No amount of training can undo the violence someone experienced at home as a child, but it can help break the cycle. Pamela Albin Moore/iStockphoto hide caption

itoggle caption Pamela Albin Moore/iStockphoto

Demonstrators gather near Columbus Circle before the start of the People's Climate March in New York Sunday. Organizers are hoping 100,000 people worldwide might participate in the rally. Craig Ruttle/AP hide caption

itoggle caption Craig Ruttle/AP

Mammuthus columbi, the Columbian mammoth, used to be common in America, but went extinct about 10,000 years ago. The specimen found south of Dallas is estimated to be 20,000 - 40,000 years old. Illustration by Karen Carr/Perot Museum of Nature and Science hide caption

itoggle caption Illustration by Karen Carr/Perot Museum of Nature and Science

The photographer Sebastiao Salgado, in New York City on Thursday, says we are at a "special moment" — our world now needs to be protected from climate change and other forces. Misha Friedman for NPR hide caption

itoggle caption Misha Friedman for NPR