On a clear summer morning at Mount Fuji’s fifth-station trailhead, the crowds look more beach ready than alpine prepared with canvas slip-ons, bare legs and lightweight jackets. Above them, Japan’s most famous peak rises to 3,776 metres (12,389 feet) and into sub-zero temperatures, even in July. For Tatsuo Nanai, a veteran climber and until recently secretary general of the Fuji‑san Club, the scene has become a source of dread. Japan’s official climbing season has only just begun, but he says he...