Three quarters of mainland France is under a “red alert” for the heat. And it may seem odd that the southeastern Mediterranean coast is not under that highest level of warning. So why doesn’t the mercury climb as high on the Côte d’Azur in the middle of a heatwave? The Mediterranean Sea allows the south-east of France to maintain lower temperatures than the rest of the country, as it cools the flow of hot air that builds up over the north-west.