Climate models have been well supplied with observational data and physical theory so they can predict steadily worsening heatwaves. But, specially in the last couple of decades, extreme heat events have turned up around the world that exceeded any modelled predictions. Evidently, future heatwaves will not appear randomly, but will be concentrated in susceptible regions - something that is so far only partly explained. In a new study [Kornhuber et al, 2024. PNAS 49, e2411258121] this trend is examined in detail to show how those hot regions are distributed; together with an attempt at a partial explanation.

This map was made by calculating, on a grided representation of the global land area (you can see the tiny grid cells) the difference between yearly heat extremes at the 99th percentile (top 1% of extreme heat days) and the median value for top quartile of daily heat records (75th to 100th percentile). If this difference has been growing, that region shows up as red on the map. This finding is related to the discussion of heatwaves in Chapter 13 - increasing the mean temperature at any place will increase the frequency of extreme heat a lot. These authors find that this effect isn’t enough to explain the existence of the red ‘hotspots’. Dessication is a significant cause - when soil is dry, the cooling effect of soil moisture evaporation is absent. But a complete understanding of this is yet to be found. You can read the study [Here]