Fig. 4: Seasonal lake heat release (LHR) changes.

Spatial pattern (a) and cumulative distribution function (CDF) (b) of seasonal difference (boreal summer minus winter) in ∆LHR. c The CDFs of seasonal difference in upward longwave radiation (LWup) changes. d Boxplots show the sensitivity of LWup to lake surface water temperature (LSWT) and the purple line shows the percentage of lakes with ice cover. In each boxplot, the central line represents the median, the box indicates the interquartile range, the whiskers extend to the non-outlier minimum and maximum, and the dots denote outliers. The red and blue colors in (b–d) indicate the ice-free and ice-covered lakes. The light shades on the top of (b) and (c) show marginal distributions, the overlapped black lines show the median, and the dark shaded boxes show the interquartile range. The CDFs in (b) and (c) and boxplots in (d) are based on outputs of lakes in Northern Hemisphere. The grid cells in the spatial map correspond to representative lakes (see Methods). All changes compare present-day (1991–2020) with pre-industrial conditions. Source data are provided as a Source Data file.