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.

Strategy Preliminary carbon cycle run in CSM 1. Updated carbon cycle now in CCSM 3. Biggest possibility of severe failure is combining updated carbon cycle with the new physical components in CCSM 4. This process needs to be done in stages, and not left until sometime in 2008. Propose a three stage strategy.

Stage 1 – starts on 1 March 2007 Version of BGC land; cf. 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? More vertical resolution in all components? Many questions: eg. should CCSM 4 have a dynamic biogeography component? Low resolution Paleo version also in 2008.

Potential Failure Points Not ready for Stage 1 by 1 March 2007. If slippage is only few months, then proceed. Timeline for Stage 2 slips. Again, if only a few months, then it’s probably okay. Timeline for Stage 2 slips by > 6 months. Then, a backup is to use the Stage 1 version for CCSM 4 with possible updates. If the IPCC AR5 schedule slips, then the Stage 2 & 3 timelines can slip by the same amount. This would be nice, but unlikely?

Verification and IPCC AR5 Runs CCSM 3 defined by present day control run. Should change to verify CCSM 4 by how well it simulates the climate of the 20th Century? If so, then we should definitely radiatively balance a 1870, not present day, control run. This requires more runs for verification. Vary the time interval between starting the 20th century runs from the 1870 control run. Number of scenarios versus ensemble size?

Short-Term Simulations Using the Community Climate System Model Background Discussed at several past CAB meetings, especially by Eric Sundquist and Tom Crowley at CAB meeting February 2006. The issue came up again at the SSC/CAB/ WG Cochairs meeting in Breckenridge. There was extensive discussion of short -term climate simulations at the Aspen WGCM/AIMES Workshop held in August. CGD discussion on Monday, 6 Nov 2006.

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

Increases in Global Ocean Temps (Results from CCSM3 Ensemble) L = Levitus et al (2005) Ensemble Members Gent et al, J Climate 11, CCSM3 Special Issue, 2006

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.

Scientific Opportunities Runs without and with data assimilation between 1980-2005 could be used to address the decadal timescale predictability of the climate system. Stimulus for multi-scale modeling activities, eg very high resolution one-way downscaling over the U.S.A. What is impact on SST biases in the upwelling regions? Changes in extremes, eg heat waves, floods, droughts. Atmospheric chemistry component added; simulations of air pollution (aerosols, ozone) in major urban areas. Several of the most pressing scientific questions regarding the climate system and its response to natural and anthropogenic forcings cannot be readily addressed with traditional models of the physical climate. While the ultimate goal is a comprehensive Earth System Model (ESM), practical considerations suggest that there will be a multitude of versions with different capabilities. The CCSM project will work towards developing a first generation coupled chemistry-climate model in the next two to three years. A project of this scope will necessarily involve scientific partnerships across ESSL, NCAR and the external CCSM community. This model could be used to study the complex interactions among biota, chemical processes, and physical climate for paleoclimate studies or scenarios for future climate change. It could also be used to study variations of the chemistry of the present-day atmosphere driven by external forcing from solar variability and major internal natural modes of variability, such as ENSO. The ocean ecosystem module includes multiple phytoplankton functional groups, limitations by several major nutrients, nitrogen fixation, and treatments of sinking and remineralization of biological material. The terrestrial module can simulate multiple agricultural plant types and human-mediated disturbance of the land surface. Both of these modules are now being tested to understand their equilibrium behavior.