It usually takes a while — a decade or two — before we can look back at a particular era of American life and see it as something coherent, something whose every aspect is marked by one overarching mood. It takes a certain amount of hindsight to notice how all the wildly different reactions people had to the moment were still, in the end, reactions to the same thing; all the different poses they adopted were still being struck against the same backdrop. But this era — this year, and the last one, and one or two before that — might be an exception. Musicians are no exception. Though there is, in certain genres, plenty of all that as. No, a lot of these songs seem focused on deeper challenges: How do we get to those joys in the first place? Who gets to have them, and who deserves them? And in one case: Which of them are worth the corresponding rise in sea levels?