Nov 29, 2006 Refocus Weekly
Emissions of carbon dioxide from
renewable energy facilities in the United States
have doubled since 1990, according to government
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
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
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%
"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.