When Thomas Steyer — a San Francisco billionaire and major Democratic donor — discusses climate change, he feels as if one of two things is true: What he’s saying is blindingly obvious, or insane. It’s a somewhat shocking statement for someone who’s in the running to succeed the cerebral Steven Chu as energy secretary. Granted, he’s a long shot — the leading contender is MIT professor Ernest Moniz, who served as the department’s undersecretary during the Clinton administration — but his backers say his strength lies in combining business savvy with an activist’s passion. But it’s not as if Steyer,...