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  • Previdi, M., and B. G. Liepert, 2008: Interdecadal variability of rainfall on a warming planet. Eos Trans. AGU, 89, 193, 195, doi:10.1029/2007ES002028.

How much will the global water cycle
accelerate with global warming? In a recent
study, Wentz et al. [2007] used satellite
observations to show that global mean precipitation
increased by 7% per °C increase
in global mean surface temperature over
the period between July 1987 and August
2006. This yields an absolute precipitation
increase of 13.2 ± 4.8 millimeters per year
per decade, a rate of increase that is 2–3
times greater than that simulated by general
circulation models (GCMs). Century-long
integrations of GCMs also yield much
smaller global precipitation increases of
about 1–3% per °C of global warming [Held
and Soden, 2006]. Nonetheless, Wentz et al.
[2007, p. 235] argue that the recent 20-year
period may “be long enough to indicate
that the observed scaling relations [e.g.,
between precipitation and temperature]
will continue on a longer time scale,”
implying significant errors in climate
model predictions.
We present evidence for large interdecadal
variability in the global precipitation
response to temperature changes, implying
that the observed response during any
given 20-year period may be unrepresentative
of longer-term precipitation changes
with global warming.
Further, we suggest that the rapid increase
in global precipitation observed during
1987–2006 occurred because decreases in
atmospheric aerosol loading accompanied
increases in greenhouse gases. These
decreases in natural and anthropogenic
aerosol concentrations should have contributed
to an increase in global rainfall that is
in addition to the increase caused by rising
greenhouse gas amounts. If the recent
reduction in aerosol loading does not persist
(e.g., if aerosol concentrations stabilize),
then the scaling relation between precipitation
and temperature observed during the
past 20 years may not hold into the future.

Last Updated: 2008-08-22

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