global warming refers to the current rise in the average temperature of earth

8/2/2019 Global Warming Refers to the Current Rise in the Average Temperature of Earth

1/37

Global warming refers to the current rise in the average temperature ofEarth's atmosphere andoceans and its projected continuation. In the last 100 years, Earth's average surface temperatureincreased by about 0.8 C (1.4 F) with about two thirds of the increase occurring over just thelast three decades.[2]Warming of the climate system is unequivocal, and scientists are more than90% certain most of it is caused by increasing concentrations ofgreenhouse gases produced by

human activities such as deforestation and burning fossil fuels.

[3][4][5][6]

These findings arerecognized by the national science academies of all the major industrialized countries.[7][A]

Climate model projections are summarized in the 2007 Fourth Assessment Report (AR4) by theIntergovernmental Panel on Climate Change (IPCC). They indicate that during the 21st centurythe global surface temperature is likely to rise a further 1.1 to 2.9 C (2 to 5.2 F) for their lowestemissions scenario and 2.4 to 6.4 C (4.3 to 11.5 F) for their highest.[8]The ranges of theseestimates arise from the use of models with differing sensitivity to greenhouse gasconcentrations.[9][10]

An increase in global temperature will cause sea levels to rise and will change the amount and

pattern ofprecipitation, and a probable expansion ofsubtropical deserts.

[11]

Warming is expectedto 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 ofextreme weather events including heat waves, droughts and heavy rainfall events, speciesextinctions due to shifting temperature regimes, and changes in crop yields. Warming and relatedchanges will vary from region to region around the globe, with projections being more robust insome areas than others.[12]In a 4 C world[clarification needed], the limits for human adaptation arelikely to be exceeded in many parts of the world, while the limits for adaptation for naturalsystems would largely be exceeded throughout the world. Hence, the ecosystem services uponwhich human livelihoods depend would not be preserved.[13]

Most countries are parties to the United Nations Framework Convention on Climate Change(UNFCCC),[14]whose ultimate objective is to prevent "dangerous" anthropogenic (i.e., human-induced) climate change.[15]Parties to the UNFCCC have adopted a range of policies designed toreduce greenhouse gas emissions[16]:10[17][18][19]:9 and to assist in adaptation to global warming.

Parties to the UNFCCC have agreed that deep cuts in emissions are required,[22]and that futureglobal warming should be limited to below 2.0 C (3.6 F) relative to the pre-industriallevel.[22][B]2011 analyses by the United Nations Environment Programme[23]and InternationalEnergy Agency[24]suggest that current efforts to reduce emissions may be inadequately stringentto meet the UNFCCC's 2 C target.

Observed temperature changes

Evidence for warming of the climate system includes observed increases in global average airand ocean temperatures, widespread melting of snow and ice, and rising global average sealevel.[25][26][27]The Earth's average surface temperature, expressed as a linear trend, rose by0.740.18 C over the period 19062005. The rate of warming over the last half of that period
http://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Global_warming#cite_note-AmericasClimateChoices-2011-FullReport-1http://en.wikipedia.org/wiki/Global_warming#cite_note-AmericasClimateChoices-2011-FullReport-1http://en.wikipedia.org/wiki/Global_warming#cite_note-AmericasClimateChoices-2011-FullReport-1http://en.wikipedia.org/wiki/Climatehttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Deforestationhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://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-4http://en.wikipedia.org/wiki/Global_warming#cite_note-4http://en.wikipedia.org/wiki/Global_warming#cite_note-SciAcademy_Statement-6http://en.wikipedia.org/wiki/Global_warming#cite_note-SciAcademy_Statement-6http://en.wikipedia.org/wiki/Global_warming#cite_note-SciAcademy_Statement-6http://en.wikipedia.org/wiki/Climate_modelhttp://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Reporthttp://en.wikipedia.org/wiki/Intergovernmental_Panel_on_Climate_Changehttp://en.wikipedia.org/wiki/Special_Report_on_Emissions_Scenarioshttp://en.wikipedia.org/wiki/Global_warming#cite_note-7http://en.wikipedia.org/wiki/Global_warming#cite_note-7http://en.wikipedia.org/wiki/Global_warming#cite_note-7http://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-8http://en.wikipedia.org/wiki/Global_warming#cite_note-8http://en.wikipedia.org/wiki/Global_warming#cite_note-8http://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29http://en.wikipedia.org/wiki/Subtropicshttp://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Global_warming#cite_note-Lu-2007-10http://en.wikipedia.org/wiki/Global_warming#cite_note-Lu-2007-10http://en.wikipedia.org/wiki/Global_warming#cite_note-Lu-2007-10http://en.wikipedia.org/wiki/Arctic_shrinkagehttp://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850http://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Sea_icehttp://en.wikipedia.org/wiki/Extreme_weatherhttp://en.wikipedia.org/wiki/Heat_wavehttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Crop_yieldhttp://en.wikipedia.org/wiki/Global_warming#cite_note-11http://en.wikipedia.org/wiki/Global_warming#cite_note-11http://en.wikipedia.org/wiki/Global_warming#cite_note-11http://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Wikipedia:Please_clarifyhttp://en.wikipedia.org/wiki/Wikipedia:Please_clarifyhttp://en.wikipedia.org/wiki/Wikipedia:Please_clarifyhttp://en.wikipedia.org/wiki/Ecosystem_serviceshttp://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-12http://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-12http://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-12http://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-13http://en.wikipedia.org/wiki/Global_warming#cite_note-13http://en.wikipedia.org/wiki/Global_warming#cite_note-13http://en.wikipedia.org/wiki/Avoiding_dangerous_climate_changehttp://en.wikipedia.org/wiki/Avoiding_dangerous_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-14http://en.wikipedia.org/wiki/Global_warming#cite_note-14http://en.wikipedia.org/wiki/Global_warming#cite_note-14http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-15http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-15http://en.wikipedia.org/wiki/Global_warming#cite_note-16http://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-18http://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/Global_warming#cite_note-23http://en.wikipedia.org/wiki/Global_warming#cite_note-23http://en.wikipedia.org/wiki/Global_warming#cite_note-23http://en.wikipedia.org/wiki/Global_warming#cite_note-24http://en.wikipedia.org/wiki/Global_warming#cite_note-24http://en.wikipedia.org/wiki/Global_warming#cite_note-26http://en.wikipedia.org/wiki/Global_warming#cite_note-26http://en.wikipedia.org/wiki/Global_average_surface_temperaturehttp://en.wikipedia.org/wiki/Linear_trendhttp://en.wikipedia.org/wiki/Linear_trendhttp://en.wikipedia.org/wiki/Global_average_surface_temperaturehttp://en.wikipedia.org/wiki/Global_warming#cite_note-26http://en.wikipedia.org/wiki/Global_warming#cite_note-24http://en.wikipedia.org/wiki/Global_warming#cite_note-24http://en.wikipedia.org/wiki/Global_warming#cite_note-23http://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-21http://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-18http://en.wikipedia.org/wiki/Global_warming#cite_note-16http://en.wikipedia.org/wiki/Global_warming#cite_note-16http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-15http://en.wikipedia.org/wiki/Global_warming#cite_note-14http://en.wikipedia.org/wiki/Avoiding_dangerous_climate_changehttp://en.wikipedia.org/wiki/Avoiding_dangerous_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-13http://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-12http://en.wikipedia.org/wiki/Ecosystem_serviceshttp://en.wikipedia.org/wiki/Wikipedia:Please_clarifyhttp://en.wikipedia.org/wiki/Celsiushttp://en.wikipedia.org/wiki/Global_warming#cite_note-11http://en.wikipedia.org/wiki/Crop_yieldhttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Heat_wavehttp://en.wikipedia.org/wiki/Extreme_weatherhttp://en.wikipedia.org/wiki/Sea_icehttp://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850http://en.wikipedia.org/wiki/Arctic_shrinkagehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Lu-2007-10http://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Subtropicshttp://en.wikipedia.org/wiki/Precipitation_%28meteorology%29http://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Global_warming#cite_note-8http://en.wikipedia.org/wiki/Global_warming#cite_note-8http://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-7http://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/Global_warming#cite_note-SciAcademy_Statement-6http://en.wikipedia.org/wiki/Global_warming#cite_note-SciAcademy_Statement-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/Fossil_fuelhttp://en.wikipedia.org/wiki/Deforestationhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Climatehttp://en.wikipedia.org/wiki/Global_warming#cite_note-AmericasClimateChoices-2011-FullReport-1http://en.wikipedia.org/wiki/Earthhttp://en.wikipedia.org/wiki/Instrumental_temperature_record


2/37

was almost double that for the period as a whole (0.130.03 C per decade, versus 0.070.02 Cper decade). The urban heat island effect is very small, estimated to account for less than0.002 C of warming per decade since 1900.[28]Temperatures in the lower troposphere haveincreased between 0.13 and 0.22 C (0.22 and 0.4 F) per decade since 1979, according tosatellite temperature measurements. Climate proxies show the temperature to have been

relatively stable over the one or two thousand years before 1850, with regionally varyingfluctuations such as the Medieval Warm Period and the Little Ice Age.[29]

The thermal inertia of the oceans and slow responses of other indirect effects mean that climatecan take centuries or longer to adjust to changes in forcing. Climate commitment studies indicatethat even if greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 C(0.9 F) would still occur.[42]

Initial causes of temperature changes (external forcings)

Greenhouse effect schematic showing energy flows between space, the atmosphere, and earth'ssurface. Energy exchanges are expressed in watts per square meter (W/m2).

External forcing refers to processes external to the climate system (though not necessarilyexternal to Earth) that influence climate. Climate responds to several types of external forcing,such as radiative forcing due to changes in atmospheric composition (mainly greenhouse gasconcentrations), changes in solar luminosity, volcanic eruptions, and variations in Earth's orbitaround the Sun.*[43]:0 Attribution of recent climate change focuses on the first three types offorcing. Orbital cycles vary slowly over tens of thousands of years and at present are in anoverall cooling trend which would be expected to lead towards an ice age, but the 20th centuryinstrumental temperature record shows a sudden rise in global temperatures.[44]

Greenhouse gases

The greenhouse effect is the process by which absorption and emission ofinfrared radiation bygases in the atmosphere warm a planet's lower atmosphere and surface. It was proposed byJoseph Fourier in 1824 and was first investigated quantitatively by Svante Arrhenius in 1896.[45]

Naturally occurring amounts of greenhouse gases have a mean warming effect of about 33 C(59 F).[46][C]The major greenhouse gases are water vapor, which causes about 3670% of thegreenhouse effect; carbon dioxide (CO2), which causes 926%; methane (CH4), which causes 4
http://en.wikipedia.org/wiki/Urban_heat_islandhttp://en.wikipedia.org/wiki/Global_warming#cite_note-27http://en.wikipedia.org/wiki/Global_warming#cite_note-27http://en.wikipedia.org/wiki/Global_warming#cite_note-27http://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Satellite_temperature_measurementshttp://en.wikipedia.org/wiki/Proxy_%28climate%29http://en.wikipedia.org/wiki/Temperature_record_of_the_past_1000_yearshttp://en.wikipedia.org/wiki/Medieval_Warm_Periodhttp://en.wikipedia.org/wiki/Little_Ice_Agehttp://en.wikipedia.org/wiki/Global_warming#cite_note-28http://en.wikipedia.org/wiki/Global_warming#cite_note-28http://en.wikipedia.org/wiki/Global_warming#cite_note-28http://en.wikipedia.org/wiki/Volumetric_heat_capacityhttp://en.wikipedia.org/wiki/Climate_commitmenthttp://en.wikipedia.org/wiki/Global_warming#cite_note-41http://en.wikipedia.org/wiki/Global_warming#cite_note-41http://en.wikipedia.org/wiki/Global_warming#cite_note-41http://en.wikipedia.org/wiki/Radiative_forcinghttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Solar_luminosityhttp://en.wikipedia.org/wiki/Volcanohttp://en.wikipedia.org/wiki/Orbital_forcinghttp://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Milankovitch_cycleshttp://en.wikipedia.org/wiki/Ice_agehttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Global_warming#cite_note-43http://en.wikipedia.org/wiki/Global_warming#cite_note-43http://en.wikipedia.org/wiki/Global_warming#cite_note-43http://en.wikipedia.org/wiki/Absorption_%28electromagnetic_radiation%29http://en.wikipedia.org/wiki/Emission_spectrumhttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Atmospherehttp://en.wikipedia.org/wiki/Planethttp://en.wikipedia.org/wiki/Joseph_Fourierhttp://en.wikipedia.org/wiki/Svante_Arrheniushttp://en.wikipedia.org/wiki/Global_warming#cite_note-44http://en.wikipedia.org/wiki/Global_warming#cite_note-44http://en.wikipedia.org/wiki/Global_warming#cite_note-44http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_WG1_AR4_Ch1-45http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_WG1_AR4_Ch1-45http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_WG1_AR4_Ch1-45http://en.wikipedia.org/wiki/Water_vaporhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Methanehttp://en.wikipedia.org/wiki/File:Greenhouse_Effect.svghttp://en.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_Ch1-45http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_WG1_AR4_Ch1-45http://en.wikipedia.org/wiki/Global_warming#cite_note-44http://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_%28electromagnetic_radiation%29http://en.wikipedia.org/wiki/Global_warming#cite_note-43http://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Ice_agehttp://en.wikipedia.org/wiki/Milankovitch_cycleshttp://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Orbital_forcinghttp://en.wikipedia.org/wiki/Volcanohttp://en.wikipedia.org/wiki/Solar_luminosityhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Radiative_forcinghttp://en.wikipedia.org/wiki/Global_warming#cite_note-41http://en.wikipedia.org/wiki/Climate_commitmenthttp://en.wikipedia.org/wiki/Volumetric_heat_capacityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-28http://en.wikipedia.org/wiki/Little_Ice_Agehttp://en.wikipedia.org/wiki/Medieval_Warm_Periodhttp://en.wikipedia.org/wiki/Temperature_record_of_the_past_1000_yearshttp://en.wikipedia.org/wiki/Proxy_%28climate%29http://en.wikipedia.org/wiki/Satellite_temperature_measurementshttp://en.wikipedia.org/wiki/Fahrenheithttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Global_warming#cite_note-27http://en.wikipedia.org/wiki/Urban_heat_island


3/37

9%; and ozone (O3), which causes 37%.[47][48][49]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 inthe 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% and148% respectively since 1750.[50]These levels are much higher than at any time during the last800,000 years, the period for which reliable data has been extracted from ice cores.[51][52][53][54]Less direct geological evidence indicates that CO2 values higher than this were last seen about 20million years ago.[55] Fossil fuel burning has produced about three-quarters of the increase inCO2 from human activity over the past 20 years. The rest of this increase is caused mostly bychanges in land-use, particularly deforestation.[56]

Emissions scenarios, estimates of changes in future emission levels of greenhouse gases, havebeen projected that depend upon uncertain economic, sociological, technological, and naturaldevelopments.[62]In most scenarios, emissions continue to rise over the century, while in a few,

emissions are reduced.

[63][64]

Fossil fuel reserves are abundant, and will not limit carbonemissions in the 21st century.[65]Emission scenarios, combined with modelling of the carboncycle, have been used to produce estimates of how atmospheric concentrations of greenhousegases might change in the future. Using the six IPCC SRES "marker" scenarios, models suggestthat by the year 2100, the atmospheric concentration of CO2 could range between 541 and 970ppm.[66]This is an increase of 90250% above the concentration in the year 1750.

The popular media and the public often confuse global warming with ozone depletion, i.e., thedestruction ofstratospheric ozone by chlorofluorocarbons.[67][68]Although there are a few areasof linkage, the relationship between the two is not strong. Reduced stratospheric ozone has had aslight cooling influence on surface temperatures, while increased tropospheric ozone has had a

somewhat larger warming effect.

[69]

Particulates and soot

Global dimming, a gradual reduction in the amount of global direct irradiance at the Earth'ssurface, has partially counteracted global warming from 1960 to the present.[70][dated info] The maincause of this dimming is particulates produced by volcanoes and human made pollutants, whichexerts a cooling effect by increasing the reflection of incoming sunlight. The effects of theproducts of fossil fuel combustionCO2 and aerosolshave largely offset one another in recentdecades, so that net warming has been due to the increase in non-CO2 greenhouse gases such asmethane.[71]Radiative forcing due to particulates is temporally limited due to wet deposition

which causes them to have an atmospheric lifetime of one week. Carbon dioxide has a lifetime ofa century or more, and as such, changes in particulate concentrations will only delay climatechanges due to carbon dioxide.[72]

In addition to their direct effect by scattering and absorbing solar radiation, particulates haveindirect effects on the radiation budget.[73]Sulfates act as cloud condensation nuclei and thuslead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiationmore efficiently than clouds with fewer and larger droplets, known as the Twomey effect.[74]
http://en.wikipedia.org/wiki/Ozonehttp://en.wikipedia.org/wiki/Global_warming#cite_note-46http://en.wikipedia.org/wiki/Global_warming#cite_note-46http://en.wikipedia.org/wiki/Global_warming#cite_note-48http://en.wikipedia.org/wiki/Global_warming#cite_note-48http://en.wikipedia.org/wiki/Cloud_forcinghttp://en.wikipedia.org/wiki/Industrial_Revolutionhttp://en.wikipedia.org/wiki/Chlorofluorocarbonhttp://en.wikipedia.org/wiki/Nitrous_oxidehttp://en.wikipedia.org/wiki/Greenhouse_gas#Anthropogenic_greenhouse_gaseshttp://en.wikipedia.org/wiki/Global_warming#cite_note-49http://en.wikipedia.org/wiki/Global_warming#cite_note-49http://en.wikipedia.org/wiki/Global_warming#cite_note-49http://en.wikipedia.org/wiki/Ice_corehttp://en.wikipedia.org/wiki/Global_warming#cite_note-50http://en.wikipedia.org/wiki/Global_warming#cite_note-50http://en.wikipedia.org/wiki/Global_warming#cite_note-52http://en.wikipedia.org/wiki/Global_warming#cite_note-52http://en.wikipedia.org/wiki/Global_warming#cite_note-54http://en.wikipedia.org/wiki/Global_warming#cite_note-54http://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Deforestationhttp://en.wikipedia.org/wiki/Global_warming#cite_note-55http://en.wikipedia.org/wiki/Global_warming#cite_note-55http://en.wikipedia.org/wiki/Global_warming#cite_note-55http://en.wikipedia.org/wiki/Climate_change_scenario#Emissions_scenarioshttp://en.wikipedia.org/wiki/Sociologyhttp://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Global_warming#cite_note-61http://en.wikipedia.org/wiki/Global_warming#cite_note-61http://en.wikipedia.org/wiki/Global_warming#cite_note-61http://en.wikipedia.org/wiki/Global_warming#cite_note-62http://en.wikipedia.org/wiki/Global_warming#cite_note-62http://en.wikipedia.org/wiki/Global_warming#cite_note-62http://en.wikipedia.org/wiki/Global_warming#cite_note-64http://en.wikipedia.org/wiki/Global_warming#cite_note-64http://en.wikipedia.org/wiki/Global_warming#cite_note-64http://en.wikipedia.org/wiki/Carbon_cyclehttp://en.wikipedia.org/wiki/Carbon_cyclehttp://en.wikipedia.org/wiki/Global_warming#cite_note-65http://en.wikipedia.org/wiki/Global_warming#cite_note-65http://en.wikipedia.org/wiki/Global_warming#cite_note-65http://en.wikipedia.org/wiki/Ozone_depletionhttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Global_warming#cite_note-66http://en.wikipedia.org/wiki/Global_warming#cite_note-66http://en.wikipedia.org/wiki/Global_warming#cite_note-66http://en.wikipedia.org/wiki/Ozone_depletion#Ozone_depletion_and_global_warminghttp://en.wikipedia.org/wiki/Ozone_depletion#Ozone_depletion_and_global_warminghttp://en.wikipedia.org/wiki/Tropospheric_ozonehttp://en.wikipedia.org/wiki/Global_warming#cite_note-68http://en.wikipedia.org/wiki/Global_warming#cite_note-68http://en.wikipedia.org/wiki/Global_warming#cite_note-68http://en.wikipedia.org/wiki/Global_dimminghttp://en.wikipedia.org/wiki/Irradiancehttp://en.wikipedia.org/wiki/Global_warming#cite_note-69http://en.wikipedia.org/wiki/Global_warming#cite_note-69http://en.wikipedia.org/wiki/Talk:Global_warming#obsoletehttp://en.wikipedia.org/wiki/Talk:Global_warming#obsoletehttp://en.wikipedia.org/wiki/Talk:Global_warming#obsoletehttp://en.wikipedia.org/wiki/Pollutanthttp://en.wikipedia.org/wiki/Global_warming#cite_note-pmid10944197-70http://en.wikipedia.org/wiki/Global_warming#cite_note-pmid10944197-70http://en.wikipedia.org/wiki/Global_warming#cite_note-pmid10944197-70http://en.wikipedia.org/wiki/Wet_depositionhttp://en.wikipedia.org/wiki/Atmospheric_lifetimehttp://en.wikipedia.org/wiki/Global_warming#cite_note-71http://en.wikipedia.org/wiki/Global_warming#cite_note-71http://en.wikipedia.org/wiki/Global_warming#cite_note-71http://en.wikipedia.org/wiki/Global_warming#cite_note-72http://en.wikipedia.org/wiki/Global_warming#cite_note-72http://en.wikipedia.org/wiki/Global_warming#cite_note-72http://en.wikipedia.org/wiki/Cloud_condensation_nucleihttp://en.wikipedia.org/wiki/Twomey_effecthttp://en.wikipedia.org/wiki/Global_warming#cite_note-73http://en.wikipedia.org/wiki/Global_warming#cite_note-73http://en.wikipedia.org/wiki/Global_warming#cite_note-73http://en.wikipedia.org/wiki/Global_warming#cite_note-73http://en.wikipedia.org/wiki/Twomey_effecthttp://en.wikipedia.org/wiki/Cloud_condensation_nucleihttp://en.wikipedia.org/wiki/Global_warming#cite_note-72http://en.wikipedia.org/wiki/Global_warming#cite_note-71http://en.wikipedia.org/wiki/Atmospheric_lifetimehttp://en.wikipedia.org/wiki/Wet_depositionhttp://en.wikipedia.org/wiki/Global_warming#cite_note-pmid10944197-70http://en.wikipedia.org/wiki/Pollutanthttp://en.wikipedia.org/wiki/Talk:Global_warming#obsoletehttp://en.wikipedia.org/wiki/Global_warming#cite_note-69http://en.wikipedia.org/wiki/Irradiancehttp://en.wikipedia.org/wiki/Global_dimminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-68http://en.wikipedia.org/wiki/Tropospheric_ozonehttp://en.wikipedia.org/wiki/Ozone_depletion#Ozone_depletion_and_global_warminghttp://en.wikipedia.org/wiki/Ozone_depletion#Ozone_depletion_and_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-66http://en.wikipedia.org/wiki/Global_warming#cite_note-66http://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Ozone_depletionhttp://en.wikipedia.org/wiki/Global_warming#cite_note-65http://en.wikipedia.org/wiki/Carbon_cyclehttp://en.wikipedia.org/wiki/Carbon_cyclehttp://en.wikipedia.org/wiki/Global_warming#cite_note-64http://en.wikipedia.org/wiki/Global_warming#cite_note-62http://en.wikipedia.org/wiki/Global_warming#cite_note-62http://en.wikipedia.org/wiki/Global_warming#cite_note-61http://en.wikipedia.org/wiki/Technologyhttp://en.wikipedia.org/wiki/Sociologyhttp://en.wikipedia.org/wiki/Climate_change_scenario#Emissions_scenarioshttp://en.wikipedia.org/wiki/Global_warming#cite_note-55http://en.wikipedia.org/wiki/Deforestationhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Global_warming#cite_note-54http://en.wikipedia.org/wiki/Global_warming#cite_note-52http://en.wikipedia.org/wiki/Global_warming#cite_note-52http://en.wikipedia.org/wiki/Global_warming#cite_note-50http://en.wikipedia.org/wiki/Global_warming#cite_note-50http://en.wikipedia.org/wiki/Ice_corehttp://en.wikipedia.org/wiki/Global_warming#cite_note-49http://en.wikipedia.org/wiki/Greenhouse_gas#Anthropogenic_greenhouse_gaseshttp://en.wikipedia.org/wiki/Nitrous_oxidehttp://en.wikipedia.org/wiki/Chlorofluorocarbonhttp://en.wikipedia.org/wiki/Industrial_Revolutionhttp://en.wikipedia.org/wiki/Cloud_forcinghttp://en.wikipedia.org/wiki/Global_warming#cite_note-48http://en.wikipedia.org/wiki/Global_warming#cite_note-46http://en.wikipedia.org/wiki/Global_warming#cite_note-46http://en.wikipedia.org/wiki/Ozone


4/37

This effect also causes droplets to be of more uniform size, which reduces growth of raindropsand makes the cloud more reflective to incoming sunlight, known as the Albrecht effect.[75]Indirect effects are most noticeable in marine stratiform clouds, and have very little radiativeeffect on convective clouds. Indirect effects of particulates represent the largest uncertainty inradiative forcing.[76]

Soot may cool or warm the surface, depending on whether it is airborne or deposited.Atmospheric soot directly absorb solar radiation, which heats the atmosphere and cools thesurface. In isolated areas with high soot production, such as rural India, as much as 50% ofsurface warming due to greenhouse gases may be masked by atmospheric brown clouds.[77]When deposited, especially on glaciers or on ice in arctic regions, the lower surface albedo canalso directly heat the surface.[78]The influences of particulates, including black carbon, are mostpronounced in the tropics and sub-tropics, particularly in Asia, while the effects of greenhousegases are dominant in the extratropics and southern hemisphere.[79]

Solar activity

Variations in solar output have been the cause of past climate changes.[80]The effect of changesin solar forcing in recent decades is uncertain, but small, with some studies showing a slightcooling effect,[81]while others studies suggest a slight warming effect.*[43][82][83][84]

Greenhouse gases and solar forcing affect temperatures in different ways. While both increasedsolar activity and increased greenhouse gases are expected to warm the troposphere, an increasein solar activity should warm the stratosphere while an increase in greenhouse gases should coolthe stratosphere.*[43] Radiosonde (weather balloon) data show the stratosphere has cooled overthe period since observations began (1958), though there is greater uncertainty in the earlyradiosonde record. Satellite observations, which have been available since 1979, also show

cooling.

[85]

A related hypothesis, proposed by Henrik Svensmark, is that magnetic activity of the sun deflectscosmic rays that may influence the generation ofcloud condensation nuclei and thereby affectthe climate.[86]Other research has found no relation between warming in recent decades andcosmic rays.[87][88]The influence of cosmic rays on cloud cover is about a factor of 100 lowerthan needed to explain the observed changes in clouds or to be a significant contributor topresent-day climate change.[89]

Studies in 2011 have indicated that solar activity may be slowing, and that the next solar cyclecould be delayed. To what extent is not yet clear; Solar Cycle 25 is due to start in 2020, but may

be delayed to 2022 or even longer. It is even possible that Sol could be heading towards anotherMaunder Minimum. While there is not yet a definitive link between solar sunspot activity andglobal temperatures, the scientists conducting the solar activity study believe that globalgreenhouse gas emissions would prevent any possible cold snap.[90]
http://en.wikipedia.org/wiki/Global_warming#cite_note-73http://en.wikipedia.org/wiki/Cloud_physics#Collision-coalescencehttp://en.wikipedia.org/wiki/Albrecht_effecthttp://en.wikipedia.org/wiki/Global_warming#cite_note-74http://en.wikipedia.org/wiki/Global_warming#cite_note-74http://en.wikipedia.org/wiki/Global_warming#cite_note-74http://en.wikipedia.org/wiki/Global_warming#cite_note-75http://en.wikipedia.org/wiki/Global_warming#cite_note-75http://en.wikipedia.org/wiki/Global_warming#cite_note-75http://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Atmospheric_brown_cloudhttp://en.wikipedia.org/wiki/Global_warming#cite_note-76http://en.wikipedia.org/wiki/Global_warming#cite_note-76http://en.wikipedia.org/wiki/Global_warming#cite_note-76http://en.wikipedia.org/wiki/Albedohttp://en.wikipedia.org/wiki/Global_warming#cite_note-77http://en.wikipedia.org/wiki/Global_warming#cite_note-77http://en.wikipedia.org/wiki/Global_warming#cite_note-77http://en.wikipedia.org/wiki/Global_warming#cite_note-78http://en.wikipedia.org/wiki/Global_warming#cite_note-78http://en.wikipedia.org/wiki/Global_warming#cite_note-78http://en.wikipedia.org/wiki/Solar_outputhttp://en.wikipedia.org/wiki/Climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-79http://en.wikipedia.org/wiki/Global_warming#cite_note-79http://en.wikipedia.org/wiki/Global_warming#cite_note-79http://en.wikipedia.org/wiki/Global_warming#cite_note-80http://en.wikipedia.org/wiki/Global_warming#cite_note-80http://en.wikipedia.org/wiki/Global_warming#cite_note-80http://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Global_warming#cite_note-82http://en.wikipedia.org/wiki/Global_warming#cite_note-82http://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Radiosondehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Randel2009-84http://en.wikipedia.org/wiki/Global_warming#cite_note-Randel2009-84http://en.wikipedia.org/wiki/Global_warming#cite_note-Randel2009-84http://en.wikipedia.org/wiki/Henrik_Svensmarkhttp://en.wikipedia.org/wiki/Cosmic_rayhttp://en.wikipedia.org/wiki/Cloud_condensation_nucleihttp://en.wikipedia.org/wiki/Global_warming#cite_note-85http://en.wikipedia.org/wiki/Global_warming#cite_note-85http://en.wikipedia.org/wiki/Global_warming#cite_note-85http://en.wikipedia.org/wiki/Cosmic_rayhttp://en.wikipedia.org/wiki/Global_warming#cite_note-86http://en.wikipedia.org/wiki/Global_warming#cite_note-86http://en.wikipedia.org/wiki/Global_warming#cite_note-86http://en.wikipedia.org/wiki/Global_warming#cite_note-88http://en.wikipedia.org/wiki/Global_warming#cite_note-88http://en.wikipedia.org/wiki/Global_warming#cite_note-88http://en.wikipedia.org/wiki/Maunder_Minimumhttp://en.wikipedia.org/wiki/Global_warming#cite_note-89http://en.wikipedia.org/wiki/Global_warming#cite_note-89http://en.wikipedia.org/wiki/Global_warming#cite_note-89http://en.wikipedia.org/wiki/Global_warming#cite_note-89http://en.wikipedia.org/wiki/Maunder_Minimumhttp://en.wikipedia.org/wiki/Global_warming#cite_note-88http://en.wikipedia.org/wiki/Global_warming#cite_note-86http://en.wikipedia.org/wiki/Global_warming#cite_note-86http://en.wikipedia.org/wiki/Cosmic_rayhttp://en.wikipedia.org/wiki/Global_warming#cite_note-85http://en.wikipedia.org/wiki/Cloud_condensation_nucleihttp://en.wikipedia.org/wiki/Cosmic_rayhttp://en.wikipedia.org/wiki/Henrik_Svensmarkhttp://en.wikipedia.org/wiki/Global_warming#cite_note-Randel2009-84http://en.wikipedia.org/wiki/Radiosondehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Tropospherehttp://en.wikipedia.org/wiki/Global_warming#cite_note-82http://en.wikipedia.org/wiki/Global_warming#cite_note-82http://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Global_warming#cite_note-80http://en.wikipedia.org/wiki/Global_warming#cite_note-79http://en.wikipedia.org/wiki/Climate_changehttp://en.wikipedia.org/wiki/Solar_outputhttp://en.wikipedia.org/wiki/Global_warming#cite_note-78http://en.wikipedia.org/wiki/Global_warming#cite_note-77http://en.wikipedia.org/wiki/Albedohttp://en.wikipedia.org/wiki/Global_warming#cite_note-76http://en.wikipedia.org/wiki/Atmospheric_brown_cloudhttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Global_warming#cite_note-75http://en.wikipedia.org/wiki/Global_warming#cite_note-74http://en.wikipedia.org/wiki/Albrecht_effecthttp://en.wikipedia.org/wiki/Cloud_physics#Collision-coalescence


5/37

Feedback

Feedbackis a process in which changing one quantity changes a second quantity, and the changein the second quantity in turn changes the first. Positive feedbackincreases the change in the firstquantity while negative feedbackreduces 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 negativefeedback is radiative cooling through the StefanBoltzmann law, which increases as the fourthpower of temperature. Positive and negative feedbacks are not imposed as assumptions in themodels, but are instead emergent properties that result from the interactions of basic dynamicaland thermodynamic processes.

A wide range of potential feedback processes exist, such as Arctic methane release and ice-albedo feedback. Consequentially, potential tipping points may exist, which may have thepotential to cause abrupt climate change.[91]

For example, the "emission scenarios" used by IPCC in its 2007 report primarily examinedgreenhouse gas emissions from human sources. In 2011, a joint study by the US National Snowand Ice Data Center and National Oceanic and Atmospheric Administration calculated theadditional greenhouse gas emissions that would emanate from melted and decomposingpermafrost, even if policymakers attempt to reduce human emissions from the currently-unfolding A1FI scenario to the A1B scenario.[92]The team found that even at the much lowerlevel of human emissions, permafrost thawing and decomposition would still result in 190 Gt Cof permafrost carbon being added to the atmosphere on top of the human sources. Importantly,the team made three extremely conservative assumptions: (1) that policymakers will embrace theA1B 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 yearlifetime has 72x the greenhouse warming power of CO2, and (3) their model did not projectadditional temperature rise caused by the release of these additional gases.[92][93]These veryconservative permafrost carbon dioxide emissions are equivalent to about 1/2 of all carbonreleased from fossil fuel burning since the dawn of the Industrial Age,[94]and is enough to raiseatmospheric concentrations by an additional 8729 ppm, beyond human emissions. Onceinitiated, permafrost carbon forcing (PCF) is irreversible, is strong compared to other globalsources and sinks of atmospheric CO2, and due to thermal inertia will continue for many yearseven if atmospheric warming stops.[92]A great deal of this permafrost carbon is actually beingreleased as highly flammable methane instead of carbon dioxide.[95]IPCC 2007's temperatureprojections did not take any of the permafrost carbon emissions into account and therefore

underestimate the degree of expected climate change.[92][93]

Other research published in 2011 found that increased emissions of methane could instigatesignificant feedbacks that amplify the warming attributable to the methane alone. Theresearchers found that a 2.5-fold increase in methane emissions would cause indirect effects thatincrease the warming 250% above that of the methane alone. For a 5.2-fold increase, the indirecteffects would be 400% of the warming from the methane alone.[96]
http://en.wikipedia.org/wiki/Feedbackhttp://en.wikipedia.org/wiki/Positive_feedbackhttp://en.wikipedia.org/wiki/Negative_feedbackhttp://en.wikipedia.org/wiki/Water_vapor_feedbackhttp://en.wikipedia.org/wiki/Radiative_coolinghttp://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_lawhttp://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_lawhttp://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_lawhttp://en.wikipedia.org/wiki/Emergent_propertieshttp://en.wikipedia.org/wiki/Arctic_methane_releasehttp://en.wikipedia.org/wiki/Ice-albedo_feedbackhttp://en.wikipedia.org/wiki/Ice-albedo_feedbackhttp://en.wikipedia.org/wiki/Tipping_point_%28climatology%29http://en.wikipedia.org/wiki/Abrupt_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-90http://en.wikipedia.org/wiki/Global_warming#cite_note-90http://en.wikipedia.org/wiki/Global_warming#cite_note-90http://en.wikipedia.org/wiki/National_Snow_and_Ice_Data_Centerhttp://en.wikipedia.org/wiki/National_Snow_and_Ice_Data_Centerhttp://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming_potential#Valueshttp://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-SciDaily-permafrost-93http://en.wikipedia.org/wiki/Global_warming#cite_note-SciDaily-permafrost-93http://en.wikipedia.org/wiki/Global_warming#cite_note-SciDaily-permafrost-93http://en.wikipedia.org/wiki/Parts-per_notationhttp://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-94http://en.wikipedia.org/wiki/Global_warming#cite_note-94http://en.wikipedia.org/wiki/Global_warming#cite_note-94http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-95http://en.wikipedia.org/wiki/Global_warming#cite_note-95http://en.wikipedia.org/wiki/Global_warming#cite_note-95http://en.wikipedia.org/wiki/Global_warming#cite_note-95http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-94http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Parts-per_notationhttp://en.wikipedia.org/wiki/Global_warming#cite_note-SciDaily-permafrost-93http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming_potential#Valueshttp://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/National_Oceanic_and_Atmospheric_Administrationhttp://en.wikipedia.org/wiki/National_Snow_and_Ice_Data_Centerhttp://en.wikipedia.org/wiki/National_Snow_and_Ice_Data_Centerhttp://en.wikipedia.org/wiki/Global_warming#cite_note-90http://en.wikipedia.org/wiki/Abrupt_climate_changehttp://en.wikipedia.org/wiki/Tipping_point_%28climatology%29http://en.wikipedia.org/wiki/Ice-albedo_feedbackhttp://en.wikipedia.org/wiki/Ice-albedo_feedbackhttp://en.wikipedia.org/wiki/Arctic_methane_releasehttp://en.wikipedia.org/wiki/Emergent_propertieshttp://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_lawhttp://en.wikipedia.org/wiki/Radiative_coolinghttp://en.wikipedia.org/wiki/Water_vapor_feedbackhttp://en.wikipedia.org/wiki/Negative_feedbackhttp://en.wikipedia.org/wiki/Positive_feedbackhttp://en.wikipedia.org/wiki/Feedback


6/37

Climate models

A climate model is a computerized representation of the five components of the climate system:Atmosphere, hydrosphere, cryosphere, land surface, and biosphere.[97]Such models are based onphysical principles including fluid dynamics, thermodynamics and radiative transfer. There can

be components which represent air movement, temperature, clouds, and other atmosphericproperties; ocean temperature, salt content, and circulation; ice cover on land and sea; thetransfer of heat and moisture from soil and vegetation to the atmosphere; chemical and biologicalprocesses; and others.[98]

Although researchers attempt to include as many processes as possible, simplifications of theactual climate system are inevitable because of the constraints of available computer power andlimitations in knowledge of the climate system. Results from models can also vary due todifferent greenhouse gas inputs and the model's climate sensitivity. For example, the uncertaintyin IPCC's 2007 projections is caused by (1) the use of multiple models with differing sensitivityto greenhouse gas concentrations, (2) the use of differing estimates of humanities' future

greenhouse gas emissions, (3) any additional emissions from climate feedbacks that were notincluded in the models IPCC used to prepare its report, i.e., greenhouse gas releases frompermafrost.[92]

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 otherphysical processes. One of the mathematical results of these complex equations is a predictionwhether warming or cooling will occur.[99]

Recent research has called special attention to the need to refine models with respect to the effectof clouds[100]and the carbon cycle.

Models are also used to help investigate the causes of recent climate change by comparing theobserved changes to those that the models project from various natural and human-derivedcauses. Although these models do not unambiguously attribute the warming that occurred fromapproximately 1910 to 1945 to either natural variation or human effects, they do indicate that thewarming since 1970 is dominated by man-made greenhouse gas emissions.* [43]

Expected effects

"Detection" is the process of demonstrating that climate has changed in some defined statisticalsense, without providing a reason for that change. Detection does not imply attribution of thedetected change to a particular cause. "Attribution" of causes of climate change is the process ofestablishing the most likely causes for the detected change with some defined level ofconfidence.[109]Detection and attribution may also be applied to observed changes in physical,ecological and social systems.[110]

Natural systems
http://en.wikipedia.org/wiki/Global_warming#cite_note-95http://en.wikipedia.org/wiki/Global_warming#cite_note-95http://en.wikipedia.org/wiki/Climate_modelhttp://en.wikipedia.org/wiki/Mathematical_modelshttp://en.wikipedia.org/wiki/Earth%27s_Atmospherehttp://en.wikipedia.org/wiki/Hydrospherehttp://en.wikipedia.org/wiki/Cryospherehttp://en.wikipedia.org/wiki/Biospherehttp://en.wikipedia.org/wiki/Global_warming#cite_note-96http://en.wikipedia.org/wiki/Global_warming#cite_note-96http://en.wikipedia.org/wiki/Global_warming#cite_note-96http://en.wikipedia.org/wiki/Fluid_dynamicshttp://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Radiative_transferhttp://en.wikipedia.org/wiki/Salinityhttp://en.wikipedia.org/wiki/Ocean_circulationhttp://en.wikipedia.org/wiki/Global_warming#cite_note-97http://en.wikipedia.org/wiki/Global_warming#cite_note-97http://en.wikipedia.org/wiki/Global_warming#cite_note-97http://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Global_warming#cite_note-98http://en.wikipedia.org/wiki/Global_warming#cite_note-98http://en.wikipedia.org/wiki/Global_warming#cite_note-98http://en.wikipedia.org/wiki/Global_warming#cite_note-99http://en.wikipedia.org/wiki/Global_warming#cite_note-99http://en.wikipedia.org/wiki/Carbon_cyclehttp://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Statisticshttp://en.wikipedia.org/wiki/Global_warming#cite_note-108http://en.wikipedia.org/wiki/Global_warming#cite_note-108http://en.wikipedia.org/wiki/Global_warming#cite_note-108http://en.wikipedia.org/wiki/Global_warming#cite_note-109http://en.wikipedia.org/wiki/Global_warming#cite_note-109http://en.wikipedia.org/wiki/Global_warming#cite_note-109http://en.wikipedia.org/wiki/Global_warming#cite_note-109http://en.wikipedia.org/wiki/Global_warming#cite_note-108http://en.wikipedia.org/wiki/Statisticshttp://en.wikipedia.org/wiki/Global_warming#cite_note-Hegerl-2001-42http://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Carbon_cyclehttp://en.wikipedia.org/wiki/Global_warming#cite_note-99http://en.wikipedia.org/wiki/Global_warming#cite_note-98http://en.wikipedia.org/wiki/Global_warming#cite_note-NSDIC_permafrost_study-91http://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-97http://en.wikipedia.org/wiki/Ocean_circulationhttp://en.wikipedia.org/wiki/Salinityhttp://en.wikipedia.org/wiki/Radiative_transferhttp://en.wikipedia.org/wiki/Thermodynamicshttp://en.wikipedia.org/wiki/Fluid_dynamicshttp://en.wikipedia.org/wiki/Global_warming#cite_note-96http://en.wikipedia.org/wiki/Biospherehttp://en.wikipedia.org/wiki/Cryospherehttp://en.wikipedia.org/wiki/Hydrospherehttp://en.wikipedia.org/wiki/Earth%27s_Atmospherehttp://en.wikipedia.org/wiki/Mathematical_modelshttp://en.wikipedia.org/wiki/Climate_model


7/37

Global warming has been detected in a number of systems. Some of these changes, e.g., based onthe 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.[111]Most of the increase in global average temperature since the mid-20th century is, with highprobability,[D]attributable to human-induced changes in greenhouse gas concentrations.[112]

Even with current policies to reduce emissions, global emissions are still expected to continue togrow over the coming decades.[113]Over the course of the 21st century, increases in emissions ator above their current rate would very likely induce changes in the climate system larger thanthose observed in the 20th century.

In the IPCC Fourth Assessment Report, across a range of future emission scenarios, model-basedestimates of sea level rise for the end of the 21st century (the year 20902099, relative to 19801999) range from 0.18 to 0.59 m. These estimates, however, were not given a likelihood due to alack of scientific understanding, nor was an upper bound given for sea level rise. On thetimescale of centuries to millennia, the melting ofice sheets could result in even higher sea level

rise. Partial deglaciation of the Greenland ice sheet, and possibly the West Antarctic Ice Sheet,could contribute 46 metres (13 to 20 ft) or more to sea level rise.[114]

Changes in regional climate are expected to include greater warming over land, with mostwarming at high northern latitudes, and least warming over the Southern Ocean and parts of theNorth Atlantic Ocean.[113]Snow cover area and sea ice extent are expected to decrease, with theArctic expected to be largely ice-free in September by 2037.[115]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 and upward shifts inplant and animal ranges, have been linked with high confidence to recent warming.[111]Futureclimate change is expected to particularly affect certain ecosystems, including tundra,mangroves, and coral reefs.[113]It is expected that most ecosystems will be affected by higheratmospheric CO2 levels, combined with higher global temperatures.

[116]Overall, it is expectedthat climate change will result in the extinction of many species and reduced diversity ofecosystems.[117]

Social systems

Vulnerability of human societies to climate change mainly lies in the effects of extreme weather

events rather than gradual climate change.[118]

Impacts of climate change so far include adverseeffects on small islands,[119]adverse effects on indigenous populations in high-latitude areas,[120]and small but discernable effects on human health.[121]Over the 21st century, climate change islikely to adversely affect hundreds of millions of people through increased coastal flooding,reductions in water supplies, increased malnutrition and increased health impacts.[122]

Future warming of around 3 C (by 2100, relative to 19902000) could result in increased cropyields in mid- and high-latitude areas, but in low-latitude areas, yields could decline, increasing
http://en.wikipedia.org/wiki/Global_warming/temphttp://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Global_warming#cnote_Dhttp://en.wikipedia.org/wiki/Global_warming#cnote_Dhttp://en.wikipedia.org/wiki/Global_warming#cnote_Dhttp://en.wikipedia.org/wiki/Global_warming#cite_note-111http://en.wikipedia.org/wiki/Global_warming#cite_note-111http://en.wikipedia.org/wiki/Global_warming#cite_note-111http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Ice_sheethttp://en.wikipedia.org/wiki/Greenland_ice_sheethttp://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheethttp://en.wikipedia.org/wiki/Global_warming#cite_note-113http://en.wikipedia.org/wiki/Global_warming#cite_note-113http://en.wikipedia.org/wiki/Global_warming#cite_note-113http://en.wikipedia.org/wiki/Latitudeshttp://en.wikipedia.org/wiki/Southern_Oceanhttp://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-114http://en.wikipedia.org/wiki/Global_warming#cite_note-114http://en.wikipedia.org/wiki/Global_warming#cite_note-114http://en.wikipedia.org/wiki/Heat_waveshttp://en.wikipedia.org/wiki/Ecosystemhttp://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Tundrahttp://en.wikipedia.org/wiki/Mangrovehttp://en.wikipedia.org/wiki/Coral_reefhttp://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-115http://en.wikipedia.org/wiki/Global_warming#cite_note-115http://en.wikipedia.org/wiki/Global_warming#cite_note-115http://en.wikipedia.org/wiki/Extinctionhttp://en.wikipedia.org/wiki/Global_warming#cite_note-116http://en.wikipedia.org/wiki/Global_warming#cite_note-116http://en.wikipedia.org/wiki/Global_warming#cite_note-116http://en.wikipedia.org/wiki/Climate_change,_industry_and_society#Vulnerabilityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-117http://en.wikipedia.org/wiki/Global_warming#cite_note-117http://en.wikipedia.org/wiki/Global_warming#cite_note-117http://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118http://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118http://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118http://en.wikipedia.org/wiki/Global_warming#cite_note-119http://en.wikipedia.org/wiki/Global_warming#cite_note-119http://en.wikipedia.org/wiki/Global_warming#cite_note-119http://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Floodhttp://en.wikipedia.org/wiki/Malnutritionhttp://en.wikipedia.org/wiki/Global_warming#cite_note-121http://en.wikipedia.org/wiki/Global_warming#cite_note-121http://en.wikipedia.org/wiki/Global_warming#cite_note-121http://en.wikipedia.org/wiki/Climate_change_and_agriculture#Regionalhttp://en.wikipedia.org/wiki/Climate_change_and_agriculture#Regionalhttp://en.wikipedia.org/wiki/Climate_change_and_agriculture#Regionalhttp://en.wikipedia.org/wiki/Climate_change_and_agriculture#Regionalhttp://en.wikipedia.org/wiki/Global_warming#cite_note-121http://en.wikipedia.org/wiki/Malnutritionhttp://en.wikipedia.org/wiki/Floodhttp://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Global_warming#cite_note-119http://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118http://en.wikipedia.org/wiki/Global_warming#cite_note-117http://en.wikipedia.org/wiki/Climate_change,_industry_and_society#Vulnerabilityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-116http://en.wikipedia.org/wiki/Extinctionhttp://en.wikipedia.org/wiki/Global_warming#cite_note-115http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Coral_reefhttp://en.wikipedia.org/wiki/Mangrovehttp://en.wikipedia.org/wiki/Tundrahttp://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Ecosystemhttp://en.wikipedia.org/wiki/Heat_waveshttp://en.wikipedia.org/wiki/Global_warming#cite_note-114http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Southern_Oceanhttp://en.wikipedia.org/wiki/Latitudeshttp://en.wikipedia.org/wiki/Global_warming#cite_note-113http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheethttp://en.wikipedia.org/wiki/Greenland_ice_sheethttp://en.wikipedia.org/wiki/Ice_sheethttp://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_SYR_2007-112http://en.wikipedia.org/wiki/Global_warming#cite_note-111http://en.wikipedia.org/wiki/Global_warming#cnote_Dhttp://en.wikipedia.org/wiki/Global_warming#cite_note-ipcc.ch-110http://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Global_warming/temp


8/37

the risk of malnutrition.[119]A similar regional pattern of net benefits and costs could occur foreconomic (market-sector) effects.[121]Warming above 3 C could result in crop yields falling intemperate regions, leading to a reduction in global food production.[123]Most economic studiessuggest losses of world gross domestic product (GDP) for this magnitude of warming.[124][125]

Responses to global warming

Mitigation

Reducing the amount of future climate change is called mitigation of climate change. The IPCCdefines mitigation as activities that reduce greenhouse gas (GHG) emissions, or enhance thecapacity ofcarbon sinks to absorb GHGs from the atmosphere.[126]Many countries, bothdeveloping and developed, are aiming to use cleaner, less polluting, technologies.[59]:192 Use ofthese technologies aids mitigation and could result in substantial reductions in CO2 emissions.Policies include targets for emissions reductions, increased use ofrenewable energy, andincreased energy efficiency. Studies indicate substantial potential for future reductions in

emissions.[127]

To limit warming to the lower range in the overall IPCC's "Summary Report forPolicymakers"[128]means adopting policies that will limit emissions to one of the significantlydifferent scenarios described in the full report.[129]This will become more and more difficult,since each year of high emissions will require even more drastic measures in later years tostabilize 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 in2008.[130]

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 byfactories and gas or coal power stations and then stores it, usually underground.[131]

Adaptation

Other policy responses include adaptation to climate change. Adaptation to climate change maybe planned, e.g., by local or national government, or spontaneous, i.e., done privately withoutgovernment intervention.[132]The ability to adapt is closely linked to social and economicdevelopment.[127]Even societies with high capacities to adapt are still vulnerable to climatechange. Planned adaptation is already occurring on a limited basis. The barriers, limits, and costsof future adaptation are not fully understood.

Geoengineering

A body of the scientific literature has developed which considers alternative geoengineeringtechniques for climate change mitigation.[133]In the IPCC's Fourth Assessment Report (publishedin 2007) Working Group III (WG3) assessed some "apparently promising" geoengineeringtechniques, including ocean fertilization, capturing and sequestering CO2, and techniques for
http://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118http://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118http://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118http://en.wikipedia.org/wiki/Economic_impacts_of_climate_change#Distribution_of_impactshttp://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Global_warming#cite_note-122http://en.wikipedia.org/wiki/Global_warming#cite_note-122http://en.wikipedia.org/wiki/Global_warming#cite_note-122http://en.wikipedia.org/wiki/Global_warming#cite_note-123http://en.wikipedia.org/wiki/Global_warming#cite_note-123http://en.wikipedia.org/wiki/Global_warming#cite_note-123http://en.wikipedia.org/wiki/Climate_change_mitigationhttp://en.wikipedia.org/wiki/Carbon_sinkhttp://en.wikipedia.org/wiki/Global_warming#cite_note-125http://en.wikipedia.org/wiki/Global_warming#cite_note-125http://en.wikipedia.org/wiki/Global_warming#cite_note-125http://en.wikipedia.org/wiki/Developing_countryhttp://en.wikipedia.org/wiki/Developed_countryhttp://en.wikipedia.org/wiki/Global_warming#cite_note-worldbank2010-58http://en.wikipedia.org/wiki/Global_warming#cite_note-worldbank2010-58http://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Efficient_energy_usehttp://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Global_warming#cite_note-127http://en.wikipedia.org/wiki/Global_warming#cite_note-127http://en.wikipedia.org/wiki/Global_warming#cite_note-127http://en.wikipedia.org/wiki/Global_warming#cite_note-128http://en.wikipedia.org/wiki/Global_warming#cite_note-128http://en.wikipedia.org/wiki/Global_warming#cite_note-128http://en.wikipedia.org/wiki/Global_warming#cite_note-129http://en.wikipedia.org/wiki/Global_warming#cite_note-129http://en.wikipedia.org/wiki/Global_warming#cite_note-129http://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Carbon_capture_and_storagehttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Power_stationhttp://en.wikipedia.org/wiki/Global_warming#cite_note-futureenergysummit-130http://en.wikipedia.org/wiki/Global_warming#cite_note-futureenergysummit-130http://en.wikipedia.org/wiki/Global_warming#cite_note-futureenergysummit-130http://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-131http://en.wikipedia.org/wiki/Global_warming#cite_note-131http://en.wikipedia.org/wiki/Global_warming#cite_note-131http://en.wikipedia.org/wiki/Adaptive_capacityhttp://en.wikipedia.org/wiki/Social_developmenthttp://en.wikipedia.org/wiki/Economic_developmenthttp://en.wikipedia.org/wiki/Economic_developmenthttp://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Geoengineeringhttp://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132http://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132http://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132http://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Reporthttp://en.wikipedia.org/wiki/Ocean_fertilizationhttp://en.wikipedia.org/wiki/Ocean_fertilizationhttp://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Reporthttp://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132http://en.wikipedia.org/wiki/Geoengineeringhttp://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Economic_developmenthttp://en.wikipedia.org/wiki/Economic_developmenthttp://en.wikipedia.org/wiki/Social_developmenthttp://en.wikipedia.org/wiki/Adaptive_capacityhttp://en.wikipedia.org/wiki/Global_warming#cite_note-131http://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-futureenergysummit-130http://en.wikipedia.org/wiki/Power_stationhttp://en.wikipedia.org/wiki/Natural_gashttp://en.wikipedia.org/wiki/Carbon_capture_and_storagehttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Global_warming#cite_note-129http://en.wikipedia.org/wiki/Global_warming#cite_note-128http://en.wikipedia.org/wiki/Global_warming#cite_note-127http://en.wikipedia.org/wiki/Global_warming#cite_note-autogenerated2007-126http://en.wikipedia.org/wiki/Efficient_energy_usehttp://en.wikipedia.org/wiki/Renewable_energyhttp://en.wikipedia.org/wiki/Global_warming#cite_note-worldbank2010-58http://en.wikipedia.org/wiki/Developed_countryhttp://en.wikipedia.org/wiki/Developing_countryhttp://en.wikipedia.org/wiki/Global_warming#cite_note-125http://en.wikipedia.org/wiki/Carbon_sinkhttp://en.wikipedia.org/wiki/Climate_change_mitigationhttp://en.wikipedia.org/wiki/Global_warming#cite_note-123http://en.wikipedia.org/wiki/Global_warming#cite_note-123http://en.wikipedia.org/wiki/Global_warming#cite_note-122http://en.wikipedia.org/wiki/Global_warming#cite_note-schtab-120http://en.wikipedia.org/wiki/Economic_impacts_of_climate_change#Distribution_of_impactshttp://en.wikipedia.org/wiki/Global_warming#cite_note-schreg-118


9/37

reducing the amount of sunlight absorbed by the Earth's atmospheric system.[133]The IPCC'soverall conclusion was that geoengineering options remained "largely speculative and unproven,(...) with the risk of unknown side-effects."[134]In the IPCC's judgement, reliable cost estimatesfor geoengineering options had not yet been published.

As most geoengineering techniques would affect the entire globe, deployment would likelyrequire global public acceptance and an adequate global legal and regulatory framework, as wellas significant further scientific research.[135]

Views on global warming

There are different views over what the appropriate policy response to climate change shouldbe.[136]These competing views weigh the benefits of limiting emissions of greenhouse gasesagainst the costs. In general, it seems likely that climate change will impose greater damages andrisks in poorer regions.[137]

Global warming controversy

The global warming controversy refers to a variety of disputes, significantly more pronouncedin the popular media than in the scientific literature,[138][139]regarding the nature, causes, andconsequences of global warming. The disputed issues include the causes of increased globalaverage air temperature, especially since the mid-20th century, whether this warming trend isunprecedented or within normal climatic variations, whether humankind has contributedsignificantly to it, and whether the increase is wholly or partially an artifact of poormeasurements. Additional disputes concern estimates ofclimate sensitivity, predictions ofadditional warming, and what the consequences of global warming will be.

In the scientific literature, there is a strong consensus that global surface temperatures haveincreased in recent decades and that the trend is caused mainly by human-induced emissions ofgreenhouse gases. No scientific body of national or international standing disagrees with thisview,[140][141]though a few organisations hold non-committal positions.

From 1990-1997 in the United States, conservative think tanks mobilized to undermine thelegitimacy of global warming as a social problem. They challenged the scientific evidence;argued that global warming will have benefits; and asserted that proposed solutions would domore harm than good.[142]

Politics

Most countries are Parties to the United Nations Framework Convention on Climate Change(UNFCCC).[145]The ultimate objective of the Convention is to prevent "dangerous" humaninterference of the climate system.[146]As is stated in the Convention, this requires that GHGconcentrations are stabilized in the atmosphere at a level where ecosystems can adapt naturally toclimate change, food production is not threatened, and economic development can proceed in asustainable fashion.[147]The Framework Convention was agreed in 1992, but since then, globalemissions have risen.[148]During negotiations, the G77 (a lobbying group in the United Nations
http://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132http://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132http://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_WG3_SPM_geoengineering-133http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_WG3_SPM_geoengineering-133http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_WG3_SPM_geoengineering-133http://en.wikipedia.org/wiki/Global_warming#cite_note-134http://en.wikipedia.org/wiki/Global_warming#cite_note-134http://en.wikipedia.org/wiki/Global_warming#cite_note-134http://en.wikipedia.org/wiki/Global_warming#cite_note-135http://en.wikipedia.org/wiki/Global_warming#cite_note-135http://en.wikipedia.org/wiki/Global_warming#cite_note-135http://en.wikipedia.org/wiki/Global_warming#cite_note-136http://en.wikipedia.org/wiki/Global_warming#cite_note-136http://en.wikipedia.org/wiki/Global_warming#cite_note-136http://en.wikipedia.org/wiki/Media_coverage_of_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-137http://en.wikipedia.org/wiki/Global_warming#cite_note-137http://en.wikipedia.org/wiki/Global_warming#cite_note-137http://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Scientific_opinion_on_climate_changehttp://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change#Statements_by_dissenting_organizationshttp://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change#Statements_by_dissenting_organizationshttp://en.wikipedia.org/wiki/Global_warming#cite_note-AQAonAAPG-139http://en.wikipedia.org/wiki/Global_warming#cite_note-AQAonAAPG-139http://en.wikipedia.org/wiki/Global_warming#cite_note-AQAonAAPG-139http://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change#Non-committal_statementshttp://en.wikipedia.org/wiki/Conservatism_in_the_United_Stateshttp://en.wikipedia.org/wiki/Global_warming#cite_note-141http://en.wikipedia.org/wiki/Global_warming#cite_note-141http://en.wikipedia.org/wiki/Global_warming#cite_note-141http://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-144http://en.wikipedia.org/wiki/Global_warming#cite_note-144http://en.wikipedia.org/wiki/Global_warming#cite_note-144http://en.wikipedia.org/wiki/Global_warming#cite_note-145http://en.wikipedia.org/wiki/Global_warming#cite_note-145http://en.wikipedia.org/wiki/Global_warming#cite_note-145http://en.wikipedia.org/wiki/Climate_change_and_ecosystemshttp://en.wikipedia.org/wiki/Climate_change_and_agriculturehttp://en.wikipedia.org/wiki/Economics_of_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-146http://en.wikipedia.org/wiki/Global_warming#cite_note-146http://en.wikipedia.org/wiki/Global_warming#cite_note-146http://en.wikipedia.org/wiki/Global_warming#cite_note-147http://en.wikipedia.org/wiki/Global_warming#cite_note-147http://en.wikipedia.org/wiki/Global_warming#cite_note-147http://en.wikipedia.org/wiki/Group_of_77http://en.wikipedia.org/wiki/Group_of_77http://en.wikipedia.org/wiki/Global_warming#cite_note-147http://en.wikipedia.org/wiki/Global_warming#cite_note-146http://en.wikipedia.org/wiki/Economics_of_global_warminghttp://en.wikipedia.org/wiki/Climate_change_and_agriculturehttp://en.wikipedia.org/wiki/Climate_change_and_ecosystemshttp://en.wikipedia.org/wiki/Global_warming#cite_note-145http://en.wikipedia.org/wiki/Global_warming#cite_note-144http://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-141http://en.wikipedia.org/wiki/Conservatism_in_the_United_Stateshttp://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change#Non-committal_statementshttp://en.wikipedia.org/wiki/Global_warming#cite_note-AQAonAAPG-139http://en.wikipedia.org/wiki/Global_warming#cite_note-AQAonAAPG-139http://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change#Statements_by_dissenting_organizationshttp://en.wikipedia.org/wiki/Scientific_opinion_on_climate_change#Statements_by_dissenting_organizationshttp://en.wikipedia.org/wiki/Scientific_opinion_on_climate_changehttp://en.wikipedia.org/wiki/Climate_sensitivityhttp://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Attribution_of_recent_climate_changehttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Global_warming#cite_note-137http://en.wikipedia.org/wiki/Global_warming#cite_note-137http://en.wikipedia.org/wiki/Media_coverage_of_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-136http://en.wikipedia.org/wiki/Global_warming#cite_note-135http://en.wikipedia.org/wiki/Global_warming#cite_note-134http://en.wikipedia.org/wiki/Global_warming#cite_note-IPCC_AR4_WG3_SPM_geoengineering-133http://en.wikipedia.org/wiki/Global_warming#cite_note-Barker_11.2.2-132


10/37

representing 133 developing nations)[149]:4 pushed for a mandate requiring developed countries to"[take] the lead" in reducing their emissions.[150]This was justified on the basis that: thedeveloped world's emissions had contributed most to the stockof GHGs in the atmosphere; per-capita emissions (i.e., emissions per head of population) were still relatively low in developingcountries; and the emissions of developing countries would grow to meet their development

needs.

[61]:290

This mandate was sustained in the Kyoto Protocol to the FrameworkConvention,[61]:290 which entered into legal effect in 2005.[151]

In ratifying the Kyoto Protocol, most developed countries accepted legally binding commitmentsto limit their emissions. These first-round commitments expire in 2012.[151]US President GeorgeW. Bush rejected the treaty on the basis that "it exempts 80% of the world, including majorpopulation centers such as China and India, from compliance, and would cause serious harm tothe US economy."[149]:5

At the 15th UNFCCC Conference of the Parties, held in 2009 at Copenhagen, several UNFCCCParties produced the Copenhagen Accord.[152]Parties associated with the Accord (140 countries,

as of November 2010)

[153]:9

aim to limit the future increase in global mean temperature to below2 C.[154]A preliminary assessment published in November 2010 by the United NationsEnvironment Programme (UNEP) suggests a possible "emissions gap" between the voluntarypledges made in the Accord and the emissions cuts necessary to have a "likely" (greater than66% probability) chance of meeting the 2 C objective. The 16th Conference of the Parties(COP16) was held at Cancn in 2010. It produced an agreement, not a binding treaty, that theParties should take urgent action to reduce greenhouse gas emissions to meet a goal of limitingglobal warming to 2 C above pre-industrial temperatures. It also recognized the need to considerstrengthening the goal to a global average rise of 1.5 C.[155]

By 2010, with 111 countries surveyed, Gallup determined that there was a substantial decrease in

the number of Americans and Europeans who viewed Global Warming as a serious threat. In theUS, a little over half the population (53%) now viewed it as a serious concern for eitherthemselves or their families; this was 10% below the 2008 poll (63%). Latin America had thebiggest rise in concern, with 73% saying global warming was a serious threat to theirfamilies.[165]That global poll also found that people are more likely to attribute global warmingto human activities than to natural causes, except in the USA where nearly half (47%) of thepopulation attributed global warming to natural causes.[166]

On the other hand, in May 2011 a joint poll by Yale and George Mason Universities found thatnearly half the people in the USA (47%) attribute global warming to human activities, comparedto 36% blaming it on natural causes. Only 5% of the 35% who were "disengaged", "doubtful", or"dismissive" of global warming were aware that 97% of publishing US climate scientists agreeglobal warming is happening and is primarily caused by humans.[167]

Researchers at the University of Michigan have found that the public's belief as to the causes ofglobal warming depends on the wording choice used in the polls.[168]
http://en.wikipedia.org/wiki/Global_warming#cite_note-dessai-148http://en.wikipedia.org/wiki/Global_warming#cite_note-dessai-148http://en.wikipedia.org/wiki/Global_warming#cite_note-149http://en.wikipedia.org/wiki/Global_warming#cite_note-149http://en.wikipedia.org/wiki/Global_warming#cite_note-149http://en.wikipedia.org/wiki/Greenhouse_gas#Cumulative_and_historical_emissionshttp://en.wikipedia.org/wiki/Greenhouse_gas#Annual_and_per_capita_emissionshttp://en.wikipedia.org/wiki/Greenhouse_gas#Annual_and_per_capita_emissionshttp://en.wikipedia.org/wiki/Global_warming#cite_note-liverman-60http://en.wikipedia.org/wiki/Global_warming#cite_note-liverman-60http://en.wikipedia.org/wiki/Kyoto_Protocolhttp://en.wikipedia.org/wiki/Global_warming#cite_note-liverman-60http://en.wikipedia.org/wiki/Global_warming#cite_note-liverman-60http://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/George_W._Bushhttp://en.wikipedia.org/wiki/George_W._Bushhttp://en.wikipedia.org/wiki/Global_warming#cite_note-dessai-148http://en.wikipedia.org/wiki/Global_warming#cite_note-dessai-148http://en.wikipedia.org/wiki/2009_United_Nations_Climate_Change_Conferencehttp://en.wikipedia.org/wiki/Copenhagenhttp://en.wikipedia.org/wiki/Copenhagen_Accordhttp://en.wikipedia.org/wiki/Global_warming#cite_note-151http://en.wikipedia.org/wiki/Global_warming#cite_note-151http://en.wikipedia.org/wiki/Global_warming#cite_note-151http://en.wikipedia.org/wiki/Global_warming#cite_note-unep-152http://en.wikipedia.org/wiki/Global_warming#cite_note-unep-152http://en.wikipedia.org/wiki/Global_warming#cite_note-153http://en.wikipedia.org/wiki/Global_warming#cite_note-153http://en.wikipedia.org/wiki/Global_warming#cite_note-153http://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/2010_United_Nations_Climate_Change_Conferencehttp://en.wikipedia.org/wiki/Canc%C3%BAnhttp://en.wikipedia.org/wiki/Global_warming#cite_note-154http://en.wikipedia.org/wiki/Global_warming#cite_note-154http://en.wikipedia.org/wiki/Global_warming#cite_note-154http://en.wikipedia.org/wiki/Global_warming#cite_note-164http://en.wikipedia.org/wiki/Global_warming#cite_note-164http://en.wikipedia.org/wiki/Global_warming#cite_note-164http://en.wikipedia.org/wiki/Global_warming#cite_note-165http://en.wikipedia.org/wiki/Global_warming#cite_note-165http://en.wikipedia.org/wiki/Global_warming#cite_note-165http://en.wikipedia.org/wiki/Global_warming#cite_note-YaleMay2011-166http://en.wikipedia.org/wiki/Global_warming#cite_note-YaleMay2011-166http://en.wikipedia.org/wiki/Global_warming#cite_note-YaleMay2011-166http://en.wikipedia.org/wiki/Opinion_poll#Wording_of_questionshttp://en.wikipedia.org/wiki/Global_warming#cite_note-167http://en.wikipedia.org/wiki/Global_warming#cite_note-167http://en.wikipedia.org/wiki/Global_warming#cite_note-167http://en.wikipedia.org/wiki/Global_warming#cite_note-167http://en.wikipedia.org/wiki/Opinion_poll#Wording_of_questionshttp://en.wikipedia.org/wiki/Global_warming#cite_note-YaleMay2011-166http://en.wikipedia.org/wiki/Global_warming#cite_note-165http://en.wikipedia.org/wiki/Global_warming#cite_note-164http://en.wikipedia.org/wiki/Global_warming#cite_note-154http://en.wikipedia.org/wiki/Canc%C3%BAnhttp://en.wikipedia.org/wiki/2010_United_Nations_Climate_Change_Conferencehttp://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/Global_warming#cite_note-153http://en.wikipedia.org/wiki/Global_warming#cite_note-unep-152http://en.wikipedia.org/wiki/Global_warming#cite_note-151http://en.wikipedia.org/wiki/Copenhagen_Accordhttp://en.wikipedia.org/wiki/Copenhagenhttp://en.wikipedia.org/wiki/2009_United_Nations_Climate_Change_Conferencehttp://en.wikipedia.org/wiki/Global_warming#cite_note-dessai-148http://en.wikipedia.org/wiki/George_W._Bushhttp://en.wikipedia.org/wiki/George_W._Bushhttp://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/Global_warming#cite_note-kyoto-150http://en.wikipedia.org/wiki/Global_warming#cite_note-liverman-60http://en.wikipedia.org/wiki/Kyoto_Protocolhttp://en.wikipedia.org/wiki/Global_warming#cite_note-liverman-60http://en.wikipedia.org/wiki/Greenhouse_gas#Annual_and_per_capita_emissionshttp://en.wikipedia.org/wiki/Greenhouse_gas#Annual_and_per_capita_emissionshttp://en.wikipedia.org/wiki/Greenhouse_gas#Cumulative_and_historical_emissionshttp://en.wikipedia.org/wiki/Global_warming#cite_note-149http://en.wikipedia.org/wiki/Global_warming#cite_note-dessai-148


11/37

In the United States, according to the Public Policy Institute of California's (PPIC) eleventhannual survey on environmental policy issues, 75% said they believe global warming is a veryserious or somewhat serious threat to the economy and quality of life in California.[169]

A July 2011 Rasmussen Reports poll found that 69% of adults in the USA believe it is at least

somewhat likely that some scientists have falsified global warming research.

[156]

A September 2011 Angus Reid Public Opinion poll found that Britons (43%) are less likely thanAmericans (49%) or Canadians (52%) to say that "global warming is a fact and is mostly causedby emissions from vehicles and industrial facilities." The same poll found that 20% ofAmericans, 20% of Britons and 14% of Canadians think "global warming is a theory that has notyet been proven."[170]

.

Climate change mitigation is action to decrease the intensity ofradiative forcing in order to

reduce the potential effects ofglobal warming.[1]

Mitigation is distinguished from adaptation toglobal warming, which involves acting to tolerate the effects of global warming. Most often,climate change mitigation scenarios involve reductions in the concentrations ofgreenhousegases, either by reducing their sources[2]or by increasing their sinks.

The UN defines mitigation in the context of climate change, as a human intervention to reducethe sources or enhance the sinks of greenhouse gases. Examples include using fossil fuels moreefficiently for industrial processes or electricity generation, switching to renewable energy (solarenergy or wind power), improving the insulation of buildings, and expanding forests and other"sinks" to remove greater amounts ofcarbon dioxide from the atmosphere.[3]

Scientific consensus on global warming, together with the precautionary principle and the fear ofabrupt climate change[4]is leading to increased effort to develop new technologies and sciencesand carefully manage others in an attempt to mitigate global warming. Most means of mitigationappear effective only for preventing further warming, not at reversing existing warming.[5]TheStern Review identifies several ways of mitigating climate change. These include reducingdemand for emissions-intensive goods and services, increasing efficiency gains, increasing useand development of low-carbon technologies, and reducing fossil fuel emissions.[6]

The energy policy of the European Union has set a target of limiting the global temperature riseto 2 C (3.6 F) compared to preindustrial levels, of which 0.8 C has already taken place andanother 0.50.7 C is already committed.[7]The 2 C rise is typically associated in climate

models with a carbon dioxide equivalent concentration of 400500 ppm by volume; the current(April 2011) level of carbon dioxide alone is 393 ppm by volume, and rising at 1-3 ppmannually. Hence, to avoid a very likely breach of the 2 C target, CO2 levels would have to bestabilised very soon; this is generally regarded as unlikely, based on current programs in place todate.[8][9]The importance of change is illustrated by the fact that world economic energyefficiency is presently improving at only half the rate of world economic growth.[10]
http://en.wikipedia.org/wiki/Global_warming#cite_note-167http://en.wikipedia.org/wiki/Global_warming#cite_note-167http://en.wikipedia.org/wiki/Global_warm

global warming refers to the current rise in the average temperature of earth

Documents