Drought is a common feature of climate; but every so often when a longer-lasting or somewhat severe drought occurs, it is not long before someone, somewhere, makes the claim that that drought was either caused or made worse by CO2-induced global warming. A simple test of this thesis can be conducted by examining the historic record of drought for the location in question. If it can be shown that similar (or greater) frequencies or magnitudes of drought have occurred in the past, prior to the modern increase in CO2, then it cannot be definitively concluded that the current drought is the product of anything other than natural climate variability.
Unfortunately, long-term historical drought records covering more than a few decades of time are lacking for most locations across the planet. As a result, scientists have sought to augment these short-term instrumental drought histories with much longer proxy records, records that will sometimes extend back in time several centuries to millennia. Such is the case in the recent study of Vance et al. (2015), who derived a 1,003-year proxy of historical drought in eastern Australia.