Fig. 3. Trend of outdoor days. Time series of outdoor days for the (a) global, (b) low-latitude, (c) mid-latitude, and (d) high-latitude residential areas for the period 1959-2021. Residential areas are defined as having a population density above 1 person per square kilometer. Horizontal black lines denote the 1961-1990 mean and the 1991-2020 mean. Difference (1991-2020 minus 1961-1990) in the number of outdoor days is represented in each plot. These time series are derived from ERA5.