Japan introduces new term for 40C-and-hotter days following record-breaking summer

Japan has launched a new label for days exceeding 40C (104F), a move prompted by the nation’s scorching summer that shattered historical records. The term kokushobi has been interpreted as “cruelly hot,” “brutally hot,” or “severely hot” in media outlets both within Japan and internationally. This label emerged as the top choice in a national survey, surpassing alternatives like “super extremely hot day.” The Japan Times reported that the Meteorological Agency (JMA) introduced the term on Friday, emphasizing the intensity of the heat through the word koku, meaning harsh or cruel.

“The description… uses koku to convey the extreme nature of the heat,” said the Japan Times.

The survey, conducted in February and March, collected around 478,000 responses, with participants selecting their preferred term from 13 options to describe the hottest days. Japan already has established terminology for temperatures surpassing 25C, 30C, and 35C. The new designation follows record temperatures in the previous summer, which was the hottest since 1898. National average temperatures during that period were 2.36C higher than usual. Nine days in June through August hit 40C or more, with Isesaki setting a new national high of 41.8C. The total number of extremely hot days also eclipsed the previous record from 2024.

For instance, Tokyo recorded 25 days above 35C, a stark increase from the typical 4.5 days. Kyoto, meanwhile, logged 52 days over the same threshold, compared to an average of 18.5 days. This summer, the JMA forecasts a high likelihood of above-average temperatures from June to August, underscoring the ongoing trend of intensifying heatwaves linked to human activities such as fossil fuel combustion.