1990s ended with US surge in greenhouse gas emissions

US greenhouse gas emissions increased at a faster rate during 1999-2000 than the average annual rate throughout the 1990s, according to the latest official US figures under the Framework Convention on Climate Change (UNFCCC).

The US Environmental Protection Agency (EPA) report attributed the 2000 increase in growth of 2.5%, compared with previous average rates of 1.5%, to robust economic growth in 2000, leading to increased demand for electricity and transportation fuels; cooler winter conditions compared to the previous two years; and decreased output from hydroelectric dams.

This is reflected in the doubling in 2000 to 3.2%, of the average annual rate of carbon dioxide emissions from fossil fuel combustion, the largest source of US greenhouse gas emissions. This was the second highest annual increase – it was 3.6% in 1995-96. Throughout the nineties fossil fuel combustion accounted for a nearly constant 79% of global warming potential (GWP) weighted emissions. The annual global increase in atmospheric CO2 concentrations is currently 0.4% per year.

Globally, the US accounted for 24% of the CO2 added to the atmosphere from fossil fuels at the end of the 1990s. In 2000, approximately 85% of the energy consumed in the US was produced from fossil fuels, with the remaining 15% from renewables and nuclear. During the 1990s, oil supplied the largest share of US energy demands, accounting for an average of 39% of total energy consumption. Natural gas and coal followed with 24% and 23%, respectively.

Electricity generation accounted for the largest portion – 34% – of emissions, followed by transport with 27%. Emissions from industry accounted for 19% and in contrast to electricity generation and transport, have declined over the past decade, reflecting structural changes in the US economy. However, the report notes that fuel switching has occurred, and efficiency improvements have been made. The remaining 20% are attributed to residential – 8%, primarily from fossil fuel combustion; agriculture – 8%, dominated by NO2; commercial – 5%; and, ‘US territory’ – less than 1%.

The report points out that the US relies on electricity to meet a significant portion of its energy demands, and that electricity generation is responsible for consuming 34% of US energy from fossil fuels and emitting 42% of the CO2 from fossil fuel combustion in 2000. The type of fuel combusted by electricity generators has a significant effect on their emissions. Electricity generators rely on coal for over half of their total energy requirements and accounted for 94% of all coal consumed in the US in 2000.

Over the decade, total US emissions rose by 14.1% over 1990 levels to 6,994.2 teragrams of carbon dioxide equivalents (Tg CO2 Eq). Carbon dioxide and nitrous oxides increased by 17% and 10%, respectively, while methane decreased 6%. During the same period, aggregate weighted emissions of hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6) rose by 30%, 27.7 Tg CO2 Eq. The report points out, despite being emitted in smaller quantities relative to the other principal greenhouse gases, these emissions are significant because many of them have extremely high global warming potentials and, in the cases of PFCs and SF6, long atmospheric lifetimes. Carbon sequestration was estimated to have offset 13% of total emissions in 2000.

The report states that the US could appear to have reduced or increased its national greenhouse gas intensity during the 1990s according to the basis of meaurement. Thus the average annual rate of 1.3% since 1990, is slightly slower than that for total energy or fossil fuel consumption, thereby indicating an improved or lower greenhouse gas emitting intensity. Also it is much slower than the growth rate for either electricity consumption or overall gross domestic product. At the same time, total emissions have grown at about the same rate as national population.

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