Why Azores High hardly works anymore

In summer, we often hear about the so-called Azores High, which has now become almost proverbial: it is a high-pressure atmospheric area, where the weather remains substantially stable. It ensured summers such as those recorded in Italy up to about the 1980s, i.e. with a relative temperature range between day and night, not too maximum highs and temporary reductions in temperature due to thunderstorms that developed at the same local level.

As the name suggests, Azores High forms in the vicinity of the Azores islands, in the North Atlantic Ocean, where it has the maximum point of high pressure. Its position is determined by the atmospheric circulation, i.e. - simplifying - by how the exchanges of currents in the atmosphere are organised according to the winds.

The anticyclone traditionally moved from the Atlantic, influencing the weather conditions of much of Europe: during the summer, it tended to expand eastwards, reaching much of the Mediterranean and central Europe, pushing north to the south of the United Kingdom. In recent years, mainly due to climate change, the anticyclone’s ability to move has been reduced and the phenomenon has thus stopped affecting the European summer season, replaced by high-pressure areas from Africa that contribute to heatwaves.

This is the case of the so-called African subtropical anticyclone which brings increased drought, reducing the likelihood of colder air currents which generate rain from passing through. This year has played an important role not only in prolonging a long period of water shortage, still ongoing, but also in causing an increase in maximum temperatures: in much of Europe, there are heatwaves that have brought the temperatures at above average levels, particularly in Italy, France, Spain, Greece and the United Kingdom, contributing to causing severe forest fires in some of these countries.

Research published in the scientific Nature Communications journal has shown how Western Europe has become increasingly prone to heatwaves over the past 40 years. The average temperatures of the first half of the year in Europe have already made 2022 one of the hottest years on record, confirming the trends recorded in recent years related to the effects of climate change. More generally, the last decade has had some of the hottest months on our continent.

In July 2022, only in Portugal, where in some areas, the temperature went as high as 47°C, according to the Ministry of Health, at least 230 people died from the heatwave, mainly the elderly. In this regard, the Spanish Prime Minister Pedro Sánchez, during a visit to a region of southern Spain among those most affected by the fires, recalled that «climate change kills. It kills people, it kills our ecosystem, our biodiversity and destroys the most precious assets of societies».

The modification of some atmospheric dynamics, such as the loss of ability of Azores High to expand eastwards which causes greater heatwaves, are a direct consequence of global warming due to human activities. In the North Atlantic, the so-called jet streams, i.e. the flows that move enormous quantities of air at high altitudes, during the summer months are less intense today than in the past and the cause, according to meteorologists and climatologists, is directly related to the increase in average temperature.