I just saw a report on CBS about hydrogen cars. They are touted as "green." Bill Whittaker presented them as "green." The auto manufacturer's spokesman said, "the only thing that comes out of the tailpipe is water vapor. Pretty cool."
That's fine but water vapor is a more efficient (i.e. better at trapping heat) greenhouse gas than carbon dioxide!
Of course, your average reporter, who has probably never been in a science classroom, wouldn't know that.
I say, the "more the merrier," let's try lots of things and see what works the best.