Fredda hesitated, and glanced toward her husband. But his impassive expression gave her no clue. “Just to be clear, Dr. Lentrall, my husband has told me nothing at all. He wanted me to hear it all from you. So please, start at the beginning.”

“Right,” Lentrall said, in a tone close enough to brusque that it made no difference. “The basic point is that I believe I have found a way to enhance the terraforming process and permanently stabilize the climate.”

“But only by putting the lives of perhaps millions of people at risk,” said Lentrall ‘ s robot from its niche.

“Be quiet, Kaelor,” Lentrall said impatiently.

“First Law compelled me to say at least that much,” the robot replied, in an aggrieved tone of voice. “Your plan of action would put many human beings in danger.”

“I would hardly call it danger,” Lentrall said testily. “Rather, very slight risk. But if my plan succeeds, it will mean greater safety and comfort for generations of humans yet to come.”

“That argument contains far too many hypotheticals to be of any interest to me,” Kaelor replied.

“You have made your point now,” Lentrall said. “I order you to be quiet.” He shook his head and looked to Fredda. “I know you are famous for building superb robots,” he said. “But there are times when I wonder if the Settlers don’t have a point.”

“The same thought has crossed my mind more than once,” said Fredda. “But please go on. How do you propose to stabilize the climate?”

“By flooding the north pole,” Lentrall said. “I call it the Polar Sea Project.”

“What, precisely, would that accomplish?” Fredda asked. Lentrall stared hard at her for a moment, as if she had just asked what use robotic labor might be. “Let me go back a bit,” he said at last. “In fact, let me go all the way back. As you might know, when the first Spacers arrived at this planet, what they found was a desert world that consisted of two large and distinct geologic regions. The southernmost two-thirds of the planet were lowlands, while the northernmost third was covered by a huge plateau, much higher in elevation than the southern hemisphere. For that precise reason, Inferno was regarded as a marginal candidate for terraforming.”

“Why?”

“Because when water was introduced onto the planet, it would obviously all pool in the south-as indeed it has. Today we call the northern uplands the continent of Terra Grande, and the southern lowlands have been flooded to form the Southern Ocean. This gives the planet one water-covered pole and one landlocked one.”

“And what difference does that make?”

“A great deal of difference. Water absorbs heat energy far more efficiently than the atmosphere can. Water can circulate, carrying that heat along with it. Temperatures in the southern hemisphere are much more moderate and stable than they are in the north, because warm water can flow over the south pole and the polar regions, warming them up. Cold polar water can move toward the temperate zones and cool them off. I am oversimplifying things tremendously, of course, but that is the basic idea.”

“And that can’ t happen in the north, because there is no water,” Fredda said, glancing toward her husband. But his face was completely expressionless. He was watching this game, not playing it.

Lentrall nodded eagerly. “Precisely. Terra Grande is a huge, monolithic continent. It completely covers the northern third of the planet’s surface. Because no water can flow over the North Pole region, there is little chance for temperatures to moderate themselves in the northern hemisphere. The tropical regions of the northern hemisphere are too hot, while the polar regions are too cold. If you look at a map, you will see that the southern edge of Terra Grande-where most of the people live-more or less borders the northern edge of the north tropical zone. Right here, in Hades, we should be right in the center of the temperate regions. But the temperate regions are shrinking, and we are very near the northern border of the habitable zone, at least by some standards. Actually, there are a few rather stringent Settler measures by which the city of Hades is, technically, uninhabitable. Because of insufficient rainfall, I believe. Be that as it may, the habitable zone of this planet is already little more than a narrow strip, five or six hundred kilometers wide, along the southern coast of Terra Grande. And that strip is still shrinking, despite our best efforts, and despite local successes.”

“I thought the terraforming project was gaining ground,” Fredda said, looking toward her husband.

“It is,” said Alvar. “In places. Mostly in the places where people live. We are losing ground elsewhere-but we are doing much better around Hades and in the Great Bay region generally. Once we have this part of the world under control, we hope to expand outward.”

“If you get the chance,” Lentrall said. “Current projections show it could go either way. You’re relying on a high-point balance. It’s unstable.”

“What’s a high-point balance?” Fredda asked.

Lentrall smiled as he reached into the breast pocket of his tunic and pulled out a large coin-a Settler coin, Fredda could not help but notice. He had it so ready to hand that Fredda assumed he had put it there deliberately, just to be ready to make his point.,

“This is a high-point balance,” he said. He held his left hand with the index finger pointed straight up, and carefully placed the coin on the tip of his index finger. “In theory, I could hold this coin here indefinitely,” he said. “All I have to do is keep my finger completely steady, keep my arm from moving, keep from being jostled-while, at the same time compensating for any minute gusts of air, any very slight tremor in the building. And of course, I have to be sure I don’t overcompensate while trying to correct for some very minor-”

But at that moment, the coin suddenly fell from his finger and landed ringingly on the stone floor of the office. Somehow the sound of it striking the floor was much louder than Fredda had expected.

“I’ve just given you a pretty fair metaphor for the present state of Inferno’s planetary climate. It is stable for the moment, but if there is the slightest perturbation, there will be trouble. There is no negative feedback in the system, nothing working against a perturbation to push the system back toward stability. Ever since the first climate engineer started to work here, the balance point for Inferno’s climate has been a high point tottering between two extremes, with the slightest shift capable of sending the whole thing crashing down into overheating or supercooling. We have to get everything exactly right every time, or else…” He nodded toward the coin on the floor.

“But you have a solution,” Fredda said, her voice not entirely friendly. Lentrall was making no effort to convince, or explain, or discuss matters. He was lecturing, dictating, instructing her. He was speaking in tones that were a strange combination of arrogance and condescension. He was talking down to her, as if she were a child, explaining to her why doing things his way, the sensible way, was for her own good.

“I have a solution,” he said. He reached down, picked up the coin, and placed it in the palm of his hand. “We put the planet in a low-point balance, like this.” He shook his hand back and forth, and jiggled it around vigorously. The coin stayed in his palm. Once or twice, he managed to dislodge it briefly, but then it dropped back into place. “As you can see, it’s much harder to perturb something out of a low-point balance, and it will tend to return to its balance point once a perturbation is removed. Now, a Polar Sea would move the global climate into a stable low-point system that would require massive effort to dislodge into instability.

“As I have said, the problem is the absence of water circulation in the northern hemisphere. If there were a way to let water accumulate in the northern polar regions, while providing inlets and outlets to the Southern Ocean, then warm water could flow north to warm the poles, and cold water could come south to cool the ocean-and the land areas near the coast. That would give us a low-point balance, where the natural force working on the planet would be self-correcting. If things got too hot, the cold polar waters would cool them off. If the temperatures dropped too much, tropical waters would warm them up. We need water over both poles.”