The perceived temperature is rising three times as fast (!) as the real temperature due to climate change

That leaves a new study of the University of California to see. The researchers warn that current methods for calculating the perceived temperature underestimate the dangers of extreme heat.

How warm it is does not always correspond to how warm it feels. This has to do with, among other things, humidity, wind and the degree of cloud cover. Yet we often use the measured temperature as a means of communication about how warm it is outside. But that official temperature is not always reliable for calculating the risks of ‘heat stress’. In other words, the risk of health problems due to high temperatures and humidity, as a result of which people are no longer able to properly regulate their body temperature. This is the conclusion of researchers from the University of California after their research. To do this, they examined temperature increases in the American state of Texas.

Texas residents have long been accustomed to feverish summer temperatures. Moreover, a temperature increase of 1.5 degrees Celsius due to climate change does not sound very worrying. But the heat index (the method that also takes humidity into account) appeared to be rising much faster than the measured temperature in Texas in recent years: as much as three times as fast. This means that on some extremely hot days it can feel as if it is 5 to 6 degrees warmer, the researchers say, compared to a situation in which the Earth would not have warmed by climate change.

The reason it feels much warmer than 1.5 degrees is that climate change affects the interaction between humidity and temperature. It used to be that the relative humidity (the ratio between the amount of moisture present and the maximum amount of moisture that can be in the air) decreased as the temperature increased, allowing the body to sweat more. This in turn caused the perceived temperature to drop again. However, due to climate change, the relative humidity remains approximately constant as the temperature rises, making sweating less effective in cooling the body and therefore increasing the perceived temperature by a factor of three.

The hit protocol
It therefore seems a good idea to include this faster-rising perceived temperature in warnings about warm weather. Such as in the Netherlands through the National Heat Plan. But advice based on the heat index is also outdated, according to lead researcher David Romps, professor of earth and planetary sciences at the University of California. He previously stated that the way most government agencies calculate the heat index is inaccurate in the extreme temperatures and humidity we see today. This leads people to underestimate their risk of overheating on the hottest days. This can pose serious health risks such as sunstroke and dehydration, which can even kill you (see box).

How dangerous is hot weather?
In the past week, Arizona’s most populous county reported that heat-related deaths increased 50% last year compared to 2022, from 425 in 2022 to 645 in 2023. According to the Associated Press, two-thirds of heat-related deaths were in Maricopa County in 2023 of people age 50 or older, and 71% occurred on days when the National Weather Service had issued an extreme heat warning. In the Netherlands, these types of warnings are distributed via the National Heat Plan. Healthcare organizations are informed through this agency if there is a chance of prolonged periods of warm weather. This way they can take measures in time to protect the elderly, chronically ill and overweight people in particular. In the heat, they are most at risk of breathing problems, dizziness and itching and of life-threatening conditions.

There is no short-term solution, says Romps. “The most obvious solution is to stop additional warming,” said the researcher. “After all, this problem is not going to get better unless we stop burning fossil fuels. We can only let the average temperature of the planet go in one direction: up. So this must come to an end quickly.” But even if we as humanity no longer produce CO2 from tomorrow, the temperature increases that have already started cannot be reversed. In fact: the increase will probably continue for a while by processes that have already been set in motion. For example, because the polar caps are melting, the layers of ice reflect fewer solar rays back into space, which means that the Earth continues to warm via that route.

It is therefore also important that people take precautions to prevent overheating themselves, says Romps. He advises people who find themselves in extreme heat and cannot use air conditioning to “use shade and water as allies.” Romps: “For example, you can cover yourself with water. Take a wet rag, hold it under the tap, wet your skin and stand in front of a fan. If you drink enough water and can keep your skin wet in front of the fan, you are doing yourself a favor.”