With the arrival of a new wave of heat due to the incursion of the African anticyclone the diatribe returns between the two Italian “schools” on the summer heat: that of “In the summer he has always done hot” and that of “The summers were once fresher”. To confuse the ideas even more, in recent days we have seen the clips of weather forecast of the 80s appear on the social media that showed temperatures even below 30 ° C in July as proof of the fact that once the summers of the Belpaese were decidedly more kind. In fact, compare two temperatures directly after forty years has no climatological meaning: climate science is based on medium and long -term trendsnot on individual point episodes.
So what do trend relating to temperatures in Italy say? Analyzing i ISPRA data (Higher Institute for Environmental Protection and Research) relating to the period between 1961 and 2024 it is undeniable that All indicators of the temperature details are showing a quick and intense heating of our country, which is leading to a real tropicalization of the Italian climate.
Summer days
Ispra defines as “summer days” the days when there is a maximum temperature above 25 ° C. To achieve this histogram, the institute took the number of summer days for each year in the reference period 1991-2020made the average and calculated for each year how many more summer days (red bars) or less (blue bars) compared to the average of the reference period. The reference period is important to establish an climatological basis with which to compare the average data of a single year: in climatology the reference period must be at least thirty years in order to “absorb” statistical fluctuations and thus emerge any trend in progress. The 1991-2020 period is the same used by ISPRA also to create all the graphs presented in this article. Note the peak of the notorious Summer of 2003which will also return to the subsequent graphics.
Tropical nights
Another must of every summer are the so -called tropical nightsor those in which the temperature never drops below 20 ° C. In the graph above we can see the increase (in red) or the decrease (in blue) of the tropical nights recorded in Italy compared to the annual average calculated in the reference period 1991-2020. Here too there is a clear increase from the 1960s onwards, and we also notice that – as in the graphs above – we begin to go above average and remain quite permanently starting from the early 2000s.
Hot days
As you can see, even the hot days in Italy are definitely increasing. But what does “hot days” mean and how do you read this histogram? Ispra did this: considering the reference period 1991-2020, he took all the maximum daily temperatures recorded in Italy at that time and determined the temperature for which the 90% of the days has a lower maximum temperature. At this point, always in the reference period, the average of the days in a year with maximum temperatures higher than this value is calculated. The red bars in the Istogram indicate the percentage variations compared to this average: for example, the 2024 The days with maximum temperatures higher than this value were the 14.2% In addition to the average in the period 1991-2020. In the Istogram above, the “red” years are above average, the “blue” under media: it is clear that the number of hot days – in the definition given above – has increased drastically in Italy in recent decades.
Hot nights
This histogram is analogous to the one relating to the hot days, with the difference that here the anomalies shown refer to Minimum daily temperatures instead of the maxims. Here too it is impossible not to notice a progressive increase in minimum temperatures in Italy over the last decades.
Duration of the heat periods
Not only are the temperature peaks increasing, but also theirs duration. The graph above does something similar to what we explained for the hot days, but shows the number of days when the maximum daily temperatures remain above the threshold value for At least 6 consecutive days. In short, the heat waves in Italy are longer as well as more intense.
Because the Italian climate is heating
From the graphs that we have shown is evident a heating of the Italian climate. But why is it happening? The main reasons are three:
- The global warming increases the climatic base towards increasingly high values;
- The Mediterranean Sea which surrounds the Italian peninsula is becoming more and more hot;
- From the 90s theanticyclone dominant in Italy in the summer period is no longer that of Azzorreof Atlantic origin, but that North African which is of sub-tropical origin and therefore brings higher temperatures.
