Total Mitigation Potential of the Agricultural Sector

In 1995, the IPCC estimated annual worldwide mitigation potential of the agricultural sector to be 1,669-3,417 million metric tons of CO2, 24-92 million metric tons of CH4, and 0.4-1.1 million metric tons of N2O (Table 12.4). Combining these estimates, total mitigation potential would be 620-1,546 million metric tons of carbon equivalent. This represents 13-33 percent of 1990 emissions of CO2, CH4, and N2O from all sectors in Annex I countries,105 a sizable amount given protocol commitments ranging from -8 to +10 percent of 1990 levels.

The carbon sink value in Table 12.4 is similar to other recent estimates.106 The IPCC Special Report on LULUCF has further divided carbon sinks geographically (Annex I and non-Annex I) and by agricultural practice (Table 12.5). This latest estimate is based on peer-reviewed studies in the literature and assumptions about the economic, social, and technical constraints that limit land available for these practices.107

Estimates of mitigation potential such as these must be used cautiously. The scientific literature available to support analyses is still limited. Inaccuracies in measurement and estimation of emissions and carbon storage are inherent in the estimates. Even in the United States, where data sets are large, the estimates of carbon storage vary more than twofold.108 These analyses also do not reflect the recent decisions of the COP in the Bonn Agreement (e.g., projects involving agricultural soils are not eligible for credit under the CDM in the first commitment period), and current estimates cannot anticipate policies beyond the first commitment period. According to the IPCC Special Report on LULUCF, the largest uncertainty in carbon sequestration estimates is where and to what

TABLE 12.4. Estimated Worldwide Mitigation Potential of the Agricultural Sector (Excluding Biofuel Production)

Estimated Decrease Estimated Decrease Through Category Through Practice (Mtgas/yr) Practice (MMTCE/yr)*

CO2.

Emission reductionsf Increasing carbon sinksf

Total ch4

Ruminant animals Animal waste Rice paddies Biomass burning

Total no

Mineral and organic fertilizers Tropical biomass burning and land conversion§

Total

37-183 1,632-3,234 1,669-3,417

10-50 445-882 455-932

69-258 11-40 46-200 9-26 135-524

25-76 5-14

30-90

Source: Tables 23-5 and 23-11 in V. Cole, C. Cerri, K. Minami, A. Mosier, N. Rosenberg, and D. Sauerbeck, 1996: "Agricultural options for mitigation of greenhouse gas emissions," in R. T. Watson, M. C. Zinyowera, and R. H. Moss (eds.), Climate Change 1995: Impacts, Adaptations and Mitigation of Climate Change: Scientific-Technical Analyses (Cambridge, England: Cambridge University Press).

*In converting Mt of gas to million metric tons of carbon equivalent (MMTCE), a 100-year time horizon was assumed, with global warming potentials of 21 and 310 for CH4 and N2O, respectively. fAssuming a reduction of 10—50% in developed countries only.

fBased on carbon sequestration over a 100-year period. Category includes better management of existing agricultural soils globally, permanent set-aside of 15% of surplus agricultural land in temperate regions, and restoration of soil carbon on degraded lands globally. §Includes biomass burning, management of soils after burning, and forest conversion.

extent LULUCF activities may occur.109 Finally, the IPCC estimates do not yet take into account the effects of climate change and elevated CO2 on agricultural production or soil carbon storage.110 Instead, they reflect current agricultural conditions. Thus, although estimates can be useful for conducting near-term policy analyses and stimulating additional climate change research, assessment of mitigation options for coming decades must consider additional factors.

TABLE 12.5. Estimated Carbon Storage Potential of Agricultural Activities in Two Time Periods

Adoption or Storage Potential

Practices

Site

Area (106 ha)

2010

2040

Rate of Storage (t C ha-1 yr 1)

2010

2040

Improved management Cropland (includes conser-

Annex I

589

40

70

0.32

75

132

vation tillage, crop rotation,

Non-Annex I

700

20

50

0.36

50

126

cover crops, erosion control,

fertility and irrigation

management)

Rice paddies (irrigation,

Annex I

4

80

100

0.10

<1

<1

fertilizer, and plant residue

Non-Annex I

149

50

80

0.10

7

12

management)

Agroforestry (improved man-

Annex I

83

30

40

0.50

12

17

agement of trees on cropland)

Non-Annex I

317

20

40

0.22

14

28

Grazing land (improved herd,

Annex I

1,297

10

20

0.53

69

137

plant, and fire management)

Non-Annex I

2,104

10

20

0.80

168

337

Land-use change

Agroforestry (conversion from

Annex I

-0

-0

-0

-0

0

0

unproductive cropland and

Non-Annex I

630

20

30

3.1

391

586

grasslands)

Grassland (conversion from

Annex I

602

5

10

0.8

24

48

cropland)

Non-Annex I

855

2

5

0.8

14

34

Source: Table 4-1 in Intergovernmental Panel on Climate Change, 2000: Land Use, Land-Use Change, and Forestry (Cambridge, England: Cambridge University Press), pp. 198—204. Note that all listed activities will not be eligible for credit in Annex I and non-Annex I countries under the Kyoto Protocol and Bonn Agreement.

*Rates of carbon gain are averages for approximately 20-40 years; after this period of accumulation, rates typically will approach zero. Uncertainty in estimates may be as high as +50%.

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