Sheffield, J., Andreadis, K.M., Wood, E.F. and Lettenmaier, D.P. 2009. Global and continental drought in the second half of the twentieth century: severity-area-duration analysis and temporal variability of large-scale events. Journal of Climate 22: 1962-1981.
The authors note that drought is "among the costliest and most widespread of natural disasters," and that it is "generally driven by extremes in the natural variation of climate … modulated by external forcings such as variations in solar input and atmospheric composition, either natural or anthropogenic."
What was done
Using "observation-driven simulations of global terrestrial hydrology and a cluster algorithm that searches for spatially connected regions of soil moisture," Sheffield et al. "identified 296 large scale drought events (greater than 500,000 km2 and longer than 3 months) globally for 1950-2000."
What was learned
The four U.S. researchers report that "the mid-1950s showed the highest drought activity and the mid-1970s to mid-1980s the lowest activity."
What it means
If anthropogenic CO2 emissions and the global warming they are supposed to produce are responsible for catastrophic droughts, as the U.S. Environmental Protection Agency has recently declared them to be, it seems strange indeed that the global drought activity of the last half of the 20th century was greatest at the start of that period, when atmospheric CO2 concentrations and mean global temperatures were far less than they were at its end. So, no; we do not believe that these twin evils of the radical environmentalist movement are in any way responsible for the temporal variation of extreme drought activity over the last half of the 20th century.