Greenhouse Gas Emissions, Global Climate Models, and California Climate Change Impacts

GCM SelectionThe projected future climate depends on the Global Climate Model (GCM) used:Different parameterization of physical processes (e.g., clouds, precipitation)Varying sensitivity to changes in atmospheric forcing (e.g. CO2, aerosol concentrations)

Future GHG EmissionsHow society changes in the future:

Scenarios of greenhouse gas emissions:

A1fi: Rapid economic growth and introduction of new, efficient technologies, technology emphasizes fossil fuels Highest estimate of IPCC

A2: Technological change and economic growth more fragmented, slower, higher population growth Less high for 21st century

B1: Rapid change in economic structures toward service and information, with emphasis on clean, sustainable technology. Reduced material intensity and improved social equity - Lowest estimate for 21st centuryScenarios of CO2 emissionsCO2 concentrationsLag

GCM Selection Model CharacteristicsGFDL 2.1 Geophysical Fluid Dynamics Lab, resolution about 2.0 x 2.5 degrees (latitude x longitude)

PCM National Center for Atmospheric Research/Dept. of Energy Parallel Climate Model, resolution about 2.8 degrees

Model Characteristics:Both are Coupled Atmosphere-Ocean-Land modelsNeither uses flux adjustments: can simulate stable climate without adjustmentsBoth are state-of-the-artParticipating in IPCC AR4 simulations archived at PCMDI, archiving daily datarealistic simulation El Nio SST anomalies important for CA climate

GCM Selection SensitivityAverage Annual T change over CAB1 Emission ScenarioA2 Emission ScenarioAt end of 21st Century:GFDL slightly drierPCM slightly wetter

Using GCMs in Impact StudiesThe problems:GCM spatial scale incompatible with local/regional processesroughly 2 5 degrees resolutionsome important processes not capturedGCMs have biases Resolved by:Bias CorrectionSpatial Downscaling

Bias Correction EffectsMean and variability of observed data are reproduced for historical periodTemperature trends into future in GCM output are preservedRelative changes in mean and variance in future period GCM output are preserved, mapped onto observed variance

Spatial DisaggregationGFDL A2 ScenarioAssumes processes responsible for current precipitation pattern also apply to future precipitation

Results for CA Annual AverageAnnual P trend small, though impacts can be sensitive

T trend strongly influenced by GHG emission scenario and GCM

For PCM, A1fi scenario is 1-2 C warmer than A2.

Temperature Changes, CGFDL-B1PCM-B1GFDL-A2PCM-A21961-1990

1961-90B1A2DJFJJADJFJJADJFJJAGFDL2.220.3+2.2+3.6+3.5+6.4PCM+1.9+1.7+2.6+3.2

Precipitation Changes, mm/dGFDL-B1PCM-B1GFDL-A2PCM-A21 mm/d 14 inches/year1961-1990

1961-90B1A2DJFJJADJFJJADJFJJAGFDL2.30.4-4.9%-26.7%-7.2%-46.7%PCM+7.6%+15.9%+10.6-6.8%

Derived data for impact modelersDownscaled GCM climate and derived meteorologyprecipitationtemperaturehumidityradiation

Hydrologic model simulations for specific river basins, have produced:streamflowsnowpacksnowmelt timingsoil moisture

GCM processing time for CCSM about 4 years per day on 192 processors.

Dynamical downscaling for California (UCSD): For the 40km resolution runs it takes about 5 wallclock days to get 1 year of model simulation. This is of course dependent on the size of the domain as well as the resolution.

Fully-coupled atmosphere-ocean general circulation models that do not require flux adjustment to maintain a relatively stable climate over long control simulationsModel estimates of global annual mean temperature lie within 1oC of observed averages, while precipitation is over-estimated by 0.1 to 0.4 mm/day

PCM: a high-resolution ocean model with a displaced North Pole that allows realistic simulation of Arctic Ocean circulation and other oceanic features such as the E-W equatorial gradient of SST in the equatorial Pacific.HadCM3: a detailed land-surface scheme that accounts for such processes as phase transitions in soil moisture and the effects of CO2 on evaporation

Elevations in meters at 2.8125 degree resolutionMax elev about 2200 mActual peaks over 4000