GFDL - Geophysical Fluid Dynamics Laboratory

GFDL?s ESM2 global coupled
climate-carbon Earth System Models Part I: Physical formulation and
baseline simulation characteristics

Dunne, J. P., J. G. John, A. J.
Adcroft
, S. M. Griffies, R. W. Hallberg, E. N. Shevliakova, R. J.
Stouffer, W. Cooke, K. A. Dunne, M. J. Harrison, J. P. Krasting, S. L. Malyshev, P. C. D. Milly, P. J. Phillips, L. T. Sentman, B. L. Samuels,
M. Spelman, M. Winton, A. T. Wittenberg, and N. Zadeh, Journal of Climate, 25(19), DOI:10.1175/JCLI-D-11-00560.1. 10/12

Key Findings

  • GFDL has developed two new earth
    system models to study climate-carbon interactions on diurnal to
    millennial timescales.

  • The models differ only in the
    physical ocean component ? one the Modular Ocean Model version 4.1
    pressure-based vertical coordinate, and the other the Generalized
    Ocean Layer Dynamics density-based coordinate. Comparison between
    the two allows us to assess the sensitivity of the coupled
    climate-carbon system to our assumptions about ocean formulation.

  • While the models demonstrate
    similar overall scale fidelity, they have important differences in
    both their thermocline characteristics, deep circulation,
    ventilation patterns and El Nino variability that suggest critical
    roles for details of ocean configuration in the coupled carbon
    climate system.

Goals of the research

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.