* gravity (and bone density)
* radiation
Over Earth? Absolutely no advantage, other than maybe it is easier to get approval to build a giant blimp. But I feel like if you wanted to build a floating city in international waters nobody would get in your way. They might rob you, though.
But, yes, building in the middle of Antarctica would be overwhelmingly easier, safer, and cheaper. Nobody does, though.
Maximum solar irradiance at 1AU is 1351 W/m^2.
Maximum solar irradiance at 0.723AU is 2584 W/m^2.
It seems very likely the Earth will also benefit. The technology developed to sustain humans in other places in the solar system possible will be impactful back home.
While climate change is super-important, and we absolutely need to do whatever we can to negate it, it is not a threat to global civilization.
Even if the effects of climate change are orders of magnitude worse than we expect, the planet most suitable for human life will remain Earth. Because, um, we can breathe the air, drink the water and the temperature is within the ranges we easily tolerate. (not to even get into issues of magnetic fields etc)
Will the earth of the future support 7 billion people? Probably yes, possibly no, but whatever number it does support will forever dwarf the people living in venus or mars.
Will our "civilisation" look different 50 years from now? Undoubtedly yes. But it's radically changed in the last 50,100 and 150. Certainly those times counted as civilised did they not?
There will be civilisations on earth for a long long time (baring nuclear anialation) - our adaptability (think Sahara /Siberia) is, if anything, a little too aggressive.
Worldwide, governments are responding to the crisis in almost perfectly maladaptive ways. As hundreds of millions of refugees are barely beginning take flight, fascist governments are arising to keep them out of temperate zones, tending ultimately toward global war. Certainly, pockets will survive, but global civilization, as such, is much less secure.
We're centuries away from self-sustaining colonies on either Venus or Mars, so if your timeline was right, that's be a reason not to bother with either.
https://www.resilience.org/stories/2020-06-08/collapse-of-ci...
https://en.wikipedia.org/wiki/Will_Steffen
From https://www.sciencedirect.com/science/article/abs/pii/S09593... :
> This paper focuses on a comparison of recently collated historical data for 1970–2000 with scenarios presented in the Limits to Growth. The analysis shows that 30 years of historical data compare favorably with key features of a business-as-usual scenario called the “standard run” scenario, which results in collapse of the global system midway through the 21st century. The data do not compare well with other scenarios involving comprehensive use of technology or stabilizing behaviour and policies. The results indicate the particular importance of understanding and controlling global pollution.
https://www.theguardian.com/environment/2019/dec/30/environm...