The role of forcings in 20 th century North Atlan6c- Mediterranean decadal variability

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1 The role of forcings in 20 th century North Atlan6c- Mediterranean decadal variability Alessio Bellucci 1, A. Mario* 3, S. Gualdi 1, e1. CMCC Centro Euro- Mediterraneo sui Cambiamen? Clima?ci, Bologna, Italy 2. INGV Is?tuto Nazionale di Geofisica e Vulcanologia, Bologna, Italy 3. NOAA Climate Program Office, Silver Spring, MD

CMCC Centro Euro- Mediterraneo sui Cambiamen? Clima?ci, Bologna, Italy 2. INGV Is?

2 Mediterranean mul?- decadal variability Med SST [Marullo et al., 2011] [Mario*, 2010] JJA Ta corr. with AMO [Mario* & dell Aquila, 2011] Mul?- decadal variability is found in the Mediterranean region affec?ng (e.g.) SSTs [Marullo et al., 2011],surface air temperature [Mario* & dell Aquila, 2011], evapora?on [Mario*, 2011], coherent with the Atlan?c Mul?decadal Oscilla?on

- decadal variability is found in the Mediterranean region affec?ng (e.g.) SSTs [Marullo et al.

3 Mediterranean mul?- decadal variability T2M: ACC Ini?alized- Unini?alized 2-5 lead- year [Guemas et al., 2014] However, ini?alized hindcasts show rela?vely li]le skill improvement, compared to non- ini?alized externally- forced integra?ons. [Guemas et al., 2014]

4 Mediterranean mul?- decadal variability T2M: ACC Ini?alized- Unini?alized 2-5 lead- year [Guemas et al., 2014] Role of forcings on the 20 th C mul?- decadal variability?

5 A hierarchy of CMIP5 historical integra6ons under different forcing condi6ons. HISTORICAL NATURAL ANTHROPOGENIC HISTMISC Anthropogenic ANTHROPOGENIC only HISTMISC NoAA NATURAL ANTHROPOGENIC NO Ant. Aerosols FORCINGS: Natural: Volcanoes, Solar Anthropogenic: GHG, Anthrop. Aerosols, Land Use Changes, Ozone

HISTORICAL NATURAL ANTHROPOGENIC HISTMISC Anthropogenic ANTHROPOGENIC only

6 A hierarchy of CMIP5 historical integra6ons under different forcing condi6ons. ENS. SIZE ONLY MODELS PROVIDING A MINIMUM 3- MEMBER ENSEMBLE WERE RETAINED FOR THE ANALYSIS SO AS TO FILTER- OUT THE INTERNAL, UNFORCED VARIABILITY SIGNAL.

SIZE 69 53 14 ONLY MODELS PROVIDING A MINIMUM 3- MEMBER

7 Mediterranean- Atlan6c mul6- decadal SST variability in HIST CMIP5 simula6ons Mediterranean SSTA North Atlan?c SSTA OBS (HadISST) HISTORICAL MME Model Members HIST MME MEAN PERFORMED OVER 13 MODELS (69 MEMBERS) SHOWS RESIDUAL MULTI- DECADAL VARIABILITY, HIGHLY COHERENT WITH THE OBSERVED RECORD.

c SSTA OBS (HadISST) HISTORICAL MME Model Members HIST MME MEAN PERFORMED

8 Mid- 20 th C cooling pa^ern reveals a comma shaped AMV- like structure with an amplified subpolar response consistent across HIST and OBS. ( ) ( ) composite HIST MME (69- mem.) OBS

9 Mid- 20 th C cooling pa^ern reveals a comma shaped AMV- like structure with an amplified subpolar response consistent across HIST and OBS. ( ) ( ) composite HIST MME (69- mem.) The purely- forced response (MME) accounts for the observed mid- 20C cooling: but what kind of forcing is that? natural vs anthropogenic? OBS

(1930-1950) (1960-1980) composite HIST MME (69- mem.

10 Natural or anthropogenic forcing?

11 Histmisc Anthropogenic Ensemble: two behavioral clusters 1 Within the ANTHROPOGENIC ensemble a large model- to- model uncertainty exists: a mid- 20C cooling is detected under purely- anthropogenic forcing condi?ons, but only in a subset of models ANTHROPOGENIC- A ANTHROPOGENIC- B

under purely- anthropogenic forcing condi?ons, but only in a sub- set of models 0.

12 Histmisc Anthropogenic Ensemble: two behavioral clusters 1 Thus, mid- 20C cooling found in HIST simula?ons is largely determined by ANT forcings. Late 19th/Early 20 th century variability more likely a]ributable to NATURAL forcings HISTORICAL ANTHROPOGENIC- A ANTHROPOGENIC- B

Late 19th/Early 20 th century variability more likely a]ributable to NATURAL

13 Histmisc Anthropogenic Ensemble: two behavioral clusters 1 The phase- mismatch between simulated and observed mid- 20C cooling persists even under ANT forcings OBSERVATIONS HISTORICAL ANTHROPOGENIC- A ANTHROPOGENIC- B

persists even under ANT forcings 0.5 0 0.

14 WARM [ ] COLD [ ] composite pa^erns HISTORICAL ANTHROPOGENIC- A ANTHROPOGENIC- B HISTORICAL ANTHROPOGENIC- B OBSERVATIONS ANTHROPOGENIC- A Models belonging to Cluster- B ANTHROPOGENIC simula6ons (green curve) show a pa^ern bearing strong similari6es with HISTORICAL and OBS (comma- shaped structure & subpolar basin amplified response)

5 1840 1860 1880 1900 1920 1940 1960 1980 2000 OBSERVATIONS ANTHROPOGENIC- A Models belonging to

15 If it were anthropogenic.what kind of anthropogenic would that be?

16 Did the anthropogenic aerosols determine the mid- 20th century cooling? OBS (HadISST) HISTORICAL NoAA (*) Same models used in HIST and NoAA to allow a fair comparison (*) NoAA: Same forcings as HISTORICAL but without Anthropogenic Aerosols Aker removing the Anthropogenic Aerosols forcings, the simulated SSTs do not show the mid20- Century cooling anymore, but only a monotonic increase with 6me.

NoAA: Same forcings as HISTORICAL but without Anthropogenic Aerosols Aker removing the

17 CONCLUSIONS The MME mean of 69 HISTORICAL simula6ons display mul6- decadal SST variability over the N.Atlan6c- Mediterranean area, coherent with the OBS 20th century record, indica6ng the influence of non- sta6onary forcings. The MME anomaly map associated with the mid- 20th century SST dip features a comma- shaped structure over the N. Atlan6c domain, encompassing the Mediterranean, and a subpolar enhanced response, consistent with OBS. A subset of the HISTMISC simula6ons performed with ANTHROPOGENIC- only forcings reproduce a forced response bearing strong resemblance with the HISTORICAL pa^ern. An analysis of the NoAA integra6ons suggests that the observed mid- 20C mul6- decadal SST fluctua6ons over the N Atl- Med region may be forced by anthropogenic aerosols.

The MME anomaly map associated with the mid- 20th century SST dip features a comma- shaped structure over the N.

18 20C AMV resul?ng from a combina?on of different drivers Natural Forcings +Internal Anthropogenic Aerosols

19 A Frankenstein- AMV? Natural Forcings +Internal Anthropogenic Aerosols

21 ENS1: 13 mod. 69 mem. Warm(30-50)- Cold(60-80) 90 W 60 W 30 W 0 30 E 75 N Warm(30-50)- Cold(00-20) 90 W 60 W 30 W 0 30 E 75 N N 45 N 30 N N 45 N 30 N N 0 HIST N 0 HIST N 90 W 60 W 30 W 0 30 E N 90 W 60 W 30 W 0 30 E N 45 N 30 N N 45 N 30 N N 0 OBS N 0 OBS

Decadal predictions using the higher resolution HiGEM climate model Len Shaffrey, National Centre for Atmospheric Science, University of Reading

Decadal predictions using the higher resolution HiGEM climate model Len Shaffrey, National Centre for Atmospheric Science, University of Reading Dave Stevens, Ian Stevens, Dan Hodson, Jon Robson, Ed Hawkins,