Summertime high temperatures in Phoenix will average 10 degrees hotter by the year 2100 — as hot as current-day Kuwait City — according to new projections by the nonprofit group Climate Central.
Worse, average daily temperatures in the hottest months will probably be three to five degrees hotter as soon as 2050, if humans continue pumping out greenhouse gases at current rates, a representative of the climate-change news and activism organization said.
"Consider your typical summers now, when you have a run of several days where it's really hot — put a blanket of a few more degrees on it, and that's what you're looking at by the middle of the century," said Alyson Kenward, Climate Central vice president for creative production.
It's not just Phoenix getting warmer, of course. As part of Climate Central's "States at Risk" series, the new study looked at 360 U.S. cities to examine changes in the number of "danger days" — when heat and humidity combine to create a heat index of 105 degrees Fahrenheit or higher. The group looked at 29 different global climate models and analyzed historical data to come up with its projections.
It's a timely study, given the early-summer temperature records shattered in Arizona and elsewhere in the country in June.
The study predicts that Arizona will be "hard hit" with danger days: Whereas Phoenix had 121 such days in 2000, for instance, Climate Central foresees 147 in 2050.
Here's where the implications of the study begin to look better for Phoenix than for other cities, though.
Looking strictly at temperatures, global warming may feel like a thermopocalypse to residents of many U.S. cities. Climate Central sees Miami going from 24 danger days in 2000 to 151 in 2050. New York City's danger days see a quintupling, from five in 2000 to 28 in 2050.
Phoenix, however, already experiences weeks of 105 and above every summer, and sometimes much hotter. The temperature change by 2050 won't be as dramatic to residents here.
The predictions for 2100 are starker: Ten degrees hotter any given summer day would be much more noticeable. But it's unclear how accurate Climate Central's projection truly is when it comes to Phoenix.
The Phoenix-to-Kuwait projection looks at previous temperatures and how they've increased, then charts that out to the future, Kenward explained. It didn't take into account humidity, and it didn't take account of the urban heat-island effect, in which the concrete-and-steel infrastructure of a burgeoning metropolis traps heat in the day and releases it slowly at night, raising regional temperatures. Scientists believe the effect is responsible for a significant temperature rise in the past 50 years in Phoenix, causing average daytime temperatures to go up by about five degrees and at night by about 10 degrees.
Kenward wasn't immediately able to say how much of the increase in past Phoenix temperatures was specifically due to climate change and how much to the heat-island effect. Nor was she able to say precisely what impact the heat-island-effect forecast had on the Phoenix projections going forward. But she did say urban changes have exacerbated the increase over time.
Matthew Hirsch, a meteorologist with the National Weather Service in Phoenix, said that predicting how hot Phoenix may get owing to climate change is a dicey exercise.
True, there has been a clear trend in warmer temperatures here over the past few decades, owing to global warming, regional warming in the Western United States in the past 20 years or so, and urbanization. But assuming the rate of warming will remain steady throughout the century, he cautioned, might not be realistic.
"It's unfair to say there'll be an additional 10 degrees of warming," Hirsch said. "That does seem a little extreme to me."
These days, daytime Phoenix temperatures range from an average of 65 in the winter months to 107 in the hottest part of the year, late June and early July.
"I'd be very surprised if we were approaching 117 for normals," Hirsch said. "I think what's fair to say is we'll see more extreme temperatures on a day-to-day basis."
The all-time-high recorded temperature in Phoenix — 122 degrees in June of 1990 — is probably in jeopardy, Hirsch said.
"We came very close to breaking it this year," he said, referring to reported highs of 118 to 119 on June 19 and 20.
Nature might have a self-limiting effect, he added. "As you get more warm temperatures, the atmosphere can hold more moisture. What if the temperature was offset by more monsoon activity?"
Nancy Selover, Arizona's state climatologist, said that if Climate Central's "States at Risk" information intends to bring attention to climate change and the possibility of more extreme heat in the future, great. Other than that, the comparison to Kuwait City and prediction of 10 degrees hotter in Phoenix by 2100 simply isn't believable, Selover said.
"I don't consider it a credible scientific study," Selover said.
Global climate models like those used for the study don't take Arizona's summer rainfall into account, but the monsoons have a limiting effect on local temperatures, Selover points out.
In Kuwait, summers are hot for a different reason, and the Middle Eastern nation receives almost no summer precipitation. Besides the vastly different climate, experts believe there is no clear "linear trend" that would enable someone to easily predict average temperatures here by 2100. But there is "extreme variability," Selover said.
Also, even the extreme temperature in Kuwait has its limits. It was 126 on Kuwait City's hottest day ever — but Lake Havasu City has reached that. And the hottest recorded temperature anywhere in the world, 134 degrees, was reached not in the Middle East but in California's Death Valley, a low-moisture sink of rock and canyons that traps heat.
The Phoenix overall record high of 122 degrees is now 26 years old, Selover noted. The city’s highest recorded overnight low temperature, meanwhile, is 96 degrees, set in 2003.
Selover agrees that the "huge" heat-island effect presents future Phoenix residents with an opportunity to lower average temperatures in the city.
"We've been doing that for the past 10 years, actively," she said. "It's not just, 'Oh, you paint everything white.' They have materials that don't absorb the solar radiation. They're using different kind of pavement materials that won't hold the heat as much. Every city in the Valley is participating to mitigate the heat island."
Climate Central argues in its November 2015 "report card" on climate-change preparedness that Arizona could do a lot more to prepare for a hotter future: It gives the state an overall grade of C-. In a blistering review that would draw the ire of the state's drought planners, Climate Central claims that "the state has done almost nothing to understand, plan for, and address its future risks."
That's not a true statement, but there's no doubt Arizona leaders and residents have big decisions to make in the coming decades when it comes to managing the scarce resources of the Sonoran Desert. Global warming will likely make droughts and heat waves worse, as experts have been warning for years.
But Phoenix is not about to shrivel up and blow away, even in the unlikely event that Climate Central's prediction comes true. After all, Kuwait City has a population of four million. And air-conditioning.