
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 differingsensitivity to greenhouse
gas concentrations, (2) the use of differing estimates of humanities' 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.[84]
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. One of the mathematical results
of these complex equations is a prediction whether warming or cooling will occur.[91]
Recent research has called special attention to the need to refine models withrespect to the effect of clouds[92]and thecarbon cycle.[93][94][95]
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-derived 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 man-made greenhouse gas emissions.[35]
The physical realism of models is tested by examining their ability to simulate current
or past climates.[96]
Current climate models produce a good match to observations of global temperature
changes over the last century, but do not simulate all aspects of climate.[48]Not
all effects of global warming are accurately predicted by the climate models used by
the IPCC. Observed Arctic shrinkage has been faster than that
predicted.[97]Precipitation increased proportional to atmospheric humidity, and hence
significantly faster than current global climate models predict.[98][99]
Attribution and expected effects
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Main articles:Effects of global warmingandRegional effects of global warming
Global warming may be detected in natural, ecological or social systems as a
change having statistical significance.[2][not in citation given] Attribution of these changes
e.g., to natural or human activities, is the next step following detection.[4]
Sparse records indicate that glaciers have been retreating since the early 1800s. In
the 1950s measurements began that allow the monitoring of glacial mass balance,
reported to the WGMS and the NSIDC.
Natural systems
Global warming has been detected in a number of systems. Some of these changes,e.g., based on the instrumental temperature record, have been described in the
section on temperature changes. Rising sea levels and observed decreases in snow
and ice extent are consistent with warming.[20]Most of the increase in global average
temperature since the mid-20th century is, with high probability,[D]attributable to
human-induced changes in greenhouse gas concentrations.[100]
Even with current policies to reduce emissions, global emissions are still expected to
continue to grow over the coming decades.[101]Over the course of the 21st century,
increases in emissions at or above their current rate would very likely inducechanges in the climate system larger than those observed in the 20th century.
In the IPCC Fourth Assessment Report, across a range of future emission scenarios,
model-based estimates of sea level rise for the end of the 21st century (the year
2090-2099, relative to 1980-1999) range from 0.18 to 0.59 m. These estimates,
however, were not given a likelihood due to a lack of scientific understanding, nor
was an upper bound given for sea level rise. Over the course of centuries to
millennia, the melting of ice sheets could result in sea level rise of 46 m or more.[102]
Changes in regional climate are expected to include greater warming over land, with
most warming at high northern latitudes, and least warming over the Southern
Ocean and parts of the North Atlantic Ocean.[101]Snow cover area and sea ice
extent are expected to decrease, with the Arctic expected to be largely ice-free in
September by 2037.[103]The frequency of hot extremes, heat waves, and heavy
precipitation will very likely increase.
Ecological systems
In terrestrial ecosystems, the earlier timing of spring events, and poleward andupward shifts in plant and animal ranges, have been linked with high confidence to
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recent warming.[20]Future climate change is expected to particularly affect certain
ecosystems, including tundra, mangroves, and coral reefs.[101]It is expected that
most ecosystems will be affected by higher atmospheric CO2 levels, combined with
higher global temperatures.[104]Overall, it is expected that climate change will result
in the extinction of many species and reduced diversity of ecosystems.[105]
Species migration
In 2010, a gray whale was found in the Mediterranean Sea, even though the species
had not been seen in the North Atlantic Ocean since the 18th century. The whale is
thought to have migrated from the Pacific Ocean via the Arctic. Climate Change &
European Marine Ecosystem Research (CLAMER) has also reported that
the Neodenticula seminae alga has been found in the North Atlantic, where it had
gone extinct nearly 800,000 years ago. The alga has drifted from the Pacific Oceanthrough the Arctic, following the reduction in polar ice.[106]
In the Siberian sub-arctic, species migration is contributing to another warming
albedo-feedback, as needle-shedding larch trees are being replaced with dark-
foliage evergreen conifers which can absorb some of the solar radiation that
previously reflected off the snowpack beneath the forest canopy.[107][108]
Social systems
Vulnerability of human societies to climate change mainly lies in the effects ofextreme weather events rather than gradual climate change.[109]Impacts of climate
change so far include adverse effects on small islands,[110]adverse effects on
indigenous populations in high-latitude areas,[111]and small but discernable effects
on human health.[112]Over the 21st century, climate change is likely to adversely
affect hundreds of millions of people through increased coastal flooding, reductions
in water supplies, increased malnutrition and increased health impacts.[113]
Future warming of around 3 C (by 2100, relative to 1990-2000) could result in
increased crop yields in mid- and high-latitude areas, but in low-latitude areas, yieldscould decline, increasing the risk of malnutrition.[110]A similar regional pattern of net
benefits and costs could occur for economic (market-sector) effects.[112]Warming
above 3 C could result in crop yields falling in temperate regions, leading to a
reduction in global food production.[114]Most economic studies suggest losses of
world gross domestic product (GDP) for this magnitude of warming.[115][116]
Some areas of the world would start to surpass the wet-bulb temperature limit of
human survivability with global warming of about 6.7C (12F) while a warming of
11.7C (21F) would put half of the world's population in an uninhabitableenvironment.[117][118]In practice the survivable limit of global warming in these areas
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is probably lower and in practice some areas may experience lethal wet bulb
tempatures even earlier, because this study conservatively projected the survival
limit for persons who are out of the sun, in gale-force winds, doused with water,
wearing no clothing, and not working.[118]
Responses to global warming
Mitigation
Main article:Climate change mitigation
See also:Fee and dividend
Reducing the amount of future climate change is called mitigation of climate change.
The IPCC defines mitigation as activities that reduce greenhouse gas (GHG)
emissions, or enhance the capacity of carbon sinks to absorb GHGs from the
atmosphere.[119]Many countries, both developing and developed, are aiming to use
cleaner, less polluting, technologies.[51]:192 Use of these technologies aids mitigation
and could result in substantial reductions in CO2 emissions. Policies include targets
for emissions reductions, increased use of renewable energy, and increased energy
efficiency. Studies indicate substantial potential for future reductions in
emissions.[120]
To limit warming to the lower range in the overall IPCC's "Summary Report for
Policymakers"[9]means adopting policies that will limit emissions to one of the
significantly different scenarios described in the full report.[121]This will become more
and more difficult, since each year of high emissions will require even more drastic
measures in later years to stabilize at a desired atmospheric concentration of
greenhouse gases, and energy-related carbon-dioxide (CO2) emissions in 2010
were the highest in history, breaking the prior record set in 2008.[122]
Since even in the most optimistic scenario, fossil fuels are going to be used for years
to come, mitigation may also involve carbon capture and storage, a process that
traps CO2 produced by factories and gas or coal power stations and then stores it,
usually underground.[123]
Adaptation
Main article:Adaptation to global warming
Other policy responses include adaptation to climate change. Adaptation to climate
change may be planned, e.g., by local or national government, or spontaneous, i.e.,
done privately without government intervention.[124]The ability to adapt is closely
linked to social and economic development.[120]Even societies with high capacities
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to adapt are still vulnerable to climate change. Planned adaptation is already
occurring on a limited basis. The barriers, limits, and costs of future adaptation are
not fully understood.
Geoengineering
Another policy response is deliberate modifications to the climate system, known as
(geoengineering). This policy response is sometimes grouped together with
mitigation.[125]Although some proposed geoengineering techniques are well
understood, the most promising are under ongoing development, and reliable cost
estimates for them have not yet been published.[126]Geoengineering encompasses a
range of techniques to remove CO2 from the atmosphere or to reflect incoming
sunlight. As most geoengineering techniques would affect the entire globe,
deployment would likely require global public acceptance and an adequate globallegal and regulatory framework, as well as significant further scientific research.[127]
Views on global warming
Main articles:Global warming controversyandPolitics of global warming
See also:Scientific opinion on climate changeandPublic opinion on climate change
There are different views over what the appropriate policy response to climate
change should be.[128][129]These competing views weigh the benefits of limiting
emissions of greenhouse gases against the costs. In general, it seems likely that
climate change will impose greater damages and risks in poorer regions.[130]
Global warming controversy
The global warming controversy refers to a variety of disputes, significantly more
pronounced in the popular media than in the scientific literature,[131][132]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 climaticvariations, whether humankind has contributed significantly to it, and whether the
increase is wholly or partially an artifact of poor measurements. Additional disputes
concern estimates of climate sensitivity, predictions of additional warming, and what
the consequences of global warming will be.
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,[133][134]though a few organisations
hold non-committal positions.
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Politics
Article 2 of the UN Framework Convention refers explicitly to "stabilization of
greenhouse gas concentrations."[135]In order to stabilize the atmospheric
concentration of CO2, emissions worldwide would need to be dramatically reduced
from their present level.[136]
Most countries are Parties to the United Nations Framework Convention on Climate
Change (UNFCCC).[137]The ultimate objective of the Convention is to prevent
"dangerous" human interference of the climate system.[138]As is stated in the
Convention, this requires that GHG 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 proceed in asustainable fashion.
The Framework Convention was agreed in 1992, but since then, global emissions
have risen.[129][139]During negotiations, the G77 (a lobbying group in the United
Nations representing 133 developing nations)[140]:4 pushed for a mandate requiring
developed countries to "[take] the lead" in reducing their emissions.[141]This was
justified on the basis that: the developed world's emissions had contributed most to
the stock 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 ofdeveloping countries would grow to meet their development needs.[53]:290 This
mandate was sustained in the Kyoto Protocol to the Framework
Convention,[53]:290 which entered into legal effect in 2005.[142]
In ratifying the Kyoto Protocol, most developed countries accepted legally binding
commitments to limit their emissions. These first-round commitments expire in
2012.[142]US President George W. Bush rejected the treaty on the basis that "it
exempts 80% of the world, including major population centers such as China and
India, from compliance, and would cause serious harm to the US economy."[140]:5
At the 15th UNFCCC Conference of the Parties, held in 2009 at Copenhagen, several
UNFCCC Parties produced theCopenhagen Accord.[143]Parties associated with the
Accord (140 countries, as of November 2010)[144]:9 aim to limit the future increase in
global mean temperature to below 2 C.[145]A preliminary assessment published in
November 2010 by the United Nations Environment Programme (UNEP) suggests a
possible "emissions gap" between the voluntary pledges made in the Accord and the
emissions cuts necessary to have a "likely" (greater than 66% probability) chance of
meeting the 2 C objective.[144]:10-14
The UNEP assessment takes the 2 C objectiveas being measured against the pre-industrial global mean temperature level. To
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having a likely chance of meeting the 2 C objective, assessed studies generally
indicated the need for global emissions to peak before 2020, with substantial
declines in emissions thereafter.
The 16
th
Conference of the Parties (COP16) was held at Cancn in 2010. Itproduced an agreement, not a binding treaty, that the Parties should take urgent
action to reduce greenhouse gas emissions to meet a goal of limiting global warming
to 2 C above pre-industrial temperatures. It also recognized the need to consider
strengthening the goal to a global average rise of 1.5 C.[146]
Public opinion
In 20072008 Gallup Polls surveyed 127 countries. Over a third of the world's
population was unaware of global warming, with people in developing countries less
aware than those in developed, and those in Africa the least aware. Of those aware,
Latin America leads in belief that temperature changes are a result of human
activities while Africa, parts of Asia and the Middle East, and a few countries from
the Former Soviet Union lead in the opposite belief.[147]In the Western world,
opinions over the concept and the appropriate responses are divided. Nick Pidgeon
of Cardiff University said that "results show the different stages of engagement about
global warming on each side of the Atlantic", adding, "The debate in Europe is about
what action needs to be taken, while many in the U.S. still debate whether climate
change is happening."[148][149]
A 2010 poll by the Office of National Statistics foundthat 75% of UK respondents were at least "fairly convinced" that the world's climate
is changing, compared to 87% in a similar survey in 2006.[150]A January
2011 ICM poll in the UK found 83% of respondents viewed climate change as a
current or imminent threat, while 14% said it was no threat. Opinion was unchanged
from an August 2009 poll asking the same question, though there had been a slight
polarisation of opposing views.[151]
A survey in October, 2009 by the Pew Research Center for the People & the
Press showed decreasing public perception in the United States that global warmingwas a serious problem. All political persuasions showed reduced concern with lowest
concern among Republicans, only 35% of whom considered there to be solid
evidence of global warming.[152]The cause of this marked difference in public opinion
between the United States and the global public is uncertain but the hypothesis has
been advanced that clearer communication by scientists both directly and through
the media would be helpful in adequately informing the American public of the
scientific consensus and the basis for it.[153]The U.S. public appears to be unaware
of the extent of scientific consensus regarding the issue, with 59% believing thatscientists disagree "significantly" on global warming.[154]
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fossil fuel companies have scaled back their efforts in recent years,[172]or called for
policies to reduce global warming.[173]
Etymology
The term global warmingwas probably first used in its modern sense on 8 August
1975 in a science paper by Wally Broecker in the journalSciencecalled "Are we on
the brink of a pronounced global warming?".[174][175][176]Broecker's choice of words
was new and represented a significant recognition that the climate was warming;
previously the phrasing used by scientists was "inadvertent climate modification,"
because while it was recognized humans could change the climate, no one was sure
which direction it was going.[177]The National Academy of Sciences first used global
warmingin a 1979 paper called the Charney Report, it said: "if carbon dioxide
continues to increase, [we find] no reason to doubt that climate changes will result
and no reason to believe that these changes will be negligible."[178]The report made
a distinction between referring to surface temperature changes as global warming,
while referring to other changes caused by increased CO2 as climate
change.[177]Global warmingbecame more widely popular after 1988 when NASA
climate scientist James Hansen used the term in a testimony to Congress.[177]He
said: "global warming has reached a level such that we can ascribe with a high
degree of confidence a cause and effect relationship between the greenhouse effect
and the observed warming."[179]
His testimony was widely reported andafterward global warmingwas commonly used by the press and in public
discourse.[177]
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