Some idylls are born in tragedy. In March 1999 a Belgian truck hauling an innocuous but highly flammable load of margarine and flour caught fire, turning the 11.6-km Mont Blanc Tunnel into a 1,000C inferno that killed 39 people. The tunnel's subsequent closure has kept what was a daily average of more than 2,000 diesel-burning rigs out of the approaches to one of Western Europe's busiest tunnels, burrowed beneath its largest mountain on the French-Italian border.
As a result, residents of the Chamonix Valley began noticing that the butterflies were back. They say their children cough less and have...