Atmosphere-Ocean Model Simulations: 1950-2099

[Source: NASA/GISS]

The global coupled Atmosphere-Ocean Model was designed at GISS for climate predictions at decade to century time scales. Atmospheric Models at GISS have been under continual development since 1970; the Ocean and Coupled Models since 1990.

The Atmosphere-Ocean Model is a computer program that simulates the Earth's climate in three dimensions on a gridded domain. The Model requires two kinds of input, specified parameters and prognostic variables, and generates two kinds of output, climate diagnostics and prognostic variables. The specified input parameters include physical constants, the Earth's orbital parameters, the Earth's atmospheric constituents, the Earth's topography, the Earth's surface distribution of ocean, glacial ice, or vegetation, and many others. The time varying prognostic variables include fluid mass, horizontal velocity, heat, water vapor, salt, and subsurface mass and energy fields. Each simulated month, the Model produces an output "D" file that contain numerous unscaled climate diagnostics. Subsequent programs read these D files and produce scaled climate variables.

A 120-year control simulation (C023) of the 1995 version of the Atmosphere-Ocean Model was published in the Canadian journal "Atmosphere-Ocean". It and a companion 80-year experiment (C024) with compounded annual 1% CO2 increases were contributed to CMIP (Coupled Model Intercomparison Project) and to IPCC (Intergovernmental Panel on Climate Change) for their "Second Scientific Assessment of Climate Change".

For the 1999 version of the Atmosphere-Ocean Model, six 150-year simulations were run: C089 and C092 are control simulations with constant 1950 atmospheric composition; C090 and C093 use observed greenhouse gases from 1950 to 1990 and compounded annual .5% CO2 increases from 1991 to 2099; C091 and C094 use the varying greenhouse gases plus tropospheric sulfate aerosol changes. Annual .5% CO2 increases after 1990 were chosen because they match the current radiative forcing caused by all greenhouse gases [Hansen et al., 1998, "Climate forcings in the Industrial era"].