Understanding Global Environmental Trends and Projections. Ants Leetmaa Geophysical Fluid Dynamics Laboratory Princeton, NJ 08542

Transcription

1 Understanding Global Environmental Trends and Projections Ants Leetmaa Geophysical Fluid Dynamics Laboratory Princeton, NJ 08542

2 Climate Scenarios Used for Attribution Studies of Climate Variability and Change Talk will focus on Climate of 20 th Century (C20C) runs model ensembles starting in 1860 driven by radiative forcing changes resulting from volcanic, solar, anthropogenic effects.

3 Global Trends Result from Natural and Anthropogenic Effects Credible assessments and predictions come from synergistic use of simulations, observations, and numerical diagnostic experiments. Natural Modes of Variability Radiative forcing - natural and anthropogenic Annular Modes Unknown Others Tropical Coupled oceanatmosphere interactions -ENSO Changes to mean circulations - (tropics and related changes) Changes to modes Surprises - abrupt change Direct effects Changes to oceanic - thermohaline circulation A firm basis is developing for understanding tropically forced climate variability. Small changes in tropical ocean temperatures can have big global impacts

4 Preliminary Results from GFDL C20C Studies (uncertainties are least for this period) Understanding origins of recent droughts and heat waves importance of sea surface temperature trends in tropical Indo-Pacific Well- simulated global trends - a central role for natural and anthropogenic radiative forcings changes Changing tropical convection helps define regional impacts - simulations plus diagnostics lead to physical understanding of: Sahelian drought - role of changes in radiative forcings North American trends - a start towards attribution Oceanic temperature, salinity and atmospheric height field trends support picture of slowly changing tropical rainfall patterns

5 Global Average Sea Surface Temperature Trends observed 3 member model ensemble Volcanic forcing by Krakatoa in late 1980 s probably overestimated

6 Equatorial Trends in Temperature and Rainfall (observed T and model 8 member mean T & P) Gradual warming of tropics Eastward shift of mean rainfall Is the eastward rainfall shift real? Agreement with related fields suggests that it is, e.g. a real change in the global circulation has occurred.

7 Changes in Tropical Convection on Variety of Timescales Alter Global Circulation Patterns Multi-year to decadal time scales implicated in global droughts, heat waves, other environmental impacts Seasonal to Interannual Time Scales ENSO related impacts small but persistent trend in eastward shift of convection Large interannual east-west shifts in convection

8 Explaining Recent Major Climate Anomalies: Warm and Dry Conditions during

9 Major Climate Anomalies can be Linked to Regional Sea Surface Temperature Changes Through Model Experiments GOGA EPOGA Observed anomalies prescribed for global ocean Observed anomalies prescribed for ENSO region IWPOGA Observed anomalies prescribed for Indo-Pacific region

10 Explaining Origins of Air Temperature Anomalies GOGA Observed With specified global SSTAs a good simulation EPOGA IWPOGA ENSO impacts provide minor contribution Forcing by SSTA in Indo-Pacific region of dominant importance

11 Explaining Origin of Rainfall Anomalies GOGA Observed With global SSTAs model does good simulation EPOGA IWPOGA ENSO a factor Indo-Pacific SSTA s critical

12 Observed Standardized SST Anomaly June 1998 May 2002 Indo - Pacific Eastern Pacific Recent Years from a Persistent Warming Trend Adapted from Hoerling & Kumar (Science, 2002.)

13 Central Africa is Undergoing Persistent Drought Conditions: Sahel rainfall: ( ) minus ( ) 8 member Model ensemble mm/month

14 Simulations and Diagnostic Studies are Leading to an Understanding of the Origins of Central African Drought Simulations with observed SSTs A prediction starting in 1860 observed observed Spread from 10 member ensemble One ensemble member Diagnostic studies show the trends to be driven primarily by warming trends in the Indo-Pacific region (results from many climate models) These simulation suggest an anthropogenic impact; previously the observed trends were thought to be result of natural variability. Idealized runs show similar drought development (1% per year increase of CO2)

15 U.S. Temperature Trends: Observations vs. GFDL Runs Historical forcing runs of CM2.0 and CM2.1 show fair agreement with the US (48- state) mean series (using as reference period) CM2.0 Ensemble Mean CM2.1 Ensemble Mean

16 Simulation and Prediction of North American and Surrounding Seas Temperature Trends Model forced with observed SSTs Specified radiative forcing from 1860 Ocean specified - land predicted Ocean and Land predicted

17 Observed and Modeled Temperature and Salinity (0-500m) Trends Last 50 Years Salinity Temperature Model Obs

18 Global Mean Atmospheric Temperature Trends: MSU and GFDL GCM Troposphere Stratosphere Linear Trends ( ) MSU: 0.14 K/decade GCM: / K/decade Satellite and Model Estimates of Atmospheric Temperature Trends are Being Reconciled

19 Comments The new generation of climate models are more credible having been tested and scored/verified against current climate variability and trends Some regional trends over the past 100 years can be attributed with more confidence to changes in natural and anthropogenically induced radiative forcing changes The resulting small trends in tropical ocean temperatures have already lead to shifts in tropical convection and consequently impacted ocean and atmospheric circulation patterns Climate projections for the next years, representing partly continuations of existing trends, will be more credible