If the human's effort can move the catastrofic subsequences of the global warming from say 25 years to 250 years in the future it will be still worthy...If we were to find out that only a portion of it is our emissions problems we wouldn't need to be so hasty in changing it.
Because the longer time till the X day may give enough technology strength to prevent Armageddon to happen...
So I think, it depens and say: "Hey! we are not only ones responsible" is not enough.
