Fig. 2: Alterations to the timing and duration of summer in lakes.

Shown are (a, b) calculated shifts (days decade⁻¹) in the timing of summer (June–August) temperatures across Northern Hemisphere (NH) lakes during the historic to contemporary period (1980–2021). Positive and negative values indicate when the timing of summer has advanced or been delayed, respectively. Results for Southern Hemisphere (SH) lakes are shown in Fig. S8. Also shown in panels (c) and (d) are calculated changes to the duration of summer, estimated as the difference between the seasonal shifts in the start of summer and the start of autumn (September–November). Positive and negative values indicate when the summer season has lengthened or shortened, respectively. Stipple markings represents regions that were not included in the analysis, either due to the presence of lake ice cover (grey points) or when lakes experienced a minimal (<0.5 °C month⁻¹) seasonal rate of change in surface water temperature (black points) during the season of interest.