SUPPLEMENTARY INFORMATION

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1 doi: /nture11097 Supplementl Text Supplementry Figure 8 shows the zonl nnul men ensemle men temperture trends for the CAM individul forcing experiments. Both lck cron (BC) nd tropospheric ozone (TO3) yield mximum wrming in the NH mid-ltitudes, etween 30-55N. Although this is in generl greement with the loction of mximum incresing BC nd TO3 trends (Supplementry Figures 1-2), differences do exist. Although we do not hve simple explntion, there is no rel reson why wrming should occur exctly where het is dded. Possile resons for the mismtch likely involves ltent heting effects, clouds, vritions in rditive dmping rtes, or the lnd-ocen rrngement. In ddition to the NH mid-ltitude wrming, oth BC nd TO3 yield NH high-ltitude cooling. In terms of BC, this is consistent with reduced Europen emissions, resulting in negtive zonl BC trends polewrd of 55N. Both of these temperture responses contriute to positive vlue of the Expnsion Index (EI), since twice the mid-ltitude wrming exceeds the sum of low- nd high-ltitude wrming. As Figure 4 shows, EI for BC is 0.15 decde -1 nd decde -1 for TO3. We expect positive EI to e ssocited with polewrd displcement of the tropospheric jet nd the ltitude of the mximum meridionl temperture grdient (T y ). Supplementry Figures 9 nd 10 show this to e the cse. Both BC nd TO3 feture reduced roclinicity on the equtorwrd flnk of the mximum (ner 45N) nd incresed roclinicity on the polewrd flnk. Similrly, 1

2 oth BC nd TO3 feture reduced zonl winds (U) on the equtorwrd flnk of the climtologicl jet nd incresed U on the polewrd flnk. Supplementry Figure 11 shows tht geostrophic djustment to the ltered meridionl temperture grdient explins most of the BC nd TO3 response. Zonl wind sher for ech pressure level is estimted from the corresponding meridionl temperture grdient, ccording to therml wind lnce. To estimte the zonl wind, we use the 900 hp zonl wind s oundry condition. Tking trend over the pproprite time period ( ) yields the corresponding response, s shown in the center pnel of Figure S11. The ctul zonl wind trend closely corresponds to tht estimted from therml wind lnce. The trend of the difference (estimte-ctul) is generlly smll, lthough some significnt differences do exist in the NH mid-ltitudes. For exmple, the estimted trend shows lrger decrese in U on the equtorwrd flnk of the jet. Supplementry Figure 12 shows the tropospheric jet response, s well s the 500 hp temperture response, occurs cross ll longitudes. The corresponding polewrd tropospheric jet displcement is 0.11 decde -1 for oth BC nd TO3. We note similr, ut weker response occurs for sulfte erosols. The Expnsion Index lso helps to explin why GHGs hve resulted in less tropicl expnsion, compred to BC nd TO3, over recent decdes. Becuse GHGs re wellmixed throughout the tmosphere, they yield more uniform wrming of the troposphere, with the chrcteristic mxim in the tropicl upper troposphere nd t high-ltitudes due 2

3 to ltent heting nd snow/ice ledo effects, respectively. This results in smll, ut positive vlue of the Expnsion Index (0.06 decde -1, out hlf s lrge s tht for BC nd TO3), which is consistent with the weker polewrd displcement of the mximum T y nd tropospheric jet (0.04 decde -1 ). To test the roustness of the CAM results, we conducted series of simultions with the GFDL tmospheric model AM2.1 using climtologicl SSTs. Our first set of simultions investigted the equilirium response to idelized mid-ltitude heting. The experiment is forced with mid-ltitude (30-60 N/S) lower-tropospheric (surfce to ~700 hp) heting source of 0.4 K dy -1, nd compred to corresponding control simultion without the het source. Both integrtions were performed over 30 yers, the lst 20 of which re used to estimte the response. Supplementry Figure 13 shows the corresponding zonl nnul men temperture nd zonl wind response. Mximum wrming generlly occurs t the heted ltitudes, with some spillover to much of the troposphere. The weker SH wrming is likely due to the use of climtologicl SSTs, which leds to het sink over the Southern Ocen, nd smller temperture increse. The zonl wind (U) response is consistent with polewrd jet displcement, s U increses on the polewrd flnk of the climtologicl jet, while decresing on the equtorwrd flnk, prticulrly in the NH where wrming is lrgest. The corresponding polewrd jet displcement is 1.98 in the NH nd 0.45 in the SH, the former of which is significnt t the 99% confidence level (sed on stndrd t-test using the pooled vrince). Similr to the prior discussion, such response is consistent with mid-ltitude heting shifting the ltitude of the mximum meridionl temperture grdient (T y ) 3

4 polewrd (now shown), nd corresponding geostrophic djustment of the zonl winds, ccording to therml wind lnce. Our second set of GFDL simultions investigted the tropospheric jet response to timevrying lck cron nd tropospheric ozone, which hve incresed over much of the NH low- to mid-ltitudes in recent decdes. Similr to the CAM trnsient simultions, ech of the ensemle memers is integrted from n independent initil condition; the response is evluted y compring simultion without BC or TO3 with corresponding simultion with ll time-vrying forcings (GHGs, BC, OC, sulfte, ozone, solr nd volcnic erosols). A totl of eight ensemle memers were run. Unlike CAM, which used CMIP5 forcings, the GFDL time-vrying forcing comes from GFDL's CMIP3 forcing dt set. Aerosol concentrtions, s well s tropospheric ozone, re otined from the Model for Ozone nd Relted Chemicl Trcers version 2.4 (MOZART-2) chemicl trnsport model sed on the EDGAR-HYDE emission inventory 44. Emissions fter yer 2000 re sed on the SRESA1B scenrio. Both ozone nd erosol concentrtions re therefore prescried in GFDL AM2.1. Supplementry Figure 14 shows the BC nd TO3 nnul men ensemle men temperture nd zonl wind trend for Similr to the CAM results, oth BC nd TO3 yield significnt NH mid-ltitude wrming in the GFDL model, s well s U response consistent with polewrd displcement of the NH tropospheric jet significnt positive trends occur on the polewrd flnk of the climtologicl jet, while negtive trends occur on the equtorwrd flnk. The corresponding NH polewrd jet displcement 4

5 is lso similr to tht sed on CAM t 0.11± 0.18 decde -1 for BC nd 0.16± 0.19 decde -1 for TO3. We lso note tht the corresponding GFDL GHG response, like CAM, is less thn hlf s lrge t 0.05± 0.15 decde -1 (not shown). Thus, two different models with two different forcing inventories result in the sme conclusion: BC nd TO3, y preferentilly wrming the NH mid-ltitudes, result in significnt polewrd jet displcement, which is lrger thn tht ssocited with GHGs. Supplementl References 44. Horowitz, L. W. Pst, present, nd future concentrtions of tropospheric ozone nd erosols: Methodology, ozone evlution, nd sensitivity to erosol wet removl. J. Geophys. Res. 111, D22211 (2006) 5

6 Supplementry Figures ng/kg per yer ppv per yer Figure S1. Zonl nnul men tropospheric trends for two time periods. () Blck cron; () Ozone. BC concentrtion trends include hydrophoic nd hydrophilic BC nd re sed on CAM simultions using CMIP5 BC emissions. Ozone trends come directly from the CMIP5 forcing dt set. 6

7 Figure S nnul men time series nd trend of tropospheric lck cron for select regions. Vlues re n re-weighted sum over Europe (30-50N; 0-90E), Asi (30-50N; E), oth Europe nd Asi (30-50N; 0-180E) nd ll longitudes (30-50N; 0-360E). 7

8 Figure S CMIP3 Northern Hemisphere tropicl expnsion sed on five metrics. () Annul men polewrd displcement of ech metric, s well s the comined ALL metric. () Sesonl polewrd displcement of ll metrics comined. CMIP3 models re grouped y the 9 models tht included time-vrying BC nd ozone (red); the 3 models tht included time-vrying ozone only (green); nd the 6 models tht did not include time vrying BC or ozone (lue). Boxes show the men response (center line) nd its 2-sigm uncertinty. In the cse of one oservtionl dt set (i.e., JET, P-E nd PMIN), uncertinty is estimted s the 95% confidence level, ccounting for utocorreltion. Also included re oservtions sed on

9 Figure S4. Northern Hemisphere nnul men tropicl expnsion sed on five metrics for CAM3 experiments. () ; () Oservtions re lso included for the time period. Boxes show the men response (center line) nd its 2-sigm uncertinty. In the cse of one oservtionl dt set (i.e., JET, P-E nd PMIN), uncertinty is estimted s the 95% confidence level, ccounting for utocorreltion. 9

10 Figure S Southern Hemisphere tropicl expnsion sed on CAM3 experiments nd oservtions. () Annul men polewrd displcement for ech metric seprtely, nd the comined metric. () Sesonl displcement of the comined ALL metric. Boxes show the men response (center line) nd its 2-sigm uncertinty. In the cse of one oservtionl dt set (i.e., JET, P-E nd PMIN), uncertinty is estimted s the 95% confidence level, ccounting for utocorreltion. 10

11 Figure S Northern Hemisphere sesonl tropicl expnsion for individul forcings. Pnels show the difference etween CAM experiments with ll forcings nd ll forcings without (red) tropospheric ozone, (lue) lck cron, (green) lck cron nd tropospheric ozone, (purple) GHGs, (light lue) sulfte, nd (gry) orgnic cron. Boxes show the men response (center line) nd its 2-sigm uncertinty. 11

12 Figure S7. Northern Hemisphere nnul men tropicl expnsion sed on five metrics, nd the comined ALL metric. () ; () Pnels show the difference etween CAM experiments with ll forcings nd ll forcings without (red) tropospheric ozone, (lue) lck cron, (green) lck cron nd tropospheric ozone, (purple) GHGs, (light lue) sulfte, nd (gry) orgnic cron. Boxes show the men response (center line) nd its 2-sigm uncertinty. 12

13 All Forcings GHG BC c TO3 d SO2 e OC f K per decde Figure S zonl nnul men ensemle men temperture trends for the listed CAM experiments. Except for the ll forcings experiment, trends re estimted from the difference series of the ll forcing experiment, nd the corresponding ll forcing experiment without given forcing gent. Thin lck lines show the climtologicl temperture [K]. Symols represent significnce t the 90% (dimond); 95% (cross) nd 99% (dot) confidence level, ccounting for utocorreltion. 13

14 All Forcings GHG BC c TO3 d SO2 e OC f K/km per decde x10-3 Figure S zonl nnul men ensemle men temperture grdient trends for the listed CAM experiments. Thin lck lines show the climtologicl zonl temperture grdient [K km -1 x10-3 ]. Southern hemisphere vlues hve een multiplied y -1 such tht negtive contours lwys represent colder ir polewrds. Symols represent significnce s in Fig. S

15 All Forcings GHG c BC d TO3 e SO2 f OC m/s per decde Figure S zonl nnul men ensemle men zonl wind trends for the listed CAM experiments. Thin lck lines show the climtologicl zonl winds [m s -1 ]. Symols represent significnce s in Fig. S

16 BC U Trend TO3 c Estimted U Trend d e Trend of Difference f m/s per decde Figure S zonl nnul men ensemle men zonl wind trends for the CAM BC nd TO3 experiments. (,) Actul U trend (s in Fig. S10); (c,d) Estimted U trend; (e,f) Trend of difference (estimte-ctul). The estimted U trend is sed on therml wind lnce, using the 900 hp winds s lower oundry condition. Thin lck lines show the climtologicl zonl winds [m s -1 ]. Symols represent significnce s in Fig. S

17 BC+TO3 T 500 hp Trend K per decde BC+TO3 Tropospheric Jet Trend m/s per decde Figure S nnul men ensemle men 500 hp sptil trends for the BC+TO3 CAM experiment. () temperture; () Tropospheric zonl wind. Thin lck lines show the climtologicl jet [m s -1 ]. Symols represent significnce s in Fig. S

18 Temperture Response K Zonl Wind Response m/s Figure S13. Zonl nnul men temperture nd zonl wind response for GFDL AM2.1 equilirium experiments for idelized mid-ltitude heting. Thin lck lines show the climtologicl vlues. Symols represent significnce s in Fig. S

19 BC Temperture Trend TO3 K per decde c Zonl Wind Trend d m/s per decde Figure S zonl nnul men ensemle men temperture nd zonl wind trends for GFDL AM2.1 trnsient experiments. (,c) Blck cron; (,d) Tropospheric ozone. Symols represent significnce s in Fig. S

20 BC JJA TO3 DJF c d K per decde Figure S zonl men ensemle men sesonl temperture trends for CAM BC nd TO3 experiments. (,) June-July-August; (c,d) Decemer-Jnury- Ferury. Thin lck lines show the climtologicl temperture [K]. Symols represent significnce s in Fig. S

21 Supplementry Tles Model Acronym Institution ES CCSM3 Ntionl Center for Atmospheric Reserch 8 CNRM-CM3 Meteo-Frnce/CNRM 1 GFDL-CM2.0 Geophysicl Fluid Dynmics Lortory 3 GFDL-CM2.1 Geophysicl Fluid Dynmics Lortory 3 GISS-EH Goddrd Institute for Spce Studies 5 GISS-ER Goddrd Institute for Spce Studies 9 MIROC3.2 (medres) Center for Climte System Reserch/NIES/JAMSTEC 3 MIROC3.2 (hires) Center for Climte System Reserch/NIES/JAMSTEC 1 UKMO-HdGEM1 Hdley Center for Climte Prediction nd Reserch 2 PCM Ntionl Center for Atmospheric Reserch 4 UKMO-HdCM3 Hdley Centre for Climte Prediction nd Reserch 2 ECHAM5/MPI-OM Mx-Plnck Institute for Meteorology 3 CCCm-CGCM3.1(T47) Cndin Center for Climte Modeling nd Anlysis 5 CCCm-CGCM3.1(T63) Cndin Center for Climte Modeling nd Anlysis 3 FGOALS-g1.0 Institute for Atmospheric Physics 3 INM-CM3.0 Institute for Numericl Mthemtics 1 IPSL-CM4 Institute Pierre Simon Lplce 1 MRI-CGCM2.3.2 Meteorologicl Reserch Institute 1 Tle S1. Definition of the 18 CMIP3 models. ES is the numer of independent reliztions of the 20 th century climte chnge experiment. The first 9 models include time-vrying lck cron (BC) nd ozone forcing, with chnges on internnul nd longer time scles; the next 3 models including time-vrying ozone forcing ut lcked time-vrying BC; nd the lst 6 models lcked time-vrying BC nd ozone. 21