The correct answer, according to “Train Wreck Earth,” the new novel by Dr. Harvard G. Ayers, professor emeritus in Appalachian State University’s Department of Anthropology, and David Harman, a retired North Carolina certified public accountant, is climate change. The book, set in novel format but filled with scientific information presented in a “classroom” setting, offers the latest research and legislation affecting our climate, as well as viewpoints from prominent climate activists and scientists, including Dr. Michael Mann, distinguished professor of atmospheric science at Penn State and director of Penn State’s Earth System Science Center; Bill McKibben, founder of 350.org, scholar in residence in environmental studies at Middlebury College and author of “The End of Nature”; and Dr.