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Renewables increase carbon emissions despite declining output

Nov 29, 2006 Refocus Weekly

Emissions of carbon dioxide from renewable energy facilities in the United States have doubled since 1990, according to government reports.

While net generation of electricity increased 2% from 2004 to 2005, CO2 emissions from the power sector increased 2.8%, from 2,309 million metric tons (Mt) to 2,375 Mt, according to the annual inventory of anthropogenic (human-caused) greenhouse gases published by the Energy Information Administration. This increase caused the overall carbon intensity of U.S. electricity production to increase by 0.9%, which resulted from an increase in the use of fossil fuels to generate electricity, while generation from nuclear and renewables fell 1%, by 10.6 billion kWh.

The country's total GHG emissions were 7,147 Mt of CO2 equivalent last year, up 0.6% from 2004 levels, the report notes. Since 1990, GHG emissions in the U.S. have grown at an average annual rate of 1%.

Total emissions in 2005 were 6,009 Mt of carbon dioxide (84% of total emissions), 612 Mt of methane, 367 Mt of nitrous oxide and 160 Mt of HFC, PFCs and SF6. GHG emissions per unit of GDP fell 2.5% last year, compared with an annual average decline since 1990 of 1.9%.

In energy consumption, 4,985 Mt of CO2 were released in 1990, of which renewables were responsible for 6.2 Mt; by 1995, the total was 5,266 Mt with renewables at 10.4 Mt; by 2005, national total emissions were 5,945 Mt and renewables were 11.5 Mt. Emissions from renewables peaked in 2002 at 13 Mt.

The emissions come from hydro, biomass, solar and wind. Both geothermal and waste combustion produce some CO2 emissions, and wood-fired generation is "considered carbon-neutral so long as it does not lead to deforestation," the report explains. To eliminate double counting or miscounting of emissions, EIA says ethanol is a biofuel and the carbon it contains is not counted as an emission.

Geothermal steam at The Geysers in California, where most U.S. geothermal electric power is generated, contains dissolved CO2 in the steam which is released into the atmosphere when the steam is brought to the surface. EIA adds emissions from this source, at a rate of 0.1 Mt of carbon per year.

Carbon emissions from the plastics portion of municipal solid waste were 11.1 Mt combusted for electricity generation and very small amounts (0.4 Mt) of geothermal-related emissions.

The report excludes CO2 emissions from biofuels (wood, wood waste, alcohol fuels, biogenic municipal solid waste, and other biomass burned for energy) because carbon found in biofuels is the result of the natural process of atmospheric uptake of CO2 by plants. During combustion of biofuels, there is an immediate release of carbon in the form of CO2 but biofuels are assumed to be produced as renewable resources, and the carbon released through burning is assumed to be reabsorbed over time as part of the natural carbon cycle.

Emissions from biofuel combustion produce no net change in the overall carbon budget although, if the initial flux had been counted, CO2 emissions from biofuel combustion in 2001 were estimated to have been 65 Mt.

The increase in total emissions last year "is well below the rate of economic growth of 3.2% and below the average annual growth rate of 1% percent in GHG emissions since 1990," the report explains. Emissions of CO2 from energy consumption and industrial processes, which have been rising at an average annual rate of 1.2% since 1990, grew by only 0.3% in 2005.

"Slow growth in CO2 emissions from 2004 to 2005 can be attributed mainly to higher energy prices that suppressed energy demand, low or negative growth in several energy-intensive industries, and weather-related disruptions in the energy infrastructure along the Gulf Coast that shut down both petroleum and natural gas operations," it adds.