Researchers have announced findings that humid days with temperatures of 34℃ (93.2℉) can stress the heart and put people with cardiovascular disease at risk. As the world’s temperatures soar this year to new records and extreme weather — including heat domes that have struck the Southeast and Southwest — becomes more common, be careful to check both the temperature and humidity before going outside.

The journal Nature reports that a team at Pennsylvania State University in State College found that more regions are experiencing extremely hot humid days and people need to take steps to prepare. With few air-conditioned homes or cooling stations, some regions are ill-prepared for rising temperatures.

The team studied the heart rates and internal body temperatures of 51 subjects in good health while they walked slowly in an enclosed environmental chamber that got hotter and more humid every five minutes. They found that cardiovascular strain began at 93.2℉ in humid conditions, while in drier conditions, the test subjects could endure 105.8℉ without stressing the heart. Earlier research had suggested people could endure humid environments of up to 95℉ and dry temperatures of 115℉.

“If all of a sudden you notice your heart rate going up quickly and progressively, then that might mean that your core temperature will start to rise,” Rachel Cottle, one of the researchers, told Nature. “That’s when you need to take precautionary measures.”

The heart increases its rhythm to move cooler blood to keep organs functioning correctly — the researchers found that heart rate increases before the body’s core temperature rises as a preventative measure. Consequently, the research shows that lower temperatures are more dangerous than previously thought. Even when resting outside on an extremely hot day, heart rates are up to 64% higher when humidity reaches 50%, another team of researchers at the University of Roehampton have reported.

What Can You Do To Prepare for The Hottest Weather in History?

Unfortunately, one immediate solution to overheating — air conditioning — is a big contributor to climate change because so many regions still burn coal and oil to power them. Setting the air conditioning higher than room temperature can reduce you climate impact, but in our perversely ironic self-made situation, this necessary evil remains the most convenient option. Stay at home or in air-conditioned spaces as much as you can. The Environmental Protection Agency recommends setting air conditioners to 78℉ to minimize emissions and your cooling bill.

If you don’t have air conditioning, and 10% of Americans did not in 2020, there are steps you can take to keep cool at home. If your place is too hot, find public cooling stations near you using the National Center for Healthy Housing’s guide to cooling centers by state. Communities are also sure to open new cooling stations, so check local media for pop-up centers near you for the latest updates.

A new concept for many, is the “wet-bulb temperature,” which describes the body’s ability to cool itself with evaporation — sweating — in humid environments. When more moisture is in the atmosphere, sweating is a less effective way to cool down. At the wet-bulb temperature, sweat no longer cools the body. Before you go outside, check your weather app for the wet-bulb temperature or, if it is not available, you can enter the current temperature and humidity level at Omni Calculator. Remember to look at the expected high temperature for the day, as that is when the risk will be greatest.

After the hottest days in recorded history — and mostly likely the last 125,000 years, it’s time to take steps to adapt to our consistently warmer, more dangerous climate. We can take steps to reduce emissions and eliminate waste that contributes to global warming, but we must stay healthy to make these changes. Stay safe in these hotter, often deadly times.

By Mitch Ratcliffe

Mitch is the publisher at Earth911.com and the sustainability leader at Metaforce, a global marketing firm. A veteran tech journalist, Mitch is passionate about helping people understand sustainability and the impact of their buying decisions on the planet.