Human beings spend a lot more time perceiving the social structures they are in (even when they're not aware that they are doing so) than they do reacting to "objective" reality or nature. A lot of people in the world see themselves as being cast aside or outside the current dominant social structures. Convincing them to make sacrifices for the future when the present already seems irredeemably shitty is a losing political argument. Casting nature as yet another political constituency that they need to pay deference too is foolish.
Messages of hope are the only ones that will work to build consensus (even if hope seems irrational at this point).
Edit:
Personally, I think the only rational message of hope right now is that we should be ploughing as much money into science and technology as we can. We certainly shouldn't take our eye off the ball for dealing with climate change, but it seems obvious that we're going to need some pretty amazing technological breakthroughs if we're going to survive as a species.