The CSIRO coupled global climatic model has been integrated for transi
ent increasing atmospheric CO2, conditions from 1 to 3 x CO2. The basi
s for this experiment is that there is little expectation that atmosph
eric CO2 levels will be stabilised at or below 2 x CO2, concentrations
given projected emission levels. Examination of changes in climatic v
ariables between 1 and 2 x CO2, and 2 and 3 x CO2, states revealed an
expected general diminution in the magnitude of the changes for the la
tter state. This is attributed to the progressive saturation of the CO
2, absorption spectrum at the higher CO2, concentrations. An examinati
on of annual mean surface temperature changes at decadal intervals ass
ociated with the increasing CO2, indicated that it takes 60-70 years b
efore temperature fluctuations due to natural climatic variability are
finally overwhelmed by the greenhouse effect. Surface temperatures at
3 x CO2, under transient conditions were similar to those obtained un
der 2 x CO2, equilibrium conditions with a slab ocean, except for much
reduced warmings in high southern latitudes. Time series of climatic
variables for selected variables for the control and transient runs re
vealed noticeable interannual and decadal fluctuations in both runs, a
nd highlighted the potential problems of 'sampling' data at arbitrary
timeframes. The model maintained El Nino/Southern Oscillation events t
hroughout the transient run, suggesting that this feature is a robust
characteristic of the climatic system. No untoward climatic fluctuatio
ns were noted during the transient run, implying that climatic 'surpri
ses' are unlikely, at least for present model formulations. (C) 1998 E
lsevier Science B.V. All rights reserved.