Mediterranean Sea response to climate change in an
st
ensemble of 21 century climate change scenarios
(1) Météo-France, CNRM-GAME, Toulouse, FR
(2) IRD, LEGOS, Toulouse, FR
(3) Puertos del Estado, Madrid, SP
(4) IMEDEA, UIB, Palma de Mallorca, SP
F. Adloff (1), S. Somot (1), F. Sevault (1), G. Jorda (4), R.
Aznar (3), M. Déqué (1), M. Herrmann (2), C. Dubois (1),
E. Padorno (3), E. Alvarez-Fanjul (3), and D. Gomis (4)
01 | INTRODUCTION
02 | MODEL AND SIMULATIONS
During the past, variations of heat and water fluxes
acting on the Mediterranean Sea have led to
changes
of
the
circulation
state.
The
Mediterranean climate is expected to become
warmer and drier during the 21st century, what may
again modify the current state of the Mediterranean
thermohaline circulation (MTHC). This response to
various scenarios could be modulated by the
choice of the boundary conditions such as the
Atlantic hydrography, the river runoffs and the airsea fluxes, and by the socio-economic scenarios.
The NEMOMED8 regional ocean model
was set-up for the Mediterranean region
and is forced by air-sea fluxes from the
regional climate model ARPEGE-Climate
on a 50-km streched grid. Fresh water
inputs from the rivers are prescribed from
the RivDis climatology (Vörösmarty et al.,
1996) and the prescribed net Black Sea
inflow comes from the dataset by Stanev
et al. (2000). At the Atlantic boundary,
temperature and salinity are relaxed
towards climatological values (Reynaud et
al., 1998). In the scenario simulations,
anomalies derived from global coupled
model simulations are added to the
climatological values.
This study aims to investigate the changes in the
MTHC, hydrographic content and mean sea level
under climate change scenarios and to estimate
the uncertainty linked to each boundary forcing.
From baseline simulations respresenting
the historical period 1960-2000, we
performed various sensitivity experiments
for the period 2001-2099 to assess the
sensitivity to (i) the Atlantic hydrography,
(ii) river runoffs, (iii) air-sea fluxes and (iv)
Simulation set
socio-economic scenarios.
- 50 km res.
- 31 levels
- 1/8° res.
- 43 levels
03 | GENERAL FEATURES OF PROJECTIONS (1961-1990 vs. 2070-2099)
Fresh water budget
2070-2099 : increase of water loss and a decrease of
the heat loss (not shown here) over the basin
associated to a warming. The net water inflow at
Gibraltar increases to compensate.
Surface changes composites
Density and vertical stratification changes
The balearic region and the North Ionian display a
weaker response, even a freshening in some
simulations. The choice of the scenario does not
induce strong variations in the SSS anomalies but
the choice of the boundary conditions does.
A general decrease of the Mediterranean surface
potential density is simulated. However, the density
over the basin increases, especially in the deep
layers. This results in an increase of the stratification
(IS value). This response is strongly modulated by the
choice of the scenario and of the Atlantic conditions.
-
04 | PROJECTIONS OF MTHC AND MEAN SEA LEVEL / SENSITIVITY
Zonal overturning circulation Meridional overturning
of the Mediterranean
circulation of the Adriatic
1961-1990
2070-2099
1961-1990
2070-2099
Meridional overturning
circulation of the Aegean
1961-1990
2070-2099
1961-1990
2070-2099
1961-1990
2070-2099
1961-1990
2070-2099
2070-2099
2070-2099
2070-2099
2070-2099
2070-2099
2070-2099
The future MTHC simulated in the scenarios is strongly related with
the state of the vertical stratification (IS index) in the historical
simulations: weak in HIS but strong in HIS-F. In all the scenario
simulations starting from HIS-F, the MTHC increases in the eastern
basin and converges toward an EMT-like situation with a
strengthening of the MOC of the Aegean and a weakening of the
MOC in the Adriatic basin.
Mean Sea Leval anomalies
Projected changes in the
MTHC lead to changes in the
penetration
of
the
heat
anomalies, especially in the
Eastern basin, where the
surface warming is large and
the deep water production
intensified. This results to an
increase in the thermosteric
mean sea level.
Sensitivity to boundary forcings
2070-2099
2070-2099
2070-2099
2070-2099
2070-2099
2070-2099
[°C
]
EMT-Index vs. Aegean buoyancy fluxes
05 | CONCLUSIONS
With our 6-members scenario simulations, we
provide estimates of the uncertainties related
to regional modelling, which are linked to the
choice of (i) the socio-economic scenario, (ii)
the surface fluxes, (iii) the river runoffs and
(iv) the Atlantic hydrography. We found the
latest having the major impact on the
simulated future ocean climate. Not assessed
here, the uncertainty linked to the choice of
the regional ocean model can only be tackled
in the frame of a multi-model analysis.
The EMT-index characterizes
the strength of an EMT
circulation. We manage to
relate this index to the
changes in Aegean buoyancy
fluxes in the scenarios. A
buoyancy decrease in the
Aegean clearly pushes toward
an EMT-situation and is mainly
expected
in
the
future
Mediterranean ocean climate.
Sensitivity to the forcings
The response of the Mediterranean Sea to climate change
is strongly modulated by the chosen boundary conditions
and socio-economic scenarios. The Atlantic forcing has the
largest effect on the long-term future evolution of the
Mediterranean followed by the socio-economic scenarios.
Adloff, F., S. Somot, F. Sevault, G. Jorda, R. Aznar, M. Déqué, M. Herrmann, C. Dubois, E. Padorno, E. Alvarez-Fanjul, D. Gomis
(2014): Mediterranean Sea response to climate change in an ensemble of 21st century scenarios, Climate Dynamics, in revision.