Executive Summary
2017_executive_summary 2017_executive_summary
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 Agriculture The Agriculture chapter contains anthropogenic emissions from agricultural activities (except fuel combustion, which is addressed in the Energy chapter, and agricultural CO 2 fluxes, which are addressed in the Land Use, Land- Use Change, and Forestry chapter). Agricultural activities contribute directly to emissions of greenhouse gases through a variety of processes, including the following source categories: enteric fermentation in domestic livestock, livestock manure management, rice cultivation, agricultural soil management, liming, urea fertilization, and field burning of agricultural residues. CO 2, CH 4 and N 2O were the primary greenhouse gases emitted by agricultural activities. CO 2 emissions from the application of crushed limestone and dolomite (i.e., soil liming) and urea fertilization represented 0.2 percent of total CO 2 emissions from anthropogenic activities. CH 4 emissions from enteric fermentation and manure management represented 25.4 percent and 10.1 percent of total CH 4 emissions from anthropogenic activities, respectively, in 2015. Agricultural soil management activities such as fertilizer application and other cropping practices were the largest source of U.S. N 2O emissions in 2015, accounting for 75.0 percent. In 2015, emission sources accounted for in the Agricultural chapters were responsible for 7.9 percent of total U.S. greenhouse gas emissions. Land Use, Land-Use Change, and Forestry The Land Use, Land-Use Change, and Forestry chapter contains emissions of CH 4 and N 2O, and emissions and removals of CO 2 from managed lands in the United States. Overall, managed land is a net sink for CO 2 (C sequestration) in the United States. The drivers of fluxes on managed lands include, for example, forest management practices, tree planting in urban areas, the management of agricultural soils, the landfilling of yard trimmings and food scraps, and activities that cause changes in C stocks in coastal wetlands. The main drivers for net forest sequestration include net forest growth and increasing forest area, as well as a net accumulation of C stocks in harvested wood pools. The net sequestration in Settlements Remaining Settlements, which occurs predominantly from urban forests and landfilled yard trimmings and food scraps, is a result of net tree growth and increased urban forest size, as well as long-term accumulation of yard trimmings and food scraps carbon in landfills. Forest Land Remaining Forest Land (including vegetation, soils, and harvested wood) represented the largest carbon sink from LULUCF, accounting for 77 percent of total 2015 negative C fluxes; Settlements Remaining Settlements (urban trees and landfilled yard trimmings and food scraps) accounted for 12 percent; Land Converted to Forest Land accounted for 9 percent; and Cropland Remaining Cropland, Wetlands Remaining Wetlands, and Land Converted to Wetlands accounted for 3 percent of the total negative C fluxes in 2015. Conversely, Land Converted to Grassland represented the largest carbon source from LULUCF, accounting for 61 percent of total 2015 positive C fluxes, while Land Converted to Settlements accounted for 31 percent. Land Converted to Cropland accounted for 6 percent. Grassland Remaining Grassland accounted for 2 percent, and settlement soils in Settlements Remaining Settlements accounted for less than 0.5 percent of the total positive C fluxes in 2015. Overall, positive C fluxes totaled 481.6 MMT CO 2 Eq. in 2015, while negative C fluxes totaled 868.5 MMT CO 2 Eq. in 2015. The LULUCF sector in 2015 resulted in a net increase in C stocks (i.e., net CO 2 removals) of 386.8 MMT CO 2 Eq. (Table ES-5). 22 This represents an offset of 5.9 percent of total (i.e., gross) greenhouse gas emissions in 2015. Emissions from LULUCF activities in 2015 are 20.4 MMT CO 2 Eq. and represent 0.3 percent of total greenhouse gas emissions. 23 Between 1990 and 2015, total C sequestration in the LULUCF sector decreased by 16.0 percent, 22 LULUCF C Stock Change is the net C stock change from the following categories: Forest Land Remaining Forest Land, Land Converted to Forest Land, Cropland Remaining Cropland, Land Converted to Cropland, Grassland Remaining Grassland, Land Converted to Grassland, Wetlands Remaining Wetlands, Land Converted to Wetlands, Settlements Remaining Settlements, and Land Converted to Settlements. 23 LULUCF emissions include the CO2, CH4, and N2O emissions from Peatlands Remaining Peatlands; CH4 and N2O emissions reported for Non-CO2 Emissions from Forest Fires, Non-CO2 Emissions from Grassland Fires, and Coastal Wetlands Remaining Coastal Wetlands; CH4 emissions from Land Converted to Coastal Wetlands; and N2O Fluxes from Forest Soils and Settlement Soils. 20 DRAFT Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2015
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 primarily due to a decrease in the rate of net C accumulation in forests and an increase in emissions from Land Converted to Grassland. 24 Carbon dioxide removals are presented in Table ES-5 along with CO 2, CH 4, and N 2O emissions for LULUCF source categories. Lands undergoing peat extraction (i.e., Peatlands Remaining Peatlands) resulted in CO 2 emissions of 0.8 MMT CO 2 Eq. (763 kt of CO 2). Forest fires were the largest source of CH 4 emissions from LULUCF in 2015, totaling 7.3 MMT CO 2 Eq. (292 kt of CH 4). Coastal Wetlands Remaining Coastal Wetlands resulted in CH 4 emissions of 3.5 MMT CO 2 Eq. (141 kt of CH 4). Grassland fires resulted in CH 4 emissions of 0.4 MMT CO 2 Eq. (16 kt of CH 4). Peatlands Remaining Peatlands and Land Converted to Wetlands resulted in CH 4 emissions of less than 0.05 MMT CO 2 Eq. Forest fires were also the largest source of N 2O emissions from LULUCF in 2015, totaling 4.8 MMT CO 2 Eq. (16 kt of N 2O). Nitrous oxide emissions from fertilizer application to settlement soils in 2015 totaled to 2.6 MMT CO 2 Eq. (9 kt of N 2O). This represents an increase of 81.5 percent since 1990. Additionally, the application of synthetic fertilizers to forest soils in 2015 resulted in N 2O emissions of 0.5 MMT CO 2 Eq. (2 kt of N 2O). Nitrous oxide emissions from fertilizer application to forest soils have increased by 455 percent since 1990, but still account for a relatively small portion of overall emissions. Grassland fires resulted in N 2O emissions of 0.4 MMT CO 2 Eq. (1 kt of N 2O). Coastal Wetlands Remaining Coastal Wetlands resulted in N 2O emissions of 0.1 MMT CO 2 Eq. (0.5 kt of N 2O), and Peatlands Remaining Peatlands resulted in N 2O emissions of less than 0.05 MMT CO 2 Eq. Table ES-5: U.S. Greenhouse Gas Emissions and Removals (Net Flux) from Land Use, Land- Use Change, and Forestry (MMT CO2 Eq.) Gas/Land-Use Category 1990 2005 2011 2012 2013 2014 2015 Net CO2 Flux a (460.7) (339.3) (395.8) (414.5) (390.3) (389.2) (386.8) Forest Land Remaining Forest Land b (698.4) (665.3) (670.8) (667.8) (671.7) (670.1) (667.0) Land Converted to Forest Land (92.0) (81.4) (75.8) (75.2) (75.2) (75.2) (75.2) Cropland Remaining Cropland c (40.9) (26.5) (19.1) (21.4) (15.6) (14.8) (14.0) Land Converted to Cropland c 100.7 42.6 35.3 35.3 28.6 28.6 28.6 Grassland Remaining Grassland c (4.2) 5.5 (12.5) (20.8) 7.7 7.8 7.3 Land Converted to Grassland c 245.2 323.8 296.9 293.2 294.2 294.2 294.2 Wetlands Remaining Wetlands (8.6) (10.1) (8.7) (8.7) (8.7) (8.7) (8.7) Land Converted to Wetlands (+) (+) (+) (+) (+) (+) (+) Settlements Remaining Settlements (86.2) (91.4) (98.7) (99.2) (99.8) (101.2) (102.1) Land Converted to Settlements 123.8 163.6 157.6 150.2 150.2 150.2 150.2 CO2 1.1 1.1 0.9 0.8 0.8 0.8 0.8 Wetlands Remaining Wetlands: Peatlands Remaining Peatlands 1.1 1.1 0.9 0.8 0.8 0.8 0.8 CH4 6.7 13.3 11.2 14.9 11.0 11.2 11.2 Forest Land Remaining Forest Land: Non-CO2 Emissions from Forest Fires 3.2 9.4 6.8 10.8 7.2 7.3 7.3 Wetlands Remaining Wetlands: Coastal Wetlands Remaining Coastal Wetlands 3.4 3.5 3.5 3.5 3.5 3.5 3.5 Grassland Remaining Grassland: Non-CO2 Emissions from Grassland Fires 0.1 0.3 0.8 0.6 0.2 0.4 0.4 Land Converted to Wetlands: Land Converted to Coastal Wetlands + + + + + + + Wetlands Remaining Wetlands: Peatlands Remaining Peatlands + + + + + + + N2O 3.8 9.6 8.6 11.0 8.1 8.4 8.4 Forest Land Remaining Forest Land: Non-CO2 Emissions from Forest Fires 2.1 6.2 4.5 7.1 4.7 4.8 4.8 Settlements Remaining Settlements: N2O Fluxes from Settlement Soils d 1.4 2.5 2.6 2.7 2.6 2.6 2.6 24 Quality control uncovered errors in the estimate and uncertainty of soil C stock changes for 2013, 2014, 2015, which will be updated following public review. Corrected estimates are provided in footnotes of the emission summary tables for Cropland Remaining Cropland, Land Converted to Cropland, Grassland Remaining Grassland, and Land Converted to Grassland sections in the LULUCF chapter of this report. Executive Summary ES-21
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primarily due to a decrease in the rate of net C accumulation in forests and an increase in emissions from Land<br />
Converted to Grassland. 24<br />
Carbon dioxide removals are presented in Table ES-5 along with CO 2, CH 4, and N 2O emissions for LULUCF source<br />
categories. Lands undergoing peat extraction (i.e., Peatlands Remaining Peatlands) resulted in CO 2 emissions of 0.8<br />
MMT CO 2 Eq. (763 kt of CO 2). Forest fires were the largest source of CH 4 emissions from LULUCF in 2015,<br />
totaling 7.3 MMT CO 2 Eq. (292 kt of CH 4). Coastal Wetlands Remaining Coastal Wetlands resulted in CH 4<br />
emissions of 3.5 MMT CO 2 Eq. (141 kt of CH 4). Grassland fires resulted in CH 4 emissions of 0.4 MMT CO 2 Eq. (16<br />
kt of CH 4). Peatlands Remaining Peatlands and Land Converted to Wetlands resulted in CH 4 emissions of less than<br />
0.05 MMT CO 2 Eq.<br />
Forest fires were also the largest source of N 2O emissions from LULUCF in 2015, totaling 4.8 MMT CO 2 Eq. (16 kt<br />
of N 2O). Nitrous oxide emissions from fertilizer application to settlement soils in 2015 totaled to 2.6 MMT CO 2 Eq.<br />
(9 kt of N 2O). This represents an increase of 81.5 percent since 1990. Additionally, the application of synthetic<br />
fertilizers to forest soils in 2015 resulted in N 2O emissions of 0.5 MMT CO 2 Eq. (2 kt of N 2O). Nitrous oxide<br />
emissions from fertilizer application to forest soils have increased by 455 percent since 1990, but still account for a<br />
relatively small portion of overall emissions. Grassland fires resulted in N 2O emissions of 0.4 MMT CO 2 Eq. (1 kt<br />
of N 2O). Coastal Wetlands Remaining Coastal Wetlands resulted in N 2O emissions of 0.1 MMT CO 2 Eq. (0.5 kt of<br />
N 2O), and Peatlands Remaining Peatlands resulted in N 2O emissions of less than 0.05 MMT CO 2 Eq.<br />
Table ES-5: U.S. Greenhouse Gas Emissions and Removals (Net Flux) from Land Use, Land-<br />
Use Change, and Forestry (MMT CO2 Eq.)<br />
Gas/Land-Use Category 1990 2005 2011 2012 2013 2014 2015<br />
Net CO2 Flux a (460.7) (339.3) (395.8) (414.5) (390.3) (389.2) (386.8)<br />
Forest Land Remaining Forest Land b (698.4) (665.3) (670.8) (667.8) (671.7) (670.1) (667.0)<br />
Land Converted to Forest Land (92.0) (81.4) (75.8) (75.2) (75.2) (75.2) (75.2)<br />
Cropland Remaining Cropland c (40.9) (26.5) (19.1) (21.4) (15.6) (14.8) (14.0)<br />
Land Converted to Cropland c 100.7 42.6 35.3 35.3 28.6 28.6 28.6<br />
Grassland Remaining Grassland c (4.2) 5.5 (12.5) (20.8) 7.7 7.8 7.3<br />
Land Converted to Grassland c 245.2 323.8 296.9 293.2 294.2 294.2 294.2<br />
Wetlands Remaining Wetlands (8.6) (10.1) (8.7) (8.7) (8.7) (8.7) (8.7)<br />
Land Converted to Wetlands (+) (+) (+) (+) (+) (+) (+)<br />
Settlements Remaining Settlements (86.2) (91.4) (98.7) (99.2) (99.8) (101.2) (102.1)<br />
Land Converted to Settlements 123.8 163.6 157.6 150.2 150.2 150.2 150.2<br />
CO2 1.1 1.1 0.9 0.8 0.8 0.8 0.8<br />
Wetlands Remaining Wetlands: Peatlands<br />
Remaining Peatlands 1.1 1.1 0.9 0.8 0.8 0.8 0.8<br />
CH4 6.7 13.3 11.2 14.9 11.0 11.2 11.2<br />
Forest Land Remaining Forest Land:<br />
Non-CO2 Emissions from Forest Fires 3.2 9.4 6.8 10.8 7.2 7.3 7.3<br />
Wetlands Remaining Wetlands: Coastal<br />
Wetlands Remaining Coastal Wetlands 3.4 3.5 3.5 3.5 3.5 3.5 3.5<br />
Grassland Remaining Grassland:<br />
Non-CO2 Emissions from Grassland Fires 0.1 0.3 0.8 0.6 0.2 0.4 0.4<br />
Land Converted to Wetlands: Land<br />
Converted to Coastal Wetlands + + + + + + +<br />
Wetlands Remaining Wetlands: Peatlands<br />
Remaining Peatlands + + + + + + +<br />
N2O 3.8 9.6 8.6 11.0 8.1 8.4 8.4<br />
Forest Land Remaining Forest Land:<br />
Non-CO2 Emissions from Forest Fires 2.1 6.2 4.5 7.1 4.7 4.8 4.8<br />
Settlements Remaining Settlements:<br />
N2O Fluxes from Settlement Soils d 1.4 2.5 2.6 2.7 2.6 2.6 2.6<br />
24 Quality control uncovered errors in the estimate and uncertainty of soil C stock changes for 2013, 2014, 2015, which will be<br />
updated following public review. Corrected estimates are provided in footnotes of the emission summary tables for Cropland<br />
Remaining Cropland, Land Converted to Cropland, Grassland Remaining Grassland, and Land Converted to Grassland sections<br />
in the LULUCF chapter of this report.<br />
<strong>Executive</strong> <strong>Summary</strong><br />
ES-21
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