GFDL’s ESM2 global coupled climate-carbon Earth System Models Part II: Carbon system formulation and baseline simulation characteristics
Dunne, J. P., J. G. John, E. N. Shevliakova, R. J. Stouffer, J. P. Krasting, S. L. Malyshev, P. C. D. Milly, L. T. Sentman, A. J. Adcroft, W. Cooke, K. A. Dunne, S. M. Griffies, R. W. Hallberg, M. J. Harrison, H. Levy, A. T. Wittenberg, P. J. Phillips, and N. Zadeh, Journal of Climate, 26(7). DOI:10.1175/JCLI-D-12-00150.1. 04/13.
The primary objective of this work was to expand upon the capabilities of past GFDL models used to study climate on seasonal to centennial time scales by the addition of a comprehensive and interactive carbon cycle in the land, ocean and atmosphere to “close the carbon cycle” in the same way we do for water and energy in a traditional climate model. While the primary contribution is in improving our ability to anticipate how earth system interactions will modulate the rate of increase of carbon dioxide in the atmosphere, the fact that the models require simulation of land and ocean ecosystems make them extremely valuable for a range of applications in ecosystem impacts and feedbacks as well. Our approach has been to develop two models with different ocean dynamical/physical cores while keeping all other components the same in order to test the sensitivity of our results to our assumptions inherent in our ocean configuration.
Relevance to NOAA science
This effort is a critical component of NOAA’s research into the future of the earth as a system under the influence of anthropogenic forcing to better understand how emissions of carbon dioxide from fossil fuels, land use decisions and climate and ecological interactions will determine future carbon dioxide levels and the corresponding climate change. These models are also critical to projection of the impacts of climate change and carbon dioxide fertilization and acidification on ecosystems.
Relevance to society
The models whose physical formulation and simulation characteristics are described here are intended to be supplied to the public as part of the Coupled Model Intercomparison Project Phase 5 in support of the IPCC Fifth Assessment.
Unique aspects of this study
This research is unique in utilizing GFDL’s highly successful CM2.1 climate model as a carbon model backbone, in incorporating GFDL’s state of the art ocean biogeochemical and terrestrial ecology models, and in comparing two models of starkly differing ocean physical configuration in the same configuration elsewhere.
Description of the methodology
We based the development of these new earth system models on GFDL’s highly successful CM2.1 climate model and made sure to maintain climate fidelity as interacting carbon system components were built in. We incorporated GFDL’s state of the art ocean biogeochemical model into two models of starkly differing ocean physical configuration and built a new terrestrial ecology model.
Known weaknesses or uncertainties
While state of the art in their design, these models suffer from many of the weaknesses typical of this class of model including the double ITCZ, weak Amazonian rainfall, and others. Fortunately, many of the weaknesses of these two models are opposing (e.g. one has weak El Nino, the other strong) that will allow us improved overall characterization of climate sensitivity.