As yet another heat record fell on Wednesday in Phoenix — 144 days this year when temperatures reached or exceeded 100 degrees — the people who sweltered through it all might be wondering if this is the new normal.

Will every summer be as hot as this one?

Experts say it’s possible this summer is an anomaly, but hasten to add that a combination of the urban heat island effect and human-driven climate change will continue to worsen extreme, and sometimes deadly, heat.

“We’ve been ratcheting up in our average temperatures,” said Nancy Selover, the state climatologist and a professor at Arizona State University. “We’re not necessarily going to be setting new records every single year, but ultimately we’re moving in that direction.”

On Wednesday, the record for most days at or above 100 degrees was broken at Phoenix Sky Harbor International Airport. The previous record of 143 days was set back in 1989. The streak means temperatures on more than half the days this year so far have reached at least 100.

“Almost every heat record that we have here in Phoenix, we’ve broken this year — shattered some of those records even,” said Jaret Rogers, a meteorologist for the National Weather Service in Phoenix.

It’s also been an exceptionally dry summer throughout the state. The lack of summer storms led some to call the monsoon the “non-soon,” after it finished last month as the driest monsoon on record.

Climate change sped up by human-made emissions has led to a trend of increasing temperatures and contributed to extended drought throughout the Southwest.

In Phoenix, those warming temperatures are exacerbated by the urban heat island effect, created as the metro area’s heavily paved and sprawling development keeps heat particularly high at night, and keeps it higher during the day.

“The pattern was set up to have multiple heat episodes, and we never got a chance to cool off and get that moisture in,” Rogers said. “The urban heat island is more of a local thing; the climate impacts are a larger-scale process. You can see that trend of warming across the whole Southwest, and we expect that to continue.”

Under normal circumstances, Arizona’s air pattern comes from the west, across the Pacific Ocean. In the summer, the pressure systems move around, Selover said.

In the summer, that jet stream that hits Arizona from the west for much of the year moves up into Canada, and a huge column of warm air, or a high pressure system, pulls moisture up from Mexico into the state, fueling the monsoon and often cooling temperatures. That didn’t happen this year.

While it’s too soon to tell if this will be a new pattern, global warming will have an impact on those atmospheric patterns, Selover said.

Temperatures, too, will continue to trend upward if people don’t drastically cut planet-heating greenhouse gas emissions.

But climate experts concede it’s hard to say if the extremes of this summer will become a new normal. Temperatures can fluctuate yearly, but it’s the decades-long averages that indicate how the climate is changing overall.

“This was very unusual,” Selover said. “This may be a start of a new pattern, it’s a little too soon to tell. But I do know for sure that we’re seeing the trend of warmer temperatures.”

In Phoenix, extreme temperatures are becoming more normal. The heat season has expanded, with high temperatures starting earlier and lasting longer than they did in past decades, according to National Weather Service data. There are more warmer days overall, said Rogers, with the number of days in the 110- to 115-degree range increasing.

“Previously, we had more 108 to 110 days, but those shift up to 110 to 112 days, and that shift is throughout the temperature curve,” Rogers said. “The number of 110 days is slowly increasing each decade. This year, it was just off the charts.”

This year, there were 53 days of temperatures at or above 110 degrees, with 14 days of 115 degrees or greater — both all-time records. The record for 110-degree days was last set in 2011, when there were 33 days at 110 or higher.

Those kinds of temperatures have very real public health consequences. Heat-related illnesses are common during the summer, with nearly 3,000 people visiting Arizona emergency rooms every year because of heat-related illnesses, according to the Arizona Department of Health Services. 

Since 2009, more than 2,000 people have died from exposure to excessive natural heat.

Heat-related deaths are continuing to rise, according to data from the Maricopa County Department of Public Health. This year, 134 people have died from heat so far, with 212 possible heat-related deaths still under investigation.

And now the dry summer may be followed by a drier-than-average winter, Selover said. Scientists say La Niña conditions have been observed in the Pacific Ocean, a weather event that tends to create warmer temperatures in the Southwest.

“The reservoirs kind of filled up from last winter, but we didn’t have anything in the summer, so people are pumping more groundwater,” Selover said. “Plus, we have all these dry forests that didn’t get their drinking water over the summer, so the fire danger is going to continue to be high until we actually get some good rain. So that’s something we really need to be careful of and watch out for and keep our eye on.”

Erin Stone covers the environment for The Arizona Republic and azcentral.com. Send her story tips and ideas at [email protected] and follow her on Twitter @Erstone7.

Environmental coverage on azcentral.com and in The Arizona Republic is supported by a grant from the Nina Mason Pulliam Charitable Trust. Follow The Republic environmental reporting team at environment.azcentral.com and @azcenvironment on Facebook, Twitter and Instagram.

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