Life has evolved over hundreds of millions of years, influenced by the earths environment, which itself has been influenced by its size/gravity, proximity to the sun, axial tilt, air composition, our atmosphere, and countless other macro scale variables, many of which are random and independent of each other. Most of these quantities have exceedingly small windows that can support human life. Furthermore, the particular sequence of these variables changing over millions of years has shaped evolution.
Think of it like this: there are 68 teams in the NCAA men's basketball tournament. This makes for 9.2 quintillion possible outcomes. There are certainly many orders of magnitude more variables that have shaped the evolution of life on earth. I'm not saying only one of those permutations results in a planet suitable for humans, just that the sheer scale of how large of a cosmic accident we are makes me think we'll run out of time before we ever find another earth suitable for normal human life.
I guess I should spend more time being productive and less time considering how I could survive the heat death of the universe.
Curious what you think.
Douglas Adams had some things to say about designing planets.
I think the other reason we want to be on multiple planets is less about climate change, but cataclysmic shocks (asteroid impact, nuclear war, etc.) -- if we're on multiple planets, we have a greater chance of surviving a cataclysmic shock to one planet.
Your point on climate change is great, though -- you're right that if we can terraform Mars or the Moon, we have the technology to fix whatever climate issues are happening on Earth! Funny that this doesn't come up more.