  The mean world climate has warmed since the 19th Century as the anthropogenic
emission of greenhouse gases has increased the atmospheric opacity to thermal
infrared radiation. Has this warming increased the frequency or severity of
droughts? We define an objective aridity index that quantifies the
precipitation forcing function of drought. Using the GHCN daily database from
{\it c.\}~1900 to the present and averaging over hundreds or thousands of sites
in each of eight continental or semi-continental regions, we evaluate trends in
aridity. Seven of these regions have sufficient data for significant
conclusions. In them the mean aridity decreased at logarithmic rates from
$(-2.2 \pm 0.6) \times 10^{-4}$ to $(-5.1 \pm 0.2) \times 10^{-3}$ per year,
three or more times their nominal ($1\sigma$) uncertainties.
