But the “Vespers” are prayers, not a requiem. Even if Adams said that this score is one of the saddest and most austere that he has composed, it still celebrates the splendor of the enduring Earth, and is more melodic than some of his music has been. “If ‘Ocean’ and ‘Desert’ are Brucknerian,” he suggested, “this is almost Mozartean.”

That dynamic of beauty and grief going hand in hand is especially apparent in “Night Shining Clouds,” a movement for strings alone that depicts cloud structures whose chemistry means that they are “getting more beautiful because we’re polluting the Earth more,” Adams said. It’s also clear in “Aria of the Ghost Bird,” the desolate final movement, a setting for soprano of the unrequited mating call of the last Kauai oo, a bird native to Hawaii that has not been heard since the 1980s.

“It’s the song of an extinct bird, and yet it’s so beautiful,” Adams said. “One of my friends looked at the score and said, ‘Well, you just can’t help yourself, can you J.L.A., you have to end on a hopeful note.’ I said, ‘Jim, the bird’s extinct.’”

Adams has not lost hope yet, though he admits that “the odds don’t look good for us as a species, and regardless even the best-case scenario isn’t very rosy.” The Biden administration’s recent decision to approve further oil drilling in his beloved Alaska is “kind of unbelievable,” he said.

What gives Adams succor, even now, is a younger group of activists coming to the fore and working in new ways. Following the example of Greta Thunberg, he has cut back on travel and become more deliberate about his choices when it is unavoidable. To attend the back-to-back premieres of “Vespers” and “Night” — his part in “Proximity,” the triptych that opened last week at Lyric Opera of Chicago — he took the train from Albuquerque, rather than fly.

“It’s these next generations that are going to have to sort through the rubble that my generation is leaving to them,” Adams said, “and imagine new ways of living together with one another, and living within the limits of biology — or our goose is cooked. But I’m not betting against them, in the face of all of it.”