Could we terraform both Venus and Mars by moving the carbon dioxide from Venus to Mars?

Look at the finances involved, then reconsider.

@jerv Eventually the price will decrease as new technologies make trips become routine.

Mars needs a thicker atmosphere and the most potent greenhouse gas…water vapor. It also needs a magnetosphere to keep it which it does not have.
Venus however is habitable right now but only in the upper atmosphere it has the correct pressure, temperature and breathable atmosphere at ~30 miles.

Floating Cities
An enclosed city with earth equivalent (breathable) air inside would float around like a weather balloon.

The Mars Trilogy by Kim Stanley Robinson has a lot of ideas for terraforming Mars, and much later Venus. Most of them are just a little past the reach of today’s science, and the main thing holding us back would be money.

The characters used a combination of approaches to warm the atmosphere bit by bit. None of the strategies on its own was enough to reach their goal (breathable air and liquid water on the surface.) One of the first things they tried was genetically engineering arctic plants from earth to survive on the Martian surface.

This series is at least as long as Lord of the Rings, and terraforming was one of the major concerns, so you got to see every gradual step of the process. The author thought of everything, like whether stuff on the surface reflects or absorbs light, and the tiny difference that would make in the surface temperature. Even in an imaginative sci-fi novel, it took 200 years.

You should read it, it’s really cool.

Prices won’t drop that far any time soon. Look at the cost to resupply Mir with a payload many, many orders of magnitude smaller, then consider the distance is many orders of magnitude longer. When you multiply millions by billions, we’re talking cost reduction that I don’t see happening. Even if the space program reduced it’s costs as much as computers have come down in my lifetime, it’d still cost more money than has ever been printed.

Isn’t Venus full of acid rain?

Absolutely not Venus. There isn’t the technology to harvest any energy source there to enable a factory to start the process. Anything sent there with our current technology corrodes and decomposes too quickly. It simply isn’t workable. Mars is a different story, but the raw materials to create an atmosphere isn’t available. The atmosphere can never be recreated because of a lack of the electromagnetic system that needs to surround a planet. That goes to the very core of the planet. Literally.

The problems are much bigger than CO2. Watch some more or read some more about it.