We use a tropospheric energy budget argument to analyze
20th century precipitation changes. We find that global and ocean-mean
General Circulation Model (GCM) precipitation changes can be
understood as being due to the competing direct and surface
temperature dependent effects of external climate forcings. In
agreement with previous work, we find that precipitation responds more
strongly to anthropogenic and volcanic sulfate aerosol and solar
forcing than to greenhouse gas and black carbon aerosol forcing per
unit temperature. This is due to the significant direct effects of
greenhouse gas and black carbon forcing. Given that the relative
importance of different
forcings may change in the 21st century, the
ratio of global precipitation change to global temperature change may
be quite different. Differences in GCM 20th and 21st century values
are tractable via the energy budget framework in some, but not all
models. Changes in land-mean precipitation, on the other
hand, cannot be understood with our method at all, even if land-ocean
heat transfer is considered. We conclude
that the tropospheric energy budget is a useful concept for
understanding precipitation response to different forcings, but that
it does not fully explain precipitation changes even in the global
mean.

Last Updated: 2008-08-26