i. i.climate change – greenhouse gases a. a.background greenhouse effect gases absorb heat natural...

Download I. I.Climate Change – Greenhouse Gases A. A.Background Greenhouse Effect Gases absorb heat Natural Greenhouse Effect Mean planetary temperature = 15 o

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  • Climate Change Greenhouse Gases

    BackgroundGreenhouse EffectGases absorb heatNatural Greenhouse EffectMean planetary temperature = 15 oC vs. -6 oCEnhanced Greenhouse EffectDue to GHGs emitted from human activityGreenhouse GasesMost important GHG is water vaporAccounts for ~50% of natural GHE

  • Greenhouse Gases

  • http://calspace.ucsd.edu/virtualmuseum/climatechange2/07_2.shtml

  • Climate Change Greenhouse Gases

    Greenhouse GasesLong residence times indicate atmospheric concentrations will remain high even if emissions stopOther factors besides GHGs may influence global climate

  • Climate Change Other Factors

    Cloud CoverReflects incoming radiationDifficult to estimate in climate modelsEffects vary in relation to altitude, thickness, compositionAtmospheric DustImportant factor in cool period from 1930s to 1960sOverwhelmed effects of rising CO2 during this periodProduced by volcanic eruptions, dust from areas experiencing droughtCool period following eruption of Mt. Pinatubo in 1992Mechanism behind Nuclear Winter scenario

  • Climate Change Other Factors

    SunspotsMay affect amount of incoming radiationSolar output varies sunspots, solar flaresSunspots are magnetic storms that appear as dark patches on suns surfaceNumber and size are maximal every 11 yearsSolar output ca. 0.1% higher than normal during maxima

  • http://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml

  • Climate Change Other Factors

    SunspotsMay affect amount of incoming radiationSolar output varies sunspots, solar flaresResearchers have correlated minima with Little Ice Age in Europe during 17th and early 18th centuries when sun was 0.25% dimmer than normal20th century dominated by sunspot maximaSome predictions that 21st century will see minimaEstimated that sunspot variability may have contributed to half of 0.55 oC warming since 1860 and one third of warming since 1970 (Lean et al.)

  • http://calspace.ucsd.edu/virtualmuseum/climatechange2/06_3.shtml

  • Climate Change Other Factors

    VolcanismAffects water vapor, particles, sulfides, nitratesGenerally leads to planetary coolingTheory about extinctions at P/T & K/T boundariesMt. St. Helens and Mt. Pinatubo eruptions caused planetary cooling, and those were small eruptionsPhotosynthesis & TranspirationAffect CO2, water vaporAs [CO2] rises, some plantsPhotosynthesize more rapidlyGrow fasterIncorporate more CO2 into biomassKeep their stomata open lessTranspiration releases water vapor into atmosphereLess transpiration when [CO2] is higher (stomata)

  • Climate Change Other Factors

    Soil CharacteristicsAffect heat capacity and retentionMore hydrated soil leads toDarker color (less reflective)More heat capacity (high heat capacity of water)Albedo (Reflectivity)Earths surface varies considerably (mean = 0.30-0.36)Ice/Snow highly reflective (0.9)Clouds vary in reflectivityLand generally less reflectiveChanges in land use affect albedoDesertification increases albedoForest 0.12Grassland 0.19Desert 0.30

  • Climate Change Other Factors

    Wind PatternsAffect atmospheric circulation and heat fluxAffect circulation of oceans and lakesWind mixes warm water down and brings cooler, nutrient-rich water to surfaceMay affect photosynthesis & removal of CO2 from atmosphereEx El Nio results from changes in wind patternsAstronomical FactorsEarths axis precesses on a 26,000 year cycleAxial tilt varies on a 41,000 year cycleOrbital eccentricity has a 100,000 year cycleCorrelated with glacial periods over past 750,000 years

  • http://www.clearlight.com/~mhieb/WVFossils/ice_ages.html

  • Climate Change Other Factors

    Many factors affect global climate in multiple waysEx Clouds absorb re-radiated long-wavelength radiation but also may reflect incoming short-wavelength radiationNet effect is coolingEx Particles in the atmosphere reduce the re-radiation of long-wavelength radiation but also reflect incoming short-wavelength radiationNet effect is probably warming at low levels but cooling at high levels (e.g. following a large volcanic eruption)Uncertainty about impact of many factors

  • IPCC AR4

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