US total greenhouse gas emissions rose 0.8% in 1999 to 1,833 million tonnes of carbon equivalent (MMTCe), according to government estimates, compared to 1998 levels.
Analysts at the US Energy Information Administration said the increase was slightly lower than the 1.1% average annual increase that characterized total US greenhouse gas emissions during the 1990s but significantly higher than the 0.1% growth between 1997-1998.
By comparison, US real gross domestic product grew by 4.1% from 1998-1999. The agency attributed the relatively moderate increase in total estimated greenhouse gas emissions in 1999 to warmer-than-normal winter weather and to an increase in electricity generation from nuclear power plants.
However, estimated emissions of carbon dioxide (CO2), which account for more than 80% of total US greenhouse gas emissions, increased by 1.3% in 1999 to 1,527 MMTCe in 1999. The EIA said the 1.3% growth in emissions in 1999 is more typical of the 1.4%/year average growth rate during the 1990s than the 0.1% growth experienced in 1998.
An analysis by EIA indicates that carbon dioxide emissions in 1999 could have been higher by as much as 29 MMTCe if weather patterns during the year had been normal and if electricity generation from nuclear power plants had not been higher than in recent experience.
Carbon dioxide rises
In 1999, for example, some 82% of greenhouse gas emissions consisted of CO2 released by the combustion of energy fuels�coal, petroleum, and natural gas�EIA said. In recent years, energy consumption and emissions have grown relatively slowly, with year-to-year fluctuations in energy consumption largely caused by variations in weather patterns, business cycles, fuel use for electricity generation, and domestic and international energy markets.
Per capita CO2 emissions declined in the early 1980s but rose in the 1990s at a relatively low rate of 0.3%/year. CO2 emissions per dollar of gross domestic product have declined an average 1.7% year during the 1990s. EIA said improved nuclear power plant operating rates and relatively low natural gas prices leading to an expansion of natural-gas-fired electricity generation combined to lower the carbon intensity of electric power generation.
CO2 emissions from the electric power sector in 1999 were an estimated 614 MMTCe, or 1%, higher than the 1998 level. EIA analysts said the increase is less than half the 1990-1999 average increase of 2.1%/year. The agency attributed the improvement to an 8% rise in electricity generation from nuclear plants, compared to their 1998 output.
Emissions of CO2 in the transportation sector rose 2.9% to 496 MMTCe in 1999 compared to 1998, according to EIA. Gasoline consumption, which accounted for 60% of transportation sector emissions, grew by 2.1%. Emissions from jet fuel use grew by 3.1%, and emissions from residual fuel�used mostly by oceangoing ships�grew by 14.6%. Emissions from distillate use increased by 3.8%, as a healthy US economy led to greater consumption of diesel fuel by freight trucks, the EIA said.
Methane emission declines
Methane emission declined 1.8% to 28.8 million tonnes in 1999 or 165 MMTCe. The decline resulted primarily from an increase in methane recovery for energy use at landfills and, to a lesser extent, from reductions in emissions from animal waste, coal mining, and petroleum systems, according to the EIA. Fewer pigs contributed to the drop in methane emissions from animal wastes, analysts reported.
US nitrous oxide (NOx) emissions increased by 0.1% in 1999 compared with 1998, although the rounded total remained at 103 MMTCe, the agency reported. NOx accounts for 6% of US greenhouse gases, agricultural sources account for about 71% of NO emissions, and emissions associated with nitrogen fertilization of soils account for about three-quarters of agricultural emissions.
Emissions associated with fossil fuel use account for another 23% of nitrous oxide emissions, EIA says, of which about 82% comes from mobile sources, principally motor vehicles equipped with catalytic converters. EIA analysts said the most striking trend has been a 51% decline from 1996 levels of industrial NOx emissions after emissions controls were installed at an adipic acid plant operated by the DuPont Corp.
Overall, 1999 US greenhouse gas emissions were about 10.7% higher than 1990 emissions, estimated at 1,655 MMTCe. The 1.1%/year average growth in greenhouse gas emissions from 1990-1999 compares with average growth rates of 1.0%/year for the US population, 1.5% for energy consumption, 2.2% for electric power generation, and 3.1% for real gross domestic product.