© Crown copyright Met Office AR5 Proposed runs for CMIP5 John Mitchell, after Karl Taylor, Ron Stouffer and others ENES, arch 2009

© Crown copyright Met Office Change in IPCC philosophy Short and long term predictions Runs and analysis

© Crown copyright Met Office Socio-economic variablesEmissions Surface temperature Socio-economic variablesConcentrations Surface temperature Forward approach: start with socio-economic variables Reverse approach: start with stabilization scenario concentrations Concentrations Emissions Pre AR4 used forward approach AR5 will use reverse approach mitigation costs  implied emissions  concentrations  sensitivity  impacts Requires interpolating and scaling

© Crown copyright Met Office DEFINING SCENARIOS LONG-TERM Reference concentration profiles High reference—~8.5 W/m 2 in 2100 but rising RCP8.5 High stabilization level—~6 W/m 2 RCP6 Median stabilization level—~4.5 W/m 2 RCP4.5 Low stabilization level—~2~3 W/m 2 RCP2.X ONLY the 2.x W/m 2 scenario is at its stabilization level before 2100.

© Crown copyright Met Office Strategy for AR5

© Crown copyright Met Office Two classes of models to address two time frames and two sets of science questions: 1.Near-Term ( ) high resolution (perhaps 0.5°), no carbon cycle, some chemistry and aerosols, single scenario, science question: e.g. regional extremes 2. Longer term (to 2100 and beyond) lower resolution (roughly 1.5°), carbon cycle, specified or simple chemistry and aerosols, benchmark stabilization concentration scenarios Science question: e.g. feedbacks

© Crown copyright Met Office

Groups of experiments (long term) Control, historical and AMIP simulations Future projections ( prescribed concentrations) Past and future (prescribed emissions) Runs to diagnose feedbacks, increase understanding Historical and AMIP runs Detection and attribution © Crown copyright Met Office

Basic runs Coupled AO models Control, AMIP & 20C RCP 4.5, 8.5 Carbon cycle models Emissions driven control and 20C Emissions driven RCP8.5

© Crown copyright Met Office Basic runs (ctd) 1%/increase CO2 (140 years) Abrupt 4xCO2(150 years) Fixed SST with 1x and 4x CO2

© Crown copyright Met Office Carbon cycle feedbacks: AOGCM and ESM experiment 1 (specified concentrations) -give CO2 and climate vegetation feedback ESM experiment 2 (specified concentrations, radiation sees 1XCO2 - no climate change) -with (1) gives climate vegetation feedback ESM experiment 3 (fully coupled CC, driven by emissions) -check on full carbon cycle feedback ESM experiment additional ( specified concentrations, vegetation sees 1XCO2) - With (1), check on CO2 vegetation feedback

© Crown copyright Met Office Simulations to diagnose “fast” and “slow” climate system responses 4.1* Idealized 1%/yr run to 4xCO2 in coupled model. 4.3a* Control for Hansen-style experiment (4.3b) to diagnose “fast” climate system responses (i.e. “forcing”) 4.3b* Hansen-style expt. to diagnose “fast” climate system responses, CO2 quadrupled, otherwise as in 4.3a. 4.3c** Hansen-style expt. to isolate the model’s “fast” response to CO2’s greenhouse effect alone. As 4.3b but carbon cycle “seeing” 1xCO2 (rather than 4xCO2) 4.4* Diagnose “slow” climate system responses to an instantaneous quadrupling of CO2 in coupled model. Perform a Gregory-style analysis to diagnose the “slow” responses and estimate climate sensitivity. 4.5† Gregory-method estimate of the “fast” climate response with a 12? member ensemble of 5-year runs in which CO2 is instantaneously quadrupled.

© Crown copyright Met Office Control, model evaluation

© Crown copyright Met Office

20 th Century temperature change – CMIP3 ensemble Philip Brohan

Diagnose radiative forcing – especially that due to aerosols! © Crown copyright Met Office

More Information WGCM Report Taylor, Stouffer et al cm/wgcm- 12/reports/Taylor_CMIP5_expts7.pdf

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