Thehumaninfluenceonextremeheatwavesisclear(Minetal.2013;Zwiersetal.2011).TheunusuallyhottemperaturesinCaliforniainAugust2020areacaseinpoint.BelowisanattributionstatementabouthowclimatechangehascurrentlyaffectedtheCalifornia2020heatwaveaswellassomeprojectionsofhowmuchclimatechangewillfurtherincreasetheseverityofCaliforniaheatwaves.

Currently,climatechangehascausedrareCaliforniaheatwavestobe3to4degreeswarmer(adaptedfromWehneretal2018usingthehighresolutionversionofCAM5.1describedinWehneretal.2014)

InthefuturedirectlyfromTebaldiandWehner2018(notethattemperaturecolorscalesarealldifferent:

Undereitheralow(rcp4.5)orhigh(rcp8.5)emissionsscenarios,Californiaheatwaveswouldbe0.5to1degreeFahrenheitwarmerattheendofthedecade.

Undertheloweremissionsscenario,Californiaheatwaveswouldbeabout2degreesFahrenheitwarmeratmid-century(2050).

Underthehigheremissionsscenario,Californiaheatwaveswouldbeabout3degreesFahrenheitwarmeratmid-century(2050).

Undertheloweremissionsscenario,Californiaheatwaveswouldbeabout3degreesFahrenheitwarmeratlate-century(2080).

Underthehigheremissionsscenario,Californiaheatwaveswouldbeabout5degreesFahrenheitwarmeratlate-century(2080).

References:MichaelF.Wehner,KevinReed,FuyuLi,Prabhat,JulioBacmeister,Cheng-TaChen,ChrisPaciorek,PeterGleckler,KenSperber,WilliamD.Collins,AndrewGettelman,ChristianeJablonowski(2014)TheeffectofhorizontalresolutiononsimulationqualityintheCommunityAtmosphericModel,CAM5.1.JournalofModelingtheEarthSystem06,980-997.doi:10.1002/2013MS000276MichaelWehner,DáithíStone,HideoShiogama,PiotrWolski,AndrewCiavarella,NikolaosChristidis,HarinarayanKrishnan(2018)Early21stcenturyanthropogenicchangesinextremelyhotdaysassimulatedbytheC20C+DetectionandAttributionmulti-modelensemble.SpecialC20C+issueofWeatherandClimateExtremes201-8.https://doi.org/10.1016/j.wace.2018.03.001

ClaudiaTebaldiandMichaelWehner(2018)BenefitsofmitigationforfutureheatextremesunderRCP4.5comparedtoRCP8.5.ClimaticChange.146,349-361.DOI:10.1007/s10584-016-1605-5

Seung-KiMin,XuebinZhang,FrancisZwiers,HideoShiogama,Yu-ShiangTung,andMichaelWehner(2013)Multi-ModelDetectionandAttributionofExtremeTemperatureChanges,JournalofClimate26,7430–7451.doi:http://dx.doi.org/10.1175/JCLI-D-12-00551.1

Zwiers,F.W.,X.Zhang,andY.Feng,2011:AnthropogenicInfluenceonLongReturnPeriodDailyTemperatureExtremesatRegionalScales.J.Climate,24,881–892,https://doi.org/10.1175/2010JCLI3908.1.

ThesestatementsaremyownscientificopinionanddonotnecessarilyreflectthepositionsoftheLawrenceBerkeleyNationalLaboratory,theUniversityofCalifornianortheUSDepartmentofEnergy.August20,2020MichaelWehnerSeniorScientistComputationalResearchDivisionLawrenceBerkeleyNationalLaboratory