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Environment > Emission of Greenhouse Gases > Land Use
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Emissions of Greenhouse Gases Report
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Land Use
Overview | Forest Lands and Harvested Wood Pools | Croplands and Grasslands |
Urban Trees, Yard Trimmings, and Food Scraps |
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Overview |
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Land use, land-use change, and forestry activities in 2006 resulted in net
sequestration of 883.7 MMTCO2e (see Table 30 below), equal to about 12 percent of
U.S. greenhouse gas emissions in 2006.
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Net carbon sequestration from land use, land-use change, and forestry activities
in 2006 was 20 percent greater than in 1990 (see Figure 27 on right). The increase resulted
primarily from a higher rate of net carbon accumulation in forest carbon
stocks. |
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Net carbon accumulation in cropland remaining cropland, land converted
to grassland, and settlements remaining settlements increased from 1990
to 2006. |
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Net carbon accumulation in landfilled yard trimmings and food scraps decreased
from 1990 to 2006. Grassland remaining grassland was a small carbon sink
in 1990, but since 1995 it has become an emissions source. |
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Emissions from land converted to cropland declined from 1990 to 2006.
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figure data
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| Forest Lands and Harvested Wood Pools |
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Carbon sequestration attributed to forest land remaining forest land in
2006 totaled 745.1 million metric tons carbon dioxide equivalent (see Figure
28 on right and Table 31 below). This carbon pool has grown by 20 percent since 1990,
and it is the primary source of growth in U.S. terrestrial carbon stocks.
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The increase in annual carbon sequestration on forested lands (146 MMTCO2e
higher in 2006 than in 1990) more than equals the decrease in sequestration
of carbon in harvested wood over the same period (23 MMTCO2e lower in 2006
than in 1990). |
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The national sequestration estimates shown below12 are based on individual
State surveys, which are performed at different times and irregular frequencies
in the different States. For the first time, this year’s inventory includes
a portion of Alaskan forest. |
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Because new data or changes in data for some years and/or States can affect
the calculations for intervening years, the annual estimation process generally
results in revisions of the national estimates for all years in the series.
In this year’s inventory, data for 31 of the 48 States were changed from
those in the previous year’s inventory. |
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figure data
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| Croplands and Grasslands |
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For 2006, the aggregate flux of carbon dioxide in the four agricultural
categories (cropland remaining cropland, land converted to cropland, grassland
remaining grassland, and land converted to grassland) was 32.5 MMTCO2e.
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Cropland remaining cropland and land converted to grassland sequestered
41.8 and 16.3 MMTCO2e, respectively, in 2006. Land converted to cropland
and grassland remaining grassland emitted 9.4 and 16.2 MMTCO2e, respectively
(see Figure 29 on right and Table 32 below). |
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This year’s inventory differs from last year’s in the classification of
agricultural land use. Last year, if surveys classified a given area of
land as, for example, cropland remaining cropland in 2005, that categorization
was applied over the entire period from 1990 to 2005. In this year’s inventory,
the classification of an area is determined separately for each year. |
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| Urban Trees, Yard Trimmings, and Food Scraps |
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Urban trees accounted for nearly all (90 percent) of the carbon sequestration
attributed to urban trees, yard trimmings, and food scraps in 2006 (see Figure
30 on right and Table 33 below).
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The half-lives of branches and food scraps were updated this year to match
the values for food scraps and woody materials provided in the IPCC guidelines
for analyzing landfill methane. |
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The increase in annual carbon sequestration in urban trees (34.9 MMTCO2e
higher in 2006 than in 1990) more than equals the decrease in sequestration
of carbon in yard trimmings over the same period (14.6 MMTCO2e lower in
2006 than in 1990). |
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This year’s inventory uses new carbon content estimates for leaves and
grass, as well as new data on municipal solid waste that eliminate the
need for interpolation. As a result of those changes, net flux estimates
across the entire time series are 7 percent higher on average, and the
estimate for 2005 is 13 percent higher, than in last year’s inventory. |
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figure data
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Notes and Sources |
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