LONDON — Last season, a hot new trend emerged during fashion month. Gabriela Hearst, Burberry and then Gucci all staged “carbon neutral” runway shows.

Then Kering, the owner of Saint Laurent, Balenciaga and Bottega Veneta, among other big-name brands, announced that its entire group would offset 2.4 million tons of carbon dioxide in a bid to become, that’s right, “carbon neutral.”

Carbon, or how to offset it, was all the rage.

To some bemused observers, it was a strange time for fashion to begin touting its carbon-neutral credentials. To merely attend the ready-to-wear collections, tens of thousands of professionals fly to four separate countries in a single month. Simple math dictates that the entire exercise is a veritable bonanza of carbon emissions.

Now, just in time for another season of shows, comes a report that attempts to measure the carbon impact of a slice of the fashion world for what its authors say is the very first time.