New study predicts higher high temperatures for Florida thanks to climate change

Amid Florida's ongoing July heat wave, a new study released Tuesday by the Union of Concerned Scientists predicts that by mid-century the state will experience some of the highest frequencies of extreme heat in the nation.

How hot? The Tampa Bay area may face four months with a heat index of 105 degrees or more — in other words, it will be unsafe to work outdoors for a third of the year.

Kristina Dahl, lead author of the study published Tuesday in the journal Environmental Research Communications, said the group put out its findings "because we wanted to give people a sense of what's coming down the pike." The Union of Concerned Scientists advocates for taking steps to curb climate change, such as imposing a carbon tax to reduce greenhouse gas emissions.

The study predicts that, in an average year, Florida will face "105 days with a heat index over 100 degrees F (up from just 25 days historically) and 63 days with a heat index over 105 degrees F."

The study's authors were able to break down the increase in hot days by location. For instance, they found that in the Tampa-St. Petersburg area, the region has until now experienced only four days a year with feels-like temperatures above 105 degrees. If steps are not taken to slow the pace of climate change, the study found, by mid-century the frequency of days with a heat index of 105 degrees or more will increase to 127 days annually — about four months of the year.

In Zephyrhills, it would go from four to 125 days, and Spring Hill would go from five to 129 days of temperatures above 105 degrees, the study found.

Rising heat indexes will be most pronounced in South Florida, but North Florida will have more hot days as well. Tallahassee, which normally averages five days above 105 degrees, would see that increase to 50 days a year.

The health impacts of rising heat indexes are particularly worrying, Dahl said, noting that "we know extreme heat can be extremely dangerous and can even be deadly."

A soaring heat that lasts for so long each year in Florida would pose an increased health risk for people who work outdoors in such industries as construction, fishing and farming, the study noted.

This is far from the first study to say Florida is in the cross hairs of climate change, which is expected to bring not just more heat but also more flooding, stronger hurricanes, more toxic algae blooms and other woes to the Sunshine State. The Third National Climate Assessment, produced by a team of federal scientists in 2014, sounded a siren about Florida's risk from climate change.

David Zierden, who is Florida's official state climatologist, reviewed the new study and said its findings are in line with other research on this topic.

"It's all very sound science," he said. "The main theme, that as we continue to warm, these daily heat thresholds are going to rise, is not surprising."

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May was already the hottest May on record for Florida since record-keeping began in 1895. Zierden noted that June ranked as the third-warmest June in the state's history. The biggest increase, he said, has been in nighttime temperatures, not daytime ones.

"We think it goes hand-in-hand with the higher humidity we're seeing," he said. "Also we've got higher ocean temperatures." A third factor, he said, is the state's continued development, which creates "heat islands" that retain warmth even after the sun goes down.

For the study, Dahl said, the scientists used climate model data from 18 different models of temperature and relative humidity to calculate the heat index. The models have a resolution of four kilometers (about 2½ miles), she said, enabling them to pinpoint the effects on individual cities.

"Once we had a full picture across the U.S., we could pull out specific locations," she said.

She acknowledged that many people will handle the hotter days cranking their air conditioning down to compensate.

"Air conditioning is a double-edged sword," Dahl said. "It has saved lives, but there are certain limits … Running your air conditioner in the cities makes things slightly hotter."

In addition, in most places in America, the electrical power to run your air conditioning comes from burning fossil fuels, which is what's driving climate change.

Contact Craig Pittman at craig@tampabay.com. Follow @craigtimes.