Oh, we can do a lot to make that planet inhospitable. You are right that it would take quite a while to reach anything resembling martian levels and we still ha

Oh, we can do a lot to make that planet inhospitable. You are right that it would take quite a while to reach anything resembling martian levels and we still have a magnetic core which helps with many things. But I wouldn't underestimate the multitude of ways in which this planet could be made inhospitable by us. We are trusting a lot on the self-correcting power of nature on this planet, but we just don't know if there isn't some tipping point after which there is no return.