Uncertainties in regional climate change projections

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Uncertainties in regional climate change
projections
Filippo Giorgi Abdus Salam ICTP, Trieste,
Italy IPCC WG1 Bureau
Bridging the Gap Conference, Portoroz, 15 May
2008
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Human factors
Natural factors
Different natural and human factors need to be
accounted for in climate change prediction


Imperfect knowledge
Topography
Land-use change
Natural variability (ENSO, NAO)
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Cascade of uncertainty in climate change
prediction
Socio-Economic Assumptions
Emissions Scenarios
Concentration Calculations Biogeochemical/Chemistr
y Models
Interactions and Feedbacks Land Use Change
Policy Responses Adaptation and Mitigation
Global Climate Change Simulation AOGCMs,
Radiative Forcing
Natural Forcings
Regional Climate Change Simulat. Regionalization
Techniques
Impacts Impact Models
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Cascade of uncertainty in climate change
prediction
Socio-Economic Assumptions
Emissions Scenarios
Concentration Calculations Biogeochemical/Chemistr
y Models
Interactions and Feedbacks Land Use Change
Policy Responses Adaptation and Mitigation
Global Climate Change Simulation AOGCMs,
Radiative Forcing
Natural Forcings
Regional Climate Change Simulat. Regionalization
Techniques
Impacts Impact Models
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IPCC Emission and Concentration Scenarios
CO2 Emissions
CO2 Concentrations
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Cascade of uncertainty in climate change
prediction
Socio-Economic Assumptions
Emissions Scenarios
Concentration Calculations Biogeochemical/Chemistr
y Models
Interactions and Feedbacks Land Use Change
Policy Responses Adaptation and Mitigation
Global Climate Change Simulation AOGCMs,
Radiative Forcing
Natural Forcings
Regional Climate Change Simulat. Regionalization
Techniques
Impacts Impact Models
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Model configuration uncertainty Global climate
response for different GCMs
Temperature change, A2
Precipitation change, A2
Temperature change, B2
Precipitation change, B2
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IPCC 2007 Global temperature change
projections for the 21st century
Model configuration and scenario uncertainty
contribute approximately equally to the global
warming projection uncertainty
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Regional distribution of projected temperature
and precipitation change (A1B, 2090-2100) Relative
ly insensitive to the GHG forcing
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IPCC-AR4 Climate change projections over
Europe (21 Models, A1B scenario, 2090-2100)
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IPCC-AR4 Climate change projections over
Africa (21 Models, A1B scenario, 2090-2100)
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Regional to local informationis needed for
adaptation studies
Global
Continental
Regional



Local
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Different Downscaling techniques aree available
to enhance the AOGCM information

• High Resolution Time-Slice AGCM Experiments
• Variable Resolution AGCM
• Nested Regional Climate Model (RCM)
• Empirical/Statistical and Statistical/Dynamical
  Downscaling
• Combined use of different techniques (e.g. RCM
  nested in high resolution AGCM)

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Nested Regional Climate ModelingTechnique and
Strategy

• Motivation The resolution of GCMs is still too
  coarse to capture regional and local climate
  processes
• TechniqueA Regional Climate Model (RCM) is
  nested within a GCM in order to locally
  increase the model resolution.
• Initial conditions (IC) and lateral boundary
  conditions (LBC) for the RCM are obtained from
  the GCM (One-way Nesting) or analyses of
  observations.
• Strategy The GCM simulates the response of the
  general circulation to the large scale forcings,
  the RCM simulates the effect of sub-GCM-grid
  scale forcings and provides fine scale regional
  information
• Technique borrowed from NWP

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WINTER PRECIPITATION OVER BRITAIN
300km Global Model
50km Regional Model
25km Regional Model
Observed
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Precipitation change ()- dx20 km A2 (2071-2100)
Control (1961-1990) (Gao et al. 2006)
DJF
MAM
JJA
SON
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In order to characterize uncertainties climate
change prediction needs to be approach in a
probabilistic way
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Plans for the next IPCC cycle

• Carry out sets of predictions for the next
  decades (2030)
• High global resolution and large ensembles
• Initialized ocean conditions
• GHG trajectory not critical
• Downscaling to very fine scales
• For the climate model simulations emission
  scenarios will be initially replaced by GHG
  Reference Concentration Pathways (RCPs)
• Stabilization at different GHG levels
• Development of consistent sets of underlying
  socio-economic scenarios
• The RCPs will be used for long term climate
  change simulations (21st century and beyond)
• Medium resolution and large ensembles
• Downscaling to very fine scales

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Thank You
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