PORTLAND, Maine (AP) — A retired admiral who once commanded all U.S. fleet forces is taking part in a forum in Maine that focuses on climate change and energy issues.

Retired Adm. John Nathman will be one of three panelists at Tuesday afternoon’s event at the Portland campus of the University of New England. It is hosted by the university and the Pew Project on National Security, Energy and Climate.

Former U.S. Sen. John Warner of Virginia was originally scheduled to participate but had to cancel because of a family emergency.

Other panelists include John Kerry of the Maine Office of Energy Independence and Security, as well as the director of Pew’s climate and energy programs.