“The Pattern Effect”: Sea Surface Temperature modulation of radiative damping and climate sensitivity Cristian Proistosescu JISAO, University of Washington
Equilibrium Climate Sensitivity: First estimate “d oubling of the percentage of CO 2 in the air would raise the temperature of the earth's surface by 5° “
Equilibrium Climate Sensitivity: First estimate “d oubling of the percentage of CO 2 in the air would raise the temperature of the earth's surface by 5° “ Svante Arrhenius (1896)
How have we been doing? Charney likely (1 ) σ Report ECS ( o C)
Uncertainty has been recalcitrant Charney likely (1 ) σ Report ECS ( o C)
Some small measure of progress Charney likely (1 ) σ Report ECS ( o C)
Or not… Charney likely (1 ) σ Report ECS ( o C)
Lines of evidence disagree Changes in “No best estimate for ECS is given because of a Energy Content lack of agreement across lines of evidence“ IPCC 2014 Numerical models (GCMs) Hypotheses: • models are too sensitive • inadequate treatment of observations • they are not measuring the same process What are they measuring? Charney likely (1 ) • Models are run to equilibrium σ Report • Instrumental: We make an inference from present day energy budget ECS ( o C)
Estimates from the instrumental record Consider the energy budget at equilibrium Energy Input Radiative damping (radiative forcing) Δ F 2 × CO 2 Δ R 2 × CO 2 Δ T 2 × CO 2 :black body radiation + atmospheric feedbacks Δ R (clouds, water-vapor, lapse rate, surface albedo)
Estimates from the instrumental record Key physics: radiative feedback & Climate Sensitivity Energy balance Δ R 2 × CO 2 = Δ F 2 × CO 2 Energy Input Radiative damping (radiative forcing) Δ F 2 × CO 2 Δ R 2 × CO 2 Radiative feedback (efficiency of radiative damping) Δ T 2 × CO 2 Δ F 2 × CO 2 λ = Δ R Δ T = Δ T 2 × CO 2 Δ F 2 × CO 2 ECS = λ
Estimates from the instrumental record Inferred Climate Sensitivity Energy balance Δ R = Δ F − Δ Q Energy Input Radiative damping (radiative forcing) Δ R Δ F Radiative feedback (inferred) (efficiency of radiative damping) Δ T λ = Δ R Δ T = Δ F − Δ Q Δ Q Δ T Ocean heat uptake Inferred ECS: Δ T ECS = Δ F 2 × CO 2 Δ F − Δ Q
Estimates from the instrumental record Present day energy budget 2000:2017 - 1850:1870 Δ T Energy Input Radiative damping (radiative forcing) o C Δ R Δ F Δ T HadCRUT4 Δ Q Ocean heat uptake Inferred ECS: Δ T = 0.91 ± 0.1 o C Δ T ECS = Δ F 2 × CO 2 Δ F − Δ Q
Estimates from the instrumental record Present day energy budget Energy Input Radiative damping (radiative forcing) Δ R Δ F Δ T Δ Q Ocean heat uptake Inferred ECS: Δ T = 0.91 ± 0.1 o C Δ T ECS = Δ F 2 × CO 2 Δ Q = 0.61 ± 0.1 W/m 2 Δ F − Δ Q
Estimates from the instrumental record Δ F 2011-1850 Present day energy budget GHGs Energy Input Radiative damping Anthropogenic (radiative forcing) Aerosols Total Δ R Δ F Anthrop. Natural Δ T W/m 2 (IPCC AR5) Δ Q Ocean heat uptake Inferred ECS: Δ T = 0.91 ± 0.1 o C Δ T ECS = Δ F 2 × CO 2 Δ Q = 0.61 ± 0.1 W/m 2 Δ F − Δ Q Δ F = 2.33 ± 0.8 W/m 2 Δ F 2 × CO 2 = 3.7 W/m 2
Estimates from the instrumental record Inferred Climate Sensitivity Count / PDF Count / PDF Count / PDF Inferred ECS: ECS ( o C) Δ T = 0.91 ± 0.1 o C Δ T ECS = Δ F 2 × CO 2 Δ Q = 0.61 ± 0.1 W/m 2 Δ F − Δ Q Δ F = 2.33 ± 0.8 W/m 2 Δ F 2 × CO 2 = 3.7 W/m 2
Equilibrium Climate Sensitivity: Apples to oranges Observations Count / PDF Models ECS ( o C) Estimated from Estimated at Transient Equilibrium
Equilibrium Climate Sensitivity: Time-dependent climate-sensitivity in models: tied to SSTs Model: year 150 ECS ( o C) 4 True ECS 3 Inferred from transient Model: year 20 2 F 2 × CO 2 ECS = 1 λ ( t ) CCSM4 CMIP5 abrupt4xCO2 mean -3 3 Δ SST ( o C) from Proistosescu & Huybers 2017 0 0 50 100 150 Time since CO2 quadrupling Murphy 1995, Senior and Mitchell 2000, Winton et al 2009, Held et al 2010, (years) Armour et al 2013, Andrews et al 2015
Equilibrium Climate Sensitivity: State of the knowledge ECS ( o C) 4 •ECS determined by the net radiative feedback True ECS •Disagreement between numerical models and 3 observations of the Earth’s energy budget Inferred from transient •Radiative feedback has time-dependency tied to SST changes 2 Questions: F 2 × CO 2 ECS = 1 •Can SST-driven changes in feedback account λ ( t ) for the discrepancy? CMIP5 abrupt4xCO2 mean from Proistosescu & Huybers 2017 •What is the underlying physics? 0 0 50 100 150 •How do we empirically constrain radiative Time since CO2 quadrupling feedbacks? (years)
Comparing apples to apples SSTs are different Observations : 2000-1850 Model: year 150 CAM 4 simulations Observations Count / PDF Count / PDF HadSST CCSM4 3 -3 -1.5 1.5 Δ SST ( o C) Δ SST ( o C) Model •We can’t get a true equilibrium from obs (coupled) •But we can get a transient from the models ECS ( o C)
Takeaway: Low sensitivity now is consistent with high ECS in the future Observations : 2000-1850 Model: year 150 CAM 4 simulations Observations Count / PDF Count / PDF HadSST CCSM4 3 -3 -1.5 1.5 Δ SST ( o C) Δ SST ( o C) Model Model •SST-driven changes in feedback explains discrepancy (coupled) w/ SST obs •Models are consistent with observations •Models are not too sensitive. Sensitivity increase. •Delayed warming in regions of heat uptake ECS ( o C) Proistosescu & Huybers 2017
Takeaway: Low sensitivity now is consistent with high ECS in the future Observations : 2000-1850 Model: year 150 CAM4, CAM5, HadGEM2, HadAM3, ECHAM6, AM2.1, AM3, AM4 Count / PDF R obs ( T obs ) Observations Count / PDF HadSST CCSM4 R GCM ( T obs ) R GCM ( T GCM ( ∞ )) 3 -3 -1.5 1.5 Δ SST ( o C) Δ SST ( o C) Models Model •SST-driven changes in feedback explains discrepancy (coupled) w/ SST obs •Models are consistent with observations •Models are not too sensitive. Sensitivity increase. T 2 × CO 2 •Delayed warming in regions of heat uptake ECS ( o C) Proistosescu & Huybers 2017 in prep: w/ Kyle Armour, Malte Stuecker, Yue Dong, Tim Andrews, Jonathan Gregory, Thorsten Mauritsen, Levi Silvers & David Paynter
How does radiation depend on the pattern of warming? Key physics: radiative feedback λ = Δ R Key physics: radiative feedback Δ T Δ R = Δ R ( Δ T ( x , t ) ) Feedback depends on spatial and temporal changes in temperature ∂ R Approximations: ∂ T ( x ) Δ T ( x , t ) + 𝒫 ( Δ T 2 ) Δ R = •Radiation depends only on spatial pattern of SSTs •System is linear R ( y , t ) ≈ ∂ R ( y ) ∂ T ( x ) ∑ ψ n ( x ) ϕ n ( t ) Theory and modal decomposition EOFs Principle components Proistosescu & Huybers 2017 eigenvectors of Exponential decay state space
How does radiation depend on the pattern of warming? Key physics: radiative feedback λ = Δ R Key physics: radiative feedback Δ T Δ R = Δ R ( Δ T ( x , t ) ) Feedback depends on spatial and temporal changes in temperature ∂ R Approximations: ∂ T ( x ) Δ T ( x , t ) + 𝒫 ( Δ T 2 ) Δ R = •Radiation depends only on spatial pattern of SSTs •System is linear R ( y , t ) ≈ ∂ R ( y ) ∂ T ( x ) ∑ ψ n ( x ) ϕ n ( t ) General question: how does radiation EOFs Principle components depend on local warming eigenvectors of Exponential decay Dong, Proistosescu, Armour, Battisti, in review state space
How does radiation depend on the pattern of warming? Compute response to local warming ∂ R ∂ T ( x ) 137 fixedSST runs on CAM4 Warm SSTs in a single patch. Keep SST and SIC fixed everywhere else Dong, Proistosescu, Armour, Battisti, in review Zhou, Zelinka, Klein, 2017
How does radiation depend on the pattern of warming? Radiative response to local warming W/m 2 / o C Outgoing Radiation ∂ R ∂ T ( x ) Global radiation response to •1 o C of warming in West Pacific: +30 W/m 2 •1 o C of warming in East Pacific: -10 W/m 2 Dong, Proistosescu, Armour, Battisti, in review
How does radiation depend on the pattern of warming? Radiative response to local warming (sanity check) W/m 2 / o C Outgoing Radiation ∂ R ∂ T ( x ) Δ R (W/m 2 ) — Full model 2 — Reconstruction ∂ R ∂ T ( x ) ⋆ T obs ( x , t ) 1 0 -1 1950 1980 2010
How does radiation depend on the pattern of warming? Radiative response to local warming tied to SST climatology W/m 2 / o C Outgoing Radiation ∂ R ∂ T ( x ) SST climatology o C Global radiation response to •1K of warming in West Pacific: 30 W/m 2 •1K of warming in East Pacific: 10 W/m 2
W/m 2 / o C o C Subtropics Warm Pool Low cloud amount depends on strength of inversion and local temperature Klein and Hartman 1993, Wood & Bretherton 2006 , Bretherton & Blossey 2014
W/m 2 / o C o C +SST Subtropics Warm Pool Controlled by East Pacific SST +EP SST - LCC
W/m 2 / o C +T +T o C +SST Subtropics Warm Pool Controlled by West Pacific SST +WP SST + LCC
How does radiation depend on the pattern of warming?: Local warming Near-Surface air temperature change to single patch of SST warming Fixed: Sea Surface Temp and Sea Ice Concentration Temperature changes over land and Sea Ice Dong, Proistosescu, Armour, Battisti, in review
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