Implementation Plan for CCSM 4

CCSM 4 needs to be ready by the end of 2008 for AR5 in early 2013.

Most important items to address for CCSM 4

• Physical biases in CCSM 3. Double ITCZ, ENSO frequency, continental precipitation, high latitude land temperatures, too large windstress, and too much Arctic low cloud.

• CCSM 4 should have some form of carbon cycle.

• The indirect effects of aerosols should be included, which were omitted in CCSM 3.

HadiSST data set 1949-2004

B31.002

Changes to FV deep convection scheme and momentum transport due to convection

Stage 1 – starts on 1 March 2007

• BGC land is CLM-CN; results of C-LAMP• Aerosol indirect effect scheme: NOT NOW.• Atmosphere: updated version of the FV • Land: Community Hydrology Project • Ocean: POP 2 base code plus updates • Sea Ice: merged CICE4 and CSIM4 codes • Resolution: FV 1.9x2.5, ocean x1• Significant advance on current BGC control

runs in the T31x3 CCSM 3

Stage 2 – complete by end of 2007

• Developments in all components designed to reduce the significant CCSM 3 biases.

• Include in prognostic mode the land ice component being worked on by Lipscomb.

• Why so early? I’m afraid if we say June 2008, then won’t be ready by end of 2008.

• CAM should just include the troposphere. • Not include interactive chemistry. This was

controversial – include time slices?

Stage 3 – complete by end of 2008

• 2008 is year to validate and understand CCSM 4 that includes BGC, indirect aerosol effects, and land ice component.

• Target resolution? FV 1.9x2.5 for carbon cycle – higher resolution for short-term simulations: FV 1x1.25, x1 Ocean?

• Many questions: eg. should CCSM 4 have a dynamic biogeography component?

• Low resolution Paleo version also in 2008; this might still be the T31x3 version?

Short-Term Simulations: Proposed Form

• Start in about 1980, then run in pure simulation or simulation/assimilation mode until 2005. The short-term simulation would be from 2006 to 2030.

• Need an ensemble size of >10 to address extremes. • Does it make an important difference if the CCSM

is initialized to the actual climate of 2005? • This requires data assimilation into the ocean, and

possibly sea ice extent. Do we need to initialize the tropical Pacific for ENSO and N Atlantic for MOC?

Blue: T85, 1 Red: T42, 1 Black: T31, 3

CCSM3: Present Day Control Runs Maximum MOC in North Atlantic

Advantages of Short-Term Simulations

• Because the runs are short, the atmosphere model can be run at higher resolution: produces relevant regional information for the relatively near-term.

• Most of the climate change is already committed, so the projections are much less dependent on the highly uncertain future greenhouse gas scenarios.

• There is a much smaller range between models in their transient climate response, so that the multi-model ensemble is less dependent on the quite wide range of sensitivities among climate models.

Projections for Arctic Land Temp

Challenges of Short-Term Simulations

• No experience so far with assimilating data into the CCSM ocean and sea ice components, or with coupled model assimilation as at Hadley Centre.

• Should run chemistry in prognostic mode or with time slices? Should carbon cycle be included?

• This increases the CCSM project workload as these S-T simulations would be in addition to the more familiar, long future scenario runs planned for CCSM4 that includes a form of carbon cycle.