Rising Risks: The Danger of Extreme Heat and Humidity for Millions Worldwide

Scientists use wet bulb temperature as a key metric to evaluate the risk posed by heat, which is the temperature at which the human body can no longer cool down effectively. While many countries have recently faced extreme heat events, most habitable regions do not experience temperatures that are too hot for human survival, especially in arid climates. In dry areas, the body typically cools down by sweating and evaporating water from the skin when it’s hot outside. However, certain regions, such as hot deserts near warm oceans, can become dangerously hot and humid. In such areas, sweating becomes less effective due to the reduced evaporation caused by high humidity.

Summer heat waves in certain parts of the Middle East, Pakistan, and India can be particularly hazardous when combined with moist air blowing in from the sea. These conditions affect hundreds of millions of people living in these areas, a majority of whom lack air conditioning in their homes. Scientists use wet bulb thermometers to illustrate the risks more clearly. When the wet bulb temperature exceeds 35 degrees Celsius, the body struggles to cool down adequately, posing severe health risks. Prolonged exposure to high wet bulb temperatures can be life-threatening.

In 2023, a severe heatwave affected the Mississippi Valley, where wet bulb temperatures were very high but not deadly. In May 2024, Delhi experienced air temperatures exceeding 49 degrees Celsius for several days