Future projections in the Mediterranean Sea under global warming scenarios

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Future projections in the Mediterranean Sea under
global warming scenarios
Marta Marcos, Mikis Tsimplis
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Motivation

• Results from an Atmosphere-Ocean Regional
  Climate Model provide with a value of 13 cm in
  average of steric sea level rise in the
  Mediterranean for the 21st century.
• IPCC projects a GSLR of 18-59 cm by 2100
• Need to compare projections within the
  Mediterranean, associated to T, S changes

Resolution 1/8 x 1/8 and 43 vertical
levels Simulations SRES A2 scenario for the
21st century Somot, S., Sevault, F., Déqué, M.
2006. Transient climate change scenario
simulation of the Mediterranean Sea for the 21st
century using a high-resolution ocean circulation
model. Clim Dyn (in press), DOI
10.1007/s00382-006-0167-z
Tsimplis, M, M. Marcos, S. Somot, 2008. 21st
century Mediterranean sea level rise. Regional
model predictions. Glob and Planetary Change
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Objective
Use the projections of atmosphere-ocean general
circulation models currently available to
determine the range of potential changes in the
thermohaline properties of the Mediterranean Sea
and the associated sea level variations
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Climate change scenarios
A1. Very Rapid Economic Growth Population peaks
mid-century, decline after Global Governance
(reduction in income/capita, convergence)
(A1FI-fossil, A1T-nonfossil,A1B-balance) A2.
Heterogenous world, Local governance/
identities, continuously increasing
population, Regionally variable economic
development B1. Population as in A1 Global
Governance Green Economy EquityGreen values B2.
Local solutions/Governance Population growing
continously (ltA2) Intermediate Economic
development Green Values at local/regional level
The scenarios are NOT policy recommendation and
DO NOT include mitigation strategies.
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Climate change scenarios

• 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.
• 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.
• Climate of the 20th century
• Includes changes in the forcing according to
  historical data

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Climate change projections

• Climate change projections are based on the
  outputs of Atmosphere-Ocean General Circulation
  Models (AOGCMs)
• These models have been evaluated against
  observations. Some of the observed features of
  climate are reproduced by the models and they
  provide with estimates of future changes, mainly
  at large scale.

Global mean T anomalies from observations (black)
and models (yellow-red) Source AR4 IPCC, Chapter
8
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Models
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Models
Parameterization of the Strait of Gibraltar
The barotropic transport is well reproduced by 2D
models but the baroclinic may need resolution at
tidal frequencies to be able to be reliable.
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Methodology

• Monthly T and S data are extracted from the
  global models for the domain -15º to 36ºE and 30º
  to 47º N
• Steric sea level is computed for each grid point
  as the vertical integration of the specific
  volume anomaly from surface to bottom

T and S are compared with MEDAR/MEDATLAS data
base for the 20th century T and S projections as
well as steric sea level changes are estimated
from the models for the 21st century
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Changes in T,S in the 20th century
Temperature
Salinity
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T,S projections in the 21st century
Temperature
Salinity
Committed CC
T changes 0-2.5 ºC S changes 0-2 psu
SRES A1B
SRES A2
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Sea level projections in the 21st century
Halosteric component
Thermosteric component
Halosteric sea level -70 to 20 cm Thermosteric
sea level 5 to 55 cm
Committed CC
SRES A1B
SRES A2
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Sea level projections in the 21st century
Range of variation -42 to 52 cm in
average Ignoring the two non-consistent
models The steric contribution of sea level in
the Mediterranean Sea is in average from -42 to
22 cm
Committed CC
SRES A1B
SRES A2
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Sea level projections in the 21st century
Spatial patterns of steric sea level variations
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Sea level projections in the 21st century
Contributions to projected sea level rise from
AOGCMs for the 21st century in the Mediterranean
Sea (in cm)
PLUS circulation changes
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Sea level projections in the 21st century
Circulation changes
UKMO-HadCM3 SRESA1B
Yearly steric (black line) and total (grey line)
sea level averaged over the Mediterranean Sea
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Conclusions

• Climate models often provide unrealistic values
  for T and S in the Mediterranean Sea. However,
  relative variations are more important in terms
  of steric sea level
• T and S projections for the 21st century predict
  warming and salinification of the Mediterranean
  Sea in the 3 scenarios considered of up to 2.5 ºC
  and 2 psu in average.
• The effects of such large changes can seriously
  affect ecosystems.
• The effects on sea level are opposite.
  Thermosteric and halosteric changes compensate
  each other thus keeping the steric sea level
  component nearly constant during the 21st
  century. Thermal expansion only would induce a
  sea level rise between 18 and 52 cm under
  SRESA1B.
• The climate regional model available projects
  an average increase of 13 cm by 2100 under SRES
  A2.

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Conclusions

• Changes at coastal sites steric sea level has
  lower impact. But sea level variations reflect
  circulation changes too. It is necessary the
  development of high resolution regional models
  describing different climate scenarios in order
  to improve future estimates.

Steric sea level range of variation -42 to 20
cm by 2100 PLUS maximum sea level rise from mass
addition -22 to 40 cm
Many thanks to J. Gregory for his comments on
this work