This scientific article, by Aiguo Dai and others, was originally published in September 1998 in Geophysical Research Letters (Vol 25 No 17, Pps. 3367-3370). The authors calculated the Palmer Drought Severity Index (PDSI) globally, "using gridded monthly air temperature and precipitation." Since the late 1970s, the authors found, tracking El Nino cycles, that there were large changes in dry and wet areas. However, these changes "are qualitatively consistent with those expected from increased greenhouse gases in the atmosphere." The article is available in full-text, including figures and references.
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