PMI is looking at green PM from a slightly different angle. Basically, it is called "sustainable project management" and it permeates everything that we do. You should be thinking about sustainability during initiating, planning , executing, monitoring & controlling, as well as closing. And you should also think about it in all the Knowledge areas (scope, schedule, cost, quality, etc.).
So it is not considered a separate discipline, but - like good ethics - sustainability must be thought about all the time.
This means that it will most likely be discussed in the upcoming PMBOK v6, but don't expect a new Knowledge Area on the topics. But instead expect to find it throughout.
Until Next Time,
Cornelius Fichtner, PMP, CSM
President, OSP International LLC