Will Texas become too hot for humans?
Getty ImagesTexas is in the grip of a relentless heatwave – but how much hotter could summers get in years to come?
It's 9.15 pm in San Antonio on 17 June. At this time, young children would usually be asleep and their parents enjoying a balmy summer's evening. But not this year, when temperatures have reached triple figures in parts of Texas, and extreme humidity has made it feel hotter still, even after sunset.
Millions of people have been issued with excessive heat warnings and the extreme temperatures have claimed the lives of several people already. Temperatures peaked at 119F (48C), smashing countless high-temperature records across the state. More are expected to be broken in the coming week as the heatwave expands to the north and east.
These unusually-high temperatures have primarily been sparked by a ridge of high pressure parked over the Southern US called a "heat dome", which occurs when the atmosphere traps hot ocean air like a lid. (Learn more about how the heat dome is causing record temperatures.)
John Nielsen-Gammon, Texas State Climatologist and director of the Southern Regional Climate Centre at Texas A&M University, says there are other short-term contributing factors too. "The Gulf of Mexico is unusually warm… and it's also around the time of the summer solstice."
There are longer-term trends at work too. The frequency and intensity of extreme heat events have increased around the globe due to climate change and are predicted to get worse.
The hotter bigger picture
Texas has warmed between 0.5-1F in the past century. "In the coming decades … summers are likely to become increasingly hot and dry, creating problems for agriculture and possibly human health," warns the Environmental Protection Agency (EPA). It predicts that 70 years from now, the state will have three or four times as many days per year above 100F (38C) as it has today.
Getty ImagesThe National Integrated Heat Health Information System's Climate Explorer tool also offers a worrying glimpse into Texas's future. It predicts that Austin and Travis County's average daily maximum temperature in June could rise to 99.7F (37.6C) between 2060 and 2090 if no steps are taken to mitigate the potentially crippling effects of climate change. Austin's Office of Sustainability's estimate is even higher with a summer average high temperature of 103.8F (39.9C) at the end of the century for the city.
The human cost
Extreme heat is currently the deadliest natural hazard in the US, with young children and adults over the age of 65 among the most vulnerable to heat-related illness and death. Analysis by The Texas Tribune found more than 275 people in Texas died from heat-related illness in 2022, which was a two-decade high, and this year's heatwave appears to be worse.
Young children, the elderly, the sick, and the poor who cannot afford technology including air-conditioning to help keep them cool are particularly vulnerable to the effects of extreme heat. High air temperatures can cause heat stroke, dehydration and affect people's cardiovascular and nervous systems.
"This heatwave has been very stressful for people in the region, and especially dangerous for people with underlying health risks," says Andrew Pershing, vice president for science at Climate Central, a non-profit that analyses climate science. Research by Climate Central found a "significant increase" in the number of days above local "risky heat thresholds" in several Texas cities, when heat-related health risks increase. For example, Austin has 53 more risky heat days per year than in 1970.
"Climate change is increasing the number of risky heat days in most places, mostly by increasing the length of the heat season," he explains. So far, the current heat dome has claimed at least a dozen lives in Texas and Louisiana.
At what point the heat becomes unbearable is personal, but a study published in 2010 estimated that a "wet-bulb" temperature of 95F (35C) at 100% humidity, or 115F at 50% humidity is probably as hot as most humans can maintain a healthy core body temperature by sweating. Above that "critical environmental limit" our body temperature rises continuously and the risk of heat-related illnesses such as heat stroke increases.
But a team of researchers from Penn State University discovered our resilience to heat is probably lower than this after testing how healthy people handle hot temperatures in a sweaty experiment in their laboratory. They showed that the upper environmental limit is a lower wet-bulb temperature of 95F (31C) at 100% humidity.
The heatwave in Texas has in places exceeded this band of dangerous temperatures, so whether people can live happily in the state also largely depends on whether they have access to air conditioning and can afford to use it, or whether they have to work outside under the hot Sun.
This has left people asking: when it is too hot to work? In Houston, McDonalds workers went on strike this week after experiencing issues with their air conditioning. Meanwhile roofers, welders and those in professions that can't rely on these technologies have been struggling to keep their body temperatures within the normal range.
And even when they aren't life-threatening, hotter temperatures can impair cognition, motor control and affect our ability to perform everyday tasks. This is problematic, because whatever happens to the climate in Texas, most people will still need to work.
There are also wider implications for society. It's well-established that warmer weather can make us more aggressive, increasing rates of violent crime and the probability of social unrest. (Read more from BBC Future about the strange ways heatwaves can warp the mind).
Getty ImagesJames Doss-Gollin, assistant professor of civil and environmental engineering at Rice University, in Houston, Texas, believes infrastructure upgrades could help people to cope with future heatwaves in the US, but they come at a cost.
There are plans to improve wind and solar resources in Texas between now and 2030 at an estimated cost of US$66.5 bn (£52.7bn), while residents could add rooftop solar panels or back-up batteries to their homes, which could lighten the load on the transmission system during peak hours, he explains. "It's important to make sure the things that benefit people who can afford them also provide benefit to others and we're not leaving people behind."
Those who cannot afford technology to help them adapt may consider moving somewhere cooler if extreme heat becomes the norm in Texas and elsewhere in the US. (Read more from BBC Future about how to stay cool in a heatwave.)
A wider problem
The prospect of more unbearable heatwaves each summer is not unique to Texas. According to a 2021 report by researchers at Rutgers university, if the Earth reaches three degrees of global warming – which some estimates suggest is likely – around 1.2 billion people will be at risk of heat stress every year.
Moving on
"Over the next 50 years, millions of Americans will be caught up in this churn of displacement, forced inland and northward in what will be the largest migration in our country's history," says author Jake Bittle, whose book The Great Displacement, tell stories of people forced to leave their homes due to extreme weather events.
Around 162 million Americans are expected to experience a decline in the quality of their environment and by 2070, with four million could be living outside "the ideal niche for human life," according to a collaborative effort between ProPublica and The New York Times
For now, people are moving to Texas from other US states to escape other weather-related problems such as frequent tornadoes to drought. One study found Houston to be a "receiving community" for climate migrants from New Orleans looking to put down new roots following the devastation caused by Hurricane Katrina in 2005.
Another study predicts that rising sea levels will force 13 million Americans to move away from the coasts, with Houston and Dallas potentially getting thousands of new residents. But predicting the movement of people is notoriously difficult, and people may seek refuge from extreme weather within and out of the US Gulf Coast region.
Whether Texas one day becomes so uncomfortably hot for humans that they decide to leave remains to be seen. Nielsen-Gammon says the highest temperature ever recorded in Texas was 120F (49C), which is just one degree higher than the peak recorded in this heatwave.
"Gradually, as the global climate warms, there is the possibility temperatures keep increasing (in Texas) in tandem," warns Nielsen-Gammon.
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