A method is described for evaluating the 'partial derivatives' of glob
ally averaged top-of-atmosphere (TOA) radiation changes with respect t
o basic climate model physical parameters. This method is used to anal
yse feedbacks in the Australian Bureau of Meteorology Research Centre
general circulation model. The parameters considered are surface tempe
rature, water vapour, lapse rate and cloud cover. The climate forcing
which produces the changes is a globally uniform sea surface temperatu
re (SST) perturbation. The first and second order differentials of mod
el parameters with respect to the forcing (i.e. SST changes)are estima
ted from quadratic least square fitting. Except for total cloud cover,
variables are found to be strong functions of global SST. Strongly no
n-linear variations of lapse rate and high cloud amount and height app
ear to relate to the non-linear response in penetrative convection. Gl
obally averaged TOA radiation differentials with respect to model para
meters are also evaluated. With the exception of total cloud contribut
ions, a high correlation is generally found to exist, on the global me
an level, between TOA radiation and the respective parameter perturbat
ions. The largest non-linear terms contributing to radiative changes a
re those due to lapse rate and high cloud. The contributions of linear
and non-linear terms to the overall radiative response from a 4 K SST
perturbation are assessed. Significant non-linear responses are found
to be associated with lapse rate, water vapour and cloud changes. Alt
hough the exact magnitude of these responses is likely to be a functio
n of the particular model as well as the imposed SST perturbation patt
ern, the present experiments flag these as processes which cannot prop
erly be understood from linear theory in the evaluation of climate cha
nge sensitivity.