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Suppose all areas of the Earth is suddenly covered in indestructible mirrors (assume they reflect 70% of solar energy that would hit the land/ocean), how quickly will the increase in albedo cause the temperatures to drop? What temperature would it stabilize at?

I'm mostly looking for rough estimates, like, would the temperature be cold enough solidify gases? Would the cooling take years or centuries to approach equilibrium etc.

If more information/complicating factors can greatly alter the answer, please let me know.

user289661
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    Do your mirrors let out the heat from under them? If so, at what rate? – Allan Jul 31 '21 at 00:06
  • @Allan interesting consideration, for the time being, perhaps consider the mirrors to conduct heat like normal glass. If this has drastic effect on the answers, please explain the broad strokes of the effects – user289661 Jul 31 '21 at 00:11
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    I think this might happen rather unexpectedly quickly. For example, a solar eclipse can drop temperatures dramatically : https://www.space.com/37201-solar-eclipse-temperature-drop.html – JonSG Jul 31 '21 at 01:26
  • Seems very similar to https://worldbuilding.stackexchange.com/questions/100211. – user535733 Jul 31 '21 at 04:07
  • mirrors on the surface or above the atmosphere? – Jasen Jul 31 '21 at 04:55
  • Don't know how your mirror would be indestructable - I would try painting it black - or if "the complete planet" would include oceans and other water (the measure would prevent evaporation), but in the real world, covering young ice with a protective reflectant has been tried.. It turned out to be very effective to prevent ice from melting. In this case glass beads were used instead of solid mirrors.. https://www.bbc.com/future/article/20200923-could-geoengineering-save-the-arctic-sea-ice – Goodies Jul 31 '21 at 12:47
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    I asked a question about the correlation of distance from sun x global average surface temperature if the Earth ever went rogue. I also answered it. I think if you plug into the analysis the point where Earth receives only 30% of its regular sunlight you may find what you seek. I'll try to math it out later as an answer here. – The Square-Cube Law Jul 31 '21 at 14:14

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Ignoring the greenhouse gas effects of the atmosphere and the earth's internal heat, and taking an albedo of 70%, Stephen Boltzman's law gives us a temperature of 206K (not showing the working here). That's -66 deg C, warmer than the lowest ever recorded temperature in Antarctica. Certainly not cold enough to freeze most gases (even CO2 freezes at -78). The actual heat conserving effect from the atmosphere keeps our (normal) earth warmer by 33 deg C than it otherwise would (actual avg temp of 15 deg C vs prediction of -18 deg C at an albedo of 30). Therefore, adding this to the -66 deg C gives us -33 deg C. That's warmer than a cold January night in Tomsk.

hurreechunder
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  • That's just an average, though. The coldest places will also get colder, which could easily result in CO2 freezing out. – Logan R. Kearsley Nov 30 '21 at 02:56
  • Yes, of course....CO2 could freeze at the more extreme latitudes in winter. And water vapour everywhere. But argon, oxygen, nitrogen....unlikely to get to the -180 deg C range for those to freeze – hurreechunder Nov 30 '21 at 03:42