Showing papers by "Paul J. Valdes published in 2004"

Transient simulations of Holocene atmospheric carbon dioxide and terrestrial carbon since the Last Glacial Maximum

Abstract: [1] Conflicting hypotheses are investigated for the observed atmospheric CO2 increase of 20 ppm between 8 ka BP and pre-industrial time. The carbon component of the Bern Carbon Cycle Climate (Bern CC) model, which couples the Lund-Potsdam-Jena Dynamic Global Vegetation Model to an atmosphere-ocean-sediment component, is driven by climate fields from time-slice simulations of the past 21 ka with the Hadley Centre Unified Model or the NCAR Climate System Model. The entire Holocene ice core record of CO2 is matched within a few ppm for the standard model setup, and results are broadly consistent with proxy data of atmospheric 13 CO2, mean ocean d 13 C, and pollen data, within their uncertainties. Our analysis suggests that a range of mechanisms, including calcite compensation in response to earlier terrestrial uptake, terrestrial carbon uptake and release, SST changes, and coral reef buildup, contributed to the 20 ppm rise. The deep sea d 13 C record constrains the contribution of the calcite compensation mechanism to 4–10 ppm. Terrestrial carbon inventory changes related to climate and CO2 forcing, the greening of the Sahara, peat buildup, and land use have probably influenced atmospheric CO2 by a few ppm only. The early Holocene CO2 decrease is quantitatively explained by terrestrial uptake and calcite compensation in response to terrestrial uptake during the glacial-interglacial transition. The recent hypothesis by Ruddiman [2003] that anthropogenic land use caused a 40 ppm CO2 anomaly over the past 8 ka, preventing the climate system from entering a new glacial, would imply an anthropogenic emission of 700 GtC and a decrease in atmospheric d 13 Co f 0.6 permil. This is not compatible with the ice core d 13 C record and would require an upward revision of land use emission estimates by a factor of 3 to 4. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1615 Global Change: Biogeochemical processes (4805); 1610 Global Change: Atmosphere (0315, 0325); KEYWORDS: carbon cycle modeling, carbon dioxide, Holocene

Performance guided scheduling in GENIE through ICENI

Abstract: Initial work in the Grid ENabled Integrated Earth system model (GENIE) project involved a series of parameter sweep experiments using a Grid infrastructure consisting of a flocked Condor pool, a web service oriented data management system and a web portal In this paper we introduce the Imperial College E-Science Networked Infrastructure (ICENI) Grid middleware, and describe how it can be used to increase the efficiency of GENIE parameter sweep experiments We perform several experiments using a combination of different computational resources and different job deployment mechanisms Our results suggest that ICENI does not produce any significant overhead in the sojourn time of a GENIE parameter sweep experiment and can promote the sharing of computational resources between institutions