Report. Extensive building, transportation and the use of air conditioning systems are turning cities into heat islands, where summer heat waves are killing thousands of people each year. But trees can help fix it.

It takes a tree

According to data collected by the Copernicus satellite and compiled by the European Data Journalists Network, cities are warming much faster than the rest of the planet. Compared to the 1960s, the temperature in Rome has risen by 3.7 degrees Celsius, with increases of 3.3 degrees in Milan and 3.1 in Bari, among the hottest cities in Europe. Extensive building, transportation and the use of air conditioning systems are turning these cities into “heat islands,” where summer heat waves, more and more intense due to climate change, are killing thousands of people each year, especially among the more vulnerable elderly. However, a study published on Tuesday in the medical journal The Lancet suggests that mitigating the consequences of heat islands is not impossible, quite the opposite: all it would take is bringing back trees into the cities.

The study, carried out by a team of researchers between Spain, Italy and the United Kingdom, concerns 93 large European cities with a total population of about 58 million, where, for the year 2015 (taken as a reference), mortality due to high summer temperatures was estimated at 6,700 deaths. By analyzing the relationship between mortality and temperature and that between temperature and tree-covered area, the researchers determined that if foliage covered 30 percent of the city area – instead of the current 15 percent – the temperature in cities would drop by 0.4 degrees. Forty percent of heat-related deaths would be avoided, which would be just one of the numerous positive consequences of living in less torrid cities.

“We already know that high temperatures in urban environments are associated with negative health outcomes, such as cardiorespiratory failure, hospital admission, and premature death,” explained Tamara Iungman, of the Institute of Global Health in Barcelona, Spain, the lead author of the study.

Furthermore, the study specifically quantifies the concrete benefit of actions taken by city authorities to bring green spaces back into the cities: “This is becoming increasingly urgent as Europe experiences more extreme temperature fluctuations caused by climate change,” Iungman explains. “Despite cold conditions currently causing more deaths in Europe, predictions based on current emissions reveal that heat-related illness and death will present a bigger burden to our health services over the next decade.”

This is also one of the goals of the NRP, which calls for the planting of 6.6 million trees and the creation of 6,600 hectares of “urban forest” in Italy’s 14 metropolitan cities (0.14 percent of the total area). On paper, cities are taking action. The first tranche of funding was allocated at the end of 2022, which will be used to plant the first 1.6 million trees planned by the cities. One of them is Rome, where a few days ago Mayor Roberto Gualtieri announced plans to plant a million trees in the capital using the NRP funds.

In Milan, the ForestaMI project – whose scientific committee is chaired by star architect Stefano Boeri – started as early as 2018 with an even more ambitious goal than the one in Rome: 3 million new trees in the 133 municipalities of the former outskirts of Milan by 2030. The project is also financed by prestigious investors such as Amazon, Axa, Esselunga, Prada and the SNAM Foundation, and has already raised more than €5.5 million in funding. According to the official data it has published, it is a success: by the end of 2022, 427,000 trees had already been planted.

However, as in the case of suburban reforestation, beloved by businesses but whose benefits are actually more limited than they appear, the idea of planting trees in the cities also presents a high risk of “greenwashing.” And the Milanese case seems to prove it: many of the new trees planted have reportedly already died due to a lack of water. According to ForestaMI officials, the dead trees amount to about a quarter of the total, and the project has pledged to replace them. But activists from the citizen committee “Forestami … e poi bagnami” (“Reforest me – and then water me”) and an investigation by the website MilanoToday – one of ForestaMI’s partners – have shown that the losses are much higher, affecting half of the trees already planted.

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