There were plenty of scientists letting the public know about the global warming in the 80s. The public didn't want to know about it.
In fact, this state of affairs has not even changed that significantly.
Real structural changes are hard to enforce. There is always something more pressing, just look e.g. at the 100 billion Germany spends on war (how many trees that would give?). As a politician it would be the end of the career if you tried to enforce something really drastic (and so nobody does it, incl. "the greens").
Ok I'll blame them for that then.