Aaron Denman of Bain, a consultancy, calls such bets a quest for “growth engine number two” in case the firms’ core fossil-fuel business falters. The same rationale may underlie the hydrogen efforts of other sectors with a spotty environmental record. On October 11th Andrew Forrest, a mining tycoon and Australia’s richest man, who controls Fortescue Metals Group, unveiled plans to build the world’s biggest factory for electrolyser machines, needed to produce green hydrogen from water.