The rising wealth of the top tier of earners seems to be inaugurating a new age of charitable giving. More than 150 billionaires from around the world have now signed Bill and Melinda Gates’ Giving Pledge, promising to donate at least half of their fortunes to charity. Others give money to hospitals, parks, or schools, renaming them in the process; in New York City, Lincoln Center’s Avery Fisher Hall is now known as David Geffen Hall, while the historic 42nd Street library is called the Steven A. Schwarzman Building.