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Temperature, salinity and associated sea level changes in the Mediterranean Sea under global warming

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Steric sea level is computed for each grid point as the vertical integration of ... Average steric sea level rise at the end of the 21st century respect to year ... – PowerPoint PPT presentation

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Title: Temperature, salinity and associated sea level changes in the Mediterranean Sea under global warming


1
Temperature, salinity and associated sea level
changes in the Mediterranean Sea under global
warming scenarios
  • Marta Marcos and Mikis Tsimplis

2
Objectives
  • Examine the T and S changes in the Mediterranean
    Sea as predicted by the climate models
  • Understand steric sea level changes associated
    with T and S variations

3
Outline
  • Models (global and regional) and data bases
  • Comparison of T and S for the 20th century
  • Projections of T, S for the 21st century
  • Associated steric sea level changes
  • Conclusions

4
Models output and data
IPCC models used in this work
5
Models output and data
Atmosphere-Ocean Regional Climate Model coupled
to a global variable resolution atmosphere model
with 50 km resolution over the Mediterranean
basin and forced by river runoff and influxes
from the Atlantic Ocean and the Black
Sea Resolution 1/8 x 1/8 and 43 vertical
levels Simulations SRES A2 scenario for the
21st century Hindcast for 1961-2000
(Somot et al., 2006 )
MEDAR database Yearly gridded T and S
climatology with 0.2ºx0.2º and 25 vertical levels
(Rixen et al., 2005)
6
Models output and data
Parameterization of the Strait of Gibraltar
7
Models output and data
Some climate change scenarios
Committed climate change scenario This scenario
assumes that concentrations are kept fixed at
year 2000 levels. Therefore, the committed
sea-level rise is the increase in sea surface
level associated with the historical changes in
greenhouse gases to date and the associated
trends in ocean temperature and ocean
volume. SRES A1B scenario The AOGCMs are run up
to year 2100 using the projected concentrations
forcing agents derived from the standard SRES A1B
scenario. This scenario describes a rapid
economic growth and the introduction of new and
more efficient technologies. The increase in
emissions is decelerated in the mid 21st
century. SRES A2 scenario In this scenario the
AOGCMs are run up to year 2100 using the
projected concentrations of greenhouse gases and
sulphates derived from the standard SRES A2
scenario. This scenario assumes a heterogeneous
world with regionally economic development,
implying a continuous increase of gases
emissions. Climate of the 20th century Includes
changes in the forcing according to historical
data
8
Methodology
  • Monthly T and S data are extracted from the
    global models for the domain -15º to 36ºE and 30º
    to 47º N
  • T and S given by the models for the 20th century
    are compared with MEDAR data base
  • Steric sea level is computed for each grid point
    as the vertical integration of the specific
    volume anomaly from surface to bottom
  • Steric sea levels are obtained for each global
    model and each scenarios and for the regional
    model as well
  • The influence of T and S on steric sea level are
    also estimated separately
  • Steric sea level does not account for the
    changes in sea level induced by changes in the
    barotropic circulation

9
Changes in T S during the 20th century
Average T and S yearly time series in the
Mediterranean for the layer 0-100 m
10
Changes in T S during the 20th century
Average T and S yearly time series in the
Mediterranean for the layer 0-100 m
11
Changes in T S during the 20th century
Intermediate waters 100-500m
12
Changes in T S during the 20th century
Deep waters 700-2000m
13
Projected changes in T and S
Temperature
Salinity
Committed climate change scenario
0-500 m layer
SRES A2 scenario
14
Associated steric sea level
SRES A2 scenario
Change in regional model 13 cm
Average MSL 5.9 cm
S constant
T constant
Average MSL 36.8 cm
Average MSL -30.9 cm
15
Associated steric sea level
Differences in Western and Eastern basins
SRES A2 scenario
Western basin
Eastern basin
Average MSL 3.7 cm
Average MSL 10.1 cm
Change in regional model EASTERN 11 cm WESTERN
18 cm
16
Associated steric sea level
Average steric sea level rise at the end of the
21st century respect to year 2000 (in cm)
Global average corresponds to thermal expansion
17
Conclusions
  • Climate models often provide unrealistic values
    for T and S in the Mediterranean Sea
  • Global and regional models predict warming and
    salinification of the Mediterranean Sea during
    the 21st century. The effects on sea level rise
    are opposite.
  • The worst scenario in the Mediterranean predicts
    an average sea level rise due to steric changes
    of at most 30 cm plus contributions of mass
    addition
  • Coastal values and high resolution regional
    models spatial variations of sea level changes
    reflect also the barotropic changes in the
    circulation. Regional models with high resolution
    and describing different scenarios are needed to
    improve estimates.

18
Conclusions
  • Total sea level rise steric dynamic changes
    mass addition atmospheric effects
  • Steric in the Med 30 cm max.
  • Atmospheric effects -2 cm max.
  • Mass addition -7 to 18 cm globally (IPCC AR4)
  • Sea level rise in the worst case scenario 46 cm
    averaged over the Med according to the AOGCMs
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