Ten years ago representatives from more than 178 nations convened in Rio de Janeiro to devise a plan to protect the world’s resources. Now in a follow-up in Johannesburg, world leaders, scientists, and activists are sizing up what, if anything, has changed. National Geographic asked seven scientists to weigh in on the condition of the planet. They pointed out that people have become more aware of Earth’s health, but there has been no real slow-down in habitat destruction and the use of fossil fuels that contribute to global warming. Each year in the United States alone plowing causes two billion tons of topsoil to erode into rivers and flow into the Gulf of Mexico. And greenhouse gases warm the oceans and wreak havoc on marine ecosystems, doing further harm to distant oceans as waters move and mix globally. If that isn’t bad enough, every day we are exposed to synthetic chemicals that interfere with development and reproduction in wildlife and humans.