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TEXT BOOK
Variations in Earth’s Albedo Approximately 30% of theSun’sradiationisreflected back intospace •Albedo variesbasedonsurfacematerials • Snow and Ice havehigh albedos • Darkersurfaceshavelower albedos •Climatefeedback: conversion of high albedo snow and ice to lower albedo surfaces
Global ClimateChangePhysicalGeology 15/e, Chapter 21
Weather– describes whattheatmosphereisdoingover short timescalesClimate– theaverageweatherpattern in a regionoverlongperiods of time AnthropogenicClimateChange– climatechangerelated to human activitiesConcernsOver Modern ClimateChange •Rapid rate of climatechangemakesadaptabilitylesslikely •Increased human populationlimitstheability of humans to easilymoveawayfromproblems
Composition– theatmosphereiscomposed of manydifferent gases •Nitrogen and oxygen: >99% in cleandry air •Argon, carbondioxide, neon, helium, water vapor (0.0001 – 4%) Structure– atmospheredividedinto 4 layers •Troposphere: lowestlayer •Stratosphere: ozone layeroccurshere •Mesosphere •Thermosphere: alsocalledtheionosphere
EnergyfromtheSun– Earth’sprimarysource of energy (electromagneticradiation) •Albedo: percentage of radiationreflectedfromthesurfaceBlackbodyradiation– theintensity and wavelength of emittedelectromagneticradiation •Infraredradiation: terrestrialradiationorlong-wave radiationTheGreenhouseEffect– keepEarthwarm •Greenhouse gases absorblong-wave radiation •Heatsatmosphere •Act as a blanket
Earth’saverageclimateisdeterminedbyitsradiative balance •Amount of energyenteringtheEarthsystem •Amount of solar energy absorbed bytheEarthsystem •Amount of long-wave radiationemitted to space Solar Variability and the Orbital Theory of Climate •Amount of solar energyreachingEarthvaries •MilankovitchTheory • Orbital Eccentricity, Axial Obliquity and Axial Precession determine input and distribution of solar radiationoverlong time scales. •SunspotCycle
Variations in Earth’s Albedo Approximately 30% of theSun’sradiationisreflected back intospace •Albedo variesbasedonsurfacematerials • Snow and Ice havehigh albedos • Darkersurfaceshavelower albedos •Climatefeedback: conversion of high albedo snow and ice to lower albedo surfaces
Greenhouse gases– eachdifferent gas has a differentability to affectEarth’sclimate •Eachgreenhouse gas absorbsradiationwithvaryingefficiencies •Atmosphericlifetime: eachgreenhouse gas survives in theatmospherefordifferentamounts of time •Global WarmingPotential: a relativemeasure of each gases ability to trapheat in theatmosphereClouds and particles •Aerosols – smallparticles suspended in theatmosphere •Cloud droplets and aerosolsreflectapproximately 23% of incident solar radiation back to spaceVolcanoes– releasesparticles and gases intotheatmospherePlatetectonics– alterssurface albedo and oceancirculationovermillion-yeartimescales
Paleoclimatology— thestudy of ancientclimatesClimateMillions of YearsAgo •Prior to 2.6 millionyearsagotemperatures and CO2 levelswerehigher •CO2 levelsreconstructedfromisotopiccontent of carbon in fossils and density of plantstomataClimateOvertheLastMillionYears •TheMilankovitchTheory • Oxygenisotopes in foraminiferacorrelate to pasttemperatures and revealed a clearperiodicity in accordancewithMilankovitch •Ice Coresreveal CO2 variations; CO2 variationscorrelatecloselywithtemperature •Majorchanges in temperatureshavevariedon 100,000 yearcyclesthatcorrelate to periods of glaciation and subsequentwarmerinterglacialperiods
Paleoclimatology— thestudy of ancientclimatesClimateOvertheLastFewThousandYears to Present •Last glacial maximumendedabout 15,000 yearsagodue to orbital variationforces and amplifiedbychanges in CO2 and methaneconcentrations •Severalproxies are used to assesstemperaturevariations • Boreholethermometry – measuringtemperaturesdeep in theground to inferwhattemperaturesmusthavebeen in thepast • TreeRings and DirectMeasurement •Global temperaturesbegan to risesubstantially at time of industrial revolution
Temperature •Increasedapproximately 0.74 degrees Celsius between 1901 and 2012 •Rate of increaseisincreasing •However, global mean temperatureshavebeenconstantoverthelastdecade •Computermodelssuggestthatwarmingisdue to greenhouse gases Precipitation – increasing regional differences Sea Ice & Glacier Melt – decreasing sea ice, increasing glacial melting Sea-LevelRise – melting of glaciers and ice sheetsresponsiblefor a 0.19 m risebetween 1901 and 2010
Earth’sclimateiscomplex and challenging to predict Global-scalecomputermodelsindicatethatincreases in greenhouse gas concentrations are responsibleforthevastmajority of warmingoverthelastcenturyThe IPCC Intergovernmental Panel onClimateChange •2013 reportconcludedthat “Warming of theclimatesystemisunequivocal” and that “Human influenceontheclimatesystemisclear…”
Biodiversity and Agriculture •Biodiversity – could be reduced as habitatsbecome more limited. •Agriculture – cropsbecome more susceptible to extreme weathereventsOceanAcidification—as more CO2 dissolves in theocean, theoceanwillbecome more acidicCoastalregions and Sea Levelrise •>600 millionpeoplelive
GeoengineeringLarge-scaleintentionalefforts to modifyEarth’sclimate •Solar Radiation Management • Reflecting more back intospace • Should be consideredtemporaryfixes •Carbon Management • Acceleratingthereduction of CO2 concentrations • Carbon Capture and Sequestration: capture and storage of CO2
Futurereductionsmustinclude: • Reducing use of fossilfuelsbyincreasingefficiency • Switch to alternativeenergysources • Wide-spread usage of low-energyappliances • Cultural shifts to reduce demandforenergy and natural resourcesisdecreasedFate of AtmosphericCarbonDioxide • DifferentProcessesremove CO2 onvarious time-scales • Uptakebythelandbiosphere • Dissolutionintotheoceans • Reactionwithcalcium carbonate ScientificConsensus • Link betweengreenhouse gases and planetarytemperaturesiswellestablished • Broadagreementthatnegativeconsequences are alreadybeingfelt and willcontinuewithoutaction
