BALTIMORE — Last month was one of the warmest Junes on record in Baltimore, and persistent bouts of extreme heat could land Charm City’s summer on the wrong side of the record books.

As the week begins, the next brutal heat wave has arrived. Temperatures are forecast to reach triple digits Monday and Tuesday, with high humidity capable of pushing the heat indexes to between 105 and 110 degrees.

It would mark the third and fourth days this summer that the temperatures have hit 100 degrees Fahrenheit at BWI Marshall Airport. On average, over the past 30 years, that has happened only about once a year, according to the National Weather Service.

As of Thursday, the airport weather station has seen 25 days at or above 90 degrees and 12 days that reached 95. The 30-year average? Fourteen days at or above 90 degrees, and three above 95.

The sweltering temperatures have prompted heat warnings around the Baltimore area, opening cooling centers stocked with cold water. Nevertheless, dozens of Marylanders have traveled to emergency rooms and urgent care centers seeking treatment for heat-related illness. And six people have succumbed to the heat this year, including one person in Baltimore City and several in Prince George’s County.

Last week, the Maryland Department of the Environment also issued a drought watch for most of the Eastern Shore, with stream flows and groundwater levels lower than usual for the time of year. Residents were asked to begin reducing their water usage. Conditions in the rest of the state are considered normal.

Researchers say climate change could make summer in Baltimore hotter overall, and make excessively hot days more common.

That doesn’t mean every June will be as hot as last month, but it does mean that temperatures like last month’s will be about three times more common going forward because of climate change — at least according to calculations from the nonprofit Climate Central.

Compared with 50 years ago, researchers from Climate Central estimate that climate change has added about 13 extra days with above-normal temperatures. Whereas in the 1970s that number tended to be about 40 days per summer — now it is closer to 50.

“Half of your summer … is now expected to be hotter than what you remember that summers were in Baltimore — what generations before your generation remember that summers were in Baltimore, as well,” said Shel Winkley, a meteorologist for Climate Central who worked as a television forecaster in Texas for 15 years. “Which I think is really telling.”

Taking into account the average air temperature, last month was the fifth warmest June on record. But if you only include each day’s high temperature, June 2024 takes second place, compared with every other June in Baltimore going back to the late 1800s.

Baltimore’s average high temperature in June was 89.2 degrees — almost 5 degrees hotter than normal, according to the weather service.

High-pressure systems, often called heat domes, have played a role in this year’s heat.

“We just happen to be the unlucky ones, along with the Western U.S.,” said Brendon Rubin-Oster, a meteorologist for the National Weather Service in Sterling, Virginia. “Unfortunately, we’ve been under that heat dome.”

Climate change could be making those domes even more intense, Winkley said.

“The temperatures are getting hotter. They’re expanding in size, so they’re taking up more of the map than they used to,” Winkley said. “They’re lingering longer than they used to.”

AccuWeather forecasters said in a news release that temperatures early this week in Baltimore, Washington, D.C., and Roanoke, Virginia, could rival the blistering heat wave from 1988. As if that weren’t enough, it’s possible that smoke from wildfires in western and central Canada will sweep into not only the Midwest, but also parts of the Eastern U.S.

The extremely hot days take their toll. On June 22, the first day this year to cross triple digits, the Maryland Department of Health tracked 91 EMS calls due to heat-related illness, and 76 emergency room or urgent care visits, a significant jump from any other day that week.

“It has a huge impact, especially on the vulnerable and the young ones,” said Richard Damoah, assistant professor at Morgan State University’s Climate Science Division. “It also has a huge impact on your day-to-day activities, because you want to stay indoors as much as possible.”

The effect of extreme heat is particularly pronounced in urban areas with fewer trees and less greenery to provide shade and balance out the heat-absorbing asphalt and concrete. They’re often called heat islands.

Ben Zaitchik, a professor in Johns Hopkins University’s Earth & Planetary Sciences Department, is part of a group setting up weather stations around the city, particularly in underserved neighborhoods, and meeting with residents to discuss environmental issues and the weather monitoring. The goal of the project, called the Baltimore Social-Environmental Collaborative, is to inform the city’s climate change planning in the years ahead.

During the high heat event June 22, and another July 6, the collaborative’s weather stations captured broad geographic variation. In general, temperatures were at their worst in the inner part of Baltimore City, and declined the closer you got to the suburbs, Zaitchik said. At its most pronounced, the gap was about 7 degrees.

The difference is actually most dramatic at night, Zaitchik said.

“If you go out after sunset and put your hand on a dark parking lot, it’s still warm, right?” he said. “These materials retain the heat and continue to radiate overnight, whereas if you’re out in a place with more soil, grass surface, that cools a lot faster after the sun goes down.”

Zaitchik and his team are evaluating solutions that could ease the heat island effect — going beyond just planting trees and other greenery. Things like painting rowhouse roofs white and installing permeable pavers instead of giant slabs of asphalt.

They’re also looking to characterize the effect of extreme heat on vulnerable people, who have no choice but to spend time outside working or taking public transit, or who must spend time indoors without adequate air conditioning. The effort must go beyond merely counting heat-related deaths, Zaitchik said.

“It’s an extreme outcome, but well before you get to death, you’ve got asthma or COPD exacerbation,” he said. “You’ve got heat stress that doesn’t really cause you to go to the hospital, right? But it changes what you’re doing, or your kids don’t get recess outside or they’re not learning well because their school doesn’t have air conditioning.”

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