Why has Paris banned alcohol use in public? There's interesting science behind

Paris has banned drinking alcohol in public as a record-breaking heatwave pushes its hospitals to breaking point. Here is the science of why alcohol turns dangerous in extreme heat, and what is fuelling Europe's deadly temperatures.

In Short

• Paris bans public drinking as heatwave pushes hospitals to limits.
• Alcohol speeds dehydration and lowers blood pressure during severe heat.
• Scientists blame climate change for Europe's most severe recorded heatwave.

On a sweltering Friday afternoon by the Seine, the simplest Parisian ritual of all, a cold beer in the sun, briefly became against the law.

On June 26, with the city baking under record heat, police banned the drinking of alcohol in public streets and parks. The reason was not public order. It was human biology.

WHY HAS PARIS BANNED DRINKING ALCOHOL IN PUBLIC?

The Paris police chief, Patrice Faure, said the city's hospitals had reached saturation point.

Ambulance crews were fielding around 2,500 call-outs a day, roughly double the normal figure, and the health minister, Stephanie Rist, reported four times the usual number of cardiac arrests over a single 24-hour period, with young people among them.

Alcohol drunk in direct sunlight, Faure warned, has devastating effects.

The ban runs across the weekend, alongside suspended sports events, a postponed Pride march and a cancelled music festival.

WHY IS ALCOHOL DANGEROUS IN A HEATWAVE?

The danger comes down to water, and how fast the body loses it.

Alcohol is a diuretic, which means it makes the kidneys produce more urine. It does this by suppressing vasopressin, the hormone that normally tells the body to hold on to water.

In a heatwave, when you are already sweating out litres of fluid to stay cool, alcohol drains those reserves even faster and tips the body towards dehydration.

Alcohol also widens the blood vessels, a process called vasodilation.

That causes blood pressure to fall, which is why a few drinks in fierce heat can leave a person dizzy, faint or collapsed.

And because alcohol blunts judgment, drinkers often miss the early warning signs of heat exhaustion until it tips into heat stroke, a medical emergency in which the body can no longer cool itself down.

WHAT IS CAUSING THE EUROPEAN HEATWAVE?

The brutal weather is being driven by something meteorologists call an Omega block. Picture a vast dome of high pressure shaped like the Greek letter omega that parks itself over a region and refuses to budge.

It traps hot air underneath for days on end, pushing temperatures far above normal. Paris hit 40.9 degrees Celsius on Wednesday, a June record, and at least 55 people have drowned across France since June 18 while trying to cool off in rivers and lakes.

IS CLIMATE CHANGE TO BLAME?

Scientists say yes. The World Weather Attribution group, which runs rapid studies to measure how far human activity has loaded the dice on extreme weather, found this heatwave would have been virtually impossible without human-caused climate change.

The warming has made the stiflingly hot nights, when the body most needs to recover, around 100 times more likely than they were two decades ago.

For the region studied, the scientists called it the most severe heatwave ever recorded.

Faure's message was blunt. His job, he said, was to stop the emergency system being overwhelmed. In a summer like this one, that means asking Parisians to swap the wine for water.

- Ends