Some goals are impossible, to be sure. The goal of maintaining the status quo is impossible, at least insofar as energy infrastructure is concerned. It cannot be done, whether that pleases you or not. That which is unsustainable will not be sustained.
But people don't like change. So the optimum path to the future is the one which causes the least change. For instance, on the carbon front, we cannot keep emitting substantial net amounts of carbon into the air. In fact, we run plenty of risks at the trillion ton total. So planning is looking at stopping at a trillionth ton, and identifying what has to happen between today and that future. Of the possibilities raised, we have to somehow settle on the least implausible one; which has to be among those which threaten people the least.
I understand most people are worried about the politics of it: how to convince people that change is necessary.
But I think we are being hopelessly unclear about what change that is.
Let's be clear about this much. What needs to happen for us to not go past the trillionth ton, so we can peak below 500 ppmv and revert eventually to the neighborhood of 350 ppmv with a reasonable effort?
Clearly, an international agreement needs to happen. But an agreement to do what? By when? We need to be specific. So far, we are proposing nothing at all. The advocates of the status quo are ahead of us. Their suggestion is unworkable, but it's easy to imagine.