Schools closed and railways advised against travel as Britain, France, Italy and Spain issued red alerts and health warnings for much of their territory in the record-breaking heat.France sweated through its hottest night ever recorded and reported that 40 people had drowned in the past five days as citizens bathed to cool off.Scientists have shown that recurring heatwaves are a clear marker of global warming, and warn they are set to become more frequent, longer and more intense, driven by humans' burning of fossil fuels.Authorities warned of the deadly health risks.In Barcelona, 76-year-old Jose Farre said it made it harder for him to sleep and even breathe."I have a heart condition, I'm diabetic and I feel it a lot," he said, after coming out in the cooler early hours to do his shopping."We've gained several degrees between my youth and today... But what bothers you the most is the humidity."Heat health dangerNearly all of Spain was under a heat alert, with parts of the south and north of the country on the highest warning level.National weather agency AEMET issued red alerts for "extraordinary danger" in areas around the southern city of Cordoba, the northern city of Bilbao and parts of the northern region of Cantabria.Authorities urged people to take extra care of vulnerable people, drink water and avoid exertion at the hottest hours -- if possible.