GRANDE-SYNTHE, France — Colorful condominiums with low-energy fixtures have replaced dreary old buildings. Community gardens have sprouted at the foot of public housing projects. And a flashy new fleet of buses runs on natural gas — the fare free.

It is not, perhaps, what one would expect of a bleak coastal town in a crumbling industrial area of France. But Grande-Synthe, near the northern city of Dunkirk, stands out as an unlikely laboratory for working-class environmentalism.

That, at least, was the vision of Damien Carême, the town’s Green party mayor since 2001, who was elected in May to the European Parliament, which he intends to use as a larger stage to extend his idea of “social environmentalism.”