How do we terraform Venus?
Venus is so darned hot because of this thick CO2 atmosphere, the first thing we need to is cool the planet down. If you set up a huge space-based shade and block all sunlight from hitting the atmosphere, the temperature would drop, and I mean *drop*. It would cool hundreds of degrees until it was so cold the CO2 would freeze out of the atmosphere, and pile up in drifts on the ground. Then you could scoop up the carbon, bury it or shoot it off into space.
Another, equally mad idea would be to build floating cities high up in the atmosphere of Venus. They would need to contain factories which sucked carbon dioxide from the atmosphere and split it into carbon and oxygen. The carbon would be made into graphene structures, and the oxygen would become the lifting gas to keep the cities afloat. With more cities, it would block the sunlight and help cool the planet down.
Unfortunately, the slow rotation of the planet is still a big problem. A solar day on Venus is 116 Earth days in length. You could speed its rotation by close asteroid flybys, or use that crazy space shade contraption to create an artificial day/night cycle.
Read more at: http://phys.org/news/2014-07-terraform-venus.html#jCp