The New York attorney general accused Exxon Mobil Corp. Monday of withholding documents from his office as it investigates whether the energy company misrepresented its understanding of climate change to investors and the public.

Lawyers for Attorney General Eric Schneiderman’s office said in court documents that Exxon hadn’t disclosed that Rex Tillerson, the former chairman and chief executive, used an alias email address to discuss risk-management issues related to climate change. Mr. Tillerson, now the U.S. secretary of...