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Have you ever felt as though the temperatures your local weather app reported failed to capture how it felt outside? Well, you were right. As heat waves become more intense and more frequent, we need to change the way we think about outdoor temperatures. What matters is not how hot the air is but how hot the weather is to a human body. For that, we need "wet-bulb globe temperature".

Wet-bulb temperature, which athletic organizations, the military and regulators have used for decades, comes from a device with three thermometers to better capture how heat stresses the body The first is a basic thermometer, which measures the air temperature. The second is a thermometer inside a black ball, which captures the heat our bodies absorb from direct sunlight. The third is a thermometer covered in a wet cloth, mimicking our body's ability to cool itself with sweat and accounting for factors such as humidity (湿度) and air movement. The three readings are combined using a weighting system to produce the wet-bulb temperature.

Wet-bulb temperature might sound like the "heat index" - that is, when your local weatherperson says, "It's 90 degrees, but it's going to feel like 98 because of humidity" - and there are similarities. But there are also critical differences.

The heat index assumes you're in the shade and resting, but being in direct sunlight can add 15 degrees to the heat index. One way to understand the value of using wet temperatures is to look at maps comparing them with the more familiar "dry" temperatures. Take Fresno, Calif., which is forecast-to reach 102 degrees. But humidity is low, so the corresponding wet-bulb temperature is 80. New York City, for comparison, is forecast to be 98, but humidity will be high, putting the wet-bulb temperature at 88 - and making conditions even more dangerous than in Fresno.

Don't get me wrong. I just want to stress that we cannot ignore the even more dangerous weather happening elsewhere that might be less obvious. Of course, it will take time for the public to become familiar with wet-bulb temperatures. The downside is that, because they are generally lower than dry temperatures or the heat index, people could misinterpret them. The solution is to educate people about why they're necessary.

Policymakers have strategies to protect against extreme heat. For example, Portland, Ore, has begun distributing free air conditioners. Simple infrastructure enhancements such as white roofs can reflect the sun's heat and incoming solar radiation. And planting more trees adjacent to buildings helps reduce temperatures and heat deaths.

But these measures matter only if people and companies are aware there's an issue, which means using the right data. The goal should be to help people experiencing extreme heat to protect themselves. We have the tools to measure this correctly; we just need to use them.