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Dawn of the Super-Interglacial Drought?

Global warming makes droughts longer and stronger — and more likely. That has been a major theme of this blog (just plug “drought” into the search engine). Business as usual greenhouse gas emissions may lead to desertification for a stunning 30% of the Earth’s surface! And now we learn:

Severe water shortages are likely to constrain future expansion of population, agriculture and industry in the south-western US, the fastest growing part of the country, according to a report by the National Academy of Sciences.

A 2005 study led by the University of Arizona, with Los Alamos National Laboratory and the U.S. Geological Survey, 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.”

Most of this tree death was caused by bark beetle infestation, and “such outbreaks are tightly tied to drought-induced water stress.” Healthy trees defend themselves by drowning the tiny pine beetles in resin. Without water, weakened, parched trees are easy meals for bugs.

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The authors warn that the recent drought in the Four Corners area “may be a harbinger of future global-change-type drought throughout much of North America and elsewhere, in which increased temperatures in concert with multidecadal drought patterns” cause unprecedented changes in ecosystems. In a 2005 talk I attended, climatologist Jonathan Overpeck noted that this study, together with the recent evidence that temperature and annual precipitation are headed in opposite directions, raises the question of whether we are at the dawn of the super-interglacial drought.” [See slide 6]

The increased risk of severe drought we are seeing today was predicted back in 1990 by scientists at NASA’s Goddard Institute of Space Studies. Their model also suggested that, in the second half of this century, severe drought, which was already occurring with about 5 percent frequency by 1990, will occur every other year-and more frequently in the West.

It is, of course, purely an ironic coincidence that severe droughts (and wildfires) have hit Oklahoma and Texas, Wyoming, Australia, and China — states and countries with political leaders (or former leaders) opposed to climate action. But it is no coincidence that severe droughts are on the rise. We are changing the climate and much worse is to come if we don’t take action soon