We've found a habitable planet around Procyon and do have the technology to settle it. However, it is in the outer part of its systems habitable zone. So while it has a well-developed and mostly biocompatible ecosphere, its atmosphere is not very earth-like.
- 11.6 atm CO2
- 2.4 atm N2
- 0.18 atm O2
- traces of Ar, H2O, dust, and O3
- 0.8g surface gravity
- -5C average temperature
- 78° axial tilt
- 37% surface water
- stagnant lid tectonics, (drip and plume, as on Venus) but the carbon cycle is stable
- star is a young F-Type (1.85 Gyr)
- the land ecosystems are young and primitive (unicellular and colonial organisms dominate, multicellularity is only a few million years old)
- life is centered around the polar seas and the large regions around them, that get flooded by the fall rains, frozen over during winter and dry up during summer
Terraforming is out of the question because a number of powerful artilects and organizations want to study the biosphere. So, bioforming it is. The winters are dealt with with hibernation capabilities, greater temperature tolerances are easy as well and the low oxygen issue has been resolved.
However, how does one change a human to make the CO2 tolerable? This sounds bad.
When carbon dioxide dissolves in water, it forms a bit of carbonic acid. And that acid is a key part of our respiratory system. When carbon dioxide builds up in our blood, carbonic acid forms and the acidity of the blood rises. And the human body tends to handle pH changes rather poorly. The blood should have a pH of 7.35 to 7.45, and any significant deviation from that interferes with the blood’s function. Once the pH falls below 6.8, which is surprisingly easy, irreversible cell damage occurs. This acidity can be reached quite easily by breathing 30% CO2 at atmospheric pressure.
So what kind of modifications cod be made to humans to deal with this? Genetic engineering is preferred for ideological reasons, but cybernetics could be used as well.