Claire Michaud,10, of Bangor tries to beat the heat at the splash pad at Riverfront Park in Old Town. Credit: Linda Coan O'Kresik / BDN

If you think the oppressive hot weather the past several weeks was bad, there is more to come in the next 30 years, a new study found.

All Maine counties will see the number of days topping 90 degrees double over the three decades, with many experiencing more hot days in a row, a study released Monday by nonprofit climate researcher First Street Foundation said.

It may seem surprising that Maine, considered a cool state, will see those types of heat increases, which First Street attributed to a changing climate. But the quick-warming Gulf of Maine, heat trapped in large cities like Portland and even small ones including Biddeford and other factors are contributing to the build-up of warmth across the state.

Even 80-degree days can cause heat stress in older adults, pregnant women, infants and those with chronic illness. During a stretch of mid-80s temperatures in July, 60 Mainers visited emergency departments complaining of heat illnesses, according to state data.

The frequency, duration and intensity of extremely hot days will increase across the country, First Street said, with some of the most severe and dangerous heat in the central and southern U.S. Miami-Dade county in Florida, which currently suffers with seven days at around 103 degrees, will experience 34 days at that temperature by 2053, First Street said. Nationwide, the seven hottest days will become the 18 hottest days in that timeframe.

First Street measured air temperatures and considered land-surface temperatures, canopy cover, impervious surfaces, land cover and proximity to water in its estimates of all U.S. counties. Its Risk Factor web portal allows people to look up heat trends by address.

Some 50 U.S. counties are expected to experience temperatures topping 125 degrees next year, and that will rise to 1,023 counties by 2053. according to First Street. That extreme heat belt stretches from northern Texas and Louisians to Illinois, Indiana and into Wisconsin.

In Maine, the average annual temperature in Bangor rose 1.4 degrees to 45.4 degrees from the first Earth Day in 1970 through 2019, according to Climate Central data. Portland rose 2.7 degrees to 47.7 degrees in that time, higher than the U.S. average of 2.4 degrees. Statewide, the average annual temperature has risen nearly 2.5 degrees over the four decades to 40.6 degrees. The U.S. average rose 2.4 degrees to 53.8 degrees.

During a sweltering last week of July, Portland almost reached 100 degrees, a temperature last topped in July 2011, according to National Weather Service data. Portland’s record was 103 degrees on Aug. 2, 1975.

Southern Maine will be hit hardest by rising temperatures. York County’s 90-degree-plus days will almost double to 21 days and it will see the highest number of 100-degree-plus — 4 days — of any Maine county. Cumberland County is expected to see its current seven days above 90 degrees more than double to 15 days over the next three decades.

“We need to be prepared for the inevitable,” Matthew Eby, CEO of First Street, said. “And the results will be dire.”