I thought we had dispatched the notion some time ago. Anthony posted a new study which states
Drought is expected to increase in frequency and severity in the future as a result of climate change, mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming……..
More realistic calculations, based on the underlying physical principles8 that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years.
I am not aware of any global drought index on a timeseries graph. If anyone knows of one, especially if one can pull the numbers, please leave a link in the comments. The thrust of the paper is to state the “Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming.”
Well, that may be true if you cherry pick the years. It is true for the US if your start point is in the 70s, when we had many wet years, then, we’d see more drought since then, on average. However, if one goes back to the beginning of the data set for the US, we can see that the reported temp increases is accompanied by a wetter U.S.
I thought I’d try something fun by overlaying a couple of graphs. It was mostly an exercise for me, but I thought I’d share it. In the graph below, we see two graphs combined. The column graph is the US. PMDI.
I’ve been under the weather a bit lately, and it has apparently muddled my thinking. The other graph is the HadCrut3 NH temp graph with a 12 month running mean. What I should have done was to put GISS’ US temp graph in this conflation. It makes little difference because while the trend for the US is slightly lower, the general direction is the same.
As we can see, the droughts are essentially random and hold no correlation to temps. Like any two random time series graphs, people can pick out spots where there looks to be a correlation. But, to lay any doubt to rest, I would direct the reader’s attention to the US temp graph. Compare the reported temps of the 30′s to the reported temps of the 90s. They are nearly identical. Now look at the drought index graph. The drought index is inverted.
The graphics took me a lot longer than actually knowing and being able to demonstrate there is no correlation to temps and droughts. As stated in the paper, there are simply too many processes involved to get a simple linear relationship. Any scientist who has made the assertion that there is such a relationship needs to demand their parents money back from their Alma Mater ……… and turn back in any accreditations or credentials they may have. They can probably keep their membership to the UCS, in that it isn’t a scientific organization.
The scale, obviously is off, but the zero mark is lined up.