Summers Are Getting Hotter: New Data Reveals Which States Will Experience the Most Heat Waves Over Time

People across the country felt the effects of the extreme heat as temperatures reached record-breaking highs this summer. Unfortunately, the trend of hot and humid summers is only expected to continue in coming years, according to new climate projections conducted by a team of scientists from NASA's Jet Propulsion Laboratory.

Researchers in the lab used projections from 20 climate models to estimate how much heat stress people in the United States may encounter from 2075 to 2099 on the hottest days of the summer and compared it to recorded data from 1980 to 2005. The scientists combined several factors, including heat, humidity, and exposure to sunlight to project future heat stress placed on American residents. Their calculated metric is referred to as an environmental stress index (ESI).

Humidity was included in the study because humid conditions make sweating and evaporation less efficient, meaning the human body isn't able to cool itself as successfully. Not only does humidity feel uncomfortable, but it also is more likely to cause heat-related illnesses and even death, according to the researchers.

To determine which regions of the U.S. are most likely to experience extreme heat waves, the scientists started by calculating the top 1% of days on the ESI from from 1980 to 2005, specifically during May through September. They then calculated the same for years 2074 to 2099, accounting for higher levels of greenhouse gases in the atmosphere.

They found that some of the most significant changes in extreme heat stress are predicted to occur in the Upper Midwest, Northeast, and the Pacific Northwest. According to the data, the top 1% of days on the ESI could see temperatures that are about 9 degrees higher than they were during 1980 through 2005.

Luckily, coastal states like California will experience moderate changes in heat stress thanks to sea breeze, which helps circulate stagnant heat and air. Other areas that will experience less drastic effects on the hottest days to come are the Gulf Coast states. However, because there is less variability between high to low altitudes, states like Florida and Texas will experience the greatest relative increases on the ESI. These area may see extreme heat stress days up to 50 times more often—while the Pacific Northwest or Upper Midwest could be around 20 times—compared to the historical data.