[It's a fair question during a tough time. Clarke leads him to the edge of the roof, specifically picking a green-covered alleyway so that he can take a look. It's very specific to her experience back home, and even her time on Sanctum: green-covered grounds and everything in-between.

But she was still born in space, so seeing all that plant life is always going to be a wonder for her.]

If these creatures end up overtaking the city, it'll look like this. [She motions down below.] And if we're lucky, we won't lose any of the green by then. It was a world that started to grow again, until it couldn't anymore. ["Until it couldn't."]

We had a habit of taking what we had for granted, even when we didn't have it yet. I wasn't on Earth for very long, but this situation, and the one like the simulation—they're closer to home than I'd like.