In the book I am writing, I am going for a a partially terraformed Venus setting. I like the concept of floating cities, but I want to be able to make it a little easier to live up there. If colonist had around sixty years or so, could they lower the temperature at 1 bar down to 80 Fahrenheit? How would they do this?
Wikipedia has compiled many of the leading proposals in an article on the topic. The table of contents to it lays them out nicely:
1 Solar shades
1.2 Atmospheric or surface-based
2 Eliminating the dense carbon dioxide atmosphere
2.1 Biological approaches
2.2 Introduction of hydrogen
2.3 Capture in carbonates
2.4 Direct liquefaction and sequestration
2.5 Removing atmosphere
3 Day–night cycle
3.1 Space mirrors
3.2 Changing Rotation speed.
The mostly likely of the proposals to work on the desired time frame would probably be to impact the surface of Venus with about 2000 large asteroids.
The temperature of the Venusian atmosphere is 72 C at an altitude of 50 kilometres (km) where the pressure is 1 bar. This could be an uncomfortable altitude for floating cities. However, the simplest solution for colonists in the floating habitats to enjoy cooler temperatures is go higher.
Height (km) Temp. (°C) Atmospheric pressure (atm)
0 462 92.10 5 424 66.65 10 385 47.39 15 348 33.04 20 306 22.52 25 264 14.93 30 222 9.851 35 180 5.917 40 143 3.501 45 110 1.979 50 75 1.066 55 27 0.5314 60 −10 0.2357
Sorry about the formatting glitch. All attempts to rectify it have failed. Go to the source enter link description here and check out the table with the heading Atmosphere alongside the section on Troposphere.
At 50 km, the temperature is 75 C and the pressure is 1.066 bar, while at 55 km, the temperature is now 27 C and the pressure is 0.5314 bar. This is a comfortable temperature, though the atmospheric pressure is lower and this means the flotation mechanism will be correspondingly larger for floating habitats. It should be easier to go higher than attempt complex, costly and unnecessary methods to lower the atmospheric temperature.
Essentially the Venusian atmosphere does it for you with increasing height and corresponding falling temperatures.