Secretary of State Rex Tillerson is being accused by the New York attorney general's office of using the email alias Wayne Tracker when he served as Exxon Mobil's CEO to cover up climate change discussions.The accusations are part of a court fight between Exxon and Attorney General Eric Schneiderman in a case involving Schneiderman's investigation into news reports that the oil company withheld information on the harm posed by climate change to shareholders and the public.In a letter to a state judge late Monday, the attorney general's office revealed that its climate investigation showed Tillerson often used the Wayne Tracker alias between 2008 and 2015. Exxon had not included the emails in its response to a subpoena from Schneiderman's office. Exxon has tried to block Schneiderman's subpoenas in the courts, arguing that the claims that it withheld information on climate harms are untrue. "Tillerson used this secondary email address to send and receive materials regarding important matters, including those concerning to the risk-management issues related to climate change that are the focus of [the] investigation," said John Oleske, senior enforcement counsel who works for Schneiderman. But the oil company said the Wayne Tracker email "is part of the company's email system and was put in place for secure and expedited communications between select senior company officials and the former chairman for a broad range of business-related topics," a spokesman said.The company account was not used for only discussing matters related to climate change, the spokesman said. "The very fact the attorney general's office has these emails is because they were produced in response to the subpoena."The email issue is being raised amid discussion that Tillerson will play a critical role in President Trump's plans to withdraw from the Paris climate change agreement, although recent reports suggest there are conflicting opinions in the White House on whether it would be wise to do so.