And Dorian had looked upset when Luce had shown up with Nausicaa, too. Luce had the feeling he’d been waiting to talk to her alone, maybe about something important, though now it seemed like he’d forgotten about that. He was too absorbed in the conversation, not even reaching to brush away the snow that dropped from the roots overhead and landed on his neck. He was sitting cross-legged right at the edge of the softly lapping sea, leaning forward while the incoming tide soaked the frayed edges of his jeans. Nausicaa was close to him, her tail coiled in a circle around her and her emerald fins occasionally flicking above the glassy, star-streaked water.

Everything Dorian told Nausicaa provoked a stream of questions. “Okay, so the oceans soak up like a third of the carbon dioxide from the air, and that’s making the water get way more acidic. If it keeps up the acid’s going to kill all the coral reefs and maybe a lot of the plankton.” Dorian was excited and he kept going too fast, forgetting how many things Nausicaa wouldn’t know after her three thousand years apart from the life humans lived on land.

“Carbon dioxide? I’ve heard these words before, but the exact meaning . . .” Nausicaa’s brow was creased with concentration.

“It’s pollution, basically. It’s in the air naturally, but we’re putting tons more in the atmosphere all the time. From people burning fossil fuels. So we’re screwing up the balance, and that’s also why we’re getting global warming.”

“Then why do they burn these fossil fuels?”

“Well, that’s how they make all the cars go. And they make most of the electricity that way.”

“Electricity? That means all the lights at night?”

“Electricity makes the lights, but it also powers all the factories and everything. Where people make stuff.”

Nausicaa looked genuinely puzzled, even overwhelmed. Much as Luce loved her she couldn’t help enjoying it a little. For once Nausicaa couldn’t just say she’d heard it all before. “Humans can’t make things with their hands? They did so once.”

“They can make a lot more stuff, though, by using machinery and robots. And they can make it a lot more quickly. But that takes electricity.” Dorian obviously liked his new role as a teacher. “Okay, but the scariest thing about the acidification . . .”

“Yes?” Nausicaa asked; her voice was strained.

“Plankton makes a lot of the planet’s oxygen. And if the plankton dies, like, maybe extra algae or something will make the oxygen instead. But the scientists are all still arguing about whether or not that would happen.”

Luce looked up, ready to burst in with a question of her own—humans needed oxygen, too, after all—but Nausicaa was already speaking: “But the whales eat plankton? The whales with screens instead of teeth? Like the grays?”