MASSACHUSETTS HAS SEEN a striking rise in summer temperatures over the past half-century, with statewide averages climbing by approximately 2.75 degrees Fahrenheit since 1970 and leading to more frequent and intense heat waves, heightened public health risks, and dangerous conditions for essential workers. 

The state has experienced a rise in temperatures that is comparable to the national average temperature rise of 2.6 degrees Fahrenheit, according to researchers at Climate Matters, a nonprofit group of climate scientists and communications experts.

Suffolk County, which contains Boston, has experienced the steepest increase — warming by 3.3 degrees, outpacing the rest of the state and highlighting the amplifying effects of urban heat islands. Four other counties – Norfolk, Middlesex, Plymouth, and Worcester – had temperature rises above 3 degrees Fahrenheit. 

Climate Central’s analysis used monthly temperature data from the National Oceanic and Atmospheric Administration – the federal agency tasked with predicting and monitoring weather and climate – to find the average temperature change in March to May from 1970 to 2024.

“Without human-caused climate change, the temperature would not have risen as much as it did,” said Jen Brady, a senior data analyst at Climate Central who leads investigations into climate trends and impacts. “[Global] temperatures will keep increasing, and already we’re locked into a certain amount of the increase because greenhouse gases – once they’re released into the atmosphere – don’t dissipate immediately.”

The 2.75 degrees Fahrenheit might sound like a small change in a state where temperatures can vary from below zero to around 100 degrees, but it is a very significant rise over the time period given historical temperature trends, said Brady.

Warmer summers can lead to increased emergency room visits for heat-related illnesses during unprecedented heat waves. Children, adults with underlying health conditions, pregnant women, and outdoor workers are particularly impacted.

Ian Sue Wing, an economist at Boston University who researches the health impacts of heat exposure, noted that Massachusetts has an aging population with almost a quarter of all residents who are 60 or older. 

“[Older] folks are extremely sensitive to heat because it turns out that, as you age, you are less able to effectively thermo-regulate,” said Wing.

Cities are particularly likely to get hotter than the surrounding areas because there are fewer trees and green spaces that can bring the temperature down. They also have densely developed buildings, roads, concrete, and other heat sinks that absorb and release heat on hot days. That is one of the reasons why Suffolk County – which includes Boston, Chelsea, and Revere – might have warmed more than other parts of Massachusetts.

“The entire city of Boston is a heat island,” said Zoe Davis, a climate resilience project manager for Boston. “But not everyone experiences a hot day in Boston in the same way. Some areas of Boston are hotter than the rest of the city, entering high-heat conditions sooner, reaching higher air temperatures, and remaining in heat wave conditions longer.”

Ben Cares, Chelsea’s director of Housing and Community Development, said that residents of Chelsea – a city with a high proportion of immigrant and low-income residents – can be particularly vulnerable to extreme heat because many face language barriers which keep them from important information on how to protect themselves. Many are essential workers who can’t afford to not go to work even on dangerous heat days, and the city’s high levels of air pollution can make it harder to breathe with the heat.

 “As extreme heat increases, it’s not just that it’s uncomfortable; it’s becoming dangerous for our residents,” Cares said. “For low-income families, seniors, and communities of color, it isn’t just a weather issue. It’s an environmental justice crisis.”

Essential workers who have to commute into work on hot days and those who work outdoors in jobs like construction or indoors in commercial kitchens or warehouses are also vulnerable. Workers can become dehydrated and overheated without proper hydration and well-timed breaks. 

There aren’t safety protocols around extreme heat in many workplaces across the state, according to Tatiana Begault, the head of the Massachusetts Coalition for Safety and Health, a group that focuses on protecting workers. Undocumented workers are the most vulnerable because they are unable to advocate for breaks or changes in work conditions without fear of retaliation, she said. 

Begault hopes that as temperatures warm, local and state governments will do more to protect essential workers from extreme heat. 

“Heat impairs concentration, memory, and decision making, which raises a lot of risk of workplace accidents, especially for those operating heavy machinery in construction areas,” said Begault. “[Essential workers] are part of a community and a population that is severely under monitored, under served, and under prepared.”