So to protect themselves, city dwellers are turning more and more to air conditioning. But it creates a vicious circle by warming the atmosphere. An effect measured by Brice Tréméac at the Cold Laboratory of the National Conservatory of Arts and Crafts (Cnam): "We have highlighted that air conditioning can have an impact on the rise in temperature of the city. In Paris for example, we has areas, especially around Montparnasse or l'Etoile, where this rise is around 2 ° C. "

Trees, these natural air conditioners

How to get out of this trap? Vegetation is the solution that cities have adopted in recent years.

In Aubervilliers in particular, a "third forest" has been created on an old car park. Seventy trees have been planted there to form a forest ecosystem. The architect Andrej Bernik explains how they act as natural air conditioners: "Trees cool the air in two ways: on the one hand, they provide shade. On the other hand, they draw water in the soil and evaporate it through the leaves. When water evaporates, that is to say when it changes from liquid to vapor state, it consumes energy and causes a drop in temperature , on the same principle as a fogger. "  

According to the first results measured by a weather station on the site, the temperature dropped by about 2 ° C.

"A method as old as the world"

It is no coincidence that the buildings in southern Spain or Greece are white: they reflect the heat. A technique applied to roofs by the company Cool Roof (literally "fresh roofs"). In Provins, Daniel Simon applies a white resin to a black bitumen roof, which can reach a melting temperature during heat waves. "If I had to explain my job to my 10 year old son, I would explain to him that Dad is going on supermarket roofs, to put some kind of sunscreen on the supermarket roof, so that the supermarket does not suffer from excess summer sun. "

A particularly interesting method for the Picard company, king of frozen food. Dozens of freezers are constantly running at full speed in its stores. "They emit what is called a fatal heat," says Gérald Townsend, Sustainable Development Manager for the brand. "This raises the store in temperature and forces the air conditioning to take over to keep the optimal temperature. Any solution that will allow us to reduce the heat supply inside the store interests us." 

With his paint spray gun, Daniel Simon can cover 10,000 m2 during the day. A quick and inexpensive solution, which complements planting for large flat surfaces. "The paint will reflect 95% of the sunlight, which will no longer transform into heat, but will be re-emitted into the atmosphere, from where it comes," he said.

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