HOW IS OUR CLIMATE CHANGING? AscientistexaminesdataattheNASAGoddardSpaceFlightCenter

Record-breakingheat,prolongeddrought,wildfires,extremeweatherandflooding,sealevelrise,evenoceandeadzones…allofthesetrendswerepredictedbyclimatescientistsdecadesagoandtheyhavenowbecomeareality.Wearelivinginwhatmanyexpertsnowcallthe“Anthropocene”—anewgeologicepochinwhichhumanactivityistheprimarydriverofchangesonPlanetEarth,includingthegreatestchangeofall—globalwarming.Herearethe9mostimportantfactsyouneedtoknowaboutourchangingclimate.

THEWORLDISGETTINGHOTTER

Globalsurfacetemperaturesareontherise.Thisismeasuredby“anomalies,”ordifferencebetweenmeasuredtemperaturesvs.the20thcenturyaverageforcombinedlandandseasurfacetemperatures

(picturedabovecourtesyofNASA).9ofthe10hottestsummerseverrecordedhaveoccurredsince2002.Justlastyear,Australia’sBureauofMeteorologyhadtoaddanewcolor(neonpurple)totheirforecastcharts(54-56degreesC)duetocontinuedrecordheat.Thesetemperatureextremesarearesultofjust0.85°Cinglobaltemperaturerise.Mostexpertsbelievewehavelockedinatleast1.5degreesintemperaturefromthecarbonpollutionwehavealreadyemitted,andwearefastapproachingthedangerousclimatethresholdofa2°Criseintemperaturerise.

THEICEISMELTING.

ArcticSeahasbeendecreasingdramaticallyinthepastthreedecades.Between1900and1980,theextentofArcticicemeasuredinSeptemberheldconstantatapproximately8.5millionsquarekilometers.Sincethenithasdroppedfarfasterthaneventhemostextremescientificprojections—fallingbelow5millionkilometers.Thesamephenomenonisbeingdocumentedfornearlyallof160,000mountainglaciers,likeMt.Kilimanjarowhichhasdecreased80%inthepastcenturyandwilllikelydisappearwithinthenextdecade.InAugustofthisyear,theseaicedisappearedatanaveragerateofabout35,400squaremiles(91,700squarekilometers)perday—orabouttwiceasfastasnormal,NSIDCscientistssay.Scientiststhinktheoldrecord—1.61millionsquaremiles(4.17millionsquarekilometers)onSeptember18,2007—wasmadepossiblebya"perfectstorm"ofconditionsthatincludedanunusuallypersistentweatherpatternknownasananticyclone,orhigh-pressureridge,intheregionthatledtoclearskies,whichallowedmoresunlighttoreachtheiceandmeltit.Butweirdweatherdoesn'tseemtobeafactorthistimearound."There'snopersistentweatherpatternthat'semergedthissummer,"Stroevesaid."Theiceisjustthinnerthanitusedtobe.Soitdoesn'treallymattersomuchwhatthesummerweatherdoesanymore—thethinicemeltsouteasierduringthesummermeltseason."

Inanewstudy,detailedrecentlyinthejournalGeophysicalResearchLetters,StroeveandhercolleaguesanalyzednearlytwodozencomputerclimatemodelstodeterminetheextenttowhichglobalwarmingisresponsiblefortheincreasingshrinkageofArcticseaice.Herteamdeterminedthathumanactivitycanbeblamedforsome60percentoftheobservedrateofdeclinesince1979,withtherestduetonaturalclimatevariability."Ifyouruntheseclimatemodelsandyoudon'tputintheobservedrecordofgreenhousegases,noneofthemshowtheicedeclining,"Stroevesaid."Noneofthemareabletocapturewhat'shappeningtodaywithoutincludinggreenhousegases."(Learnaboutthegreenhouseeffect.)ClimatemodelsusedbytheIntergovernmentalPanelonClimateChange(IPCC)alsopredictthatArcticsummerswillbecompletelyfreeofseaiceinthecomingdecadesifglobalwarmingcontinuesunabated.

LESSICEMEANSMOREHEAT.

Icenotonlyregulatesglobaltemperatures,italsoreflectssunlightbackouttospace.Sothemoreicethatmelts,themorethedarksurfacesoftheoceanandgroundareexposed.Thesedarkersurfacesabsorbheatinsteadofreflectingit,creatingaviciouscyclethatputsevenmoreheatintotheoceansandincreasestheglobalwarmingeffect.Injustthepast5years,therateoficevolumelosshasaccelerateddramatically—doublinginGreenlandandtriplinginWestAntarctica.

WhenAmericangeologistUlyanaHorodyskyjsetupaminiweatherstationat5,800monMountHimlung,ontheNepal-Tibetborder,shelookedeasttowardsEverestandwasshocked.Theworld'shighestglacier,Khumbu,wasturningvisiblydarkerasparticlesoffinedust,blownbyfiercewinds,settledonthebright,freshsnow."One-week-oldsnowwasturningblackandbrownbeforemyeyes,"shesaid.

TheproblemwasevenworseonthenearbyNgozumpaglacier,whichsnakesdownfromChoOyu–theworld'ssixthhighestmountain.There,Horodyskyjfoundthatsomuchdusthadbeenblownontothesurfacethattheabilityoftheicetoreflectsunlight,aprocessknownasalbedo,dropped20%inasinglemonth.Thedustthatwasdarkeningthebrilliantwhitenessofthesnowwasheatingupinthestrongsunandmeltingthesnowandice,shesaid.

Thephenomenonof"darksnow"isbeingrecordedfromtheHimalayastotheArcticasincreasingamountsofdustfrombaresoil,sootfromfiresandultra-fineparticlesof"blackcarbon"fromindustryanddieselenginesarebeingwhippedupanddepositedsometimesthousandsofmilesaway.Theresult,sayscientists,isasignificantdimmingofthebrightnessoftheworld'ssnowandicefields,leadingtoalongermeltseason,whichinturncreatesfeedbackwheremoresolarheatisabsorbedandthemeltingaccelerates.

THESEASARERISING.

Oceanshaveabsorbedmorethan93%oftheincreasedheatfromglobalwarming.Theheatcontentoftheoceanshasmultiplied5-foldsince1980,causing“thermalexpansion,”whichaccountsforroughlyhalfoftotalsealevelrise.Theotherhalfisduetomeltingglaciersandpolarice.Thiscombinationhasalreadyproduced19cmofsealevelrisesincetheyear1900.Andit’sincreasingquickly–3timesfasterinthepasttwodecadesthanthecenturyaverage.Currentmodelspredictbetween8-48cm(7-19inches)ofsealevelriseby2050(relativeto2000levels)andmorethandoublethatbytheendofthecentury.Thiswillplacecoastalcommunitiesaroundtheworldatriskofextremeflooding.ReadMore»

The ocean is coming for us. Global sea levels are now rising by 3.4 millimeters per year, up from an average rate of 1.4 mm per year last century. In just 80 years, the ocean could be a full 1.3 meters (4.3 feet) taller than it is today.

That kind of planetary sea change can be hard to fathom — unless you live in a low-lying place like Miami, the Maldives or the Marshall Islands, where the effects of sea-level rise are already apparent. But within just a few decades, the problem will become unavoidable in major coastal cities around the world, from New Orleans, New York and Amsterdam to Calcutta, Bangkok and Tokyo.

We all know why this is happening. Rising seas are one of the most salient effects of man-made climate change, triggered by thermal expansion of seawater as well as the influx of melting glaciers. Yet many people still see it as a distant risk, failing to grasp how (relatively) quickly the sea is swallowing shores worldwide. And since half of all humans now live within 60 kilometers (37 miles) of a coast, this isn't a niche issue.

OCEANSAREACIDIFYING.

Oceansabsorbmorethan1/4ofalltheCO2pollutionemittedeachyear,andthisischangingtheverychemistryoftheoceans.Oceanacidityhasincreased30%since1700,andwilllikelydoublebytheendofthecentury,arateofchange10xgreaterthananythingseeninthelast50Myears.Thisiswreakinghavoconthecalcifiers(animalsthatneedcalciumtomakeshells)andcorals,whichprovidethespawninggroundforapproximately25%ofallmarinespecies(PDF).Moreacidicoceansthreatentheveryfoundationofthemarinefoodchainandthefisheriesthatfeedmorethan3billionpeople.

JETSTREAMSARECHANGING.Thearcticiswarmingtwiceasfastasthemid-latitudes,andsomeexpertsbelievethiscouldbeaffectingthePolarJetStream–theundulatingriverofairinouratmospherethatdrivesweatherpatternsinthenorthernhemisphere.Whenthejetstreamswingsnorthitpullswarmairupfromthetropics,andwhen

itswingssouthitpullsdowncoldairfromtheArctic.Thejetstreamflowswesttoeastbutitcanget“trapped,”causingunusualphenomenalikethe“polarvortex”whichrecentlybuiltupalargeandprolongedzoneofarcticairintheMidwesternU.S.Injustthepastdecade,thenumberoftrappedwaveshasdoubled,leadingtomorefrequentandmoreextremeweatherfronts.

Arctic warming is altering the heat balance between the North Pole and the equator, which is what drives the strong current of upper level winds in the northern hemisphere commonly known as the jet stream. Some studies show that if that balance is altered then some types of extreme weather events become more likely to occur.

During the past week, while much of North America has seen frigid temperatures, weather maps show a strip of orange and red hues, indicating above-average temperatures, across parts of the Arctic, Scandinavia, Europe and Asia.

Visualization of winds at the jet stream level on January 6, showing a deep dip or trough in the jet stream above the U.S., transporting Arctic air southward. Click image to enlarge. Credit: Earth/Cameron Beccario. The forecast high temperature in Fairbanks, Alaska, on Monday was in the 20s Fahrenheit — warmer than many locations in Georgia and Alabama. That fits in with the so-called “Arctic Paradox” or “Warm Arctic, Cold Continents” pattern that researchers first identified several years ago. Such patterns bring comparatively mild conditions to the Arctic while places far to the south are thrown into a deep freeze.

HURRICANESAREINTENSIFYING

ScientistsstudyingtheAtlanticOceannowknowthereisastrongcorrelationbetweenthesurfacetemperatureoftheoceanduringthesummerandtheintensityoftropicalstorms.Thewarmertheoceans,themoreenergystormshaveastheyformintheAtlantic.Thiscouldaccountinpartforthedramaticincreaseinmajorhurricanes(greaterthanCategory3)overthepast20years.BasedonrecordsfromtheHurricaneDatabase(HURDAT)intheperiodfrom1900-1980majorhurricanesoccurredanaverageof2peryear,butintheperiodsince1980theaveragehastripledtomorethan6peryear.Thebehaviorofthesestrongesthurricanesiscritical,sincetheydomostofthedamageweobserve.Overthepastcentury,Category3-5hurricanesdid85%ofUShurricanedamage,despiterepresentingonly24%ofU.S.landfallingstorms.Globalsealevelriseoverthepastdecadehasbeenaboutdoublewhatitwasinthe20thcentury,andtherateofsealevelriseisexpectedtoaccelerate.Stormsurgedoesthemajorityofdamageinmajorhurricanes,andstormsurgesridingontopofhighersealevelsaregoingtodoalotmoredamageinthecomingdecades.Wecanalsoaddontothattheincreaseinhurricanerainfallof20%expectedby2100,whichwillsharplyincreasedamagesduetofreshwaterriverflooding.

RIVERSAREFLOODING.

Warmeraircanholdmorewatervapor,andwhenallthatwatervaporcondensesintheatmosphere,itcreatesmoreintensebutlessfrequentdownpoursofrain,makingwetareaswetter.AsimilarphenomenonistriggeredbynaturallyoccurringElNinoevents,butunlikeElNinowhichpushesstormstowardsthetropics,globalwarmingpushesstormstowardshigherlatitudes.Thiscouldexplainwhyinthepastdecadetherehasbeena70%increaseofheavydownpoursinU.S.Northeastregion.Becausewatervaporitselfactslikeagreenhousegas,aviciouscycleiscreated—moremoisturemeansmoreheatwhichcreatesevenmoremoisture.ThevisualizationabovebyNOAAshowshowthispatternwillresultinintensifyingprecipitation(darkerblue)throughtheyear2100.

WATERISVANISHING.

Manyoftheworld’sgreatriversarefedbyglaciersandmountainsnowpack.Increasedtemperaturesmeanslesssnowandiceandincreasedevaporation.ThisisparticularlyworrisomeforaridregionsliketheAmericansouthwest,northernAfrica,andwesternChina,whichrelyonglacierandsnowmelttofilltheirrivers,replenishingwatersupplies.Anewreportindicatestherecord-breakingdroughtinCaliforniaandnorthernMexicomaybethewarm-upactfora“megadrought”lastingmorethan30years.TheSierrasnowpack(typicallyproviding1/3oftheState’swatersupply)isatitslowestlevelsinrecordedhistory,andtheColoradoRiverisatitslowestflowratein1200years,threateningthewatersupplyfor40millionpeople.LakeOrovilleshowsjusthowquicklyourwatercandisappear.