In Texas, the Heat Index Is Rising Faster Than the Temperature

Big Bend, Texas.

Big Bend, Texas. Pixabay

A new study of summer weather in Texas finds the heat index — an indicator of how hot it feels outside — is rising much faster than the temperature.

The reason, scientists say, is that warming is leading to a rise in humidity. Historically in Texas, the relative humidity would fall when the temperature rose, making it possible to cool off by sweating. But now Texas is seeing high heat and high humidity together. On hot, muggy days, the air is so saturated with water that sweat sticks to the skin rather than evaporating. As a result, the weather feels much warmer than a thermometer alone would suggest.

In 1979, physicist Robert Steadman developed the heat index to indicate how such weather actually feels. But Steadman did not calculate the index for the high levels of heat and humidity routinely seen today. In 2022, scientists at UC Berkeley recalculated the heat index to account for more extreme weather. And in 2023, Berkeley physicist David Romps applied the updated heat index to the summer heat in Texas.

He found that while Texas has warmed by around 3 degrees F (1.5 degrees C) on average since the preindustrial era, on some scorching summer days last year it felt up to 11 degrees F (6 degrees C) hotter than it would have without climate change. His study was published in Environmental Research Letters.

Romps wrote that, compared to the temperature, the heat index offers “a more accurate picture of the extent to which global warming has increased heat stress.”


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