Record-Breaking Heat in Japan: August 2025 Sees Highest Temperature of 41.8°C
In the sweltering summer of 2025, Japan experienced an unprecedented heatwave, with numerous cities recording temperatures above 40°C. This marked a significant shift in the country's climate, with the first recorded temperature above 40°C traced back to July 1927 in Uwajima, Ehime.
On August 16, 2007, Tajimi, Gifu, and Kumagaya, Saitama, saw their highest temperature ever at 40.9°C. However, the summer of 2025 outdid this record, with Shizuoka, Shizuoka and Hatoyama, Saitama, reaching 41.4°C on August 6, 2025. The temperature in Tajimi, Gifu, once again soared to 40.9°C on August 16, 2020.
The highest recorded temperature in Japan was 41.8°C, reached in Isesaki, Gunma, on August 5, 2025. Kiryū, Gunma, and Tanba, Hyōgo, also recorded 41.2°C and 41.0°C on the same day.
The heatwave was not limited to the southern regions of Japan. On July 24, 2025, even Japan's northernmost main island, Kitami, Hokkaidō, reached 39.0°C.
The extreme heat conditions were primarily driven by human-caused climate change exacerbated by ongoing fossil fuel use. The continuation of global warming has raised baseline temperatures, causing national average temperatures in Japan to be significantly above normal. June 2025 was 2.3°C above average, and July 2025 was 2.9°C above the 1991-2020 average, marking the hottest months in 127 years of records.
The expansion of the Pacific High-Pressure System, a weather pattern that suppressed clouds and rainfall, also contributed to the prolonged and intense heat. This weather pattern led to sustained high temperatures from mid-June to August 2025.
Climate change has increased the likelihood and severity of extreme heat events. The Climate Shift Index (CSI) level 5 across Japan indicated that human activity made such heatwaves at least five times more likely, signaling an exceptional climate event rather than natural variability.
Additional climate influences such as El Niño and Arctic ice melt have also played a role, altering atmospheric circulation patterns and further increasing the frequency and intensity of heatwaves and extreme weather globally, including Japan.
The heatwave led to concrete impacts, including multiple new high-temperature records, widespread heatstroke hospitalizations, damage to agriculture (notably rice and fruit quality), and record electricity demand due to cooling needs.
In summary, the record-breaking heat in summer 2025 results from the synergistic effects of global warming driven by fossil fuel emissions, large-scale atmospheric circulation changes (e.g., Pacific High expansion), and climate phenomena like El Niño, all combining to create unprecedented extreme heat conditions.
- The unprecedented heatwave in Japan during the summer of 2025, characterized by temperatures soaring above 40°C, was primarily driven by human-caused climate change and the expansion of the Pacific High-Pressure System.
- The Climate Shift Index (CSI) level 5 across Japan in 2025 signaled an exceptional climate event, indicating that such heatwaves were at least five times more likely due to human activity, exacerbating the natural variability in weather patterns.
