I suspect Al Gore's name to be floated- even if they have to create a 'secretary for the environment'. I don't know if he'd take such a post- but II'll be my bonnet they'll ask him to do something.
Are there historical examples of former Vice Presidents taking cabinet positions?
There's already a certain amount of overlap between what the Secretary of Energy and Secretary of Transportation need to do if we want to import less petroleum. Having a Secretary of the Environment to tell us we need to burn less petroleum just seems redundant, though granted there are other environmental issues, and maybe some of them even have less overlap.
Its not JUST about gas y'know? Its about conservation of resources, development of recyling programs, keeping a check on corporations, and preservation of our nation's natural parks and restoration of them. A Secretary of the Environment may also carry clout overseas.
These are all things that various programs and bodies have some power over- EPA, Energy, and Transportation, but the power is FAR from consolidated and is FAR from being effective. Absorb all of that power into one office that provides oversight and has more executive power.