The definition of habitable zone for an exoplanet has been based on very simple models. I commented on that once before. Now, finally the astronomers are going 3-D following the lead of Earth's very enthusiastic climate modelers. Cloud behavior expands habitable zone of alien planets Maybe we can do something with the surplus CMIP5 models after all It should certainly bring cheer to people who think the atmospheric iris is the largest control on the Earth's climate. It brings cheer to me, because according to the 1-D models Earth is very near the inner edge of habitable zone around the sun. That seems "unwise" in the long term. But in the macro sense, Earth climate has been congenial for 600 million years. Five major extinction events, yeah I know, but every one has been followed by a nice biodiversity bounce. Nifty planet we have here. Bet I'll still like it at 500 ppm CO2 on my approximate expiration date.
The sixth is well underway. Life will recover, but it may or may not include humans. Remember Einstein's "god does not play dice with the Universe"? Life takes so many chances that something is almost certain to survive.
Looks like this web site needs an upgrade: source: Chemical Fact Sheets -- Carbon Dioxide (CO2) So the "outdoor air level" is now "found in occupied spaces with good air exchange." The higher CO{2} levels, approaching 400 ppm,, suggests that over time, higher altitudes over +12,000 ft., the threshold where oxygen and pressurization are required, may decrease. I remember reading an article that claimed mammals developed an improved lung over reptiles so they survived the last dinosaur extinction. The hypothesis being the extinction came from higher CO{2} and lower O{2} ratios. However, this could have been just another case of mammalian chauvinism. Bob Wilson
Bird lungs are way better than mammal lungs. Allows ducks (geese?) to migrate over 10,000 meter mtn ranges. Every large building has (ought to have) CO2 monitors. They do increase air exchange , maybe at 1000 ppm threshhold. The CO2 sensors are relatively cheap ($200), with about 20 ppm accuracy. Short optical path, good enough. Not good enough for ecologists who pay $5000 for 0.1 ppm accuracy to study soils and decomposition and all that weird stuff. Keep up to date on exoplanets: The Extrasolar Planets Encyclopaedia N=908 presently. Most of them don't look like good real estate investments. All of them are terribly far away.
