Record-high temperatures have become increasingly common across Texas in recent summers. The Lone Star State regularly experiences triple-digit temps, humidity that sends heat index values soaring past 110 degrees, and heat advisories from the National Weather Service so frequent that they can be taken for granted.

Although sizzling daytime temperatures usually make the headlines, our warming nighttime low temperatures can be just as dangerous. In recent years, many Texas cities have been experiencing drastically more nights with 80-degree daily low temperatures. The trends are concerning, and they don’t show signs of stopping anytime soon.

Here are the numbers

In San Antonio, 80-degree daily low temperatures once were almost unheard of. From 1885 through 2008, which includes the first 124 years of weather records for the city, San Antonio only recorded 32 days when low temps stayed above 80 degrees. That’s an average of just once every four years.

That rate has gone up drastically. What once happened only as often as the Olympics, has now happened an average of 4.2 times each year since 2009. And in 2023, San Antonio recorded 18 nights that stayed above 80 degrees, the most ever for the city in one year.

It’s happening even more in other parts of Texas. From 1980 to 2008, the city of Houston averaged only two days each year with 80-degree low temperatures. Since 2009, that average has increased to 13 times per year.

Dallas has experienced even more 80-degree nights, averaging 20 such nights per year over the past 15 years. What once was a rarity, 80-degree nights are starting to become the new normal in Texas.

Major implications

Just like the triple-digit temperatures that happen during the daytime, these warm nighttime temperatures can cause big health concerns. Warm nights do not give the body a chance to properly cool down, adding heat stress and increasing the risk of heat-related illnesses. It’s especially dangerous for those without adequate air conditioning and people experiencing homelessness.

Even for those with air conditioning, these increasing nighttime temperatures are going to cause your A/C units to work longer into the night to keep your home cool. That higher energy consumption means higher electricity bills.

Why is this happening?

One reason why nighttime low temperatures have been increasing drastically in recent years is that it’s a consequence of climate change. According to National Oceanic and Atmospheric Administration, 2023 was the planet’s hottest year on record. In addition, the past 10 years have been among the planet’s warmest on record. With Earth’s daytime temperatures rising, it makes sense that nighttime low temps would warm up, too.

Another reason for the drastic change could be linked to the so-called urban heat island effect. Basically, this occurs because temperatures in an urban center tend to be hotter when natural soils, grass and other vegetation have been replaced with buildings, roads, and parking lots.

These artificial urban materials absorb heat during the day and radiate it back out at night, raising the nighttime low temperatures. As Texas cities continue to grow and populations increase, the urban heat island effect is likely to continue raising city temperatures in future decades.