Not to be too cynical but looking at all the elements- still powering forward business as usual- the worst case scenarios are becoming the beginning point of likely occurrences. Perceptions are still hampered by corporatist politics, money and media influenced science, world economics. Safe to say, if the future generations were to come back knowing all those responsible, gullible, money influenced, they would crucify them in extreme ways all around the burning dome of the Capitol. Of course that is not what happens anymore than a spiritual or common sense conversion of our addled greed corrupted generation. they will be too busy slaughtering each other or dying in place, cursing God and asking why.
Googling worst case scenarios shows concentration on a few effects, those not too troubling to Americans outside the future Florida archipelago and the Texas Sahara. They are not worst at all in fact, but future guarantees.
I figured on the bent nature of science, economics and politics that the Paris backslapping was an indication we have moved in the talking sphere of confronting the irreversible effects with an ominous nudge of trying to survive the next stage of the juggernaut.
So taking the eternal surprise of the unspotted minds as a benchmark I guess the next verboten "wild" surprise will be our last- extinction. The last thing we have to argue about and not do enough about as the only intelligent race on the planet fails utterly to do its job.
On a good note, the pathological elements of the race will not live to see their own demise at the hands of genetic engineering and an Eden Renaissance.
Perhaps in cool bunkers under mountains the computers will tick off interest earned on hoarded trillions of meaningless currency.
OK, it sounds cynical, but the trajectory of human perception and inaction is nearly as certain as global catastrophe. As a simple pre-scientific guide to consider the subject you won't go broke betting on the "worst" coming on faster than "expected".