"Hot Nights Up 100-Fold": Europe Reels from 'Disaster-Level Heatwave'... Why Was Korea Cooler? [Science Scope]

Europe Trapped by a Heat Dome vs. Korea's "Incomplete Summer"

Atmospheric Circulation Determines the Path of Heatwaves and Monsoons

The Science Behind Summer in the Era of Climate Change

June in France already felt like the height of summer. With temperatures in Paris and other areas soaring to around 40°C, schools either closed or shortened class hours. Some nuclear power plants reduced output as river water temperatures rose, and hospitals entered emergency preparedness for heat-related illnesses. What should have been early summer in Europe instead became a 'climate disaster' that shook not only daily life but also fundamental social systems.

Surface temperature distribution in Europe on June 23, 2026. Most of Western and Southern Europe, including France, Spain, and Italy, recorded surface temperatures of 32.5°C or higher, with some areas marked in purple indicating temperatures exceeding 55°C, demonstrating the intensity of the severe heatwave. In contrast, mountainous regions such as the Alps maintained relatively lower temperatures. Provided by the European Space Agency (ESA) and the Copernicus Program (based on Sentinel-3 satellite surface temperature data).

In contrast, the scene was different in Korea, which is also in the Northern Hemisphere. April and May saw cooler-than-average days, and in June, rain, clouds, and frequent changes in atmospheric pressure systems suppressed daytime heat, helping the country avoid any record-breaking heatwaves. Why, in the same Northern Hemisphere and in the era of global warming, do these two regions experience such different summers?

The answer lies not in temperature itself, but in 'atmospheric circulation.' While global warming raises the Earth's average temperature, extreme heatwaves and heavy rainfall in specific regions are determined by the arrangement of atmospheric circulation, shaped by jet streams and high- and low-pressure systems.

The 'Heat Dome' Covering Western Europe and an Atlantic Warning

At the center of the recent European heatwave was the 'Heat Dome.' This phenomenon occurs when a strong high-pressure system lingers over a region, trapping hot air beneath it like a lid. As air descends at the center of the high pressure, it compresses and heats up further, while cloud formation is suppressed, allowing intense sunlight to bake the ground. On top of this, hot and dry air from the Sahara Desert in North Africa flowed in, causing Western Europe to be gripped by record-breaking heatwaves earlier than usual.

On the 22nd of last month (local time), dogs belonging to homeless people on the Champs-Élysées in Paris, France, were panting heavily as they battled the heat. The temperature in Paris reached 41℃ that day. Photo by Yonhap News.

The dominant analysis is that the starting point for this phenomenon was not the European continent itself, but the 'North Atlantic Ocean.' Myung-In Lee, Director of the Heatwave Research Center and Professor of Urban and Environmental Engineering at Ulsan National Institute of Science and Technology (UNIST), explained, "As sea surface temperatures in the North Atlantic rose above average, Rossby atmospheric waves over Eurasia were strengthened. As these waves propagated along the mid-latitude jet stream, they contributed to the formation of a heat dome by anchoring high pressure over Europe."

He added, "Even after the strong El Niño ended, the global average sea surface temperature remained at a record high, and heat accumulated in the ocean was transferred to the atmosphere, further intensifying the current heatwave."

What prolonged the heat was 'atmospheric blocking' in the upper atmosphere. The jet stream, which flows about 10 kilometers above the ground, developed large, snake-like meanders that trapped high pressure in place—a phenomenon known as 'Omega Blocking.' As a result, the heat dome did not dissipate easily. Under normal conditions, the high pressure would have moved rapidly from west to east, but this stagnation led to a prolonged heatwave.

Even though both are in the Northern Hemisphere, Europe and East Asia experienced different atmospheric circulation patterns this summer. While Europe endured prolonged heatwaves due to a heat dome and omega blocking, the Korean Peninsula saw a relatively late start to summer as the northward advancement of the North Pacific High was delayed and rain clouds frequently developed.

Some climatologists believe that this stagnation of the jet stream is closely linked to 'Arctic amplification,' where the Arctic is warming much faster than the global average. As the temperature difference between the Arctic and the mid-latitudes narrows, the jet stream weakens, leading to more frequent blocking events—a topic of major ongoing research in the international climate science community.

"A Heatwave Impossible Without Human-Caused Climate Change"

This heatwave is a prime example of how climate change amplifies extreme weather. The international research group World Weather Attribution (WWA), which includes Imperial College London and the Royal Netherlands Meteorological Institute (KNMI), analyzed the Western European heatwave and concluded, "This heatwave would have been extremely unlikely without human-induced climate change." The rise in global average temperature since the pre-industrial era intensified the heatwave, and in particular, the frequency of nighttime high temperatures has increased more than 100-fold compared to 20 years ago.

The World Meteorological Organization (WMO) also warned that Europe is warming faster than the global average, emphasizing that heatwaves are expanding into a 'social disaster' that disrupts health, agriculture, and energy infrastructure.

Korea: "Not Because It Was Cool, But Because Summer Was Delayed"

Meanwhile, East Asia, including the Korean Peninsula, experienced atmospheric circulation patterns opposite to those in Europe. Professor Myung-In Lee explained, "While Europe was situated on the ridge of the Rossby wave, allowing a high-pressure heat dome to form, East Asia was under the influence of a trough, leading to low-pressure circulation."

As a result, the North Pacific High failed to cover the Korean Peninsula until early summer, with cold air from the north and warm air from the south locked in a standoff. Frequent rain clouds blocked solar radiation, suppressing surface heating. This does not mean Korea was safer from climate change than Europe—it simply means that the atmospheric structure typical of midsummer formed later in the season.

On the afternoon of the 16th of last month, when nationwide hot weather continued, a fog-type cooling water (cooling fog) system to prepare for heat waves was operating at a taxi stand in Seongsan-gu, Changwon City, Gyeongnam Province. Photo by Yonhap News

The unique, intense heatwaves of the Korean Peninsula begin when a 'double high-pressure' structure forms, with high pressure in both the lower and upper atmosphere stacked like layers of rice cake. For heat to accumulate, the hot and humid North Pacific High must be firmly overlain by the hot and dry Tibetan High, creating a robust two-layer structure. In early summer, neither high pressure system fully expanded, effectively postponing the heatwave for Korea.

However, this does not mean that this summer will be safe. Due to climate change, the amount of water vapor in the atmosphere has increased, raising the risk of sudden torrential downpours during the rainy season. Once the pressure systems are fully in place, Korea is likely to face extreme heatwaves characterized by high temperature and humidity. Professor Lee advised, "With the background temperature already elevated due to climate change, once the right atmospheric circulation conditions are met, the intensity of heatwaves will be even greater. In particular, as sea surface temperatures around Korea are rising sharply, we must prepare for the risk of deadly heatwaves combining high heat and humidity in the future."

The stark contrast between France and Korea this summer provides an important clue for understanding the era of climate change. Climate change does not heat every region in the same way. What we need to focus on now is not just the raw temperature numbers, but the 'anomalies of atmospheric circulation' that create different summer faces in various parts of the world.

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