There is little evidence that as the footprint grew that environment impact per person would fall correspondingly due to new technology and conservation practices. It has already proven impossible to get the world's top two greenhouse gas emitters, China and the United States, to even sign the Kyoto Protocol treaty. World greehouse gas emission grew 6% in 2010 over 2009. Climate change is only one of many environmental sustainability problems, like freshwater supply, pollution of many kinds, soil fertility lost, deforestation, and so on.