None, the market will do it.
Mark Perry notes that the unexpected reduction in carbon consumption in the US had nothing to do with government investments in wind, solar, or other forms of clean energy. Rather, the discovery and development of new sources of natural gas increased the supply of natural gas, which caused a reduction in price. The reduction in price caused consumers to shift demand towards this lower-priced, and lower-carbon substitute.
It makes me wonder about all the heated political debate, litigation, treaties, and studies that have been spilt over this issue.