H&F: Right. Are people considering making biospheres on Earth and isolating regions to preserve, instead of fix, climate if it comes to that?

Chris McKay: People have made biospheres on Earth. There was an experimental one made in the late '80s in Arizona, Biosphere 2. It was made as a way of demonstrating that it was possible. People have also talked about preserving seed banks and things like that. I'm not aware of anybody who's talking about building a habitat as a way of preserving an ecosystem against climate change, though. It's an interesting idea.

H&F: You’ve mentioned a few major geo-engineering proposals in your studies, like iron fertilization of the ocean, and spraying stratospheric aerosols. Is there a geo-engineering scenario on Earth, which is, in your opinion, most effective?

Chris McKay: I think the two you just mentioned. Iron fertilization of the ocean and putting aerosols in the atmosphere. Those seem to be the most plausible. I would imagine that if we decide to do experiments that one or the other will be taken up.

H&F: We're losing so many species, and there are so many climate-related problems that are the side effects of side effects. Do you think that geo-engineering could save species from extinction, or will species stay on that track, no matter what?

Chris McKay: It's tough doing anything ecological on Earth. There are so many of us, and Earth is so delicately interwoven. When I'm talking to students, I draw the analogy between humans on Earth and a bull in a china shop. No matter what we do, we're breaking something. But on Mars, we’re like a bull in an empty field. Anything the bull leaves behind is positive. It's a whole different paradigm.

Directly to your question, can we mitigate climate change and stop the destruction of habitat and species? Eventually, I think we will. Geo-engineering may be one part of the solution.

What I can really say, though, is that the problem on Earth is tied to all sorts of problems, like the fact that we've built all our cities on the coast, and so if the sea level rises, that's not a big problem for the biosphere. The alligators aren't going to care that the sea level is rising ten meters– they'll just move inland a little bit. But the cities of Miami and New York are going to care. I don't have an easy path forward for the Earth, except to say that eventually, we're going to have to learn how to do geo-engineering. In the long term, it's not an option, it’s mandatory.

H&F: Back to what you were saying about the bull in the empty field–scientists are predicting that it’ll be much more practical to create an atmosphere for carbon-breathing life forms on Mars. You’ve written and said that all forms of life on Mars would be good, empirically, even if Mars were never habitable for humans. Why?

Chris McKay: The point here is that it's possible to restore Mars to the conditions it once had early in its history. The change is actually straightforward: just warm up Mars, it will get a thick atmosphere and thick carbon dioxide, water, and nitrates from the soil. That will be habitable for life, and it will be very much like Earth, early in its history. We have this romantic view of Earth that it was made exactly for us, and it's always been just fine for humans. That's not true at all. If you were to randomly appear on Earth at any time in Earth's history, chances are better than even you'd step out of your spacecraft or time machine and you would not be able to breath the air because there wouldn't be enough oxygen in it.

It turns out that the easiest way to terraform Mars is for plants, insects, and maybe some animals...the naked mole rat, for example, doesn’t need much oxygen...but not for humans. It wouldn't be an environment suitable for humans to walk around naturally like they do on Earth. When we say make Mars a home to life, we really mean us. We have this conceit that we are life.