In the Sunday edition of the Arizona Daily Star we were treated with a scare story about megadroughts titled, “S. Ariz. closer to an epic drought .” The sub-headline of the story by Tony Davis (seen only in the print edition) reads, “If emissions are unchecked, upper risk is 50%, study says.” The first line in the Star story refers to “human-caused climate change.” Trouble is, the study, itself, does not mention “emissions” or “human-caused climate change.” Those statements in the Star are pure fabrication. You can read the full study here.
Just for the record, above is a scan of the Star headline and story beginning:
The study “Assessing the risk of persistent drought using climate model simulations and paleoclimate data” is an exercise in statistical manipulation and computer modeling. It does imply that warming predicted by computer models could cause drought. But we have seen that computer models have failed spectacularly in prediction of temperature (see my article: Failure of climate models shows that carbon dioxide does not drive global temperature).
Here is what the study says;
“In the current generation of global climate models, the risk of a decade-scale drought occurring this century is at least 50% for most of the greater southwestern US and may indeed be closer to 80%… The probability of multidecadal megadrought is also high: the likelihood of a 35 year event is between 10% and 50% depending on how much climate change is realized during the coming century. The probability of even longer events (> 50 year, or “permanent” megadrought) is non-negligible (5-10%) for the most intense warming scenario.”
But:
“An obvious limitation of our work is that it is ‘blind’ to certain aspects of dynamically-driven changes in prolonged drought risk. For instance, changes in the magnitude, frequency, or teleconnection patterns of El Nino and La Nina (e.g., Coats et al. 2013) may alter the statistics of interannual variability in ways that are not captured by our simple models. Further, megadrought statistics over the last millennium may be forcing-dependent, as suggested by Cook et al. (2004), for instance, which shows that megadroughts were more common during the medieval climate era of 850-1200 CE. Another very serious limitation is imposed by the reliability of the models themselves to make realistic predictions of changes in climatological precipitation for the end of the 21st century.”
And:
“Our estimates of risk are consequently only as accurate as climate model projections of changes in precipitation.”
Has global warming caused any drought conditions in the western U.S.? Let’s look at the data of drought conditions since 1900:
Let’s take a longer perspective on drought:
Is it still as scary as the Star alleges? The study authors are free to do their modeling and speculations. It seems to me, however, the Arizona Daily Star is making up data, perhaps to fit an agenda, and thereby doing a dis-service to readers.