This report (EPA 430-R-09-004) by the Environmental Protection Agency dated April 15, 2009 states that from 1990 to 2007, total emissions of CO2 increased by 1,026.7 Tg CO2 Eq. (20.2 percent), while CH4 and N2O emissions decreased by 31.2 Tg CO2 Eq. (5.1 percent) and 3.1 Tg CO2 Eq. (1.0 percent), respectively.
During the same period, aggregate weighted emissions of HFCs, PFCs, and SF6 rose by 59.0 Tg CO2 Eq. (65.2 percent). From 1990 to 2007, HFCs increased by 88.6 Tg CO2 Eq. (240.0 percent), PFCs decreased by 13.3 Tg CO2 Eq. (64.0 percent), and SF6 decreased by 16.3 Tg CO2 Eq. (49.8 percent). Despite being emitted in smaller quantities relative to the other principal greenhouse gases, emissions of HFCs, PFCs, and SF6 are significant because many of them have extremely high global warming potentials and, in the cases of PFCs and SF6, long atmospheric lifetimes.
Conversely, U.S. greenhouse gas emissions were partly offset by carbon sequestration in forests, trees in urban areas, agricultural soils, and landfilled yard trimmings and food scraps, which, in aggregate, offset 14.9 percent of total emissions in 2007. The following sections describe each gas’ contribution to total U.S. greenhouse gas
emissions in more detail.
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