a historic step in the right direction for clean air

7/31/2019 A Historic Step in the Right Direction for Clean Air

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A Historic Step in the Right Direction for Clean Air EPAs Standards for Carbon Pollution Will Help Protect Public Health

Why is EPA Moving to Limit Industrial Carbon Pollution?

RECORD-BREAKING WEATHER IN YOUR AREA

Find out how climate change impacted your neighborhood last year.

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Climate Change Heat Deaths in Top U.S. Cities

Americas power plants are our biggest industrial polluters. Each year they pump morethan two billion tons of carbon dioxide into the air. Carbon pollution is causing climatechange that drives dangerous heat waves and worsening smog pollution, which causesasthma attacks and other serious respiratory illnesses.

Thus climate change looms as one of our most serious public health threats; yet fewpeople are aware of the many dangers posed by a warming planet.

These include:

Air Pollution : Warming temperatures worsen smog pollution, which triggersasthma attacks and permanently damages and reduces the function of childrenslungs. Higher smog levels even contribute to premature deaths.

Heat-related Disease and Illness : As temperatures rise, so do deaths andillnesses related to heat stress, heatstroke, cardiovascular disease, and kidneydisease.

Infectious Disease : Climate change affects patterns of diseases such as denguefever, West Nile virus, and Lyme disease. Increasing temperatures and rainfallhave been associated with increased occurrence and transmission of insect-bornediseases like West Nile virus. Higher temperatures can lead to more rapiddevelopment of dangerous pathogens within insect carriers and allow thesediseases to expand their range into new, once cooler, regions. Approximately 173million Americans in at least 28 states live in counties with mosquitoes that cancarry dengue fever, a painful viral illness that has increased globally 30-fold in thelast 50 years.
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Drought : Projected temperature increases in the summer will increase thelikelihood of water shortages and drought, threatening the availability of water for drinking and irrigation. Droughts harm crops, diminishing food variety, nutritionalcontent, and availability.

Floods : Warmer air holds more moisture, so when it rain s its more likely to pour,

increasing the risk of flooding. Warmer ocean temperatures have also been linkedto more powerful hurricanes and other storms.The potential health impacts are also expensive. In 2011, NRDC studied six types of climate change-related types of events in the U.S. between 2002 and 2009 -- episodesof ozone air pollution, heat waves, hurricanes, outbreaks of infectious disease, river flooding, and wildfires. All are projected to increase in severity, frequency, or extent withclimate change. We found that associated health costs exceeded $14 billion. Thatincluded deaths, illnesses, and more than 760,000 visits to the doctor, hospital,emergency room or other health care facilities. (These health effects were described ina paper in the national journal Health Affairs , and can be accessed here .)

Find out how these serious climate-health threats impact your community >> ClimateChange Threatens Health

Earlier this year, the Natural Resources Defense Council launched a powerful new ad tobuild public awareness of and support for tough, new safeguards against industrialcarbon pollution from power plants and other clean air standards. Watch the videobelow and join us by telling the EPA that you support standards to reduce carbonpollution from new and existing power plants .

Climate Change, Water, and RiskCurrent Water Demands Are Not Sustainable

READ THE FACT SHEET

Get document in pdf, (5MB) View Water Supply Sustainability Index with Google Earth

Climate change will have a significant impact on the sustainability of water supplies inthe coming decades. A new analysis, performed by consulting firm Tetra Tech for theNatural Resources Defense Council (NRDC), examined the effects of global warmingon water supply and demand in the contiguous United States. The study found thatmore than 1,100 counties -- one-third of all counties in the lower 48 -- will face higher risks of water shortages by mid-century as the result of global warming. More than 400of these counties will face extremely high risks of water shortages.
http://www.nrdc.org/health/accountingforcosts/http://www.nrdc.org/health/accountingforcosts/http://www.nrdc.org/health/accountingforcosts/http://www.nrdc.org/health/climate/default.asphttp://www.nrdc.org/health/climate/default.asphttp://www.nrdc.org/health/climate/default.asphttp://www.nrdc.org/health/climate/default.asphttps://secure.nrdconline.org/site/Advocacy?cmd=display&page=UserAction&id=2733https://secure.nrdconline.org/site/Advocacy?cmd=display&page=UserAction&id=2733https://secure.nrdconline.org/site/Advocacy?cmd=display&page=UserAction&id=2733https://secure.nrdconline.org/site/Advocacy?cmd=display&page=UserAction&id=2733http://www.nrdc.org/globalwarming/watersustainability/files/WaterRisk.pdfhttp://www.nrdc.org/globalwarming/watersustainability/files/WaterRisk.pdfhttp://www.nrdc.org/googleearth/ClimateChangeWaterRisk.kmzhttp://www.nrdc.org/googleearth/ClimateChangeWaterRisk.kmzhttp://www.nrdc.org/googleearth/ClimateChangeWaterRisk.kmzhttp://www.nrdc.org/globalwarming/watersustainability/files/WaterRisk.pdfhttps://secure.nrdconline.org/site/Advocacy?cmd=display&page=UserAction&id=2733https://secure.nrdconline.org/site/Advocacy?cmd=display&page=UserAction&id=2733http://www.nrdc.org/health/climate/default.asphttp://www.nrdc.org/health/climate/default.asphttp://www.nrdc.org/health/accountingforcosts/


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< Global Warming Main Page HOW TO SOLVE IT

Overview

Step 1: Set limits on global warming pollution

Step 2: Invest in green jobs and clean energy

Step 3: Drive smarter cars

Step 4: Create green homes and buildings Step 5: Build better communities and transportation

What You Can Do >

GLOBAL WARMING SOLUTIONS

This five-step plan will repower, refuel, and rebuild America, startingtoday.

Solving global warming means investing in clean energy, green jobs and smart

energy solutions. We can't afford delay.Tell Congress to pass a law limited Greenhouse gas pollution.

Take Action Now

1. Set limits on global warming pollution 2. Invest in green jobs and clean energy 3. Drive smarter cars
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4. Create green homes and buildings 5. Build better communities and transporation networks

Extreme weather events and climate change

2011 has been a year of unparalleled extremes: 14 disastrous weather events haveresulted in over a billion dollars in property damage an all-time record breakingnumber and their estimated $53 billion price tag doesnt include health costs. Asshown recently, in a first-of-its-kind study published in the journal Health Affairs 1, whenhealth-related costs of extreme events are calculated, the total tally increasessubstantially and will likely continue to climb due to climate change. 7 of the 2011extreme events a record-high number are the type expected to worsen due toclimate change.

Climate scientists are saying that these events may be part of a troubling trendinfluenced by climate change 2. This trend has also been identified by the internationalreinsurance company MunichRe [PDF]; they concluded that from 1980 through 2011,

the frequency of extreme events in the U.S. is rising .3 A newly-released analysis byinternational climate scientists (IPCC )4 concluded that climate change will amplifyextreme heat, heavy precipitation, and the highest wind speeds of tropical storms.

We need to be prepared. Emergency planning must incorporate risks from climatechange. For example, maps describing flooding zones need to account for increasedrisks caused by extreme rainfall and sea level rise resulting from climate change. Whilethese plans are made at the local level, the Federal Emergency Management Agency(FEMA) must also prioritize addressing and preparing for climate change by providingguidance and resources to state and local governments.

Protect your family from extreme weather: Stay informed subscribe to local emergency alerts and watch for updates. Make

sure to have a battery powered radio or other device in the event you lose power. Stay connected check on relatives, friends and neighbors. Plan ahead have an evacuation plan and emergency supplies on hand. Click

here for information on how to be aware and be prepared for a natural disaster . Also see the Red Cross , the Federal Emergency Management Agency (FEMA), or the Centers for Disease Control & Prevention (CDC) lists for what you need.

Serious Threats Where You Live and What To Do About Them

Climate change is one of the most serious public health threats facing the nation, but fewpeople are aware of how it can affect them. Children, the elderly, and communities living inpoverty are among the most vulnerable. Click on a state on the map for more information onclimate-health threats, actions being taken to prepare communities, and what you can do.
http://www.nrdc.org/globalwarming/solutions/step4.asphttp://www.nrdc.org/globalwarming/solutions/step4.asphttp://www.nrdc.org/globalwarming/solutions/step5.asphttp://www.nrdc.org/globalwarming/solutions/step5.asphttp://www.nrdc.org/media/2011/111108c.asphttp://www.nrdc.org/media/2011/111108c.asphttp://www.nrdc.org/media/2011/111108c.asphttp://www.nrdc.org/media/2011/111108c.asphttp://www.nrdc.org/media/2011/111108c.asphttp://www.scientificamerican.com/article.cfm?id=extremeweathercaused-by-climate-changehttp://www.scientificamerican.com/article.cfm?id=extremeweathercaused-by-climate-changehttp://www.scientificamerican.com/article.cfm?id=extremeweathercaused-by-climate-changehttp://www.nrdc.org/health/extremeweather/#note2http://www.nrdc.org/health/extremeweather/#note2http://www.munichreamerica.com/webinars/2011_07_natcatreview/MR_III_2011_HalfYear_NatCat_Review.pdfhttp://www.munichreamerica.com/webinars/2011_07_natcatreview/MR_III_2011_HalfYear_NatCat_Review.pdfhttp://www.munichreamerica.com/webinars/2011_07_natcatreview/MR_III_2011_HalfYear_NatCat_Review.pdfhttp://www.nrdc.org/health/extremeweather/#note3http://www.nrdc.org/health/extremeweather/#note3http://www.nrdc.org/health/extremeweather/#note3http://www.nrdc.org/health/extremeweather/#note4http://www.nrdc.org/health/extremeweather/#note4http://www.nrdc.org/health/extremeweather/#note4http://www.nrdc.org/living/waterair/disaster-preparedness/defautl.asphttp://www.nrdc.org/living/waterair/disaster-preparedness/defautl.asphttp://www.nrdc.org/living/waterair/disaster-preparedness/defautl.asphttp://www.redcross.org/portal/site/en/menuitem.53fabf6cc033f17a2b1ecfbf43181aa0/?vgnextoid=537b218c37752210VgnVCM10000089f0870aRCRD&currPage=e507d7aada352210VgnVCM10000089f0870aRCRDhttp://www.redcross.org/portal/site/en/menuitem.53fabf6cc033f17a2b1ecfbf43181aa0/?vgnextoid=537b218c37752210VgnVCM10000089f0870aRCRD&currPage=e507d7aada352210VgnVCM10000089f0870aRCRDhttp://www.redcross.org/portal/site/en/menuitem.53fabf6cc033f17a2b1ecfbf43181aa0/?vgnextoid=537b218c37752210VgnVCM10000089f0870aRCRD&currPage=e507d7aada352210VgnVCM10000089f0870aRCRDhttp://www.ready.gov/are-you-ready-guidehttp://www.ready.gov/are-you-ready-guidehttp://www.ready.gov/are-you-ready-guidehttp://emergency.cdc.gov/preparedness/kit/disasters/http://emergency.cdc.gov/preparedness/kit/disasters/http://emergency.cdc.gov/preparedness/kit/disasters/http://emergency.cdc.gov/preparedness/kit/disasters/http://www.ready.gov/are-you-ready-guidehttp://www.redcross.org/portal/site/en/menuitem.53fabf6cc033f17a2b1ecfbf43181aa0/?vgnextoid=537b218c37752210VgnVCM10000089f0870aRCRD&currPage=e507d7aada352210VgnVCM10000089f0870aRCRDhttp://www.nrdc.org/living/waterair/disaster-preparedness/defautl.asphttp://www.nrdc.org/health/extremeweather/#note4http://www.nrdc.org/health/extremeweather/#note3http://www.munichreamerica.com/webinars/2011_07_natcatreview/MR_III_2011_HalfYear_NatCat_Review.pdfhttp://www.nrdc.org/health/extremeweather/#note2http://www.scientificamerican.com/article.cfm?id=extremeweathercaused-by-climate-changehttp://www.scientificamerican.com/article.cfm?id=extremeweathercaused-by-climate-changehttp://www.nrdc.org/media/2011/111108c.asphttp://www.nrdc.org/media/2011/111108c.asphttp://www.nrdc.org/globalwarming/solutions/step5.asphttp://www.nrdc.org/globalwarming/solutions/step4.asp


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Global warmingFrom Wikipedia, the free encyclopedia

This article is about the current change in Earth's climate. For general discussion of how the climate can

change, see Climate change .

]

Global mean land-ocean temperature change from 1880 2011, relative to the 1951 1980 mean. The black line is the

annual mean and the red line is the 5-year running mean . The green bars show uncertainty estimates. Source: NASAGISS

The map shows the 10-year average (2000 2009) global mean temperature anomaly relative to the 1951 1980

mean. The largest temperature increases are in the Arctic and the Antarctic Peninsula. Source :NASA EarthObservator y[1]

Fossil fuel related CO2 emissions compared to five of IPCC's emissions scenarios. The dips are related to global

recessions. Data from IPCC SRES scenarios ; Data spreadsheet included with International Energy Agency's "CO2

Emissions from Fuel Combustion 2010 Highlights" ; and Supplemental IEA data . Image source :Skeptical Science

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
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increased by about 0.8 C (1.4 F), with about two-thirds of the increase occurring since 1980 .[2] Warming of

the climate system is unequivocal, 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 .[3][4][5][6] These findings are recognized by the national science academies of all major

industrialized nations .[7][A]

Climate model projections are summarized in the 2007 Fourth Assessment Report (AR4) by

the Intergovernmental Panel on Climate Change (IPCC). They indicate that during the 21st century the global

surface temperature is likely to rise a further 1.1 to 2.9 C (2 to 5.2 F) for their lowest emissions scenario and

2.4 to 6.4 C (4.3 to 11.5 F) for their highest .[8] The ranges of these estimates arise from the use of models

with differing sensitivity to greenhouse gas concentrations .[9][10]

Warming and related changes will vary from region to region around the globe .[11] The effects of an increase in

global temperature include a rise in sea levels and a change in the amount and pattern of precipitation , as well

a probable expansion of subtropical deserts .[12]Warming is expected to be strongest in the Arctic and would be

associated with the continuing retreat of glaciers , permafrost and sea ice . Other likely effects of the warming

include a more frequent occurrence of extreme-weather events including heat waves , droughts and heavy

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

humans include the threat to food security from decreasing crop yield s [13] and the loss of habitat from

inundation. If global mean temperature increases to4 C (7.2 F) above preindustrial levels, the limits for human

adaptation are likely to be exceeded in many parts of the world, while the limits of adaptation for natural

systems would largely be exceeded throughout the world. Hence, the ecosystem services upon which human

livelihoods depend would not be preserved .[14]

Policy responses to global warming include mitigation by emissions reduction, adaptation to its effects, and

possible futur e geoengineering . Most countries are parties to the United Nations Framework Convention on

Climate Change (UNFCCC) ,[15] whose ultimate objective is to prevent dangerous anthropogenic (i.e., human-

induced) climate change .[16] Parties to the UNFCCC have adopted a range of policies designed to reduce

greenhouse gas emission s [17]:10[18][19][20]:9 and to assist in adaptation to global warming .[17]:13[20]:10[21][22] Parties to

the UNFCCC have agreed that deep cuts in emissions are required ,[23] and that future global warming should

be limited to below 2.0 C (3.6 F) relative to the pre-industrial level .[23][B] A 2011 report of analyses by

the United Nations Environment Programme[24]

and International Energy Agency[25]

suggest that efforts as of the early 21st century to reduce emissions may be inadequate to meet the UNFCCC's 2 C target.

Contents

[hide ]

1 Observed temperature changes
http://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/Climate_systemhttp://en.wikipedia.org/wiki/Climate_systemhttp://en.wikipedia.org/wiki/Climate_systemhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Deforestationhttp://en.wikipedia.org/wiki/Deforestationhttp://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-6http://en.wikipedia.org/wiki/Global_warming#cite_note-6http://en.wikipedia.org/wiki/Global_warming#cite_note-6http://en.wikipedia.org/wiki/Climate_modelhttp://en.wikipedia.org/wiki/Climate_modelhttp://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Reporthttp://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Reporthttp://en.wikipedia.org/wiki/IPCC_Fourth_Assessment_Reporthttp://en.wikipedia.org/wiki/Intergovernmental_Panel_on_Climate_Changehttp://en.wikipedia.org/wiki/Intergovernmental_Panel_on_Climate_Changehttp://en.wikipedia.org/wiki/Intergovernmental_Panel_on_Climate_Changehttp://en.wikipedia.org/wiki/Special_Report_on_Emissions_Scenarioshttp://en.wikipedia.org/wiki/Special_Report_on_Emissions_Scenarioshttp://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/Regional_effects_of_global_warminghttp://en.wikipedia.org/wiki/Regional_effects_of_global_warminghttp://en.wikipedia.org/wiki/Regional_effects_of_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-10http://en.wikipedia.org/wiki/Global_warming#cite_note-10http://en.wikipedia.org/wiki/Global_warming#cite_note-10http://en.wikipedia.org/wiki/Effects_of_global_warminghttp://en.wikipedia.org/wiki/Effects_of_global_warminghttp://en.wikipedia.org/wiki/Effects_of_global_warminghttp://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Subtropicshttp://en.wikipedia.org/wiki/Subtropicshttp://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Global_warming#cite_note-11http://en.wikipedia.org/wiki/Global_warming#cite_note-11http://en.wikipedia.org/wiki/Arctic_shrinkagehttp://en.wikipedia.org/wiki/Arctic_shrinkagehttp://en.wikipedia.org/wiki/Arctic_shrinkagehttp://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850http://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850http://en.wikipedia.org/wiki/Retreat_of_glaciers_since_1850http://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Permafrosthttp://en.wikipedia.org/wiki/Sea_icehttp://en.wikipedia.org/wiki/Sea_icehttp://en.wikipedia.org/wiki/Sea_icehttp://en.wikipedia.org/wiki/Extreme-weatherhttp://en.wikipedia.org/wiki/Extreme-weatherhttp://en.wikipedia.org/wiki/Extreme-weatherhttp://en.wikipedia.org/wiki/Heat_wavehttp://en.wikipedia.org/wiki/Heat_wavehttp://en.wikipedia.org/wiki/Heat_wavehttp://en.wikipedia.org/wiki/Ocean_acidificationhttp://en.wikipedia.org/wiki/Ocean_acidificationhttp://en.wikipedia.org/wiki/Ocean_acidificationhttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Climate_change_and_agriculturehttp://en.wikipedia.org/wiki/Climate_change_and_agriculturehttp://en.wikipedia.org/wiki/Climate_change_and_agriculturehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Battisti-12http://en.wikipedia.org/wiki/Global_warming#cite_note-Battisti-12http://en.wikipedia.org/wiki/Global_warming#cite_note-Battisti-12http://en.wikipedia.org/wiki/Climate_refugeehttp://en.wikipedia.org/wiki/Climate_refugeehttp://en.wikipedia.org/wiki/Climate_refugeehttp://en.wikipedia.org/wiki/Ecosystem_serviceshttp://en.wikipedia.org/wiki/Ecosystem_serviceshttp://en.wikipedia.org/wiki/Ecosystem_serviceshttp://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-13http://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-13http://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-13http://en.wikipedia.org/wiki/Mitigation_of_global_warminghttp://en.wikipedia.org/wiki/Mitigation_of_global_warminghttp://en.wikipedia.org/wiki/Mitigation_of_global_warminghttp://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Geoengineeringhttp://en.wikipedia.org/wiki/Geoengineeringhttp://en.wikipedia.org/wiki/Geoengineeringhttp://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_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/Avoiding_dangerous_climate_changehttp://en.wikipedia.org/wiki/Avoiding_dangerous_climate_changehttp://en.wikipedia.org/wiki/Avoiding_dangerous_climate_changehttp://en.wikipedia.org/wiki/Global_warming#cite_note-15http://en.wikipedia.org/wiki/Global_warming#cite_note-15http://en.wikipedia.org/wiki/Global_warming#cite_note-15http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Global_warming#cite_note-17http://en.wikipedia.org/wiki/Global_warming#cite_note-17http://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-19http://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-19http://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-19http://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-19http://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-19http://en.wikipedia.org/wiki/Global_warming#cite_note-20http://en.wikipedia.org/wiki/Global_warming#cite_note-20http://en.wikipedia.org/wiki/Global_warming#cite_note-20http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://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/United_Nations_Environment_Programmehttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/International_Energy_Agencyhttp://en.wikipedia.org/wiki/Global_warminghttp://en.wikipedia.org/wiki/Global_warminghttp://en.wikipedia.org/wiki/Global_warminghttp://en.wikipedia.org/wiki/Global_warming#Observed_temperature_changeshttp://en.wikipedia.org/wiki/Global_warming#Observed_temperature_changeshttp://en.wikipedia.org/wiki/Global_warming#Observed_temperature_changeshttp://en.wikipedia.org/wiki/Global_warminghttp://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-22http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://en.wikipedia.org/wiki/Global_warming#cite_note-unfccc_2_degrees_celsius_target-22http://en.wikipedia.org/wiki/Global_warming#cite_note-20http://en.wikipedia.org/wiki/Global_warming#cite_note-20http://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-19http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-2011_unfccc_synthesis_of_annex_I_communications-19http://en.wikipedia.org/wiki/Global_warming#cite_note-17http://en.wikipedia.org/wiki/Global_warming#cite_note-17http://en.wikipedia.org/wiki/Global_warming#cite_note-2005_unfccc_synthesis_of_non-annex_I_statements-16http://en.wikipedia.org/wiki/Global_warming#cite_note-15http://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/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/United_Nations_Framework_Convention_on_Climate_Changehttp://en.wikipedia.org/wiki/Geoengineeringhttp://en.wikipedia.org/wiki/Adaptation_to_global_warminghttp://en.wikipedia.org/wiki/Mitigation_of_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-Warren2011-13http://en.wikipedia.org/wiki/Ecosystem_serviceshttp://en.wikipedia.org/wiki/Climate_refugeehttp://en.wikipedia.org/wiki/Global_warming#cite_note-Battisti-12http://en.wikipedia.org/wiki/Climate_change_and_agriculturehttp://en.wikipedia.org/wiki/Extinction_risk_from_climate_changehttp://en.wikipedia.org/wiki/Ocean_acidificationhttp://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-11http://en.wikipedia.org/wiki/Deserthttp://en.wikipedia.org/wiki/Subtropicshttp://en.wikipedia.org/wiki/Precipitation_(meteorology)http://en.wikipedia.org/wiki/Current_sea_level_risehttp://en.wikipedia.org/wiki/Effects_of_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-10http://en.wikipedia.org/wiki/Regional_effects_of_global_warminghttp://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/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-6http://en.wikipedia.org/wiki/Global_warming#cite_note-6http://en.wikipedia.org/wiki/Global_warming#cite_note-4http://en.wikipedia.org/wiki/Global_warming#cite_note-4http://en.wikipedia.org/wiki/Global_warming#cite_note-2http://en.wikipedia.org/wiki/Global_warming#cite_note-2http://en.wikipedia.org/wiki/Deforestationhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Fossil_fuelhttp://en.wikipedia.org/wiki/Greenhouse_gashttp://en.wikipedia.org/wiki/Climate_systemhttp://en.wikipedia.org/wiki/Global_warming#cite_note-AmericasClimateChoices-2011-FullReport-1


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2 Initial causes of temperature changes (external forcings)

o 2.1 Greenhouse gases

o 2.2 Particulates and soot

o

2.3 Solar activity 3 Feedback

4 Climate models

5 Expected environmental effects

o 5.1 Natural systems

o 5.2 Ecological systems

6 Expected social system effects

o 6.1 Food security

o 6.2 Habitat inundation 7 Responses to global warming

o 7.1 Mitigation

o 7.2 Adaptation

o 7.3 Geoengineering

8 Views on global warming

o 8.1 Global warming controversy

o 8.2 Politics

o 8.3 Public opinion o 8.4 Other views

9 Etymology

10 See also

11 Notes

12 Citations

13 References

14 Further reading

15 External links

Observed temperature changes

Main article: Instrumental temperature record
http://en.wikipedia.org/wiki/Global_warming#Initial_causes_of_temperature_changes_.28external_forcings.29http://en.wikipedia.org/wiki/Global_warming#Initial_causes_of_temperature_changes_.28external_forcings.29http://en.wikipedia.org/wiki/Global_warming#Greenhouse_gaseshttp://en.wikipedia.org/wiki/Global_warming#Greenhouse_gaseshttp://en.wikipedia.org/wiki/Global_warming#Particulates_and_soothttp://en.wikipedia.org/wiki/Global_warming#Particulates_and_soothttp://en.wikipedia.org/wiki/Global_warming#Solar_activityhttp://en.wikipedia.org/wiki/Global_warming#Solar_activityhttp://en.wikipedia.org/wiki/Global_warming#Feedbackhttp://en.wikipedia.org/wiki/Global_warming#Feedbackhttp://en.wikipedia.org/wiki/Global_warming#Climate_modelshttp://en.wikipedia.org/wiki/Global_warming#Climate_modelshttp://en.wikipedia.org/wiki/Global_warming#Expected_environmental_effectshttp://en.wikipedia.org/wiki/Global_warming#Expected_environmental_effectshttp://en.wikipedia.org/wiki/Global_warming#Natural_systemshttp://en.wikipedia.org/wiki/Global_warming#Natural_systemshttp://en.wikipedia.org/wiki/Global_warming#Ecological_systemshttp://en.wikipedia.org/wiki/Global_warming#Ecological_systemshttp://en.wikipedia.org/wiki/Global_warming#Expected_social_system_effectshttp://en.wikipedia.org/wiki/Global_warming#Expected_social_system_effectshttp://en.wikipedia.org/wiki/Global_warming#Food_securityhttp://en.wikipedia.org/wiki/Global_warming#Food_securityhttp://en.wikipedia.org/wiki/Global_warming#Habitat_inundationhttp://en.wikipedia.org/wiki/Global_warming#Habitat_inundationhttp://en.wikipedia.org/wiki/Global_warming#Responses_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#Responses_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#Mitigationhttp://en.wikipedia.org/wiki/Global_warming#Mitigationhttp://en.wikipedia.org/wiki/Global_warming#Adaptationhttp://en.wikipedia.org/wiki/Global_warming#Adaptationhttp://en.wikipedia.org/wiki/Global_warming#Geoengineeringhttp://en.wikipedia.org/wiki/Global_warming#Geoengineeringhttp://en.wikipedia.org/wiki/Global_warming#Views_on_global_warminghttp://en.wikipedia.org/wiki/Global_warming#Views_on_global_warminghttp://en.wikipedia.org/wiki/Global_warming#Global_warming_controversyhttp://en.wikipedia.org/wiki/Global_warming#Global_warming_controversyhttp://en.wikipedia.org/wiki/Global_warming#Politicshttp://en.wikipedia.org/wiki/Global_warming#Politicshttp://en.wikipedia.org/wiki/Global_warming#Public_opinionhttp://en.wikipedia.org/wiki/Global_warming#Public_opinionhttp://en.wikipedia.org/wiki/Global_warming#Other_viewshttp://en.wikipedia.org/wiki/Global_warming#Other_viewshttp://en.wikipedia.org/wiki/Global_warming#Etymologyhttp://en.wikipedia.org/wiki/Global_warming#Etymologyhttp://en.wikipedia.org/wiki/Global_warming#See_alsohttp://en.wikipedia.org/wiki/Global_warming#See_alsohttp://en.wikipedia.org/wiki/Global_warming#Noteshttp://en.wikipedia.org/wiki/Global_warming#Noteshttp://en.wikipedia.org/wiki/Global_warming#Citationshttp://en.wikipedia.org/wiki/Global_warming#Citationshttp://en.wikipedia.org/wiki/Global_warming#Referenceshttp://en.wikipedia.org/wiki/Global_warming#Referenceshttp://en.wikipedia.org/wiki/Global_warming#Further_readinghttp://en.wikipedia.org/wiki/Global_warming#Further_readinghttp://en.wikipedia.org/wiki/Global_warming#External_linkshttp://en.wikipedia.org/wiki/Global_warming#External_linkshttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Global_warming#External_linkshttp://en.wikipedia.org/wiki/Global_warming#Further_readinghttp://en.wikipedia.org/wiki/Global_warming#Referenceshttp://en.wikipedia.org/wiki/Global_warming#Citationshttp://en.wikipedia.org/wiki/Global_warming#Noteshttp://en.wikipedia.org/wiki/Global_warming#See_alsohttp://en.wikipedia.org/wiki/Global_warming#Etymologyhttp://en.wikipedia.org/wiki/Global_warming#Other_viewshttp://en.wikipedia.org/wiki/Global_warming#Public_opinionhttp://en.wikipedia.org/wiki/Global_warming#Politicshttp://en.wikipedia.org/wiki/Global_warming#Global_warming_controversyhttp://en.wikipedia.org/wiki/Global_warming#Views_on_global_warminghttp://en.wikipedia.org/wiki/Global_warming#Geoengineeringhttp://en.wikipedia.org/wiki/Global_warming#Adaptationhttp://en.wikipedia.org/wiki/Global_warming#Mitigationhttp://en.wikipedia.org/wiki/Global_warming#Responses_to_global_warminghttp://en.wikipedia.org/wiki/Global_warming#Habitat_inundationhttp://en.wikipedia.org/wiki/Global_warming#Food_securityhttp://en.wikipedia.org/wiki/Global_warming#Expected_social_system_effectshttp://en.wikipedia.org/wiki/Global_warming#Ecological_systemshttp://en.wikipedia.org/wiki/Global_warming#Natural_systemshttp://en.wikipedia.org/wiki/Global_warming#Expected_environmental_effectshttp://en.wikipedia.org/wiki/Global_warming#Climate_modelshttp://en.wikipedia.org/wiki/Global_warming#Feedbackhttp://en.wikipedia.org/wiki/Global_warming#Solar_activityhttp://en.wikipedia.org/wiki/Global_warming#Particulates_and_soothttp://en.wikipedia.org/wiki/Global_warming#Greenhouse_gaseshttp://en.wikipedia.org/wiki/Global_warming#Initial_causes_of_temperature_changes_.28external_forcings.29


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Energy (heat) added to various parts of the climate system due to global warming.

Two millennia of mean surface temperatures according to different reconstructions from climate proxies , each

smoothed on a decadal scale, with th e instrumental temperature record overlaid in black.

Evidence for warming of the climate system includes observed increases in global average air and ocean

temperatures, widespread melting of snow and ice, and rising global average sea level .[26][27][28] The Earth's

average surface temperature , expressed as a linear trend , rose by 0.74 0.18 C over the period 1906 2005.

The rate of warming over the last half of that period was almost double that for the period as a whole

(0.13 0.03 C per decade, versus 0.07 0.02 C per decade). The urban heat island effect is very small,

estimated to account for less than 0.002 C of warming per decade since 1900 .[29] Temperatures in the

lower troposphere have increased between 0.13 and 0.22 C (0.22 and 0.4 F) per decade since 1979,

according to satellite temperature measurements . Climate proxies show the temperature to have been

relatively stable over the one or two thousand years before 1850, with regionally varying fluctuations such as

theMedieval Warm Period and the Little Ice Age .[30]

Recent estimates by NASA's Goddard Institute for Space Studies (GISS) and the National Climatic Data

Center show that 2005 and 2010 tied for the planet's warmest year since reliable, widespread instrumental

measurements became available in the late 19th century, exceeding 1998 by a few hundredths of a

degree .[31][32][33] Estimates by the Climatic Research Unit (CRU) show 2005 as the second warmest year, behind

1998 with 2003 and 2010 tied for third warmest year, however, "the error estimate for individual years ... is at

least ten times larger than the differences between these three years. "[34] The World Meteorological
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ite_note-30http://en.wikipedia.org/wiki/National_Climatic_Data_Centerhttp://en.wikipedia.org/wiki/National_Climatic_Data_Centerhttp://en.wikipedia.org/wiki/Goddard_Institute_for_Space_Studieshttp://en.wikipedia.org/wiki/NASAhttp://en.wikipedia.org/wiki/Global_warming#cite_note-29http://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_(climate)http://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-28http://en.wikipedia.org/wiki/Urban_heat_islandhttp://en.wikipedia.org/wiki/Linear_trendhttp://en.wikipedia.org/wiki/Global_average_surface_temperaturehttp://en.wikipedia.org/wiki/Global_average_surface_temperaturehttp://en.wikipedia.org/wiki/Global_warming#cite_note-27http://en.wikipedia.org/wiki/Global_warming#cite_note-25http://en.wikipedia.org/wiki/Global_warming#cite_note-25http://en.wikipedia.org/wiki/Instrumental_temperature_recordhttp://en.wikipedia.org/wiki/Proxy_(climate)


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Organization (WMO) statement on the status of the global climate in 2010 explains that, "The 2010 nominal

value of +0.53 C ranks just ahead of those of 2005 (+0.52 C) and 1998 (+0.51 C), although the differences

between the three years are not statistically significant... "[35]

NOAA graph of Global Annual Temperature Anomalies 1950 2011, showing the El Nio-Southern Oscillation

Temperatures in 1998 were unusually warm because global temperatures are affected by the El Nio-Southern

Oscillation (ENSO), and the strongest El Nio in the past century occurred during that year .[36] Global

temperature is subject to short-term fluctuations that overlay long term trends and can temporarily mask them.

The relative stability in temperature from 2002 to 2009 is consistent with such an episode . [37][38] 2010 was also

an El Nio year. On the low swing of the oscillation, 2011 as an La Nia year was cooler but it was still the 11th

warmest year since records began in 1880. Of the 13 warmest years since 1880, 11 were the years from 2001

to 2011. Over the more recent record, 2011 was the warmest La Nia year in the period from 1950 to 2011,

and was close to 1997 which was not at the lowest point of the cycle . [39]

Temperature changes vary over the globe. Since 1979, land temperatures have increased about twice as fastas ocean temperatures (0.25 C per decade against 0.13 C per decade) .[40] Ocean temperatures increase

more slowly than land temperatures because of the larger effective heat capacity of the oceans and because

the ocean loses more heat by evaporation .[41] The northern hemisphere warms faster than the southern

hemisphere because it has more land and because it has extensive areas of seasonal snow and sea-ice cover

subject to ice-albedo feedback . Although more greenhouse gases are emitted in the Northern than Southern

Hemisphere this does not contribute to the difference in warming because the major greenhouse gases persist

long enough to mix between hemispheres .[42]

The thermal inertia of the oceans and slow responses of other indirect effects mean that climate can takecenturies or longer to adjust to changes in forcing. Climate commitment studies indicate that even if

greenhouse gases were stabilized at 2000 levels, a further warming of about 0.5 C (0.9 F) would still occur .[43]

Initial causes of temperature changes (external forcings)
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Greenhouse effect schematic showing energy flows between space, the atmosphere, and earth's surface. Energy

exchanges are expressed in watts per square meter (W/m 2).

This graph, known as the Keeling Curve , shows the increase of atmospheri ccarbon dioxide (CO 2) concentrations

from 1958 2008. Monthly CO 2measurements display seasonal oscillations in an upward trend; each year's maximum

occurs during th e Northern Hemisphere 's late spring, and declines during its growing season as plants remove some

atmospheric CO 2.

External forcing refers to processes external to the climate system (though not necessarily external to Earth)

that influence climate. Climate responds to several types of external forcing, such as radiative forcing due to

changes in atmospheric composition (mainl ygreenhouse gas concentrations), changes in solar

luminosity , volcanic eruptions, and variations in Earth's orbit around the Sun .[44]:0 Attribution of recent climate

change focuses on the first three types of forcing. Orbital cycles vary slowly over tens of thousands of years

and at present are in an overall cooling trend which would be expected to lead towards an ice age , but the 20th

century instrumental temperature record shows a sudden rise in global temperatures .[45]

Greenhouse gasesMain articles: Greenhouse gas , Greenhouse effect , Radiative forcing , and Carbon dioxide in Earth's

atmosphere

The greenhouse effect is the process by which absorption and emission of infrared radiation by gases in

the atmosphere warm a planet 's lower atmosphere and surface. It was proposed by Joseph Fourier in 1824

and was first investigated quantitatively by Svante Arrhenius in 1896 .[46]

Naturally occurring amounts of greenhouse gases have a mean warming effect of about 33 C (59 F) .[47][C] The

major greenhouse gases ar e water vapor , which causes about 36 70% of the greenhouse effect; carbon
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dioxide (CO2), which causes 9 26%; methane (CH4), which causes 4 9%; and ozone (O3), which causes 3

7%.[48][49][50] Clouds also affect the radiation balance through cloud forcings similar to greenhouse gases.

Human activity since the Industrial Revolution has increased the amount of greenhouse gases in the

atmosphere, leading to increased radiative forcing from CO 2, methane, tropospheric ozone, CFCs and nitrous

oxide . The concentrations of CO 2 and methane have increased by 36% and 148% respectively since

1750 .[51] These levels are much higher than at any time during the last 800,000 years, the period for which

reliable data has been extracted from ice cores .[52][53][54][55] Less direct geological evidence indicates that

CO 2 values higher than this were last seen about 20 million years ago .[56] Fossil fuel burning has produced

about three-quarters of the increase in CO 2 from human activity over the past 20 years. The rest of this

increase is caused mostly by changes in land-use, particularly deforestation .[57]

Per capita greenhouse gas emissions in 2005, including land-use change .

Total greenhouse gas emissions in 2005, including land-use change.

Over the last three decades of the 20th century, gross domestic product per capita and population growth were

the main drivers of increases in greenhouse gas emissions . [58] CO 2emissions are continuing to rise due to the

burning of fossil fuels and land-use change .[59][60]:71Emissions can be attributed to different regions . The two

figures opposite show annual greenhouse gas emissions for the year 2005, including land-use change.

Attribution of emissions due to land-use change is a controversial issue .[61][62]:289

Emissions scenarios , estimates of changes in future emission levels of greenhouse gases, have been

projected that depend upon uncertain economic, sociological , technological , and natural developments .[63] In

most scenarios, emissions continue to rise over the century, while in a few, emissions are reduced . [64][65] Fossil

fuel reserves are abundant, and will not limit carbon emissions in the 21st century .[66] Emission scenarios,

combined with modelling of the carbon cycle , have been used to produce estimates of how atmospheric

concentrations of greenhouse gases might change in the future. Using the six IPCC SRES "marker" scenarios,

models suggest that by the year 2100, the atmospheric concentration of CO 2 could range between 541 and

970 ppm .[67] This is an increase of 90 250% above the concentration in the year 1750.
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The popular media and the public often confuse global warming with ozone depletion , i.e., the destruction

of stratospheric ozone by chlorofluorocarbons .[68][69] Although there are a few areas of linkage , the relationship

between the two is not strong. Reduced stratospheric ozone has had a slight cooling influence on surface

temperatures, while increased tropospheric ozone has had a somewhat larger warming effect .[70]

Particulates and soot

Ship tracks over the Atlantic Ocean on the east coast of the United States. The climatic impacts from particulate

forcing could have a large effect on climate through the indirect effect.

Global dimming , a gradual reduction in the amount of global direct irradiance at the Earth's surface, was

observed from 1961 until at least 1990 .[71] The main cause of this dimming is particulates produced by

volcanoes and human made pollutants , which exerts a cooling effect by increasing the reflection of incoming

sunlight. The effects of the products of fossil fuel combustion CO 2 and aerosols have largely offset one

another in recent decades, so that net warming has been due to the increase in non-CO 2 greenhouse gases

such as methane .[72] Radiative forcing due to particulates is temporally limited due to wet deposition whichcauses them to have an atmospheric lifetime of one week. Carbon dioxide has a lifetime of a century or more,

and as such, changes in particulate concentrations will only delay climate changes due to carbon dioxide . [73]

In addition to their direct effect by scattering and absorbing solar radiation, particulates have indirect effects on

the radiation budget .[74]Sulfates act as cloud condensation nuclei and thus lead to clouds that have more and

smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger

droplets, known as the Twomey effect .[75] This effect also causes droplets to be of more uniform size, which

reduces growth of raindrops and makes the cloud more reflective to incoming sunlight, known as th e Albrecht

effect .[76]

Indirect effects are most noticeable in marine stratiform clouds, and have very little radiative effect onconvective clouds. Indirect effects of particulates represent the largest uncertainty in radiative forcing . [77]

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 the surface. In isolated areas with high soot

production, such as rural India, as much as 50% of surface warming due to greenhouse gases may be masked

by atmospheric brown clouds .[78] When deposited, especially on glaciers or on ice in arctic regions, the lower
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ollutanthttp://en.wikipedia.org/wiki/Global_warming#cite_note-70http://en.wikipedia.org/wiki/Irradiancehttp://en.wikipedia.org/wiki/Global_dimminghttp://en.wikipedia.org/wiki/Ship_trackshttp://en.wikipedia.org/wiki/Global_warming#cite_note-69http://en.wikipedia.org/wiki/Tropospheric_ozonehttp://en.wikipedia.org/wiki/Ozone_depletion#Ozone_depletion_and_global_warminghttp://en.wikipedia.org/wiki/Global_warming#cite_note-67http://en.wikipedia.org/wiki/Global_warming#cite_note-67http://en.wikipedia.org/wiki/Stratospherehttp://en.wikipedia.org/wiki/Ozone_depletion


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surface albedo can also directly heat the surface .[79]The influences of particulates, including black carbon, are

most pronounced in the tropics and sub-tropics, particularly in Asia, while the effects of greenhouse gases are

dominant in the extratropics and southern hemisphere .[80]

Satellite observations of Total Solar Irradiance from 1979 2006.

Solar activityMain articles: Solar variation and Solar wind

Solar variations causing changes in solar radiation energy reaching the Earth have been the cause of

past climate changes .[81] The effect of changes in solar forcing in recent decades is uncertain, but small, with

some studies showing a slight cooling effect ,[82] while others studies suggest a slight warming effect .[44][83][84][85]

Greenhouse gases and solar forcing affect temperatures in different ways. While both increased solar activity

and increased greenhouse gases are expected to warm the troposphere , an increase in solar activity should

warm the stratosphere while an increase in greenhouse gases should cool the

stratosphere .[44]

Radiosonde (weather balloon) data show the stratosphere has cooled over the period sinceobservations began (1958), though there is greater uncertainty in the early radiosonde record. Satellite

observations, which have been available since 1979, also show cooling .[86]

A related hypothesis, proposed by Henrik Svensmark , is that magnetic activity of the sun deflects cosmic

rays that may influence the generation of cloud condensation nuclei and thereby affect the climate .[87] Other

research has found no relation between warming in recent decades and cosmic rays .[88][89] The influence of

cosmic rays on cloud cover is about a factor of 100 lower than needed to explain the observed changes in

clouds or to be a significant contributor to present-day climate change .[90]

Studies in 2011 have indicated that solar activity may be slowing, and that the next solar cycle could be

delayed. To what extent is not yet clear; Solar Cycle 25 is due to start in 2020, but may be delayed to 2022 or

even longer. It is even possible that the Sun could be heading towards another Maunder Minimum . While there

is not yet a definitive link between solar sunspot activity and global temperatures, the scientists conducting the

solar activity study believe that global greenhouse gas emissions would prevent any possible cold snap . [91]
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a historic step in the right direction for clean air

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