Production of global climate change scenarios in RT1 and RT2A

1. Production of global climate change scenarios in RT1 and RT2A Jean-Francois Royer (RT2A) James Murphy (RT1)

2. Aims of RT1 and RT2A • Produce ensembles of global climate simulations with earth system models, and provide model results needed in other RT • Use two different approaches to sample climate uncertainty: • Multi-model (RT2A) • Perturbed parameter approach (RT1)

3. Links with other RTs New models and methods RT1 Simulated datasets RT4 RT5 RT6 RT2A RT7 Updated scenarios Boundary conditions RT2B RT3

4. Organization of the work Stream 1 Year 1-2 Use existing coupled models Standard methods for simulations Use scenarios from IPCC Stream 2 Year 3-4 Improved earth system models (RT1) Methods of ensemble generation (RT1) Updated scenarios (RT7)

5. Combination of atmosphere-ocean models used to produce the multidecal coupled simulations in RT2A first stream

6. IPCC scenarios (TAR) 4xCO2 A2 A1B B1 2xCO2 historical Control

7. Advancement of coupled simulations in RT2A first stream (9-th February 2005)

8. RT2A control simulations global annual mean air temperature at 2m height

9. RT2A historical simulations global annual mean air temperature at 2m height

10. RT2A A2 scenarioglobal annual mean air temperature (2m)

11. A2 scenario t2m anomalies(difference from 1971-2000 climatology for each model)

12. B1 scenario t2m anomalies

13. A1B scenario t2m anomalies

14. RT1: Version 1 of Ensemble Prediction System • Recommended design by month18, specified system by month 24. • Will be used by RT2A to generate a second stream of “production” global climate simulations in years 3 and 4 • Will comprise separate systems for seasonal to decadal and multi-decadal prediction • Following slides show runs planned and in progress to test ideas for Version 1 of the multi-decadal system.

15. Defining Version 1 of the Centennial System • Basic idea: Compare the transient responses in a multi-model ensemble generated by RT2A during months 1-18 against those in a “perturbed parameter” ensemble based on HadCM3 • The perturbed physics ensemble will consist of: • 1860-2100 simulations with 16 HadCM3 versions with multiple perturbations to uncertain surface and atmospheric parameters • Augmented by additional pseudo-transient simulations obtained by scaling the equilibrium responses of 128 2xCO2 simulations of the “slab” version of HadCM3 with perturbed parameters • The 128 member slab ensemble has already been run. The 16 member HadCM3 ensemble is being generated.

16. Parameter Perturbations Boundary layer Turbulent mixing coefficients: stability-dependence, neutral mixing length Roughness length over sea: Charnock constant, free convective value Large Scale Cloud Ice fall speed Critical relative humidity for formation Cloud droplet to rain: conversion rate and threshold Cloud fraction calculation Dynamics Diffusion: order and e-folding time Gravity wave drag: surface and trapped lee wave constants Gravity wave drag start level Convection Entrainment rate Intensity of mass flux Shape of cloud (anvils) (*) Cloud water seen by radiation (*) Land surface processes Root depths Forest roughness lengths Surface-canopy coupling CO2 dependence of stomatal conductance (*) Radiation Ice particle size/shape Cloud overlap assumptions Water vapour continuum absorption (*) Sea ice Albedo dependence on temperature Ocean-ice heat transfer

17. Climate sensitivity in a large perturbed parameter ensemble Multiple parameter perturbations (128 runs) Single parameter perturbations (53 runs) Red histogram shows results from a ensemble of 128 HadSM3 (slab) model versions designed to produce good present day climate simulations while maximising coverage of parameter space and climate sensitivity Black histogram shows results from an earlier 53member ensemble (Murphy et al 2004) with perturbations to one parameter at a time.

18. HadCM3 perturbed parameter experiments Ensemble of 16 HadCM3 members:Members sub-selected from the 128 member HadSM3 ensemble. Ensemble designed to consist of members which produce good simulations of present climate while maximising the coverage of parameter space and the range of possible climate sensitivities.

19. HadCM3 perturbed parameter experiments:Experimental design for a single ensemble member • Haney forced spin-up • Flux corrected control • Historical forcings run (natural and anthro forcings) • 2000-2100 driven by SRES A1B, plus maybe one additional SRES scenario

20. Towards probabilities for regional climate change during the 21st century We need large ensembles of 21st century simulations.Too expensive to run 128 HadCM3 versions, so…Calibrate scaling relationships between the equilibrium response and the 21st century response using 16 HadCM3 versions.Can then generate a large ensemble of pseudo-HadCM3 simulations from the 128 member ensemble of equilibrium simulations NW Europe surface temperature for 1860-2100 inferred by scaling from equilibrium responses of 128 ensemble members Early illustration of possible results

21. Evaluating Centennial Ensemble Prediction Systems • Predictions cannot be verified • So how will we assess possible designs for the ensemble prediction system ? • We should sample the widest possible range of modelling uncertainties • We should sample the space consistent with observational uncertainties

22. Sampling modelling uncertainties (1):In RT1 we will… Compare HadSM3 perturbed parameter ensembles of a limited size against multi-thousand member ensembles which sample parameter space more thoroughly (climateprediction.net) Develop facility to run perturbed parameter ensembles with a different GCM (EGMAM) e.g., comprehensive sampling of multiple parameter perturbations can generate a wide range of climate sensitivities, Stainforth et al, 2005

23. Sampling modelling uncertainties (2) HadCM3 perturbed param ensemble already run with 1% per year CO2 forcingCan compare the results against an existing multi-model ensemble HadCM3 ensemble with perturbed parameters CMIP2 multi-model ensemble 1% per year CO2 increase