I think I might hold a little more hope than you do - not because that cooperation is any more likely, but because it is so important that we attempt it. Attempts only achieve their highest potential when backed with hope and faith.
There is another force to contend with. A growing amount of voters who might avail themselves of new ways of imposing political pressure internationally, via issue based campaigns. Groups such as Avaaz seem to me to be something greater that is still in its infancy.I foresee a continuation of blocs, like NATO, OPEC, SEATO and China, each allying with another for mutual benefit in whichever way it finds itself at odds with one or more of the others. It will be a constant standoff with the issues coming and going and alliances changing, but I don't see global agreement on anything. If any issue is important enough to demand it, then there will be global war, which is the disaster you speak of that seems likely to me.
As our predicament worsens, I think it is entirely possible that we will see populations threatening to grind society to a halt in the run up to international negotiations on the environment. We're not there yet, but it isn't crazy to foresee that we'll get there.
I recall you believed resolutely that Obama could not win the presidential elections in 2008 because of the color of his skin. I hope that you are wrong about this as you were wrong about that. I think we have our fingers on how you and I differ - I see more possibilities for humans to adapt and exhibit new behavior than you do.Too many people know only how to draw lines in the sand over any and every issue. And they're serious. That makes them very dangerous to keep around.
This doesn't mean I'm naive - only more committed to giving the world a chance to evolve.