GFDL climate model suite (CM2-O)
The suite of model experiments is based on GFDL climate model components. They represent a consistent hierarchy of models with different ocean sea-ice resolutions (see table).
|ocean horizontal resolution||1°||0.25°||0.1°|
|grid cell size at the equator||111 km||28 km||11 km|
|grid cell size at 60°||56 km||14 km||5.5 km|
|eddy parameterization||submeso-& mesoscale||submesoscale||submesoscale|
The hierarchy of climate models contain the biogeochemical ocean model miniBLING. The resulting CM2-O-miniBLING model suite is used to investigate the response of the circulation and carbon cycle to climate change.
Two simulations were run for each model:
- a preindustrial control simulation over 200 years
- an idealized sensitivity to climate change over 80 years.
The miniBLING module simulates global biogeochemistry with a minimal number of tracers (PO4, O2 and DIC). This extreme reduction of tracer number provides an order-of-magnitude decrease in computational overhead compared to typical Earth System models. Despite the small number of tracers, the model represents the most well-established nonlinear dependencies of biogeochemical cycling on environmental state by using empirical parameterizations developed for GFDL's TOPAZ and BLING models. These include an implicit size-based grazing relationship in order to determine the export fraction, iron-light colimitation using a fixed dissolved iron climatology, and alkalinity as an observationally-constrained function of local sea surface salinity. Although experimental, the simulation provides an internally-consistent, fully interactive representation of biogeochemical cycling at the global scale.
The numerous online diagnostics performed during the simulations allow study of the processes at play in this response.
In particular, the differing ocean resolutions enable comparison of the role of mesoscale eddies when resolved (as in CM2.6) or parameterized (as in CM2-1deg). Note that current climate models participating in the IPCC use parameterizations to represent the role of mesoscale eddies. Assessing how those parameterizations do compared to fully resolved eddies is an important research topic considering the conjectured crucial role that eddies play in the Southern Ocean circulation and carbon cycle responses to climate change.