A push in the US to cut emissions of carbon dioxide by 20% would strain domestic supplies of natural gas and require new supply of energy from nuclear and renewable sources for power generation.Without major technological changes, achievement of that emissions target would fall most heavily on coal, according to a modeling study by researchers at the James Baker III Institute for Public Policy at Rice University.To sustain emission cuts beyond what's possible by replacing coal with gas in electric power generation, the researchers—Rice Scholars Dagobert L. Brito and Robert F. Curl—advocate separate pricing for carbon emitted by transportation fuel.Brito and Curl calculate the ...