Causes of climate change
After thousands of studies, the scientific consensus is that it is "unequivocal that human influence has warmed the atmosphere, ocean and land since pre-industrial times.Large amounts of greenhouse gases such as carbon dioxide and methane have been released into the atmosphere through burning of fossil fuels since the industrial revolution.[6]: 450 Further, the warming per unit of greenhouse gases is also affected by feedbacks, such as the changes in water vapor concentrations or Earth's albedo (reflectivity).Thus, both effects are considered to each other out, and the warming from each unit of CO2 emitted by humans increases temperature in linear proportion to the total amount of emissions.[8]: 746 [citation needed] Further, some fraction of the greenhouse warming has been "masked" by the human-caused emissions of sulfur dioxide, which forms aerosols that have a cooling effect.However, this masking has been receding in the recent years, due to measures to combat acid rain and air pollution caused by sulfates.Between the start of the Industrial Revolution in 1750, and the year 2005, the increase in the atmospheric concentration of carbon dioxide (chemical formula: CO2) led to a positive radiative forcing, averaged over the Earth's surface area, of about 1.66 watts per square metre (abbreviated W m−2).[14]: 7 Four main lines of evidence support the dominant role of human activities in recent climate change:[17] Greenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface.[22][23]: 742 Human activity since the Industrial Revolution (about 1750), mainly extracting and burning fossil fuels (coal, oil, and natural gas), has increased the amount of greenhouse gases in the atmosphere, resulting in a radiative imbalance.[33] Additional CO2 emissions come from deforestation and industrial processes, which include the CO2 released by the chemical reactions for making cement, steel, aluminum, and fertiliser.[34] CO2 is absorbed and emitted naturally as part of the carbon cycle, through animal and plant respiration, volcanic eruptions, and ocean-atmosphere exchange.[37] These data, known as the Keeling Curve, have iconic status in climate change science as evidence of the effect of human activities on the chemical composition of the global atmosphere.[39] Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction.The Kyoto Protocol lists these together with hydrofluorocarbon (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6),[43] which are entirely artificial gases, as contributors to radiative forcing.[68] In tropic and temperate areas the net effect is to produce significant warming, and forest restoration can make local temperatures cooler.Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for CO2.[75][76] The rate at which oceans absorb atmospheric carbon will be lowered as they become more acidic and experience changes in thermohaline circulation and phytoplankton distribution.[85] Uncertainty over feedbacks, particularly cloud cover,[86] is the major reason why different climate models project different magnitudes of warming for a given amount of emissions.[98] Similarly, volcanic activity has the single largest natural impact (forcing) on temperature, yet it is equivalent to less than 1% of current human-caused CO2 emissions.
Extreme event attributionglobal warming potentialscientific consensusclimate changegreenhouse effectgreenhouse gasescarbon dioxidemethanefossil fuelsland use changenitrous oxidelogarithmiccarbon sinksfeedbackswater vaporalbedoclimate change feedbacksmaskedsulfur dioxideacid rainair pollutionclimate systemEarth's atmosphereRadiative forcingenergy balanceIndustrial Revolutionchemical formulasurface areapositive feedbacknegative feedbackcouplingEl Niño–Southern Oscillationenergy imbalancephysicalglobal surface temperatureclimate modelsGreenhouse gasGreenhouse gas emissionssunlightradiates it as heatwater vapourclimate sensitivitytropospheric ozoneexternal forcingsnatural gasradiative imbalanceatmosphereconcentrations of CO2Concentrations of methaneglobal warmingequivalent tofluorinated gasesCarbon dioxide in Earth's atmosphereGlobal Carbon ProjectKeeling Curvetransportdeforestationaluminumfertilisercarbon cyclerespirationvolcanic eruptionsCharles David KeelingNational Oceanic and Atmospheric AdministrationEl Niñocome from livestockrice cultivationcoal miningoil and gas extractionKyoto Protocolhydrofluorocarbonperfluorocarbonssulfur hexafluorideemissionspower stationsenteric fermentationfertilizersunlight reaching the Earth's surfaceglobal dimmingsulfatesulfurbunker fuelblack carbonEarth's energy budgetcloud condensation nucleiFood and Agriculture Organizationglaciersdesertsforestsshrublandagricultural landland usecarbon sinkagricultural expansionshifting cultivationloggingwildfiresheat is lost by evaporationforestGreenhouse gas emissions from agriculturemethane emissionsmanurecarbon fixationoverturning circulationwhen they are warmerthermohaline circulationphytoplanktonClimate change feedbackprocess"self-reinforcing" or "positive" feedbacks"balancing" or "negative" feedbackswater-vapour feedbackice–albedo feedbackradiative coolingit can hold more moistureamplification of Arctic temperature changespermafrostwetlandsClimate variability and changeSolar activity and climateClimate change denialFourth National Climate AssessmentIPCC Third Assessment ReportSolar irradiancesatellitestroposphere