"The magazine has a history in this area,” she told me in one of two recent conversations. “They’d published Rachel Carson. It was unoccupied territory at the time.”

This week Ms. Kolbert, 52, published her second major book on the environment, “The Sixth Extinction: An Unnatural History” (Henry Holt), which asks science-based questions about whether humans might be causing mass extinction. (Her first, “Field Notes From a Catastrophe,” was about climate change.)

What follows is an edited and condensed version of our conversations.

Q. How does a journalist take on a topic this big — mass extinction?

A. I wrote a book almost 10 years ago on climate change, and I was looking for the next project. And my thought was, “Climate change is a huge story — there can’t be a bigger one.” As I looked for a new book, what I kept bumping into was the reality that climate change was actually part of an even bigger phenomenon: the many ways humans are changing the planet. It’s not something we’re doing because our species is greedy or evil. It’s happening because humans are human. Many of the qualities that made us successful — we are smart, creative, mobile, cooperative — can be destructive to the natural world.