Britain's railways, engineered for a temperate climate that has quietly ceased to exist, are now confronting the consequences of that mismatch as a record-breaking El Niño gathers force over the Pacific. Two derailments in a single August day laid bare what engineers have long understood in theory: infrastructure built for one world cannot simply be maintained into fitness for another. The question now is whether the industry can distinguish between patching what exists and redesigning what must come — and whether it can move quickly enough to matter.