Technology for doing so does not exist. Before we can terraform other planets we'll have to learn how to terraform this one. Global warming is actually a great challenge and overcoming it would mean developing the technology that would help colonize other planets, e.g. https://www.nasa.gov/feature/ames/myco-architecture.

How would that help? If half the population of earth (randomly chosen) moved to an inhabitant planet in another solar system, wouldn’t the reduction in population shrink the economy?

I hope we do eventually and specifically outside this solar system, which has a clock that’s shorter than the heat death master clock.