“It was not a war,” Nebogipfel said. “But it was a catastrophe wrought by man, I think.”

Now I saw the strangest thing. The new, sparse trees began to die back, but not by withering before my accelerated gaze, like the dipterocarps I had watched earlier. Rather, the trees burst into flame — they burned like huge matches — and then were gone, all in an instant. I saw, too, how a great scorching spread across the grass and shrubs, a blackening which persisted through the seasons, until at last no more grass would grow, and the soil was bare and dark.

Above, those pearl-gray clouds grew thicker still, and the sun- and moon-bands were obscured.

“I think those clouds, above, are ash,” I said to Nebogipfel. “It is if the earth is burning up… Nebogipfel — what is happening?”

“It is as I feared,” he said. “Your profligate friends — these New Humans—”

“Yes?”

“With their meddling and carelessness, they have destroyed the life-bearing equilibrium of the planet’s climate.”

I shivered, for it had grown colder: it was as if the warmth was leaking out of the world through some intangible drain. At first I welcomed this relief from the scorching heat; but the chill quickly became uncomfortable.

“We are passing through a phase of excess oxygen, of higher sea-level pressure,” Nebogipfel said. “Buildings, plants and grasses — even damp wood — will combust, spontaneously, in such conditions. But it will not last long. It is a transition to a new equilibrium… It is the instability.”

The temperature plummeted now — the area took on an air of chill November — and I pulled my jungle shirt closer around me. I had a brief impression of a white flickering — it was the seasonal blanketing and uncovering of the land by winter’s snow and ice — and then the ice and permafrost settled over the ground, unyielding to the seasons, a hard gray-white surface which laid itself down with every impression of permanence.

The earth was transformed. To west, north and south, the contours of the land were masked by that layer of ice and snow. In the east, our old Palaeocene Sea had receded by some several miles; I could see ice on the beach at its fringe, and far to the north — a glint of steady white that told of bergs. The air was clear, and once more I could see the sun and green moon arcing across heaven, but now the air had about it that pearly-gray light you associate with the depths of winter, just before a snow.

Nebogipfel had huddled over on himself, with his hands tucked into his armpits and his legs folded under him. When I touched his shoulder his flesh was icy to the touch — it was as if his essence had retreated to the warmest core of his body. The hairs over his face and chest had closed over themselves, after the manner of a bird’s feathers. I felt a stab of guilt at his distress, for, as I may have indicated, I regarded Nebogipfel’s injuries as my responsibility, either directly or indirectly. “Come now, Nebogipfel. We have been through these Glacial periods before — it was far worse than this — and we survived. We pass through a millennium every couple of seconds. We’re sure to move beyond this, and back into the sunshine, soon enough.”

“You do not understand,” he hissed.

“What?”

“This is no mere Ice Age. Can’t you see that? This is qualitatively different… the instability…” His eyes closed again.

“What do you mean? Is this lot going to last longer than before? A hundred thousand, half a million years? How long?”

But he did not answer.

I wrapped my arms aground my torso and tried to keep warm. The claws of cold sank deeper into the earth’s skin, and the thickness of the ice grew, century on century, like a slowly rising tide. The sky above seemed to be clearing — the light of the sun-band was bright and hard, though apparently without heat and I guessed that the damage done to that thin layer of life-giving gases was slowly healing, now that man was no longer a force on the earth. That Orbital City still hung, glowing and inaccessible, in the sky over the frozen land, but there were no signs of life on the earth, and still less of Humanity.

After a million years of this, I began to suspect the truth!

“Nebogipfel,” I said. “It is never going to end — this Age of Ice. Is it?”

He turned his head and mumbled something.

“What?” I pressed my ear close to his mouth. “What did you say?”

His eyes had closed over, and he was insensible.

I got hold of Nebogipfel and lifted him from the bench. I laid him out on the Time-Car’s wooden floor, and then I lay down beside him and pressed my body against his. It was scarcely comfortable: the Morlock was like a slab of butcher’s meat against my chest, making me feel still colder myself; and I had to suppress my residual loathing of the Morlock race. But I bore it all, for I hoped that my body heat would keep him alive a little longer. I spoke to him, and rubbed at his shoulders and upper arms; I kept at it until he was awake, for I believed that if I let him remain unconscious — he might slip, unknowing, into Death.

“Tell me about this climatic instability of yours,” I said.

He twisted his head and mumbled. “What is the point? Your New Human friends have killed us…”

“The point is that I should prefer to know what is killing me.”

After rather more of this type of persuasion, Nebogipfel relented.

He told me that the atmosphere of the earth was a dynamic thing. The atmosphere had just two naturally stable states, Nebogipfel said, and neither of these could sustain life; and the air would fail into one of these states, away from the narrow band of conditions tolerable by life, if it were too far disturbed.

“But I don’t understand. If the atmosphere is as unstable a mixture as you suggest, how is it that the air has managed to sustain us, as it has, for so many millions of years?”

He told me that the evolution of the atmosphere had been heavily modified by the action of life itself. “There is a balance of atmospheric gases, temperature and pressure — which is ideal for life. And so life works — in great, unconscious cycles, each involving billions of blindly toiling organisms to maintain that balance.

“But this balance is inherently unstable. Do you see? It is like a pencil, balanced on its point: such a thing is ever likely to fall away, with the slightest disturbance.” He twisted his head. “We learned that you meddle with the cycles of life at your peril, we Morlocks; we learned that if you choose to disrupt the various mechanisms by which atmospheric stability is maintained, then they must be repaired or replaced. What a pity it is,” he said, heavily, “that these New Humans — these star-faring heroes of yours — had not absorbed similar simple lessons!”

“Tell me about your two stabilities, Morlock; for it seems to me we are going to be visiting one or the other!”

In the first of the lethal stable states, Nebogipfel said, the surface of earth would burn up: the atmosphere could become as opaque as the clouds over Venus, and trap the heat of the sun. Such clouds, miles thick, would obstruct most of the sunlight, leaving only a dull, reddish glow; from the surface the sun could never be seen, nor the planets or stars. Lightning would flash continually in the murky atmosphere, and the ground would be red-hot: scorched bare of life.

“That’s as may be,” I said, trying to suppress my shivers, “but compared to this damned cold, it sounds like a pleasant holiday resort… And the second of your stable states?”

“White Earth.”

He closed his eyes, and would speak to me no more.