TitleCollaborators*DemoEnergy Balance Theory of Climate ChangeAerosol vs GHG forcingForcing bargraphA-Train configurationCurrent paradigm –detection and attribution summaryRecast in premisesPremise 1: Initially self-evidentPremise 2: DetectionPremise 2: DetectionPremise 3: Attribution (to human causes)Global warming forecast in context of temperature recordPremise 1: Re-examinedPremise 1: Re-examinedstatistical sum of IPCC bar graphB&H: aerosol dominates uncertaintyTwo independent methodsForward calculation – CTM resultshuttle photo: hi resTwo independent methodsAerosol forcing estimates - refsAerosol forcing estimates - resultsApplications - referencesIPCC attributionCurrent paradigm –sidenote on attribution Hansen 1981IPCC forcing projectionThe Figure: where we standDiscussionConclusions - attributionHansen 87 -predictionHansen 87 – prediction closeupHansen 87 – prediction and actualTitleAerosol Forcing and Causal Attribution of 20th Century WarmingTad AndersonAtmospheric Sciences, University of WashingtonMarch 2, 2004Collaborators*Bob Charlson, University of WashingtonSteve Schwartz, Brookhaven National LabReto Knutti, University of BernOlivier Boucher, University of LilleHenning Rodhe, Stockholm UniversityJost Heintzenberg, IfT, Leipzig* aerosol researchclimate modelingmathematics/inverse modelingDemoDemonstration•generation of particles from gases• scattering of visible light by particlesEnergy Balance Theory of Climate ChangeEquilibrium (stable global-mean temperature)…=EINshortwave, solar energyabsorbed by EarthEOUTlongwave, infrared energy emitted by EarthForced change ...∆Ts= λ∆F∆F: forcing, change in energy balance (W/m2)∆Ts: response, change in surface temperature (K)λ: feedbacks, climate sensitivity {K/(W/m2)}Aerosol vs GHG forcingForcing bargraphKnowledge of climate forcings...Aerosol forcings are extremely uncertain, but . . .A-Train configurationA-Train satellite constellation (2005-2008). . . dramatic progress is coming over the next few years.Current paradigm –detection and attribution summaryWarming of the Earth’s surface…•Is predicted by climate models forced with GHG’s• Has in fact been detected• Match between prediction and observation is sufficiently good that attribution has been claimedCurrent global-warming paradigmConceptual framework for this paradigm:∆T = λ∆F (Eq. 6.1 of IPCC, 2001)∆F: externally imposed change in TOA energy balance (W/m2)∆T: resulting change in surface temperature (K)λ: climate sensitivityRecast in premisesCurrent GW paradigm rests on three, interconnectedpremises:Premise 1: Positive Forcing∆F is positive and of substantial magnitudePremise 2: "Detection"∆T is outside the range of natural variability.Premise 3: "Attribution" to human causes∆T is consistent with current knowledge of ∆F and of the forcing/response relationship as embodied in climate models.Premise 1: Initially self-evident1a. Unequivocal, positive forcing from greenhouse gases.1b. Substantial enough to cause significant warming (according to climate models)Premise 2: DetectionGlobalCooling?GlobalWarming?Premise 2: DetectionPremise 3: Attribution (to human causes)Global warming forecast in context of temperature recordproxyinstrumentaltheory/predictionPremise 1: Re-examined∆Ts= λ ∆FPremise 1: Climate forcing over the industrial era, ∆F, has been positive and substantial in magnitude.Premise 1: Re-examinedKnowledge of forcings as of 2001. What is missing from this graph?Statistical summation of IPCC bar graphstatistical sum of IPCC bar graphreference: Boucher and Haywood, 2001, Clim. Dyn. 18, 297.Easy question: What causes this breadth???B&H: aerosol dominates uncertaintyBoucher and Haywood (cont)Aerosol forcing dominates the uncertainty in total forcing.To evaluate Premise 1, we need to grapple with aerosol forcing.Two independent methodsWe propose a new method of examining Premise 1:• more sensitive and robust than simply summing the forcings• based on a comparison of the two, independent approaches to calculating aerosol forcings1. Forward calculations (study the aerosol)• aerosol mass from chemical transport model• mass-dependent optical and cloud-nucleating propertiesfrom measurements (* our group *)• rapidly advancing satellite data as constraint2. Inverse calculations (fit the T-record)Forward calculationForward calculation – CTM resultModel-estimated direct aerosol forcingsAnthro DustFF OC & BCSulfateBB OC & BCHaywood, J and O Boucher, Revs. Geophys., 38, 513-543, 2000Models: Penner et al., 1998; Grant et al., 1999; Tegen et al., 1996Photo credit: NASA Earth Sciences & Image Analysis Laboratory, Johnson Space CenterAerosol forcing is visible from spaceshuttle photo: hi resTwo independent methodsTesting Premise 1compare two, independent ways of calculating aerosol forcing1. Forward calculations (study the aerosol)2. Inverse calculations (fit the T-record)• assume Premise 1 (i.e. observed warming is the response toa substantial, positive forcing) • multiple runs of simple climate models with varying valuesfor the poorly known input parameters (aerosol forcing,climate sensitivity, ocean heat diffusivity)• assign probabilities based on fit to simplified versions ofthe temperature recordAerosol forcing estimatesAerosol forcing estimates - refsA. Boucher and Haywood, Clim. Dyn. 18, 297 (2001)B. Kiehl et al., JGR, 105, 1441 (2000) (sulfate only)C. Hansen and Sato, Proc. NAS 98, 14778 (2001)D. Hansen et al., Proc. NAS 95, 12753 (1998)E. Schwartz and Andreae, Science 296, 2139 (1996)F. Menon et al., J Atmos Sci 59, 692 (1998) ; Lohmannand Feichter, JGR 102, 13685 (1997) (indirect only)Forward calculations (aerosol-based):Inverse calculations (T-record and climate-model-based):G. Wigley and Raper, Science 293, 451 (2001)H. Harvey and Kaufmann, J. Clim. 15, 2837 (2002)I. Gregory et al., J. Clim. 15, 3117 (2002)J. Andronova and Schlesinger, JGR 106, 22605 (2001)K. Knutti et al., Nature 416, 719 (2002)L. Forest et al., Science 295, 113 (2002)Aerosol forcing estimates - resultsThe comparison is robust method of testing Premise 1** Premise 1: Industrial-era forcing is positive and substantial77%19%forward calcsapplicationsinverse calcsCase A:Boucher andHaywoodAerosol forcing applicationsApplications -referencesApplications in climate studies:M. Crowley, Science 289, 270 (2000) (attribution)N. Mitchell et al., 2001 (IPCC Chap 12) (attribution)O. Cubasch et al., 2001