Reducing carbon emissions is one of the great challenges of our time. This is the end claimed by New York Attorney General Eric Schneiderman for his high-profile investigation of Exxon Mobil Corp., but his end does not justify his means.

Prompted by evidence that the company’s public climate-change ­statements were at odds with what some of its own scientists were saying internally, Schneiderman has utilized New York’s Martin Act to subpoena a broad range of Exxon’s internal documents. The Martin Act grants the attorney general extraordinary powers to subpoena private documents without either obtaining a court order, which is required in most ordinary New York criminal proceedings, or the filing of a complaint, which is required in an ordinary civil action and is subject to court review. The Exxon subpoena is an abuse of these extraordinary powers.