Record-Breaking Southwest Summers Will Likely Get Worse, Scientist Says

The southwest deserts of the United States are naturally hot this time of year, with temperatures oscillating around the low 100s.  Yet this year the late spring heat climbed way past the normal averages in Phoenix and multiple other cities, prompting officials to issue an excessive heat warning for the deserts that will end Wednesday.

Experts reached said last weekend’s weather was unusually hot, but a study released this month found that summers across the globe will almost certainly break more records more often in the coming decades as global warming continues. Evidence of this can be seen now.  On Sunday, for instance, Phoenix reached 118 degrees, marking the 10th time this has happened since record keeping started in 1895. 
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While emergency personnel push to control fires and officials call for people to stay out of the heat, experts said what's happening now is but a glimpse of what global warming is doing to the world's summers.  Indeed, recurrent record hot summers will almost certainly be the norm in the coming years, according to a study from the National Center for Atmospheric Research, or NCAR ...  The study found an 80 percent probability that any summer between 2061 and 2080 will be warmer than the hottest on record across the world's land areas unless greenhouse gas emissions decrease.

In addition, in large parts of North and South America, central Europe, Asia, and Africa the probabilities are 90 percent or higher, said Flavio Lehner, lead author and post-doctoral researcher at NCAR.  This means virtually every summer will be warmer than the warmest during the period of 1920 through 2014. If emissions decline this probability drops in most areas, Lehner said.  Otherwise in some areas "we can basically plan [for] these very hot summers every year."
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The higher temperatures as projected by the NCAR study and others become a daunting problem for the arid southwest, a region already prone to droughts.  In 2015 a study from Columbia University's Lamont-Doherty Earth Observatory found that the Southwest and Great Plains will in the second half of the 21st-century experience drought conditions worse than those documented in ancient and modern times.

Increasing temperatures would only make any drought worse, Lehner said, but noted emissions reductions would make a substantial difference in reducing dangerous warming. "This risk can really be cut in half with these moderate mitigations," he said while referring to policies that promote less greenhouse gas emissions.  "Even moderate mitigation has a clear benefit."

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