Reconstruction of the Background Air Temperature Record in Japan (1916–2023): Implications for Climate Change and Urbanisation Bias in the 20th Century

Long‐term and contiguous records from the rural weather stations are necessary to estimate the rate of global warming without urbanisation bias. This study reconstructed the trends of the annual mean temperatures in rural Japan using digitised monthly maximum and minimum temperature data recorded from 1916 to 2023. Monthly temperature data from 1926 to 1940 were recently digitised from the printed materials of the Japan Meteorological Agency (JMA). While the reconstructed annual mean temperatures over Japan are in good agreement with those from previous studies for rural stations in Japan (population density < 100 people km −2 ), the linear rate of increase in the annual temperature averaged for 15 monitoring stations of the JMA showed a linear trend of + 0.15°C decade −1 for 1916–2023 higher than that averaged for our rural stations (+ 0.11°C decade −1 ) due to the urbanisation bias. Interestingly, when the urbanisation biases were subtracted, a significant decreasing trend (i.e., a climatic jump) was detected in the rural temperature record during the 1960s. Comparing our rural temperature trend with those in other regions of the Northern Hemisphere and sea surface temperatures around the Japan region, the urbanisation bias likely partially masked the importance of natural variations such as PDO and solar variability.