By OGJ editors
HOUSTON, Nov. 15 -- While volumes of greenhouse gases emitted in the US are rising, the rate of increase and amounts emitted in relation to economic growth are falling.
In an annual estimate required by Congress, the US Energy Information Administration said 2005 emissions of greenhouse gases associated with human activity totaled 7.1 billion tonnes of carbon dioxide equivalent (CO2e). That's up 0.6% from the year before and 17% from 1990.
Emissions of CO2, the target of most policy proposals for global-warming remediation, grew in 2005 at a below-average rate of 0.3%. Emissionsadjusted to CO2e to reflect global warming potentialof nitrous oxide were up 1.9% and of methane, up 0.9%.
CO2 represented 84% of US greenhouse-gas emissions in 2005. Nitrous oxide and methane together made up 14% of the total. The other greenhouse gases are hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6), emissions of which increased by a combined 7.2% in 2005.
Since 1990, US greenhouse gas emissions have increased at an average rate of 1%/year. EIA notes that the growth rate is below those of population (1.2%/year), primary energy consumption (1.1%/year), electric power generation (1.9%/year), and gross domestic product (3%/year) over the same period.
Emissions of CO2 alone have grown at an average rate of 1.2%/year since 1990, closely tracking growth in population and energy consumption. Methane emissions fell during the 1990s but have risen since 2001. Emissions of nitrous oxide are above their levels of 1990 but have fluctuated over the period.
Greenhouse gas intensityemissions per unit of real economic outputhas fallen by 25% since 1990 at a rate averaging 1.9%/year, EIA said. CO2 intensity has fallen by 23% over the same period.
CO2 emissions per person in 2005 were 1% above their 1990 level. The 2005 CO2 emissions total was 20% above its 1990 level.
Almost all emissions of CO2 are associated with energy consumption, with minor amounts coming from industrial processes.
Methane and nitrous oxide emissions result from biological decomposition of various waste streams and fertilizer; fugitive emissions from chemical processes; fossil fuel production, transmission, and combustion; and smaller sources.
HFCs are mainly refrigerants. PFCs are released from aluminum smelting and used in the manufacture of semiconductors. SF6 is used as an insulator in utility-scale electrical equipment.