albedo

Climate determinants exhibit nonlinear behavior, shifting to a very different state, often abruptly or irreversibly, as a result of self-sustaining feedbacks. Ice and especially snow have a high albedo. They reflect lots of sunlight back to space. Thus, as an ice sheet grows, the planet absorbs less energy. This has a cooling effect, which encourages the buildup of more snow and ice, which results in more reflectivity, and so on. Start to melt an ice sheet and the same cycle spins in reverse.

The New Yorker | Elizabeth Kolbert, a staff writer at The New Yorker since 1999, won the 2015 Pulitzer Prize for general nonfiction for "The Sixth Extinction." She is also the author of "H Is for Hope."