This chart displays how Americans responded in 2003 (gray) and in 2006 (black) to MIT surveys asking them to rank 10 environmental issues in order of importance. From left, measured by percentage of responses ranking the item in first or second place, the issues are: global warming, destruction of ecosystems, water pollution, overpopulation, toxic waste, ozone depletion; urban sprawl, smog, endangered species, acid rain. Credit: Thomas E. Curry