Summer humidity is an often consequence of climate change and it's time to prepare for it. Photo: MHDphonegraphy
One day a few weeks ago, I ventured outside into the summer heat. The lenses of my glasses quickly fogged up. I felt a hot blast of steam on my face, as if I were getting a salon facial, except this was for free. My clothes clung to my sweaty skin, and I sighed, knowing that I would soon be taking my third shower of the day.
And it’s not just me. Summers across New England really are getting more humid. It’s another surprising consequence of climate change. I was aware that an overheating planet would cause more extreme weather, intensify storms, warm our winters, and deep fry our summers. But I had never considered that another climate change-related extreme would be thick, oppressive humidity.
Although I hadn’t been clued in, the scientists have. They’ve told us that a warmer atmosphere holds much more moisture than a cooler one. As the planet heats up, it absorbs and retains more water, like a bloated patient in need of a good diuretic.
Meteorologists report that through July 15, Boston registered 120 hours with a dew point of 70 degrees or higher, more than twice the average based on data compiled by Iowa State University. That made the first half of the summer of 2025 the most humid summer on record in Boston. And it’s not just Boston, from Rhode Island to Vermont, hot, moist air has saturated New England both this summer and in recent years. Luckily, after those first weeks, we caught a break with drier weather, but the trend is clear.
On one of the more humid days this summer, I felt compelled to check on the humidity in Boston compared to what I had known on summer trips to the stifling Deep South. The relative humidity in my parents’ hometown of Ozark, Alabama, stood at a sodden 82%. And Boston? 87%.
The New Summer Normal: Humid AND Stormier
There’s a perverse sense of vindication in knowing that what I’ve been feeling anecdotally is being tracked by meteorologists keeping tabs on the soppiness of our atmosphere. The summer dew point through July 15 was 64.4 compared to 63.6 in 2003 and 63.4 in 1984. (Dew point is a slightly different measure than relative humidity, but they both measure the amount of moisture in the atmosphere. Dew point indicates the actual amount of moisture present. Relative humidity measures how close the air is to 100% saturation.) Those numbers may not seem impressive until you consider this: Because the atmosphere can hold 4% more water vapor for each Fahrenheit degree increase in dew point, even just one degree more in dew point makes the atmosphere much, much more uncomfortable.
The result? Summer days feel much hotter than they used to because they’re wetter. And that moist air doesn’t allow our natural cooling mechanism of sweat evaporation to kick into gear. Typically, we sweat when we’re hot, and the evaporation of the sweat from our skin helps cool us down. But when the air is already filled with moisture, there’s nowhere for that sweat to go. Even nighttime brings no relief, since high humidity still prevents our bodies from doing what they were designed to do to cool off.
And there are other consequences of so much water vapor in the air. It makes summers stormier than they used to be. A higher dew point can mean that more frequent storms unleash a 5% to 10% increase in rainfall. In fact, summer thunderstorms in New England are dumping so much water at once that flash flooding is becoming a regular occurrence. We saw this happen in Vermont in July, when, for the third consecutive year, heavy rains caused destructive flooding. And it’s not just New England. Also in July, in the week before the flooding in Vermont, Central Texas grappled with devastating floods that killed at least 130 people.
Hot, Humid Summers Have Health Consequences
We all know how hot and humid weather can make us feel: icky. But it can be deadly, too. High humidity means our lungs have to work harder to get oxygen from the air. That’s why most of us only have enough energy to hang out by a pool (if we’re lucky enough to find one) on a hot, humid day. Humidity makes it harder for our lungs to efficiently transfer oxygen into our bloodstream, which affects oxygen supply to internal organs. And for people living with chronic conditions, including asthma, heart disease, COPD, diabetes, and kidney disease, hot, humid weather can lead to dangerous medical emergencies. It’s easy to become dehydrated, develop heat exhaustion, or heat stroke. This is especially true of children and older adults whose bodies are less efficient at cooling down. It’s also a serious problem for anyone working outdoors. Farm workers, construction workers, delivery people, and warehouse workers are susceptible to heat illnesses, with farm workers in particular being 35 times more likely to die from heat-related stress than workers in other industries.
Climate Resilience Means Preparing for Higher Humidity
In New England, I am finally learning what real humidity feels like. (I’m not the only one learning. Researchers have discovered that the water retention in the atmosphere isn’t evenly distributed across the whole planet. Arid and semi-arid regions appear to be getting drier, while already humid places are getting more humid. That’s bad news, as it increases the likelihood of wildfires in areas already known for scant rain.)
With the likelihood that higher humidity will become a regular feature of New England summers, we shouldn’t keep bumbling along from one sweltering summer to the next, without a plan. Because New England’s older housing stock generally lacks central air conditioning, our population is at risk during longer, intense heat waves marked by high humidity. Communities must prepare by developing a heatwave response plan, creating cooling centers where overheated residents can take shelter, and planting more trees and green zones to help bring temperatures down. Cities must build with heat resilience in mind, insulating buildings and incorporating white roofs. Communities must incentivize energy-efficient cooling systems like electric heat pumps, so more residents can keep their homes cool for less. Finally, utilities must fortify electric grid infrastructure so it can stand up to higher electricity use. And, of course, for anything to make any sense at all, we must lower the emissions causing our planet to overheat in the first place. That means adopting cleaner energy technologies, like wind and solar.
We have a choice on our hands. Either we prepare for stickier summers and work to clean up the carbon pollution causing them, or we accept this problem as a new and deadly normal that nobody wants.
These days, the familiar adage “It’s not the heat, it’s the humidity” rings especially true. But with a caveat: It’s both the heat AND the humidity.
This is one of an occasional series revealing the truth in environmental matters.
