1. National Center for Atmospheric Research
Coordinated climate change experiments to be assessed as part of the IPCC AR5
Gerald A. Meehl
National Center for Atmospheric Research
Boulder, Colorado

2. Decadal prediction (2005-2030) 2. Longer term (to 2100 and beyond)
Coordinated climate change experiments (formulated by WGCM and AIMES) to be run for assessment in IPCC AR5
Two classes of models to address two time frames and two sets of science questions:
Decadal prediction ( )
higher resolution (~50 km), no carbon cycle, some chemistry and aerosols, single scenario,
science question: e.g. regional extremes
2. Longer term (to 2100 and beyond)
intermediate resolution (~200 km), carbon cycle, specified/ simple chemistry and aerosols, new mitigation scenarios: “representative concentration pathways” (RCPs) science question: e.g. feedbacks
(Meehl and Hibbard, 2007; Hibbard et al., 2007)

3. Improved SE USA rainfall.
Developmental version of CCSM3.5 (last 20 years of 20th century)
1995 – 1999 average.
Improved SE USA rainfall.

4. Need higher resolution to simulate extreme precipitation events
Hi-CGCM = T106 (~100 km)
Mid-CGDM = T42 (~240 km)
(Kimoto et al., 2005)

5. IPCC AR4 Fig
Greater uncertainty towards higher values due in part to uncertainty in the size and nature of the carbon cycle feedback

6. Expt #1: Diagnose climate and carbon cycle feedbacks
CO2 fluxes saved
CO2 seen by carbon cycle and atmosphere
Temperature
Compatible Emissions
Schematic of Experiment #1. The carbon cycle sees increasing CO2 concentrations and changes in temperature. The land and ocean CO2 fluxes are saved to derive emissions by WG3 scientists. The land and ocean CO2 fluxes are NOT radiatively interactive with the atmosphere.
emissions = CO2 flux + CO2 concentrations

7. Expt #2: Carbon cycle response with no climate change
Climate change (AOGCM or ESM)
Carbon cycle and compatible emissions (ESM or offline carbon cycle model)
CO2 from experiment #1 seen by carbon cycle
Constant CO2 seen by atmosphere
CO2 fluxes saved
T~ 0
Temperature
Schematic of Experiment #2. The carbon cycle (land and ocean) sees CO2 concentrations from Experiment #1.
Atmospheric CO2 is constant for the radiation calculation so there is little temperature change.
Land and ocean CO2 fluxes are saved to derive emissions by IPCC Working Group 3.
The land and ocean CO2 fluxes are NOT radiatively interactive with the atmosphere. #1 #2
#2 - #1 = effect of climate feedbacks on compatible emissions
Emissions

8. Expt #3: Fully coupled ESM climate change projection
Use emissions from RCP scenario, calculate fully
coupled climate system response, compare temperature
change to experiment 1 to determine size of carbon
cycle feedback in terms of climate change
CO2 fluxes
CO2 seen by carbon cycle and atmosphere
Temperature
Schematic of Experiment #1. The carbon cycle sees increasing CO2 concentrations and changes in temperature. The land and ocean CO2 fluxes are saved to derive emissions by WG3 scientists. The land and ocean CO2 fluxes are NOT radiatively interactive with the atmosphere.

9. CCWG recommendations:
0.5 degree AOGCM version for decadal prediction experiments
2 x 2.5 degree ESM for long term experiments

10. Next: Mitigation/adaptation
New mitigation scenarios run with earth system models will have implicit policy actions to target future levels of climate change
But we can only mitigate part of the problem, and we will have to adapt to the remaining climate change
The challenge: use climate models to quantify time-evolving regional climate changes to which human societies will have to adapt

11. KAKUSHIN: Global Warming Experiment on the Earth Simulator
(MRI; Kanada et al)
Prediction of ocean and atmosphere by AOGCM
Prediction of regional climate by one-way nested NHM
Prediction of regional climate by one-way nested NHM
Time slice
experiments
20km-AGCM
270km-AOGCM
Regional Climate Model
5km-NHM
1km-NHM A A
SST
AGCM SST
B.C.
SST
25 years O
21st century
CGCM SST difference: Future - Present
200-50km-OGCM
25 years
Nested in the 20km-AGCM
25 years
From June to Oct. for each climate.
Near future
Present climate
SST yr 11

12. SP550 SP1000 Permissible Emission = (CO2 in air) solid: Coupled run
+ Ocean/Land Uptake
“coupled” = climate and carbon cycle respond to increasing concentrations
“uncoupled” = only carbon cycle responds (climate doesn’t see increasing concentrations)
SP550
PgC/year
SP1000
dashed： Uncoupled
run
solid:
Coupled run
Green:
Fossil carbon emission
(reality)
Stabilization at SP550 requires a cumulative 24% reduction of permissible emissions due to positive carbon cycle feedback (23% for SP1000)
MIROC integrated earth system model (Kawamiya et al.)