Well, actually we all did know it to come since last month, but anyway. It’s a great day for me: US back in paris climate act. Nobody could tell for sure whether it will have any effect on climate after all. This is a symbolic act mostly.
Virtually Modelling the climate on supercomputers is a rather difficult task, involving arbitrarily many variables, an unknown number of which we even don’t know by now. But we do have only one earth, so we are liable to act in a way to keep it from irreversible damage resulting from our acting. This means for me, we should take any precaution we can handle with our best efforts, as long we don’t know what we are doing. This is not about a sandpit wherein we can destroy and rebuild our sandcastle as often we like in case we had bungled it.