The CSIRO Atmospheric Research Mark 2b climate model (Hirst et al., 1996, 1999) has recently been used for a number of climate change simulations. These start from 1880 to avoid the "cold start problem". This version of the CSIRO model includes the Gent-McWilliams mixing scheme in the ocean and shows greatly reduced climate drift relative to earlier versions (e.g. Dix and Hunt, 1998). The drift in global mean surface temperature in the new control run is about -0.02 ºC/century. Note that the model uses flux correction. The model atmosphere has 9 levels in the vertical and horizontal resolution of spectral R21 (approximately 5.6 deg. longitude by 3.2 deg. latitude). The ocean model has the same horizontal resolution with 21 levels.
In the basic greenhouse gas experiment (the one used in SCENGEN) the model combines the effect of all radiatively active trace gases into an "equivalent CO2" concentration. Observed concentrations are used from 1880 to 1990 and the IS92a projections into the future. This gives close to a 1%/year compounding increase of equivalent CO2. We acquired the results from this experiment from the IPCC Data Distribution Centre in 1999. The greenhouse gas only change fields used in SCENGEN are calculated as the difference in climate between the 30-year means of years 2071-2100 and 1961-90 in the greenhouse gas only forced simulation. The global warming by 2071-2100, with respect to 1961-90, was 3.1deg C and the increase in global precipitation was 5.92%, yielding a global precipitation sensitivity of 1.9% per degree Celsius warming. The climate sensitivity of the same atmospheric model, coupled to a mixed-layer ocean, was estimated to be 4.3deg C.
Mean monthly precipitation pattern correlation coefficient = 0.74
Dix,M.R. and Hunt,B.G. (1998) Transient climatic change to 3 x CO2 conditions Global and Planetary Change, 18, 15-36.
Hirst,A.C., Gordon,H.B. and O'Farrell,S.P. (1996) Global warming in a coupled climate model including oceanic eddy-induced advection Geophysical Research Letters, 23, 3361-3364.
Hirst.A.C., O'Farrell,S.P. and Gordon,H.B. (1999) Comparison of a coupled ocean-atmosphere model with and without oceanic eddy-induced advection. 1. Ocean spin-up and control integrations J. Climate (submitted)
Watterson,I.G., O'Farrell,S.P. and Dix,M.R. (1997) Energy and water transport in climates simulated by a general circulation model that includes dynamic sea ice Journal of Geophys. Res., 102, 11,027-11,037.