Update: a commenter below has noted that the Palmer Drought Severity Index uses an inverse scale, with more negative numbers reflecting an increase, not decrease in drought. The commenter appears to be correct and I apologize for the misinterpretation. Still unexplained, however, is why the claimed increase in atmospheric water vapor due to global warming would cause increasing drought; see comments below.
A plot of the worldwide data for the Palmer Drought Severity Index shows that there has been an unprecedented decrease in world drought severity over the past 30 years.
[The title of this post is facetious about CO2 being the cause of the decreased drought - see comments below]