We continue our fact check of Al Gore’s rant in Davos, turning now to his claim that CO2 is “sucking the moisture out of the land and creating the droughts”. So there’s Gore’s take. But the IPCC is nowhere near so confident. Regarding droughts due to deficient precipitation they report “Global studies generally show no significant trends... in derived drought frequency and severity data… with very few regional exceptions”. And then in their online atlas the IPCC summarizes evidence from around the world since 1950 in agricultural droughts (those due to dry soil). And while in most of the world there is no trend, or there are trends but no known connection to CO2, they claim that in southern Europe and Western USA there is evidence of a connection to CO2. Except the IPCC report, as Roger Pielke Jr reports, also says that the confidence in these claims is only “medium” which sounds impressive until you discover that means a 50-50 chance of being true, the same reliability as a coin toss. Whereas elsewhere in Europe they insist there is no evidence of trends in droughts.
Pielke Jr also discusses two new papers presenting very long historical time series of drought frequency in western Europe. One shows measurements of precipitation deficits from 1851 to 2018 and finds, well, nothing: “Our study stresses that from the long-term (1851–2018) perspective there are no generally consistent trends in droughts across Western Europe.” Another study looking at the post-1968 interval covering all sub-regions of Europe (including southern Europe) finds that there are no consistent trends:
“Seemingly, one of the central outcomes of this research is that there is little change in drought characteristics for 1969–2018. It also seems, no particular tendencies for more or less frequent droughts in the two major geographical domains of Europe are present. This reinforces the stochastic nature of the drought natural hazard.”
In case you don’t do statistics on a regular basis, stochastic “refers to the property of being well described by a random probability distribution.” Or, in plain language, “random”.
Summarizing, Pielke Jr. says:
“In Western and Central Europe – basically Atlantic France all the way to Moscow, north of the Mediterranean region and south of the North Sea region – the IPCC and the underlying peer reviewed research on which it assesses has concluded that drought has not increased and, logically, that increased drought cannot be attributed to human-caused climate change. The only exception here is that the IPCC has medium confidence in an increasing trend of soil moisture deficits in some subregions, however the IPCC has low confidence that this trend can be attributed to human-caused climate change. Looking to the future, at temperature changes of 2C and more, at present the IPCC does not expect the current state of scientific understandings to change.”
But it might if there are new discoveries. So, Pielke Jr. adds, stay tuned, that’s why scientists do research. As opposed to Al Gore who has no need of research since he already knows all the answers.
To be a bit nerdy, the term "stochastic" means something more specific than just generally "random". Ornery statistics mostly refer to the magnitude of some variable such as, in this case, rainfall deficit measured in mm. Stochastic analysis is different because it focuses on timing - how often something happens, how long to wait between events, the placement of record breakers along the time axis, whether the timing of events display some regularity or whether the inter-event time from one event to the next is just random. In other words it's about the properties of events along the time axis rather than the magnitude of those events. In this case I guess it refers to that latter property - no discernible pattern in their recurrence; every event is a surprise.