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Global warming is the rise in the average temperature of Earth's atmosphere and oceans since

the late 19th century and its projected continuation. Since the early 20th century, Earth's mean

surface temperature has increased by about 0. !" #1.$ !%&, ith about to(thirds of the increaseoccurring since 190.)2* +arming of the climate system is uneuivocal, and scientists are more

than 90- certain that it is primarily caused by increasing concentrations of  greenhouse gases  produced by human activities such as the burning of  fossil fuels and deforestation.)*)$*)/*)* hese

findings are recognied by the national science academies of all major industrialied nations.)3*)4*

"limate model projections ere summaried in the 2003 %ourth 4ssessment 5eport #45$& by

the 6ntergovernmental 7anel on "limate "hange #67""&. hey indicated that during the 21st

century the global surface temperature is li8ely to rise a further 1.1 to 2.9 !" #2 to /.2 !%& fortheir loest emissions scenario and 2.$ to .$ !" #$. to 11./ !%& for their highest.)* he ranges

of these estimates arise from the use of models ith differing sensitivity to greenhouse gas

concentrations.)9*)10*

%uture arming and related changes ill vary from region to region around the globe.

)11*

 heeffects of an increase in global temperature include a rise in sea levels and a change in the

amount and pattern of precipitation, as ell a probable epansion of subtropical deserts.)12* 

+arming is epected to be strongest in the 4rctic and ould be associated ith the continuing

retreat of glaciers, permafrost and sea ice. :ther li8ely effects of the arming include a morefreuent occurrence of  etreme(eather  events including heat aves, droughts and heavy

rainfall, ocean acidification and species etinctions due to shifting temperature regimes. Effects

significant to humans include the threat to food security from decreasing crop yields and the lossof habitat from inundation.)1*)1$*

7roposed policy responses to global arming include mitigation by emissions reduction,

adaptation to its effects, and possible future geoengineering. ;ost countries are parties to the<nited =ations %rameor8 "onvention on "limate "hange #<=%"""&,)1/* hose ultimateobjective is to prevent dangerous anthropogenic #i.e., human(induced& climate change.)1* 7arties

to the <=%""" have adopted a range of policies designed to reduce greenhouse gas

emissions)13*>10)1*)19*)20*>9 and to assist in adaptation to global arming.)13*>1)20*>10)21*)22* 7arties to the<=%""" have agreed that deep cuts in emissions are reuired,)2* and that future global arming

should be limited to belo 2.0 !" #. !%& relative to the pre(industrial level.)2*)?* 5eports

 published in 2011 by the <nited =ations Environment 7rogramme )2$* and the 6nternationalEnergy 4gency)2/* suggest that efforts as of the early 21st century to reduce emissions may be

inadeuate to meet the <=%"""'s 2 !" target.

Contents

• 1 :bserved temperature changes

• 2 6nitial causes of temperature changes #eternal forcings& 

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o 2.1 @reenhouse gases

o 2.2 7articulates and soot

o 2. Solar activity

• %eedbac8 

• $ "limate models

• / :bserved and epected environmental effects 

o /.1 =atural systems

o /.2 Ecological systems

o /. Aarge(scale and abrupt impacts

• :bserved and epected effects on social systems 

o .1 %ood security

o .2 Babitat inundation

• 3 5esponses to global arming 

o 3.1 ;itigation

o 3.2 4daptation

• Cies on global arming 

o .1 @lobal arming controversy

o .2 7olitics

o . 7ublic opinion

o .$ :ther vies

• 9 Etymology

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• 10 See also

• 11 =otes

• 12 "itations

• 1 5eferences

• 1$ %urther reading

• 1/ Eternal lin8s

Observed temperature changes

;ain article> 6nstrumental temperature record

he increase in ocean heat content is much larger than any other store of energy in the EarthDsheat balance over the to periods 191 to 200 and 199 to 200, and accounts for more than

90- of the possible increase in heat content of the Earth system during these periods.)2*

o millennia of mean surface temperatures according to different reconstructions from climate

 proies, each smoothed on a decadal scale, ith the instrumental temperature record overlaid in

 blac8.

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he Earth's average surface temperature rose by 0.3$0.1 !" over the period 190F200/. he

rate of arming over the last half of that period as almost double that for the period as a hole

#0.10.0 !" per decade, versus 0.030.02 !" per decade&. he urban heat island effect is verysmall, estimated to account for less than 0.002 !" of arming per decade since 1900.)23* 

emperatures in the loer troposphere have increased beteen 0.1 and 0.22 !" #0.22 and

0.$ !%& per decade since 1939, according to satellite temperature measurements. "limate proies sho the temperature to have been relatively stable over the one or to thousand years before

1/0, ith regionally varying fluctuations such as the ;edieval +arm 7eriod and the Aittle 6ce

4ge.)2*

he arming that is evident in the instrumental temperature record is consistent ith a iderange of observations, as documented by many independent scientific groups.)29* Eamples

include sea level rise #ater  epands as it arms&,)0* idespread melting of sno and ice,)1* 

increased heat content of the oceans,)29* increased humidity,)29* and the earlier timing of spring events,)2* e.g., the floering of plants.)* he  probability that these changes could have occurred

 by chance is virtually ero.)29*

5ecent estimates by =4S4's @oddard 6nstitute for Space Studies #@6SS& and the =ational

"limatic Gata "enter  sho that 200/ and 2010 tied for the planet's armest year since reliable,idespread instrumental measurements became available in the late 19th century, eceeding

199 by a fe hundredths of a degree.)$*)/*)* Estimates by the "limatic 5esearch <nit #"5<&

sho 200/ as the second armest year, behind 199 ith 200 and 2010 tied for third armestyear, hoever, Hthe error estimate for individual years ... is at least ten times larger than the

differences beteen these three years.H)3* he +orld ;eteorological :rganiation #+;:&

 statement on the status of the global climate in 2010 eplains that, Hhe 2010 nominal value of

I0./ !" ran8s just ahead of those of 200/ #I0./2 !"& and 199 #I0./1 !"&, although thedifferences beteen the three years are not statistically significant...H)*

 =:44 graph of @lobal 4nnual emperature 4nomalies 19/0F2012, shoing the El =iJo(

Southern :scillation

emperatures in 199 ere unusually arm because global temperatures are affected by the El

 =iJo(Southern :scillation #E=S:&, and the strongest El =iJo in the past century occurred during

that year.)9* @lobal temperature is subject to short(term fluctuations that overlay long term trendsand can temporarily mas8 them. he relative stability in temperature from 2002 to 2009 is

consistent ith such an episode.)$0*)$1* 2010 as also an El =iJo year. :n the lo sing of the

oscillation, 2011 as an Aa =iJa year as cooler but it as still the 11th armest year since

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records began in 10. :f the 1 armest years since 10, 11 ere the years from 2001 to

2011. :ver the more recent record, 2011 as the armest Aa =iJa year in the period from 19/0

to 2011, and as close to 1993 hich as not at the loest point of the cycle.)$2*

emperature changes vary over the globe. Since 1939, land temperatures have increased about

tice as fast as ocean temperatures #0.2/ !" per decade against 0.1 !" per decade&.)$*

 :ceantemperatures increase more sloly than land temperatures because of the larger effective heat

capacity of the oceans and because the ocean loses more heat by evaporation.)$$* he northernhemisphere arms faster than the southern hemisphere because it has more land and because it

has etensive areas of seasonal sno and sea(ice cover subject to ice(albedo feedbac8 . 4lthough

more greenhouse gases are emitted in the =orthern than Southern Bemisphere this does notcontribute to the difference in arming because the major greenhouse gases persist long enough

to mi beteen hemispheres.)$/*

he thermal inertia of the oceans and slo responses of other indirect effects mean that climate

can ta8e centuries or longer to adjust to changes in forcing.  "limate commitment studies indicate

that even if greenhouse gases ere stabilied at 2000 levels, a further arming of about 0./ !"#0.9 !%& ould still occur .)$*

Initial causes of temperature changes (external forcings)

;ain article> 4ttribution of recent climate change

@reenhouse effect schematic shoing energy flos beteen space, the atmosphere, and earth's

surface. Energy echanges are epressed in atts per suare meter #+Km2&.

his graph, 8non as the Leeling "urve, shos the increase of atmospheric carbon dioide 

#":2& concentrations from 19/F200. ;onthly ":2 measurements display seasonal oscillations

in an upard trendM each year's maimum occurs during the =orthern Bemisphere's late spring,and declines during its groing season as plants remove some atmospheric ":2.

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he climate system can respond to changes in external forcings.)$3*)$* Eternal forcings can

HpushH the climate in the direction of arming or cooling. )$9* Eamples of eternal forcings

include changes in atmospheric composition #e.g., increased concentrations of greenhousegases&, solar luminosity, volcanic eruptions, and variations in Earth's orbit around the Sun.)/0* 

:rbital cycles vary sloly over tens of thousands of years and at present are in an overall cooling

trend hich ould be epected to lead toards an ice age, but the 20th century instrumentaltemperature record shos a sudden rise in global temperatures.)/1*

Greenhouse gases

;ain articles> @reenhouse gas, @reenhouse effect, 5adiative forcing, and "arbon dioide inEarth's atmosphere

he greenhouse effect is the process by hich absorption and emission of infrared radiation by

gases in the atmosphere arm a planet's loer atmosphere and surface. 6t as proposed by

Noseph %ourier  in 12$ and as first investigated uantitatively by Svante 4rrhenius in 19.)/2*

4nnual orld greenhouse gas emissions, in 200/, by sector.

?ubble diagram shoing the share of global cumulative energy(related carbon dioide emissionsfor major emitters beteen 190(2003.)/*

 =aturally occurring amounts of greenhouse gases have a mean arming effect of about !"

#/9 !%&.)/$*)"* he major greenhouse gases are ater vapor , hich causes about F30- of the

greenhouse effectM carbon dioide #":2&, hich causes 9F2-M methane #"B$&, hich causes $F 9-M and oone #:&, hich causes F3-.)//*)/*)/3* "louds also affect the radiation balance through

cloud forcings similar to greenhouse gases.

Buman activity since the 6ndustrial 5evolution has increased the amount of greenhouse gases inthe atmosphere, leading to increased radiative forcing from ":2, methane, tropospheric oone,"%"s and nitrous oide. he concentrations of ":2 and methane have increased by - and

1$- respectively since 13/0.)/* hese levels are much higher than at any time during the last

00,000 years, the period for hich reliable data has been etracted from ice cores.)/9*)0*)1*)2* Aess direct geological evidence indicates that ":2 values higher than this ere last seen about 20

million years ago.)* %ossil fuel  burning has produced about three(uarters of the increase in ":2

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from human activity over the past 20 years. he rest of this increase is caused mostly by changes

in land(use, particularly deforestation.)$*

:ver the last three decades of the 20th century, gross domestic product per capita and populationgroth ere the main drivers of increases in greenhouse gas emissions.)/* ":2 emissions are

continuing to rise due to the burning of fossil fuels and land(use change.)*)3*>31

 Emissions can beattributed to different regions, e.g., see the figure opposite. 4ttribution of emissions due to land(

use change is a controversial issue.)*)9*>29

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.)30* 6n most scenarios, emissions continue to rise over the century, hile in a fe,emissions are reduced.)31*)32* %ossil fuel reserves are abundant, and ill not limit carbon emissions

in the 21st century.)3* Emission scenarios, combined ith modelling of the carbon cycle, have

 been used to produce estimates of ho atmospheric concentrations of greenhouse gases might

change in the future. <sing the si 67"" S5ES Hmar8erH scenarios, models suggest that by the

year 2100, the atmospheric concentration of ":2 could range beteen /$1 and 930 ppm.

)3$*

 hisis an increase of 90F2/0- above the concentration in the year 13/0.

he popular media and the public often confuse global arming ith oone depletion, i.e., the

destruction of stratospheric oone by chlorofluorocarbons.)3/*)3* 4lthough there are a fe areas of lin8age, the relationship beteen the to is not strong. 5educed stratospheric oone has had a

slight cooling influence on surface temperatures, hile increased tropospheric oone has had a

somehat larger arming effect.)33*

4tmospheric ":2 concentration from /0,000 years ago to near present, using ice core proy

data and direct measurements

Particulates and soot

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Ship trac8s over the 4tlantic :cean on the east coast of the <nited States. he climatic impactsfrom particulate forcing could have a large effect on climate through the indirect effect.

@lobal dimming, a gradual reduction in the amount of global direct irradiance at the Earth's

surface, as observed from 191 until at least 1990.)3* he main cause of this dimming is

 particulates produced by volcanoes and human made pollutants, hich eerts a cooling effect byincreasing the reflection of incoming sunlight. he effects of the products of fossil fuel

combustion F ":2 and aerosols F have largely offset one another in recent decades, so that net

arming has been due to the increase in non(":2 greenhouse gases such as methane.)39* 5adiative forcing due to particulates is temporally limited due to et deposition hich causes

them to have an atmospheric lifetime of one ee8. "arbon dioide has a lifetime of a century or

more, and as such, changes in particulate concentrations ill only delay climate changes due to

carbon dioide.)0*

6n addition to their direct effect by scattering and absorbing solar radiation, particulates have

indirect effects on the radiation budget.)1* Sulfates act as cloud condensation nuclei and thus lead

to clouds that have more and smaller cloud droplets. hese clouds reflect solar radiation moreefficiently than clouds ith feer and larger droplets, 8non as the omey effect.)2* his effect

also causes droplets to be of more uniform sie, hich reduces groth of raindrops and ma8es

the cloud more reflective to incoming sunlight, 8non as the 4lbrecht effect.)* 6ndirect effects

are most noticeable in marine stratiform clouds, and have very little radiative effect onconvective clouds. 6ndirect effects of particulates represent the largest uncertainty in radiative

forcing.)$*

Soot may cool or arm the surface, depending on hether it is airborne or deposited.

4tmospheric soot directly absorb solar radiation, hich heats the atmosphere and cools thesurface. 6n isolated areas ith high soot production, such as rural 6ndia, as much as /0- of

surface arming due to greenhouse gases may be mas8ed by atmospheric bron clouds.)/*

 +hendeposited, especially on glaciers or on ice in arctic regions, the loer surface albedo can alsodirectly heat the surface.)* he influences of particulates, including blac8 carbon, are most

 pronounced in the tropics and sub(tropics, particularly in 4sia, hile the effects of greenhouse

gases are dominant in the etratropics and southern hemisphere.)3*

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Satellite observations of otal Solar 6rradiance from 1939F200.

"ontribution of natural factors and human activities to radiative forcing of climate change.)* 

5adiative forcing values are for the year 200/, relative to the pre(industrial era #13/0&.)* he

contribution of solar irradiance to radiative forcing is /- the value of the combined radiativeforcing due to increases in the atmospheric concentrations of carbon dioide, methane and

nitrous oide.)9*

Solar activity

;ain articles> Solar variation and Solar ind

Since 193, output from the Sun has been precisely measured by satellites.)90* hese

measurements indicate that the Sun's output has not increased since 193, so the arming during

the past 0 years cannot be attributed to an increase in solar energy reaching the Earth. 6n thethree decades since 193, the combination of solar and volcanic activity probably had a slight

cooling influence on the climate.)91*

"limate models have been used to eamine the role of the sun in recent climate change.)92* ;odels are unable to reproduce the rapid arming observed in recent decades hen they only

ta8e into account variations in solar output and volcanic activity. ;odels are, hoever, able tosimulate the observed 20th century changes in temperature hen they include all of the most

important eternal forcings, including human influences and natural forcings.

4nother line of evidence against the sun having caused recent climate change comes from

loo8ing at ho temperatures at different levels in the Earth's atmosphere have changed. )9* 

;odels and observations sho that greenhouse arming results in arming of the loer

atmosphere #called the troposphere& but cooling of the upper atmosphere #called the

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stratosphere&.)9$*)9/* Gepletion of the oone layer  by chemical refrigerants has also resulted in a

strong cooling effect in the stratosphere. 6f the sun as responsible for observed arming,

arming of both the troposphere and stratosphere ould be epected.)9*

eedbac! 

;ain article> "limate change feedbac8 

Sea ice, shon here in =unavut, in northern "anada, reflects more sunshine, hile open oceanabsorbs more, accelerating melting.

he climate system includes a range of feedbacks hich alter the response of the system tochanges in eternal forcings. 7ositive feedbac8s increase the response of the climate system to an

initial forcing, hile negative feedbac8s reduce the response of the climate system to an initial

forcing.)93*

here are a range of feedbac8s in the climate system, including ater vapor , changes in ice(albedo #sno and ice cover affect ho 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&.

)9* he main negative feedbac8 is the energy hich the Earth's surface radiates into space asinfrared radiation.)99* 4ccording to the Stefan(?oltmann la, if temperature doubles, radiated

energy increases by a factor of 1 #2 to the $th poer&.)100*

%eedbac8s are an important factor in determining the sensitivity of the climate system to

increased atmospheric greenhouse gas concentrations. :ther factors being eual, a higherclimate sensitivity means that more arming ill occur for a given increase in greenhouse gas

forcing.)101* <ncertainty over the effect of feedbac8s is a major reason hy different climate

models project different magnitudes of arming for a given forcing scenario. ;ore research isneeded to understand the role of clouds)93* and carbon cycle feedbac8s in climate projections.)102*

he 67"" projections given in the lede span the Hli8elyH range #greater than - probability, based on epert judgement&)$* for the selected emissions scenarios. Boever, the 67""'s

 projections do not reflect the full range of uncertainty.)10* he loer end of the Hli8elyH rangeappears to be better constrained than the upper end of the Hli8elyH range.)10*

Climate models

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;ain article> @lobal climate model

"alculations of global arming prepared in or before 2001 from a range of climate models under 

the S5ES 42 emissions scenario, hich assumes no action is ta8en to reduce emissions and

regionally divided economic development.

7rojected change in annual mean surface air temperature from the late 20th century to the middle

21st century, based on a medium emissions scenario #S5ES 41?&.)10$* his scenario assumes that

no future policies are adopted to limit greenhouse gas emissions. 6mage credit> =:44 @%GA.)10/*

4 climate model is a computeried representation of the five components of the climate system>4tmosphere, hydrosphere, cryosphere, land surface, and biosphere.)10* Such models are based on

 physical principles including fluid dynamics, thermodynamics and radiative transfer . here can

 be components hich represent air movement, temperature, clouds, and other atmospheric propertiesM ocean temperature, salt content, and circulationM ice cover on land and seaM the

transfer of heat and moisture from soil and vegetation to the atmosphereM chemical and biological

 processesM and others.

4lthough researchers attempt to include as many processes as possible, simplifications of theactual climate system are inevitable because of the constraints of available computer poer and

limitations in 8noledge of the climate system. 5esults from models can also vary due to

different greenhouse gas inputs and the model's climate sensitivity. %or eample, the uncertaintyin 67""'s 2003 projections is caused by #1& the use of multiple models )10* ith differing

sensitivity to greenhouse gas concentrations,)103* #2& the use of differing estimates of humanities'

future greenhouse gas emissions,)10* #& any additional emissions from climate feedbac8s thatere not included in the models 67"" used to prepare its report, i.e., greenhouse gas releases

from permafrost.)10*

he models do not assume the climate ill arm due to increasing levels of greenhouse gases.

6nstead the models predict ho greenhouse gases ill interact ith radiative transfer and other physical processes. :ne of the mathematical results of these comple euations is a prediction

hether arming or cooling ill occur.)109*

5ecent research has called special attention to the need to refine models ith respect to the effect

of clouds)110* and the carbon cycle.)111*)112*)11*

;odels 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. 4lthough these models do not unambiguously attribute the arming that occurred from

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approimately 1910 to 19$/ to either natural variation or human effects, they do indicate that the

arming since 1930 is dominated by man(made greenhouse gas emissions.)/0*

he physical realism of models is tested by eamining their ability to simulate contemporary or past climates.)11$*

"limate models produce a good match to observations of global temperature changes over the

last century, but do not simulate all aspects of climate.)11/* =ot all effects of global arming are

accurately predicted by the climate models used by the 67"". :bserved 4rctic shrin8age has been faster than that predicted.)11* 7recipitation increased proportional to atmospheric humidity,

and hence significantly faster than global climate models predict.)113*)11*

Observed and expected environmental effects

;ain article> Effects of global arming

HGetectionH is the process of demonstrating that climate has changed in some defined statistical sense, ithout providing a reason for that change. Getection does not imply attribution of the

detected change to a particular cause. H4ttributionH of causes of climate change is the process of

establishing the most li8ely causes for the detected change ith some defined level ofconfidence.)119* Getection and attribution may also be applied to observed changes in physical,

ecological and social systems.)120*

Sparse records indicate that glaciers have been retreating since the early 100s. 6n the 19/0s

measurements began that allo the monitoring of glacial mass balance, reported to the +orld

@lacier ;onitoring Service #+@;S& and the =ational Sno and 6ce Gata "enter  #=S6G"&

"atural systems

;ain article> 7hysical impacts of climate change

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@lobal arming has been detected in a number of natural systems. Some of these changes are

described in the section on observed temperature changes, e.g., sea level rise and idespread

decreases in sno and ice etent.)121* ;ost of the increase in global average temperature since themid(20th century is, ith high probability,)G* attributable to human(induced changes in

greenhouse gas concentrations.)122*

Even ith policies to reduce emissions, global emissions are still epected to continue to gro

over time.)12*

6n the 67"" %ourth 4ssessment 5eport, across a range of future emission scenarios, model(based

estimates of sea level rise for the 21st century)12$* range from 0.1 to 0./9 m. hese estimates,

hoever, ere not given a li8elihood due to a lac8 of scientific understanding, nor as an upper bound given for sea level rise. :n the timescale of centuries to millennia, the melting of ice

sheets could result in even higher sea level rise. 7artial deglaciation of the @reenland ice sheet,

and possibly the +est 4ntarctic 6ce Sheet, could contribute $F metres #1 to 20 ft& or more to

sea level rise.)12/*

"hanges in regional climate are epected to include greater arming over land, ith most

arming at high northern latitudes, and least arming over the Southern :cean and parts of the

 =orth 4tlantic :cean.)12* Sno cover area and sea ice etent are epected to decrease, ith the

4rctic epected to be largely ice(free in September by 203.)12*

6t is calculated that, ith high statistical confidence, certain eather events, such as the heat

aves in eas and the 200 European heat ave, ould not have occurred ithout global

arming. Etremely hot outliers, defined as three standard deviations from climatology records,no cover about 10- of the land surface and, under present trends, ould be the norm by 20/0.

hese temperatures are epected to eacerbate the hydrological cycle, ith more intense

droughts and floods.

)123*

 he effect on hurricane activity is less certain.

)12*

#cological systems

;ain article> "limate change and ecosystems

6n terrestrial ecosystems, the earlier timing of spring events, and poleard and upard shifts in

 plant and animal ranges, have been lin8ed ith high confidence to recent arming.)121* %utureclimate change is epected to particularly affect certain ecosystems, including tundra,

mangroves, and coral reefs.)12* 6t is epected that most ecosystems ill be affected by higher

atmospheric ":2 levels, combined ith higher global temperatures.)129* :verall, it is epected

that climate change ill result in the etinction of many species and reduced diversity ofecosystems.)10*

Gissolved ":2 increases ocean acidity. his process is 8non as ocean acidification and has

 been called the Heually evil tinH of global climate change.)11* 6ncreased ocean aciditydecreases the amount of  carbonate ions, hich organisms at the base of the marine food chain, 

such as foraminifera, use to ma8e structures they need to survive. he current rate of ocean

acidification)12* is many times faster than at least the past 00 million years, hich included four

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mass etinctions that involved rising ocean acidity, such as the 7ermian mass etinction, hich

8illed 9/- of marine species. ?y the end of the century, acidity changes since the industrial

revolution ould match the 7alaeocene(Eocene hermal ;aimum, hich occurred over /000years and 8illed /F/0- of benthic foraminifera.)1*

$arge%scale and abrupt impacts

"limate change could result in global, large(scale changes in natural and social systems.)1$* oeamples are ocean acidification caused by increased atmospheric concentrations of carbon

dioide, and the long(term melting of ice sheets, hich contributes to sea level rise.)1/*

Some large(scale changes could occur abruptly, i.e., over a short time period, and might also beirreversible. 4n eample of abrupt climate change is the rapid release of methane from

 permafrost, hich ould lead to amplified global arming. )1* Scientific understanding of abrupt

climate change is generally poor .)13* Boever, the probability of abrupt changes appears to be

very lo.)1*)1* %actors that may increase the probability of abrupt climate change include higher 

magnitudes of global arming, arming that occurs more rapidly, and arming that is sustainedover longer time periods.)1*

Observed and expected effects on social systems

%urther information> Effects of global armingOSocial systems and 5egional effects of globalarmingO5egional impacts

Culnerability of human societies to climate change mainly lies in the effects of etreme(eather

events rather than gradual climate change.)19* 6mpacts of climate change so far include adverseeffects on small islands,)1$0* adverse effects on indigenous populations in high(latitude areas,)1$1* 

and small but discernable effects on human health.)1$2* :ver the 21st century, climate change isli8ely to adversely affect hundreds of millions of people through increased coastal flooding,

reductions in ater supplies, increased malnutrition and increased health impacts.)1$* ;osteconomic studies suggest losses of orld gross domestic product #@G7& for this)clarification needed * 

magnitude of arming.)1$$*)1$/*

ood security

See also> "limate change and agriculture

<nder present trends, by 200, maie production in Southern 4frica could decrease by up to 0-

hile rice, millet and maie in South 4sia could decrease by up to 10-.)1$* ?y 200, yields indeveloping countries could decrease by 10- to 2/- on average hile 6ndia could see a drop of

0- to $0-.)1$3* ?y 2100, hile the population of three billion is epected to double, rice and

maie yields in the tropics are epected to decrease by 20F$0- because of higher temperatures

ithout accounting for the decrease in yields as a result of soil moisture and ater suppliesstressed by rising temperatures.)1*

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%uture arming of around !" #by 2100, relative to 1990F2000& could result in increased crop

yields in mid( and high(latitude areas, but in lo(latitude areas, yields could decline, increasing

the ris8 of malnutrition.)1$0* 4 similar regional pattern of net benefits and costs could occur foreconomic #mar8et(sector & effects.)1$2* +arming above !" could result in crop yields falling in

temperate regions, leading to a reduction in global food production. )1$*

&abitat inundation

%urther information> Effects of climate change on humansOGisplacementKmigration

See also> "limate refugee

6n small islands and megadeltas, inundation as a result of sea level rise is epected to threatenvital infrastructure and human settlements.)1$9*)1/0* his could lead to issues of statelessness for

 populations in countries such as the ;aldives and uvalu)1/1* and homelessness in countries ith

lo lying areas such as ?angladesh.

'esponses to global warming

itigation

;ain article> "limate change mitigation

5educing the amount of future climate change is called mitigation of climate change.)citation needed * he 67"" defines mitigation as activities that reduce greenhouse gas #@B@& emissions, or

enhance the capacity of carbon sin8s to absorb @B@s from the atmosphere.)1/2* ;any countries,

 both developing and developed, are aiming to use cleaner, less polluting, technologies.)3*>192)1/* <se of these technologies aids mitigation and could result in substantial reductions in ":2 

emissions. 7olicies include targets for emissions reductions, increased reneable energy

commercialisation, energy conservation, and increased energy efficiency. Studies indicate

substantial potential for future reductions in emissions.)1/$*

6n order to limit arming to ithin the loer range described in the 67""'s HSummary 5eport

for 7olicyma8ersH)1//* it ill be necessary to adopt policies that ill limit greenhouse gas

emissions to one of several significantly different scenarios described in the full report.)1/* his

ill become more and more difficult ith each year of increasing volumes of emissions and evenmore drastic measures ill be reuired in later years to stabilie a desired atmospheric

concentration of greenhouse gases. Energy(related carbon(dioide #":2& emissions in 2010 ere

the highest in history, brea8ing the prior record set in 200.)1/3*

daptation

;ain article> 4daptation to global arming

:ther policy responses include adaptation to climate change. 4daptation to climate change may be planned, either in reaction to or anticipation of climate change, or spontaneous, i.e., ithout

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government intervention.)1/* 7lanned adaptation is already occurring on a limited basis.)1/$* he

 barriers, limits, and costs of future adaptation are not fully understood.)1/$*

4 concept related to adaptation is Hadaptive capacity,H hich is the ability of a system #human,natural or managed& to adjust to climate change #including climate variability and etremes& to

moderate potential damages, to ta8e advantage of opportunities, or to cope ith conseuences.)1/9* <nmitigated climate change #i.e., future climate change ithout efforts to limit greenhouse

gas emissions& ould, in the long term, be li8ely to eceed the capacity of natural, managed andhuman systems to adapt.)10*