The Earth recorded an unprecedented number of hazardous hot and humid days in 2024, as climate change escalates global humidity to alarming levels.

The worldwide average of humid heat days on land surpassed the 1991-2020 average, reaching 35.6 days last year, an increase of over 9.5 days from the previous record in 2023. Climate Report 2024 Status published by the American Weather Society.

Under hot and humid conditions, it is challenging for individuals to cool down, as moist air diminishes the evaporative cooling impact of sweating. Such weather poses serious risks to human health. Kate Willett from the UK Met Office, who contributed to the report, states, “Your body starts to struggle to shed heat, making it very dangerous.”

Meteorologists measure heat and humidity using “wet bulb temperature.” This is typically done by wrapping a wet cloth around a thermometer bulb, demonstrating the cooling effect of evaporated water. The readings indicate temperatures lower than in a dry bulb, as high humidity limits the cooling effect of evaporation and brings the wet bulb temperature closer to that of dry air.

As the globe heats up, the atmosphere can retain more moisture, leading to increased heavy rainfall, storms, and higher humidity levels. Willett describes 2024 as “exceptionally” humid, second only to 2023 due to higher moisture levels.

Specific regions, including the Middle East, Southeast Asia, and East China, have reached 31°C (88°F) within a short time span, with wet bulb temperatures exceeding 84°F multiple times, according to the report. At these levels, extended exposure outdoors is deemed extremely perilous and potentially lethal.

Traditionally, scientists consider a wet bulb temperature of 35°C the threshold for human survival, as people cannot withstand outdoor conditions for more than a few hours before succumbing. However, research published in 2022 suggests that the actual limit may be lower, around 31°C. “Over 30°C, your body really struggles,” Willett explains.