Green Mars - Kim Stanley Robinson [110]
300 millibars nitrogen
160 millibars oxygen
30 millibars argon, helium, etc.
10 millibars CO2 =
Total pressure at datum, 500 millibars
All these amounts had been fixed by physical requirements and limits of various kinds. The total pressure had to be high enough to drive oxygen into the blood, and 500 millibars was what was obtained on Earth at about the 4,000-meter elevation, near the upper limit of what people could live at permanently. Given that it was near the upper limit, it would be best if such a thin atmosphere had more than the Terran percentage of oxygen in it, but it could not be too much more or else fires might be hard to extinguish. Meanwhile CO2 had to be kept below 10 millibars, or else it would be poisonous. As for nitrogen, the more the better, in fact 780 millibars would be ideal, but the total nitrogen inventory on Mars was now estimated at less than 400 millibars, so 300 millibars was as much as one could reasonably ask to put into the air, and perhaps more. Lack of nitrogen was in fact one of the biggest problems the terraforming effort faced; they needed more than they had, both in the air and in their soil.
Sax stared down at his plate and ate in silence, thinking hard about all these factors. The morning’s discussions had given him cause to wonder whether he had made the right decisions back in 2042— whether the volatile inventory could justify his attempt to go straight for a human-viable surface in a single stage. Not that there was much that could be done about it now. And all things considered, he still thought they were the right decisions; shikata ga nai, really, if they wanted to walk freely on the surface of Mars in their own lifetimes. Even if their lifetimes were going to be considerably extended.
But there were people who seemed more concerned with high temperatures than breathability. Apparently they were confident that they could balloon the CO2 level, heat things tremendously, and then reduce the CO2 without problems. Sax was dubious about that; any two-phase operation was going to be messy, so messy that Sax couldn’t help wondering if they would get stuck with the 20,000-year time scales predicted in the earliest two-phase models.
It made him blink to think of it. He couldn’t see the need. Were people really willing to risk such a long-term problem? Could they be so impressed by the new gigantic technologies that were becoming available that they believed anything was possible?
“How was the pastrami?” Berkina asked.
“The what?”
“The pastrami. That’s the kind of sandwich you just ate, Stephen.”
“Oh! Fine, fine. It must have been fine.”
• • •
The afternoon’s sessions were mostly devoted to problems caused by the successes of the global warming campaign. As surface temperatures rose, and the underground biota began to penetrate deeper into the regolith, the permafrost down there was melting, just as hoped. But this was proving disastrous in certain permafrost-rich regions. One of these, unfortunately, was Isidis Planitia itself. A well-attended talk by an areologist from a Praxis lab in Burroughs described the situation; Isidis was one of the big old impact basins, about the size of Argyre, with its northern side completely erased, and its southern rim now part of the Great Escarpment. Underground ice had been creeping off the Escarpment and pooling in the basin for billions of years. Now the ice near the surface was melting, and in the winters freezing again. This thaw-freeze cycle was causing frost heaving on an unprecedented scale; it was pretty near the usual two-magnitude enlargement compared to similar phenomena on Earth, and karsts