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CCSM Paleoclimate Working Group Report
Bette Otto-Bliesner and Matthew Huber, Co-Chairs
Friday, 9 July 2004
Eldorado Hotel, Santa Fe, New Mexico
The CCSM Paleoclimate Working Group met on Friday, 9 July 2004, for one-half day. Formal presentations were given on Quaternary and "deep-time" paleoclimate applications of CCSM3, an application of the dynamic vegetation code to a "deep-time" paleoclimate period, and modeling of Holocene carbon dioxide variations. These presentations were followed by a series of brief presentations and discussions of future directions that the PaleoWG should take and how it might initiate those new directions. The working group also discussed our priorities for the CSL allocation.
CCSM3 simulations of the climate of the LGM and mid-Holocene (Otto-Bliesner, Brady, Kothavala, and Tomas)
Fully coupled CCSM3 simulations at T42x1 resolution are being integrated at NCAR for the Last Glacial Maximum (LGM, 21,000 years ago) and the mid-Holocene (6000 years ago). These simulations will be initially 300 years in length but will be extended as computer time becomes available. Boundary conditions and forcings are prescribed as per the specifications of the second phase of the Paleoclimate Modeling Intercomparison Project (PMIP2). In particular, changes are made in the atmospheric trace gases, solar constant and orbital parameters, and for the LGM, the continental ice sheets and coastlines. Vegetation is kept at modern. Preliminary results are available and show results similar to the proxy data, including an enhanced African monsoon over northern Africa in boreal summer and a reduced and shallower meridional overturning circulation in the North Atlantic.
CCSM3 simulations of the climate at the Permian-Triassic Boundary (Kiehl and Shields)
A fully coupled CCSM3 simulation of the climate for conditions at the Permian Triassic boundary (251 Ma) has been carried out. Paleogeography conditions are based on data from Rowley with atmospheric CO2 levels set at 10 times present levels. The simulation has been run for ~1400 years to date. Preliminary results indicate warm waters at high latitudes that have limited deep ocean circulation patterns, which may be important for oxygen levels at depth.
The Garden of Eocene: Reconstructing a lost paradise with the LSM-DGVM (Shellito)
The LSM Dynamic Global Vegetation Model (DGVM) has been integrated to revise the vegetation scheme used in Eocene climate modeling studies and make an initial assessment as to how flora may have responded to a short-term dramatic warming at the Paleocene-Eocene boundary. The DGVM was driven with climatologies from two Eocene modeling experiments in CSM, one with pCO2 at 560ppm and another with pCO2 at 1120ppm. The greatest differences between the two experiments in modeled plant functional types are found in the high latitudes, poleward of 60 degrees. Further studies of paleovegetation in DGVM are needed to take into account the physiological response of vegetation to CO2 for a more realistic simulation.
Modeling Holocene atmospheric CO2 variations (Joos)
Joos discussed a series of applications using the Bern carbon cycle model in conjunction with CSM 1.4 integrations to explore the interactions between CO2 and climate change during the Holocene. Ice core records indicate that non-anthropogenic CO2 over the last millennium varied within about 6 ppm suggesting a low-frequency variability of Northern Hemisphere temperature of about 0.5 deg C. Modeling results also suggest that the 20 ppm CO2 increase during the past 8 ka is explained by a combination of mechanisms, including CaCO3 compensation, SST warming, land use and desertification, and coral reef buildup.
Informal presentations and discussion
Christine Shields presented an illuminating exploration of the issues related to running and setting up a deep paleo (Permian) simulation with CCSM3.
Jean-Francois Lamarque (with Jeff Kiehl and Lisa Sloan) presented a short talk on "Chemical studies under paleoclimate conditions" that focused on plans to model atmospheric conditions using WACCM for large chemical (methane) perturbations during the Paleocene-Eocene Thermal Maximum.
Natalie Mahowald provided an update on the current state of the Biogeochemical Working Group, clearly demonstrating linkages between the PaleoWG and the BGCWG, and calling on greater involvement by the PaleoWG.
Huber introduced the Deep Paleoclimate SGER proposal and received input from the working group on his suggested initial test cases. The need for greater community building within the PaleoWG was discussed. A 'wiki' for introducing the broader community to setting up CCSM for 'deep paleoclimates' was announced at http://roskilde.eas.purdue.edu/~cdpl/phpwiki
Rodrigo Caballero Augi
J. Keith Moore