Experience the heat: Texas heat index increases three times faster than temperatures

In Texas, where the summer sun is relentless, residents are familiar with extreme heat. However, a recent study reveals a worrying trend: the heat index, which indicates how hot it feels, is rising three times faster than actual temperature readings.

During the hottest days, Texans are facing “feels like” temperatures up to 11°F (6°C) warmer than historical norms. This is also true for other places worldwide with similar extremes in temperature and humidity.

Understanding the heat index

The heat index was established in 1979 to demonstrate how the human body reacts to heat and humidity. By considering the effects of both relative humidity and air temperature, the heat index provides a more precise representation of thermal stress on our bodies.

The human body cools itself by sweating and evaporation. When the air is saturated with moisture (high humidity), sweat on our bodies doesn’t evaporate as quickly, making it difficult for the body to regulate its temperature effectively. This explains why the air temperature feels much warmer than it is.

Despite being appreciated when it was introduced, the method used to measure the heat index has not kept up with the times. It often fails to consider increasingly frequent extreme cases during heat waves. This inaccuracy can have serious consequences, as it may cause some people to underestimate the risks of hyperthermia and heat-related illnesses.

Feels like an oven

David Romps, a professor at the University of California, Berkeley, argues that current methods of calculating this metric fall short. He and colleagues have now proposed a new method that takes into account all combinations of temperatures and humidity. They selected Texas as the case study to present this revised heat index.

“I picked Texas because I had seen some high heat index values there that made me think, OK, this is a state that this summer is probably experiencing combinations of heat and humidity that are not being captured properly by NOAA’s approximation to the heat index,” Romps said in a press release.

Using their new method for calculating heat index revealed some alarming discoveries. During last summer’s heat waves across the state, Romps was shocked that Houston’s Ellington Airport experienced an extraordinary heat index of 75°C (167°F) on July 23, 2023. He attributed 12°F (6°C) of this to global warming.

“It sounds completely insane,” Romps said. “It’s beyond the physiological capacity of a young, healthy person to maintain a standard core temperature. We think it’s hyperthermic but survivable.”

The researchers believe that the human evaporation process would have intensified during these extreme days. This process, however, puts additional stress on the heart by requiring it to pump more blood to the skin. At these temperatures, it seems incredible that a human could survive. But the researchers have considered survivability before.

Previously, Romps and colleagues published a 2023 study that challenged the commonly accepted survivable temperature limit, arguing that a wet bulb temperature of 35°C (95°F) — the temperature a thermometer reads when wrapped in a wet cloth, simulating the effect of sweating — is not necessarily lethal for a fit adult, despite causing hyperthermia.

“Heat index is very much like the wet bulb thermometer, only it adds the metabolic heat that a human has that a thermometer does not have,” Romps said. “We think if you kept your skin wet and you were exposed to 167 degrees, even though we’re approaching something like a setting on the oven, you’d still be alive. Definitely not happy. But alive.”

The meaning of increasing heat stress

Romps’ current research did not predict when Texas might experience severe heat waves that could cause widespread hyperthermia, but he pointed out that such conditions are becoming more possible. He plans to expand his analysis to other areas using the improved heat index scale and expects to find similar patterns.

Romps cautioned about the serious effects of continuous use of fossil fuels, which could potentially expose half of the global population to extreme and life-threatening heat stress. This risk is especially high for older or unhealthy individuals, those involved in physical labor, or those exposed to direct sunlight.

The new discoveries emphasize a larger problem: the growing difficulty of conveying the actual risks of climate change to the public. Many people may not think that a 1.5-degree Celsius (3-degree Fahrenheit) increase in average global warming sounds significant, but climate change tends to magnify things to the extreme in all aspects. Record-breaking heat waves on land and in the ocean, heavy rains, severe floods, prolonged droughts, intense wildfires, and widespread flooding during hurricanes are all becoming more frequent and intense.

Emotional impact of numbers

Furthermore, the recent study reveals that on extremely hot summer days, the outdoor air can feel much hotter than what your thermometer indicates. This has real and severe consequences. Last summer, over 300 Texans died due to heat, marking the highest number since record-keeping began in 1989.

From 2008 to 2019, the US saw an average of 54 days each summer where the heat index (not this revised one) exceeded 90 degrees Fahrenheit. The rise in the number of extremely hot days was associated with nearly 1,700 additional deaths annually from cardiovascular problems, according to a study in the journal Circulation reported.

The research also suggests that if global fossil fuel use continues and efforts to address climate change remain minimal, the US could have up to 80 days of extreme heat each summer. Under these conditions, heat-related cardiovascular fatalities could more than triple, leading to around 5,500 additional deaths per year.

“I mean, the obvious thing to do is to cease additional warming because this is not going to get better unless we stop burning fossil fuels,” Romps said. “That’s message No. 1, without a doubt. We have only one direction we can really be taking the planet’s average temperature, and that’s up. And that’s through additional burning of fossil fuels. So that’s gotta stop and stop fast.”

The new findings were published in the journal Environmental Research Letters.