Climate change, such as global warming, can affect the sleeping environment especially during summer. Although the effects of summer heat are often explained by maximum outdoor temperatures, minimum outdoor temperatures are also increasing, and tropical nights have been recorded at many observation points in Japan. Therefore, this paper provides an overview of climate change, especially during the summer nighttime, are based on the effects of global warming and urban heat island (UHI) in several cities and relationship between these factors and sleep. Furthermore, it introduces the Sleep-Index, which allow us to adjust the thermal environment of our bedrooms based on the outdoor weather conditions. Finally, we analyzed the time-series of changes in page views of the Sleep-Index website, finding that the page views of the Sleep-Index website increased rapidly, when there was a sudden rise in the maximum or minimum outdoor temperature followed by the maintenance of high temperature. We also found that the page views of the Sleep-Index website under the COVID-19 pandemic were significantly higher during the period of dusk until dawn, than for the other contents of tenki.jp.
