(From left) Isabella Gambill, assistant director of climate, energy and resilience at A Better City; Zoe Davis, city of Boston climate resilience project coordinator; Dr. Caleb Dresser, Beth Israel Deaconess Medical Center emergency physician; and Mia Mansfield, Massachusetts assistant secretary for resilience speak on a panel about preparing and responding to extreme heat in Massachusetts.

As Boston trudges through the first heat wave of the summer, surviving high temperatures is top of mind for residents across the region. This is especially true for communities where limited greenery and dark surfaces like asphalt trap and hold heat, often correlating with historically redlined areas.

Extreme heat — and what to do about it — was also on the minds of researchers, community advocates and local leaders at a heat resilience symposium, held at Boston University June 18, the day before temperatures started to climb.

The conference, organized by Boston University’s School of Public Health and the Metropolitan Area Planning Council, brought together experts currently working to address the impacts of extreme heat in communities across the area.

For many at the symposium, the message was clear: It’s better to implement solutions sooner rather than later — which means getting started now. That kind of preparation is also about getting responses to heat in place before a heat wave sets in.

“The time to prepare is now, not when the emergency is happening. That’s go-time,” said Zoe Davis, senior climate resilience project manager with the city of Boston, during a panel at the symposium.

Increased human-caused climate change is increasing the amount and severity of high-heat days. As humans burn fossil fuels, the released carbon in the atmosphere traps more heat, causing baseline temperatures to surge and making subsequent heat waves worse.

A 2019 study published in the journal Environmental Research Communications forecasted that by the middle of this century, the number of days when the heat index — a combined measure of heat and humidity — reaches over 100°F could double compared to the end of last century; the number of days where the heat index could reach over 105°F could triple.

And already, scientists suggest we’re seeing distinct increases in high-heat days.

Scientists from Climate Central, an independent climate nonprofit, and World Weather Attribution found in a report published last month that between May 2024 and May 2025, an estimated 4 billion people experienced at least 30 more days of extreme heat due to human-caused climate change.

That same report identified 67 extreme heat events in the same time period that had record-setting temperatures or caused major impacts to people or property. All 67, the researchers found, were made more likely by climate change.

That report used attribution science. Under that approach, researchers compare real-world data with climate models of a hypothetical cooler climate that would have existed without warming caused by the burning of fossil fuels.

The impacts from those higher-heat days are more likely to be felt by communities already disparately impacted by other factors.

Lizzi Weyant, acting executive director at MAPC, said the organization started its heat-focused efforts in the spring of 2020 in recognition that, with the coming summer, many of the populations most impacted by the COVID-19 pandemic were the same populations that might struggle to cool their homes and rely, in warmer weather, on cooling centers or other public air-conditioned spaces.

“We knew that summer was fast approaching, and we knew that we were about to face a heat crisis in our communities that was on top of — but 100% related to — the public health crisis,” said Weyant. “We knew that people would have nowhere to go to cool down, as we saw public and private spaces close.”

Considering the rates of heat illness, and how they connect to equity, is a prominent lens for the work, said Amanda McNeill, an environmental analyst in the division of environmental toxicology in the state Department of Public Health, during a presentation at the event.

“Heat equity and heat-related illness is important and needs to be part of the conversation,” McNeill said. “This is a statewide issue.”

Weyant said that solutions to extreme heat will require legislative action in addition to on-the-ground work. Local efforts spearheading heat resilience efforts are especially important, she said, given federal disinvestment in climate and environmental activity.

Those kinds of local solutions were on display at the symposium in a series of “lightning talks,” quick presentations on work being pursued across the greater Boston region to better track and address extreme heat.

Patricia Fabian, an associate professor in the environmental health department at Boston University’s School of Public Health, presented three research efforts aimed at increasing heat resilience for local populations.

Those efforts included work with Boston Public Schools to install indoor sensors to track air quality and other data like heat. That temperature data — from 4,000 sensors across 125 schools — to document things like which schools and classrooms are hottest as a way to optimize the use of resources.

Fabian has also been working to install heat sensors across the city of Boston through the B-COOL study, to track how summer temperatures varied across the city. The research effort provides more granular data — currently there is one National Weather Service sensor in the city, located at Logan International Airport. In its first year, researchers on the project found that on hot days temperatures in hot-spot neighborhoods like Dorchester, Mattapan, Roxbury, Chinatown and East Boston could be significantly higher than at the official Logan Airport sensor.

She also discussed work across the harbor through the C-HEAT study, a collaboration between the Boston University School of Public Health and the Chelsea-based nonprofit GreenRoots to identify populations in Chelsea and East Boston at greater risk for extreme heat impacts, analyze factors contributing to heat exposures and build capacity for communities to respond to extreme heat events.

Staff from the city of Cambridge presented, in one lightning talk, on efforts to build new shade structures in spaces that will best serve communities, offering so-called “third spaces” away from home and work where residents can gather in cooler areas. Municipal efforts are also targeting adding seating in “strategic areas” with existing shade — the result of a $450,000 investment through the city’s participatory budgeting process in 2024.

Seth Strumwasser, a data analyst at the Boston Region Metropolitan Planning Organization, presented an overview and updates about the organization’s Neutralizing Onerous Heat Effects on Active Transportation, or NO-HEAT, initiative. That project, launched last year, is looking to identify areas that experience more extreme heat effects, especially as it relates to people walking and biking, in its first phase, which is set to wrap up this summer.

The second phase of the NO-HEAT project will work with four partner municipalities — Chelsea, Everett, Revere and Framingham — to implement individualized solutions aimed at best supporting those communities.

The development of the dataset identifying areas of extreme heat is an important step forward, Strumwasser said. Previously, heat data looked at 30-by-30- meter areas — about the size of two basketball courts side-by-side — with one value for just over every two weeks.

The new data, from the NO-HEAT work, looks at areas one meter by one meter with new data every hour. It also focuses on the areas where humans are shifting focus away from spots like highways and rooftops and takes into consideration how the human body experiences heat, with factors like humidity and shade.

“We all know that 90°F in the shade in the breeze feels much different from 90°F on a hot day in the sun,” Strumwasser said.

The need for expanded data was a priority for others at the symposium too. Dr. Caleb Dresser, an emergency medical physician at Beth Israel Deaconess Medical Center and a professor of environmental health at the Harvard School of Public Health, said that knowing what works and how it should be implemented is important to focus efforts, especially in a more resource-limited world.

“We’ll need evidence to see how these solutions work,” he said, during the symposium’s panel discussion. “How effective are they? How cost effective are they?”

Dresser views heat resilience as an education issue, both for medical professionals and community members. “The time to be figuring it out is not during a heat wave, it’s at the beginning of the summer,” he said.

Dr. Anna Goldman, a primary care physician and medical director for climate and sustainability at Boston Medical Center, said individuals should be aware of conditions like heat exhaustion, heat stroke and dehydration.

With extreme heat, community members should watch for symptoms of heat exhaustion like headaches, dizziness, nausea and weakness, said Goldman, who was not involved with the symposium. More severe heat exhaustion can cause muscle aches, fever, confusion and cold, pale or clammy skin.

If someone is experiencing heat exhaustion, Goldman recommended getting them to a cool place, like an air-conditioned room or a lukewarm shower — ice-cold water can shock the system and cause blood pressure to drop. When outside, she said people should wear light-colored, loose-fitting clothing and sun protection.

When the body’s temperature reaches even higher temperatures, heat exhaustion can become heat stroke. Marked by greater confusion and the potential for organ failure, Goldman called heat stroke “emergency-room level of illness.”

Extreme heat can also lead to dehydration, as the body lets out more water through sweating. Goldman recommended avoiding exertion in high temperatures.

Early symptoms of dehydration can include dry mouth, darker urine and fatigue. When it becomes more severe, individuals can get dizzy, become confused or faint. Goldman said electrolyte drinks are more effective at rehydrating, but if not available, individuals should drink water.

While anyone can be impacted by heat exhaustion or dehydration, more vulnerable populations like the very old, the very young and those experiencing chronic illness are at greater risk. Extreme heat, too, can increase the occurrence of cardiovascular events like heart attacks and strokes, and can exacerbate lung conditions like asthma and COPD.

Increasingly, too, medical experts warn that frequent exposure to high temperatures can have long-term impacts — something Goldman pointed to as another factor individuals should be aware of.

“There’s a whole range of health problems that are related [to extreme heat], but we’re actually seeing new diseases,” she said.

Starting in the 1990s, experts began identifying an epidemic of chronic kidney disease in parts of El Salvador, and later in other spots across the world. The affected individuals — often younger men in agricultural or construction jobs — experience kidney failure without the untreated diabetes, high blood pressure or autoimmune conditions that normally accompany the condition.

According to a news feature published in the journal Nature, June 4, with time, researchers came to suspect that the condition, dubbed chronic kidney disease of unknown cause or Mesoamerican nephropathy, is caused, at least in part, by frequent and repeated heat injury.

When the body gets warm, blood is directed toward the surface of the skin to allow heat to dissipate. That means limited flow and less oxygen and nutrients to the organs; for the kidney in particular, extreme heat also means kicking into overdrive as a loss of water through sweat threatens the body’s fluid balance.

Chronic kidney disease of unknown cause made experts reconsider how they thought about the impacts of heat on the kidneys, the article in Nature reported.

Previously, researchers believed that, aside from extreme cases, the kidney would bounce back. The emergence of chronic kidney disease of unknown cause now is making them consider that repeated injury, perhaps in combination with other factors such as exposure to pollutants like heavy metals or pesticides or over-consumption of sugary drinks instead of water, can have a lasting impact.

“I think it’s just going to increase, especially for people who have jobs that require them to be outside or [for] unhoused people,” Goldman said.

Goldman described the shifting landscape of health concerns as an indicator that the impacts of a changing climate are not a problem of tomorrow.

“Climate change is here,” Goldman said. “We’re feeling the effects of it very directly.”