On a stretch of the Garonne River in south-western France, the water has grown so warm that it can no longer safely absorb the heat discharged by a nuclear reactor. Earlier this month, EDF shut down a unit at the Golfech power station after the river approached its legally permitted thermal discharge limit. A second restriction was expected at the Nogent plant from 14 July if forecast river temperatures were reached. French environmental law requires operators to reduce or halt output rather than push overheated water back into ecosystems that are already under stress — a rule designed for ecological protection that is now colliding directly with energy security.

The underlying cause stretches far beyond a single river. Persistent high pressure has settled over western and central Europe since June, suppressing rainfall, extending sunshine hours and accelerating evaporation. River levels have fallen while water temperatures have climbed. At the same time, households and businesses across the continent have turned on air-conditioning in greater numbers, driving electricity demand upward precisely when output from water-cooled plants is being curtailed.

The tension between supply and demand is being tightened from both ends simultaneously. Across the Iberian Peninsula, the same weather pattern has produced a different but equally destructive outcome. Spain endured several significant wildfires last week, with one of the largest burning through Almería province and forcing evacuations. Exceptionally dry vegetation, low humidity and gusts of wind combined to allow fires to spread with unusual speed.