Contribution of sulphate anthropogenic aerosols to the Euro-Mediterranean climate trends since 1980 using a regional coupled modelling approach Our Common Future under Climate Change – Paris – 8 th July 2015 P. Nabat 1 , S. Somot 1 , M. Mallet 2 , A. Sanchez-Lorenzo 3 and M. Wild 4 1 Météo-France / CNRM, Toulouse (France) 2 Laboratoire d'Aérologie, Toulouse (France) 3 University of Girona (Spain) 4 ETH Zurich (Switzerland) Contact : [email protected]
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Contribution of sulphate anthropogenic aerosols
to the Euro-Mediterranean climate trends since 1980
using a regional coupled modelling approach
Our Common Future under Climate Change – Paris – 8th July 2015
P. Nabat 1,
S. Somot 1, M. Mallet 2, A. Sanchez-Lorenzo 3 and M. Wild 4
1 Météo-France / CNRM, Toulouse (France)
2 Laboratoire d'Aérologie, Toulouse (France)
3 University of Girona (Spain)
4 ETH Zurich (Switzerland)
Contact : [email protected]
2
Past climate trends in Regional Climate Models (RCMs)
- Underestimation of the observed warming since 1980 as shown by the ENSEMBLES project (Lorenz and Jacob, 2010)
Differences of linear trends
in 2m-temperature (°C/decade)
with respect to E-OBS
(for different domains in Europe)
ERA-40 forcing Constant aerosol emissions
3
Past climate trends in Regional Climate Models (RCMs)
- Underestimation of the observed warming since 1980 as shown by the ENSEMBLES project (Lorenz and Jacob, 2010)
- Difficulties to reproduce observed climate trends also when using GCM forcing (Racherla et al., 2012 + comment by Laprise, 2014 ; Paxian et al., 2014)
Differences of linear trends
in 2m-temperature (°C/decade)
with respect to E-OBS
(for different domains in Europe)
ERA-40 forcing Constant aerosol emissions
4
Past climate trends in Regional Climate Models (RCMs)
- Underestimation of the observed warming since 1980 as shown by the ENSEMBLES project (Lorenz and Jacob, 2010)
- Difficulties to reproduce observed climate trends also when using GCM forcing (Racherla et al., 2012 + comment by Laprise, 2014 ; Paxian et al., 2014)
- A more recent regional simulation with transient aerosol emissions (COSMO-CLM, Zubler et al., 2011)
shows patterns of dimming/brightening only in clear-sky fluxes
Differences of linear trends
in 2m-temperature (°C/decade)
with respect to E-OBS
(for different domains in Europe)
ERA-40 forcing Constant aerosol emissions
1980 2000
Aerosol optical depth : ACCMIP mean
Zubler et al., JGR, 2011
SW surface flux
5
- Aerosols have poorly been considered in CORDEX simulations
e.g. in the Mediterranean region (Med-CORDEX):
- several RCMs have no aerosols (PROTHEUS, EBU-POM, RegCM-3)
- others have a monthly climatology (LMDz, MORCE-MED, CNRM-RCSM, COSMO-CLM), often
without yearly variations
- only RegCM-4 is able to include interactive aerosols
=> No regional simulation with ocean-atmosphere coupling and transient aerosol emissions
Aerosols in Regional Climate Models (RCMs)
over the Euro-Mediterranean region
6
- Aerosols have poorly been considered in CORDEX simulations
e.g. in the Mediterranean region (Med-CORDEX):
- several RCMs have no aerosols (PROTHEUS, EBU-POM, RegCM-3)
- others have a monthly climatology (LMDz, MORCE-MED, CNRM-RCSM, COSMO-CLM), often
without yearly variations
- only RegCM-4 is able to include interactive aerosols
=> No regional simulation with ocean-atmosphere coupling and transient aerosol emissions
Aerosols in Regional Climate Models (RCMs)
over the Euro-Mediterranean region
Are RCMs able to reproduce the past climate change ?
How do aerosols contribute to the climatic trends over this region ?
– Surface solar radiation (brightening effect)
– Land surface temperature
– Sea surface temperature (SST) and air-sea fluxes
Objectives
7
Methodology
Approach : fully coupled regional climate model driven by a reanalysis
ALADIN-Climat v5.2 + ISBA (ERA-INTERIM forcing, 50km)
NEMO-MED8 (10km)
TRIP river routine scheme (50km)
OASIS3 (daily)
The domain includes the Med-CORDEX official domain
Déqué and Somot, 2008 Colin et al., 2010
Decharme et al., 2010
Sevault et al., 2009 Beuvier et al., 2010 Herrmann et al., 2010
The CNRM Regional Climate System Model (CNRM-RCSM4)
8
Methodology
Approach : fully coupled regional climate model driven by a reanalysis
ALADIN-Climat v5.2 + ISBA (ERA-INTERIM forcing, 50km)
NEMO-MED8 (10km)
TRIP river routine scheme (50km)
OASIS3 (daily)
The domain includes the Med-CORDEX official domain
Déqué and Somot, 2008 Colin et al., 2010
Decharme et al., 2010
Sevault et al., 2009 Beuvier et al., 2010 Herrmann et al., 2010
The CNRM Regional Climate System Model (CNRM-RCSM4)
Sulfates Organic matter
Dust Sea-salt Black carbon
=> Aerosols included with monthly AOD (Aerosol Optical Depth) fields, coming from a new climatology
based on both satellite-derived and model-simulated AOD products (Nabat et al., AMT, 2013) + the decrease of sulfate aerosols can be taken into account
AOD trend (decade-1)
9
Methodology
Approach : fully coupled regional climate model driven by a reanalysis
ALADIN-Climat v5.2 + ISBA (ERA-INTERIM forcing, 50km)
NEMO-MED8 (10km)
TRIP river routine scheme (50km)
OASIS3 (daily)
The domain includes the Med-CORDEX official domain
Déqué and Somot, 2008 Colin et al., 2010
Decharme et al., 2010
Sevault et al., 2009 Beuvier et al., 2010 Herrmann et al., 2010
The CNRM Regional Climate System Model (CNRM-RCSM4)
Sulfates Organic matter
Dust Sea-salt Black carbon
=> Aerosols included with monthly AOD (Aerosol Optical Depth) fields, coming from a new climatology
based on both satellite-derived and model-simulated AOD products (Nabat et al., AMT, 2013) + the decrease of sulfate aerosols can be taken into account
AOD trend (decade-1) → 2 simulations 1980-2012 :
- REF : without interannual variation in aerosols
- TRANS : with the sulfate aerosol trend
10
The brightening simulated in CNRM-RCSM4
Downward surface solar radiation (SSR) trend (1980-2009, all-sky)
=> Stronger brightening in TRANS than in REF,
both in clear-sky and all-sky conditions
(W/m²/decade)
Observed temporal
series (networks
GEBA and AEMET)
11
The brightening simulated in CNRM-RCSM4
Downward surface solar radiation (SSR) trend (1980-2009, all-sky)
=> Stronger brightening in TRANS than in REF,
both in clear-sky and all-sky conditions
=> Comparison with ground-based homogenized
measurements : (GEBA, Sanchez-Lorenzo et al., 2013)
- Best agreement found with TRANS,
REF underestimates the brightening
- Spatial correlation increased from 0.10 (REF)
to 0.42 (TRANS)
- 81 % of the brightening due to aerosols
- ERA-Interim also underestimates the brightening
(W/m²/decade)
Observed temporal
series (networks
GEBA and AEMET)
Trend in surface radiation (1980-2009) Calculated for each region at the locations of the stations
12
- Climate variability (evolution of the weather
conditions imposed by the lateral boundary forcing)
=> only +0.6 W/m2 over Europe (REF)
- Direct aerosol effect = 87 % of the radiation trend
over Europe
- Semi-direct (-0.4 W/m2) and indirect (+0.1 W/m2)
aerosol effects have weaker contributions
=> domination of the direct aerosol effect
The brightening simulated in CNRM-RCSM4 (1980-2012)
→ Contribution of climate variability and the different aerosol effects
13
The land surface warming simulated in CNRM-RCSM4
Land 2m-temperature trend (1980-2007)
=> Stronger warming in TRANS (0.35°C/decade) than in
REF (0.28°C/decade), in line with the differences in radiation
REF OBS
(°C/decade) Observed temporal series
(network HISTALP + ECA + Météo-France)
TRANS
14
The land surface warming simulated in CNRM-RCSM4
Land 2m-temperature trend (1980-2007)
=> Stronger warming in TRANS (0.35°C/decade) than in
REF (0.28°C/decade), in line with the differences in radiation
=> Gridded global datasets closer to TRANS :
e.g. GISS (0.37°C/decade)
=> Comparison with a set of homogenized measurements :
(Météo-France, HISTALP, ECA)
- Best agreement found with TRANS,
REF underestimates the warming
- 23 % of the warming due to aerosols
- Spatial correlation increased from 0.52 (REF)
to 0.70 (TRANS)
- ERA-Interim is in good agreement with observations
REF OBS
(°C/decade) Observed temporal series
(network HISTALP + ECA + Météo-France)
TRANS
Trend in 2m-temperature (1980-2007) Calculated for each region at the locations of the stations
15
The sea surface warming simulated in CNRM-RCSM4
Sea Surface Temperature (SST) trend (1982-2012)
=> Stronger warming of the sea surface
in TRANS (0.24°C/decade) than in
REF (0.17°C/decade)
REF TRANS OBS
(°C/decade)
16
The sea surface warming simulated in CNRM-RCSM4
Sea Surface Temperature (SST) trend (1982-2012)
=> Stronger warming of the sea surface
in TRANS (0.24°C/decade) than in
REF (0.17°C/decade)
=> Gridded global datasets closer to
TRANS (~0.3°C/decade)
=> Best agreement found with TRANS,
REF underestimates the warming
=> Induced changes in air-sea fluxes
(e.g. increase of the latent heat
loss trend)
REF TRANS OBS
(°C/decade)
REF TRANS
Trend in latent heat loss (1980-2012)
(W/m²/decade)
17
Conclusion and prospects
=> Study of the past climate trends over the Euro-Mediterranean (1980-2012) using a novel
approach based on a coupled regional climate system model driven by a reanalysis
+ inclusion of realistic aerosol variations (Nabat et al., AMT, 2013) => Since 1980, decrease in sulfate aerosol concentration over Europe :
– Increase in SW surface downward radiation (brightening)
– Increase in surface temperature (land T2m and SST)
=> The comparison with homogenized surface observations (radiation and temperature) reveals
the need of taking into account realistic aerosol variations to reproduce the past climate
trends
Nabat et al., Contribution of anthropogenic sulfate aerosols to the changing Euro-Mediterranean climate since 1980.
Geophys. Res. Lett., 41, doi:10.1002/2014GL060798, 2014.
18
Conclusion and prospects
=> Study of the past climate trends over the Euro-Mediterranean (1980-2012) using a novel
approach based on a coupled regional climate system model driven by a reanalysis
+ inclusion of realistic aerosol variations (Nabat et al., AMT, 2013) => Since 1980, decrease in sulfate aerosol concentration over Europe :
– Increase in SW surface downward radiation (brightening)
– Increase in surface temperature (land T2m and SST)
=> The comparison with homogenized surface observations (radiation and temperature) reveals
the need of taking into account realistic aerosol variations to reproduce the past climate
trends
=> Prospects :
– Multi-model studies (with the same aerosol data set ?)
– Tests of this methodology in other regions
– Aerosols in CORDEX-2 ? (evaluation and scenario modes)
Nabat et al., Contribution of anthropogenic sulfate aerosols to the changing Euro-Mediterranean climate since 1980.
Geophys. Res. Lett., 41, doi:10.1002/2014GL060798, 2014.
19
Conclusion and prospects
=> Study of the past climate trends over the Euro-Mediterranean (1980-2012) using a novel
approach based on a coupled regional climate system model driven by a reanalysis
+ inclusion of realistic aerosol variations (Nabat et al., AMT, 2013) => Since 1980, decrease in sulfate aerosol concentration over Europe :
– Increase in SW surface downward radiation (brightening)
– Increase in surface temperature (land T2m and SST)
=> The comparison with homogenized surface observations (radiation and temperature) reveals
the need of taking into account realistic aerosol variations to reproduce the past climate
trends
=> Prospects :
– Multi-model studies (with the same aerosol data set ?)
– Tests of this methodology in other regions
– Aerosols in CORDEX-2 ? (evaluation and scenario modes)
Contact : [email protected] Thanks for your attention !
Nabat et al., Contribution of anthropogenic sulfate aerosols to the changing Euro-Mediterranean climate since 1980.
Geophys. Res. Lett., 41, doi:10.1002/2014GL060798, 2014.
21
Impact of aerosol changes on river flow in Europe (1980-2012)
REF TRANS
TRANS - REF
=> Decrease in river flow in Europe in TRANS
=> For example : Danube
-46 m3/s/decade (TRANS) < 2 m3/s/decade (REF)
=> Similar results found in northern hemisphere by Gedney
et al. (2014)
22
Impact of aerosol changes on precipitation (1980-2012)
REF TRANS GPCC
GPCP
=> In Europe :
0.04 mm/day/decade (TRANS) > 0.01 mm/day/decade (REF)
GPCC : 0.04 mm/day/decade
GPCP : 0.05 mm/day/decade
=> Over the Mediterranean :
0.04 mm/day/decade (TRANS) > 0.02 mm/day/decade (REF)
GPCP : 0.00 mm/day/decade
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