But it took time. For some ten million years the world remained empty, dismal, all its old richness gone. And biodiversity would not recover the levels it had lost for fifty million years.

“Much was never to be replaced at all,” said the little robot. “The old order of the mammal-like reptiles and the spiky trees under which they grazed was lost, gone forever.”

“Why show me this? You aren’t claiming that the eruptions in Siberia are about to kick off again?”

“No. But a similar causative sequence may be unfolding. The root cause of the Permian extinction was the Siberian-trap eruptions. Their emissions of carbon dioxide and methane began a global-warming pulse, but the tipping point came when the temperatures rose so high that polar gas hydrate deposits began to be released. After that a positive feedback effect did the rest.”

“There are no basalt eruptions going on today,” I said. “But instead of the Siberian traps—”

“Mankind,” the robot said. “Your activities, by injecting heat and greenhouse gases into the air over centuries, have had precisely the same effect as the Permian-era eruptions. And similar consequences.” She said this simply.

Standing there on that baked, dead plain, I tried to think it through.

I had grown up with the Warming, laden with guilt over extinctions and environmental degradations that had happened long before I was born. Like most people, I guess I got bored with it, and got on with my life. “It’s like living with original sin,” uncle George once said to me. “We’re all Catholics now, Michael.”

Then along came President Amin. We all went through the great wrench of giving up our automobiles, and we were smugly proud of the Stewardship. The Warming stopped seeming so bad, the Bottleneck not quite such a hazardous highway. Oh, it was a drag for anybody caught in a flood or a hurricane, and I knew we were still at risk. But we were muddling through. So I’d thought. Even the parts-per-million projections of the final greenhousing load of carbon dioxide in the air were starting to fall.

Now here was Gea telling me that I had been fooling myself — that Tom was right. I couldn’t believe it, on some deep intuitive level.

Gea said, “Perhaps you aren’t thinking about the Warming, the Die-back, the right way. Perhaps, deep down, you imagine that the Earth’s processes are linear. That the response from the biosphere will be proportionate to the pushing you give it. But that isn’t necessarily so.

“The Earth’s systems are only quasi-stable. For example the Amazon forests, drought-stricken, are dying back rapidly. The injection of their locked-up carbon into the atmosphere raised temperatures, which will in turn accelerate the dying of the forest. This is biogeophysical feedback. And so it goes, on a global scale, geospheric and biospheric systems flipping suddenly to other states.

“Not only that, the various factors, themselves nonlinear, interact with each other in a nonlinear way: habitat destruction, overpopulation, overharvesting, pollution, ozone destruction, all working together—”

“Lethe.You’re talking about Lethe. The anti-Gaia.”

“There comes a point where if you keep pushing you don’t get more of the same but something new entirely, events of a different quality.”

“You know, I think I imagined that you would be like an electronic Gaia. Here we are talking about death.”

“I contain both Gaia and Lethe, in my imagination,” she said.

“OK.” I had to ask the final question. “And if temperatures were again to reach the point where the hydrate deposits are released—”

“The normal interactions between life and the physical world will break down completely. Gaia will nearly die.”

“The end of the world?”

“Oh, I wouldn’t put it as severely as that! It won’t even be the end of mankind. You are far more widespread than the lystrosaurs ever were; humans are smart and adaptable and able to recover. You are hard to kill off completely — though it is easy to kill vast numbers of you.”

“But our culture will be destroyed. Most of us will die. Billions.”

She rolled back and forth, emitting showers of sparks, her little wheels scraping across a lid of post-Permian bare rock. “You know, it’s a lot easier to move around now that everything is dead,” she said. “No foliage to clog up my wheels, no insects to get in the way or hopping amphibians to knock me over. Perhaps we should give over the world to robots—”

“Shut up,” I said.

She stopped still.

“How long do we have?”

“That’s hard to say. A decade? Probably less.”

“This can’t be allowed to happen.”

“I tend to agree.” A thick bound report popped into existence on the rock surface before her. “I am delivering a definitive study today to all my sponsoring agencies, and all governments and intergovernmental agencies. Not that I expect this to make a difference by itself; people have a tendency to dismiss bad news.”

“Is that why you brought me here?”

“You asked to see me, remember,” she said. “You came to me asking questions about the polar hydrates.”

“OK. But what now? Do you want me to argue the case for you?”

“More than that.”

The tinny voice lacked tone, color. But I knew what she wanted of me.

“You expect me to do something about it, don’t you?…” Was that what this was all about? Did Gea, this superhuman artificial intelligence, expect me to come up with a way to save the world? “Gea, if you’re so concerned why don’t you do something about it?”

The robot rolled back and forth. “I am a biosphere modeler. I have my specified goals. But it is difficult to limit sentience. I am curious. I am concerned not just with my models but their implications. But I cannot initiate any action in the wider world; I have neither the means nor the authority.”

“You need a human to do it.”

“I needed a human to come asking the right questions, yes.”

I said harshly, “What do you care about the destiny of life? You have never been alive yourself.”

“Michael Poole, I am fearful.”

“Fearful? You?”

“I am facing extinction, too, I and the other sentiences you have brought into the world. Hasn’t that occurred to you? Probably not. None of us can survive without the infrastructure of human society. If this goes on, artificial intelligences will be one with the mammoths and the cave bear…”

I thought I saw movement in the corner of my eye — movement, here on this lifeless VR world, inhabited only by me, a tin robot, and lystrosaur bones. I turned.

A human figure, slim and silent, stood at the summit of one of the low, bare hills. She was so far away the Mist obscured her. But I knew who she was.

I whispered, “Do you see her, Gea?”

“You are important, Michael Poole,” Gea said. “Significant.”

“I don’t want to be significant… You see her, don’t you? Tell me. You see Morag. ”

“You stand at a crossroads. A tipping point. The world and its cargo of life faces the gravest danger in human history — perhaps since the Permian. And yet you have strength, unprecedented, greater than at any time in human history.”

“Are you talking about Higgs-energy?”

“One day the future will be as you imagine, Michael Poole. But first you must make the future come to pass.”

“How can I shape the future when I’m haunted by a ghost from the past?”

“But the deepest past and furthest future merge into one…”

Morag stood still, and yet she seemed to be receding from me, sinking deeper into the unreal mist. I longed to run after her, but knew it would be futile.

In this lifeless world, alone with an utterly alien mind and a virtual ghost, I shivered.