Record number of tropical nights in big cities: in Milan 27 out of 30 in June. What the data say since 2010

In Milan this year, the heat in June broke all records. According to data from the Milan Duomo Meteorological Observatory, the month ended with 27 out of 30 tropical nights. This means that for almost the entire month, night temperatures never dropped below 20 degrees, not even between midnight and six in the morning. So many hot nights had never been recorded before, not even during the hellish summer of 2003 when tropical heat at night was recorded 'only' 25 times.

The increase in tropical nights, particularly in large metropolitan cities, is a recent phenomenon that has seen exponential growth numbers over the past decade. This was also certified by the latest edition of the Climate Index of the Sole 24 Ore.

Rising temperatures result in an increase in extreme heat peaks. The result, between midnight and 6 a.m., is almost 80 tropical nights per year in northern cities (with 20°C or more), 36 more than 15 years ago. In the Centre, again on average, there are 84 tropical nights per year compared to 53 years earlier (+30). In the South, where the phenomenon of tropical nights has historically been more frequent, there were 97 episodes, 21 more in the period considered.

The most pronounced trend, therefore, sees an increase in hot nights (in which the average temperature remains above or equal to 20°C) especially in the northern regions. Here it is the trend in Milan, in particular, that shows the peak: between 2010 and 2024, the moving average of tropical nights detected by 3bmeteo's columns in the city rose from 66 to 102 episodes per year, in practice 36 more extreme events in fifteen years.

More generally, in the large metropolitan cities, the increase in tropical nights is more rapid and intense (see the graph below): in Bari there are 33 more events than fifteen years ago; in Bologna 40 more, for a total of 96 a year; in Rome 48 more, for a total of 109 a year; in Turin 54 more, for a total of 84 episodes in 12 months; in Florence 32 more. Finally, Palermo peaks at 143 tropical nights a year, while Naples averages 117 a year.