"More Lethal Than Europe's Heatwave, Sweating Won't Help... Why Korea's 'Steamy Heat' Is Unique [Science Scope]"

Korea's Hot and Humid Heatwaves
More Deadly Than Europe's, Even at Lower Temperatures
The North Pacific High Brings a Wave of Moist Heat

If the heatwave that swept through France was defined by "dry heat," the summer in Korea is fundamentally different. Not only do temperatures soar, but humidity levels also rise dramatically. Even at the same 35 degrees Celsius, the combination can make it hard to breathe and cause the body to tire easily. Recently, climate scientists and health experts have been focusing on the dangers of hot and humid heatwaves, as they significantly diminish the body’s ability to cool itself, making them far more lethal than simply high temperatures alone.

A farmer harvesting crops in the heatwave cools down by drinking water. Photo by Yonhap News.

When the body is hot, it sweats, and this sweat evaporates to lower body temperature. However, when the humidity is high, the abundance of water vapor in the air prevents sweat from evaporating easily. As a result, internal heat cannot escape, making the apparent temperature much higher than the actual recorded high, and dramatically increasing the risk of heat-related illnesses. The heatwave in Korea cannot be fully explained by thermometer readings alone.

Humidity Is More Dangerous Than Temperature... Warnings from WBGT and Wet-Bulb Temperature

This is why there are increasing cases of evaluating heatwave risk using the Wet-Bulb Globe Temperature (WBGT) or wet-bulb temperature, rather than just the highest temperature. WBGT is an index that combines temperature, humidity, radiant heat, and wind to reflect the actual heat load experienced by the human body. Because it provides a more direct measurement of heat exposure than regular temperature readings, organizations like FIFA and the International Olympic Committee (IOC) use it as a standard for implementing cooling breaks to ensure athlete safety.

The limit of human endurance is often explained with "wet-bulb temperature" (the temperature that reflects the effect of atmospheric moisture on air temperature). Theoretically, when the wet-bulb temperature reaches 35 degrees Celsius, even healthy adults can no longer regulate body temperature by sweating, which can become life-threatening within hours. Vulnerable groups such as the elderly or those with chronic illnesses may face life-threatening risks at even lower temperatures. Unlike Europe's dry heat, which can be tolerable in the shade, Korea's humid and windless swelter imposes a much greater heat stress on the body.

Lee Myung-In, director of the Heatwave Research Center at Ulsan National Institute of Science and Technology (UNIST) and professor in the Department of Urban and Environmental Engineering, warned, "Due to climate change, the sea surface temperatures around the Korean Peninsula are rising rapidly, which will make the risk of simultaneous high temperatures and high humidity in future heatwaves even greater. As background temperatures increase, the intensity of heatwaves under similar pressure systems will inevitably become stronger."

The 24-Hour Disaster Brought by 'Southerly Tropical Nights'

This summer, Korea is particularly likely to be exposed to hot and humid heatwaves. The Korea Meteorological Administration forecasts that sea surface temperatures in the North Pacific will remain higher than average, increasing the likelihood that the North Pacific High will develop strongly, especially over eastern Korea.

Since the North Pacific High rotates clockwise, the Korean Peninsula will be consistently affected by warm and humid air flowing in from the southern seas along its periphery. Woo Jin-Gyu, spokesperson for the Korea Meteorological Administration, explained, "If the North Pacific High is positioned to the east of Korea, the country will experience frequent days of both high temperature and high humidity due to the influx of humid warm air along its edge."

The problem is that high humidity does not end with the daytime heat. Water vapor in the atmosphere acts as a lid, trapping heat near the ground overnight. As a result, when tropical nights—periods when the temperature does not fall at night—persist for an extended time, the body loses the chance to recover from fatigue and becomes vulnerable to heat-related illnesses.

Heatwaves can no longer be described simply by the highest temperature—a single, isolated figure. The real danger is not just how high the temperature is, but whether the body can expel internal heat. In this era of climate change, what Korea must truly be wary of is not simply "higher temperatures." The "hot and humid steam chamber" that traps heat inside the body is the new type of climate disaster our society must prepare for in the future.

This content was produced with the assistance of AI translation services.