2024 saw a record-breaking number of dangerously hot and humid days
Shanghai saw several days of extreme heat and humidity in 2024
Reuters / Nicoco Chan
The planet has experienced a record number of dangerously hot wet days in 2024 while climate change increases global humidity to unprecedented levels.
The average world number of wet heat days high on land exceeded the 1991-2020 average of 35.6 days last year, 9.5 days more than the previous record set in 2023, according to the state of the 2024 climate report published by the American Meteorological Society.
In hot and humid conditions, people find it difficult to cool, because wet air stifles the cooling effect of the evaporation of perspiration. This makes this time extremely dangerous for human health, explains Kate Willett at the UK is acting, who worked on the report. “Your body is starting to really have trouble unloading the heat, and so it can be really dangerous,” she says.
Meteorologists measure heat and humidity using “wet bulb temperature”. Traditionally, this is done by sliding a damp cloth on the bulb of a thermometer to take into account the cooling effect of the evaporation of the water, so that it records a temperature below that without this configuration, which is called dry bulb or dry air thermometer. When the humidity levels in the atmosphere are higher, the cooling effect of evaporation is more limited, bringing the temperature of the damp bulb of dry air.
As the planet warms up, the atmosphere is able to hold more humidity, producing not only more intense precipitation and storms, but also higher humidity levels. Willetts claims that 2024 was an “exceptionally” humid year, and only at 2023 for the intensity of the humid heat lived.
Some parts of the world, such as the Middle East, Southeast Asia and East China, have seen wet bulb temperatures exceed 29 ° C (84 ° F) several times, and even a 31 ° C touch (88 ° F) for short periods, depending on the report. At this level, prolonged time outside is considered extremely dangerous – even deadly – with human health.
Traditionally, scientists have considered a wet bulb temperature of 35 ° C as a limit for human survival, where people cannot face the outside for more than a few hours before perishing. But the research published in 2022 suggests that the real threshold can be much lower, at around 31 ° C. “30 ° C and above is where your body is really in difficulty,” explains Willett.
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