Climate change is having an unforeseen consequence on language — the creation of new words. The Japan Meteorological Agency (JMA) has introduced a new item of vocabulary into the Japanese lexicon. The neologism is the word "kokushobi," which literally means "cruelly hot day" or "harshly hot day". The JMA will use it when describing or forecasting days when temperatures are 40ºC or above. The JMA conducted an online poll of weather-based terminology. The questionnaire was prompted by the scorching weather experienced in Japan in recent years. Website visitors selected their most preferred word. There were 478,000 responses. The word kokushobi garnered nearly 203,000 votes.

There has been record-breaking heat in Japan in the past decade. The JMA reported days of 40ºC or above every year since 2018. In August 2025, the town of Isesaki, Gunma Prefecture, recorded the highest temperature ever observed in Japan. The mercury rose to 41.8ºC. There were a further nine days when temperatures were 40ºC. More records were broken in 2025. This was the hottest year since records began in 1898. Temperatures were 2.36ºC above average. The Mainichi newspaper wrote: "Tokyo recorded 25 days over 35ºC, compared with an annual average of just 4.5 days. Kyoto logged 52 days above that temperature, compared with an average of 18.5 days."