Carbonomics:U.S. GHG emissions were about 25% of world emissions in 1990.
Source:US emissions US emissions, 1990 = 6,200 Tg = 6.2 Gt CO2 eq./yr. Global emissions are from the IPCC 4th Report, Summary for Policy Makers, Figure SPM.3. Global GHG emissions in 1990 = 39.4 Giga tonne CO2 eq./year.