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Climate modeling Current state of climate knowledge What does the historical data (temperature, CO 2 , etc) tell us What are trends in the current observational data What do we know about the greenhouse effect

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Climatemodeling• Currentstateofclimateknowledge–Whatdoesthehistoricaldata(temperature,CO2,etc)tellus

–Whataretrendsinthecurrentobservationaldata–Whatdoweknowaboutthegreenhouseeffect

Modeling• Whatconstitutesaclimatemodel?

Climatemodelschematic

Source:IPCC,2007

Inputtomodels:EmissionscenariosofcarbonSO2,particles,etc

ModelscalculatetheatmosphericconcentrationofGHGs,aerosol,etc

Modelsdeterminetheimpactofthespeciesinteractingwithshortwaveandlong-waveradiation

Theatm.parameterssuchastemp,precip,etcarethendeterminedconsideringglobalcirculationpatterns,etc

IPCC,2007

Thelackofadequateknowledgeonaerosol-cloudinteractionsisacriticaluncertaintyinglobalclimatemodeling

Source:IPCC,2007

CurrentstateofGCMs

Source:IPCC,2007

Climatemodels• Fourcomponents:– Atmosphere,landsurface,ocean,andseaice.

• AtmosphericandOceaniccomponents–Globalcirculationmodels(GCM)– Simulatelargescalecirculationoftheatmosphereandtheoceans.

– Importantvariables• Temperature,pressure,humidity,winds,andwaterandicecondensateinclouds

Computationaldetails• TypicalAtmosphericglobalcirculationmodels(AGCMs):

– Spatialresolutionof~100kminthehorizontal– 30levelsintheverticalatmospherebelowthealtitudeof15-20

km– Timestepof10-20minutes– Withinthegrids,parameterizationsareusedtosimulate

processesthataretoocomplextocaptureintheclimatemodels.• E.g.,cloudformation,turbulence

• Oceanicglobalcirculationmodels(OGCMs)arecoupledtotheatmosphereandicemodelsthroughtheexchangeofheat,salinity,andmomentumattheboundaryamongcomponents.– Resolutionof1degreelatitudeandlongitude;30layersinthe

oceans

Climatemodels• Doublingtheresolutionwillrequire~10timesmorecomputingpower.

• Foroneyearofsimulations,needtoprocessdataover2.5milliongridcellsmorethan27,000times.

Climatemodels:Limitations• Lowresolutionlimitstheabilitytopredictfeaturessuchastornadoes,etc

• Can’tpredictEastAsianorIndianmonsoonswell

• Regionalscaleclimaticfeaturesaredifficulttopredictaccurately

Accuracyofclimatemodelpredictions

(b)Predicted

IPCC,2007

(a)Observed

(1980-1999)

Averageprecipitation Temperatureanomaly

Variabilityamongmodels

IPCC,2007

Importanceofanthropogeniccontribution

Testsofglobalclimatemodelperformance

IPCC,2007

References• Links:– Climatemodelingvideos

– NOAAGFDL:Aboutclimatemodeling» http://www.youtube.com/watch?v=HTz2YZoRLIs

– Generalclimatemodelinganimation(www.animea.com)» http://www.youtube.com/watch?v=ADf8-rmEtNg

• IPCCReport,2007• www.giss.nasa.gov/research/modeling/• http://edgcm.columbia.edu/