Must-have slide No. 2: The 'global-change-type drought' and the future of extreme weather
This must-have slide comes from a 2005 study, “Regional vegetation die-off in response to global-change-type drought.” I first saw it in a powerful 2005 presentation [PDF] by climatologist Jonathan Overpeck, “Warm climate abrupt change-paleo-perspectives,” that concluded “climate change seldom occurs gradually.”
Overpeck noted that the 2005 study, together with the recent evidence that temperature [in red] and annual precipitation [in blue] are headed in opposite directions in the U.S. Southwest, raises the question of whether we are at the “dawn of the super-interglacial drought.”
Before explaining why I like this slide and how it shows the future of extreme weather, I need to review the conclusion of the study, which was led by the University of Arizona, with Los Alamos National Laboratory and the U.S. Geological Survey:
Global climate change is projected to yield increases in frequency and intensity of drought occurring under warming temperatures, referred to here as global-change-type drought …
Our results are notable in documenting rapid, regional-scale mortality of a dominant tree species in response to subcontinental drought accompanied by anomalously high temperatures.
The researchers examined a huge three-million acre die-off of vegetation in 2002-2003 “in response to drought and associated bark beetle infestations” in the Four Corners area (Arizona, New Mexico, Colorado, and Utah).
This drought was not quite as dry as the one in that region in the 1950s, but it was much warmer, hence it was a global-warming-type drought. The recent drought had “nearly complete tree mortality across many size and age classes” whereas “most of the patchy mortality in the 1950s was associated with trees [greater than] 100 years old.”
The study concluded:
Our results quantify a trigger leading to rapid, drought-induced die-off of overstory woody plants at subcontinental scale and highlight the potential for such die-off to be more severe and extensive for future global-change-type drought under warmer conditions …
It should be obvious that warm-weather droughts are worse than cooler-weather droughts — but if it weren’t, this study shows they are.
The slide depicts annual precipitation and annual temperature in the Four Corners area (i.e. the heart of the U.S. Southwest). It shows that over at least the past 70 years, and presumably much longer, annual precipitation and annual temperature are not particularly correlated. You can have warm droughts and you can have cool droughts.
The warning of the slide to humanity is clear: All future droughts are going to be warm-weather droughts — and if we don’t change course soon — they will become hot weather droughts, then hellish droughts.
Remember, on our current emissions path, the planet is poised to be 5.5Â°C to 7Â°C warmer by 2100 (see here). The climate models predict that in mid-latitudes land masses (i.e. inland U.S), warming could be 50 percent higher. That would be 8Â°C to 10Â°C warmer — which is way, way off that chart.
And even the Bush administration acknowledged the scientific literature says that on our current emissions path, the SW is poised to get much drier (see here). And that drought will likely last a long, long time (see here).
So we have what Overpeck calls “the super-interglacial drought.” Australia, which is more sensitive to initial climate change than the SW and thus a canary in the coal mine, calls it the “permanent dry” or perhaps “collapse.”
Others might just call it a desert.
But before you get the permanent desertification, you get warm-weather droughts, the “global-change-type drought,” and that is the future of extreme weather this century.
Note: I started this new feature and a new category here for must-have PowerPoint slides last August (see here). I haven’t done a good job so far of building out the full set of PPTs, but I will endeavor to add a couple of month.