Tom Steyer, the billionaire climate activist, spent heavily to back environmentally friendly candidates for Congress in 2014.

But Tuesday's election results produced a stunning disappointment, and a low return on his $70 million investment.

Many of the environmentally friendly candidates he backed most heavily­, such as Sen. Mark Udall in Colorado  and Rep. Bruce Braley in Iowa,­  were defeated -- earning him a low "return on investment" score from the Sunlight Foundation, which ranks the major independent spending  groups that now dominate federal campaigns.

Steyer, who spent his own money launching NextGen Climate Action, had "little to show for his efforts," the foundation's staff concluded in the report  released Wednesday.