Uncertainties in regional climate change projections Filippo Giorgi Abdus Salam ICTP, Trieste, Italy IPCC WG1 Bureau Bridging the Gap Conference, Portoroz,, 15 May 2008
Human factors Greenhouse gases Volcanic activity Natural factors Atmospheric aerosols Imperfect knowledge Different natural and human factors need to be accounted for in climate change prediction Land-use change Natural variability (ENSO, NAO) Variations of Solar radiatios Topography
Cascade of uncertainty in climate change prediction Socio-Economic Assumptions Policy Responses: Adaptation and Mitigation Emissions Scenarios Concentration Calculations Biogeochemical/Chemistry Models Global Climate Change Simulation AOGCMs, Radiative Forcing Regional Climate Change Simulat. Regionalization Techniques Impacts Natural Forcings Interactions and Feedbacks Land Use Change Impact Models
Cascade of uncertainty in climate change prediction Socio-Economic Assumptions Policy Responses: Adaptation and Mitigation Emissions Scenarios Concentration Calculations Biogeochemical/Chemistry Models Global Climate Change Simulation AOGCMs, Radiative Forcing Regional Climate Change Simulat. Regionalization Techniques Impacts Natural Forcings Interactions and Feedbacks Land Use Change Impact Models
IPCC Emission and Concentration Scenarios CO2 Emissions CO2 Concentrations
Cascade of uncertainty in climate change prediction Socio-Economic Assumptions Policy Responses: Adaptation and Mitigation Emissions Scenarios Concentration Calculations Biogeochemical/Chemistry Models Global Climate Change Simulation AOGCMs, Radiative Forcing Regional Climate Change Simulat. Regionalization Techniques Impacts Natural Forcings Interactions and Feedbacks Land Use Change Impact Models
Model configuration uncertainty Global climate response for different GCMs Temperature change, A2 Precipitation change, A2 Temperature change, B2 Precipitation change, B2
IPCC 2007: Global temperature change projections for the 21 st century Model configuration and scenario uncertainty contribute approximately equally to the global warming projection uncertainty
Regional distribution of projected temperature and precipitation change (A1B, 2090-2100) Relatively insensitive to the GHG forcing Temperature change DJF Precipitation change DJF BOREAL WINTER BOREAL WINTER Temperature change JJA Precipitation change JJA BOREAL SUMMER BOREAL SUMMER
IPCC-AR4 Climate change projections over Europe (21 Models, A1B scenario, 2090-2100)
IPCC-AR4 Climate change projections over Africa (21 Models, A1B scenario, 2090-2100) Fi
Regional to local information is needed for adaptation studies Global Continental Regional Local
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)
Nested Regional Climate Modeling: Technique and Strategy Motivation: The resolution of GCMs is still too coarse to capture regional and local climate processes Technique:A 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
WINTER PRECIPITATION OVER BRITAIN (a) 300km GCM: 1979-83 (b) 50km RCM: 1979-83 300km Global Model 50km Regional Model 1 2 3 5 7 10 (c) 25km RCM: 1979-83 1 2 3 5 7 10 (d) CRU observations: 1961-90 25km Regional Model Observed 1 2 3 5 7 10 1 2 3 5 7 10
Precipitation change (%)- dx=20 km A2 (2071-2100) Control (1961-1990) (Gao et al. 2006) DJF MAM JJA SON
In order to characterize uncertainties climate change prediction needs to be approach in a probabilistic way PDF Climate change PDF Uncertainty T-Change
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 socioeconomic scenarios The RCPs will be used for long term climate change simulations (21 st century and beyond) Medium resolution and large ensembles Downscaling to very fine scales
Thank You
Precipitation change (%, 2071-2100 minus 1961 CMIP3 ensemble average, A1B scenario 2100 minus 1961-1990), 1990), DJF MAM JJA SON
Precipitation change (%, 2071-2100 minus 1961 CMIP3 ensemble average, A2 scenario 2100 minus 1961-1990), 1990), DJF MAM JJA SON
Precipitation change (%) as a function of time, CMIP3 ensemble average, A1B scenario DJF, A1B, 2020s-1970s DJF, A1B, 2050s-1970s JJA, A1B, 2020s-1970s JJA, A1B, 2050s-1970s