Our biggest problem is that we don't yet know how to terraform. Certainly we have some theories but we haven't yet been able to put any of them into practice.

Our biggest problem is that we don't yet know how to terraform. Certainly we have some theories but we haven't yet been able to put any of them into practice. We need to learn the ins and outs of how to terraform, at first, at home, on Earth. We have several current problems on Earth that are good candidates for terraforming: How to reduce CO2 in the atmosphere. How to produce drinkable water in places there aren't any. How to grow plenty of food on land that is sub-optimal. If we can do those things here on Earth, then we might possibly have some chance of success in terraforming alien places like Mars.