The thing that puzzles me about this argument is any planet we find is likely to have a worse atmosphere than even a polluted Earth. If we're able to terraform Mars or whatever then we can likely also reverse the effects of global warming on Earth.

> At the rate we're messing up this planet, we'll need to find another planet real fast - relatively speaking, off course.

We can't even handle the planet we're already on, how in hell do you think we can terraform an entire separate planet? We're still only scratching the surface of understanding ecosystems today, the big thing these days is starting to try and understand how our internal microbiomes affect us personally, we're nowhere near understanding microbiotic effects on ecosystems at large. And all CES attempts so far have been abject failures.