The Olympics are usually an environmental disaster. Can Paris be the exception?

Organisers of the Paris Olympics have promised the event will be "historic for the climate". As part of its climate strategy, the committee established a goal of generating no more than half the planet-warming gases produced by previous Summer Games in London and Rio, pledging to slash emissions in three main categories: construction, transportation and operations. So how is Paris faring, compared to its predecessors? And can a planetary event like the Olympics ever be sustainable?