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Annex 7: Uncertainty analysis (Table 6.1 of the IPCC Good Practice Guidance)

Uncertainty estimates are an essential element of a complete emissions inventory. The purpose of uncertainty information is not to dispute the validity of the inventory estimates, but to help prioritise efforts to improve the accuracy of inventories in the future and guide decisions on methodological choice (IPCC, 2000). The good practice guidance also notes that inventories prepared following the revised 1996 IPCC guidelines (IPCC, 1996) and good practice guidance (IPCC, 2000 and 2003) will typically contain a wide range of emission estimates, varying from carefully measured and demonstrably complete data on emissions to order-of-magnitude estimates of highly variable N2O fluxes from soils and waterways (IPCC, 2000).

New Zealand has included a Tier 1 uncertainty analysis as required by the Climate Change Convention inventory guidelines (UNFCCC, 2006) and IPCC good practice guidance (IPCC, 2000 and 2003). Uncertainties in the categories are combined to provide uncertainty estimates for the entire inventory in any year and the uncertainty in the overall inventory trend over time. LULUCF categories have been included using the absolute value of any removals of CO2 (Table A7.1). Table A7.2 calculates the uncertainty only in emissions, that is, excluding LULUCF removals.

A7.1 Tier 1 uncertainty calculation

The uncertainty in activity data and emission/removal factors shown in Table A7.1 and A7.2 are equal to half the 95 per cent confidence interval divided by the mean and expressed as a percentage. The reason for halving the 95 per cent confidence interval is that the value corresponds to the familiar plus or minus value when uncertainties are loosely quoted as “plus or minus x per cent”.

Where uncertainty is highly asymmetrical, the larger percentage difference between the mean and the confidence limit is entered. Where only the total uncertainty is known for a category, then:

  • if uncertainty is correlated across years, the uncertainty is entered as the emission or the removal factor uncertainty and as zero in the activity data uncertainty
  • if uncertainty is not correlated across years, the uncertainty is entered as the uncertainty in the activity data and as zero in the emission or the removal factor uncertainty.

In the Tier 1 method, uncertainties in the trend are estimated using two sensitivities.

  • Type A sensitivity is the change in the difference of total emissions between the base year and the current year, expressed as a percentage. Further, this change results from a 1 per cent increase in emissions of a given source category and a greenhouse gas in both the base year and the current year.
  • Type B sensitivity is the change in the difference of total emissions between the base year and the current year, expressed as a percentage. Further, this change results from a 1 per cent increase in emissions of a given source category and gas in the current year only.

Uncertainties that are fully correlated between years are associated with Type A sensitivities, and uncertainties that are not correlated between years are associated with Type B sensitivities.

In Tables A7.1 and A7.2, the figure labelled ‘Uncertainty in the trend’ is an estimate of the total uncertainty in the trend in emissions since the base year. This is expressed as the number of percentage points in the 95 per cent confidence interval in the per cent change in emissions since the base year, that is, “since 1990, gross emissions have gone up by 23 per cent ±5.5 per cent”. The total uncertainty in the trend is calculated by combining the contribution of emissions factor uncertainty and activity data uncertainty to the trend across all categories using equation 3.1 (IPCC, 2000).

The values for individual categories are an estimate of the uncertainty introduced into the trend by the category in question.

Table A7.1 The uncertainty calculation (including LULUCF) for New Zealand’s Greenhouse Gas Inventory 1990–2008 (IPCC Tier 1)

Table A7.1 The uncertainty calculation (including LULUCF) for New Zealand’s Greenhouse Gas Inventory 1990–2008 (IPCC Tier 1)
IPCC source category Gas Base year emissions or absolute value of removals Year t emissions or absolute value of removals Activity data uncertainty Emission or removal factor uncertainty Combined uncertainty Combined uncertainty as a per cent of the national total in year t Type A sensitivity Type B sensitvity Uncertainty in the trend in national total introduced by emission or removal factor uncertainty Uncertainty in trend in national total introduced by activity data uncertainty Uncertainty introduced into the trend in the national total Emission /removal factor quality indicator Activity data quality indicator column H^2 (Year t) column M^2 (Trend)

Energy sector

CO2

22,139.7

32,636.2

5

0

5.0

1.5

0.0786

0.3429

0.0000

2.4243

2.4

M

R

2.2798353

5.87740983

Industrial processes sector

CO2

2,740.7

3,426.0

5

0

5.0

0.2

0.0033

0.0360

0.0000

0.2545

0.3

M

R

0.02512416

0.06477003

LULUCF sector - forest land

CO2

33,200.4

29,768.9

6

9

10.8

3.0

-0.0830

0.3127

-0.7608

2.4988

2.6

M

R

8.80281466

6.8229487

LULUCF sector  other land use categories

CO2

1,162.9

3,603.2

5

38

37.8

1.3

0.0240

0.0379

0.8997

0.2507

0.9

M

R

1.58911279

0.87230322

CRF6C - waste incineration

CO2

12.9

0.9

10

40

41.2

0.0

-0.0001

0.0000

-0.0058

0.0001

0.0

D

D

1.2319E-07

3.336E-05

Energy sector

CH4

745.8

939.4

5

50

50.2

0.4

0.0010

0.0099

0.0487

0.0698

0.1

D

R

0.1907687

0.00723769

CRF2A - mineral products

CH4

0.0

0.0

0

0

0.0

0.0

0.0000

0.0000

0.0000

0.0000

0.0

 

 

0

0

CRF2B - chemical industry

CH4

0.0

0.0

0

0

0.0

0.0

0.0000

0.0000

0.0000

0.0000

0.0

D

R

0

0

CRF4A - enteric fermentation

CH4

21,837.2

22,657.5

0

16

16.0

3.4

-0.0224

0.2380

-0.3581

0.0000

0.4

M

M

11.2519568

0.1282172

CRF4B - manure management

CH4

579.1

719.5

5

100

100.1

0.7

0.0007

0.0076

0.0651

0.0534

0.1

M

M

0.44427395

0.00709224

CRF4E- prescribed burning

CH4

2.7

0.9

20

60

63.2

0.0

0.0000

0.0000

-0.0014

0.0003

0.0

D

R

2.623E-07

2.0426E-06

CRF4F - burning of residues

CH4

21.4

14.3

0

40

40.0

0.0

-0.0001

0.0002

-0.0042

0.0000

0.0

D

R

2.8208E-05

1.7387E-05

LULUCF sector

CH4

48.0

38.2

8

56

56.1

0.0

-0.0002

0.0004

-0.0095

0.0044

0.0

R

R

0.00039398

0.00010945

CRF 6A - solid waste disposal

CH4

2,063.2

1,278.4

0

40

40.0

0.5

-0.0112

0.0134

-0.4470

0.0000

0.4

M

R

0.22389763

0.19981505

CRF 6B - wastewater handling

CH4

207.0

206.3

0

20

20.0

0.0

-0.0003

0.0022

-0.0060

0.0000

0.0

D

R

0.00145686

3.6392E-05

CRF6C - waste incineration

CH4

0.0

0.0

10

100

100.5

0.0

0.0000

0.0000

0.0000

0.0000

0.0

D

D

1.12E-12

9.0471E-11

Energy sector N2O 157.3 263.2 5 50 50.2 0.1 0.0009 0.0028 0.0445 0.0196 0.0 D R 0.01497783 0.00235965
Solvents - N2O use N2O 41.5 31.0 10 0 10.0 0.0 -0.0002 0.0003 0.0000 0.0046 0.0 R   8.2279E-06 2.1211E-05
CRF4D - agricultural soils N2O 9,379.0 11,372.3 0 74 74.0 7.8 0.0076 0.1195 0.5622 0.0000 0.6 M M 60.6356373 0.31611102
CRF4B - manure management N2O 38.1 56.9 5 100 100.1 0.1 0.0001 0.0006 0.0143 0.0042 0.0 R R 0.0027773 0.00022376
CRF4E - prescribed burning N2O 0.5 0.2 20 60 63.2 0.0 0.0000 0.0000 -0.0003 0.0000 0.0 D R 8.7532E-09 6.8163E-08
CRF4F - burning of residues N2O 7.4 4.7 0 40 40.0 0.0 0.0000 0.0000 -0.0015 0.0000 0.0 D R 3.0858E-06 2.298E-06
LULUCF sector N2O 5.1 4.1 8 57 57.9 0.0 0.0000 0.0000 -0.0011 0.0005 0.0 R R 4.7567E-06 1.3626E-06
CRF6B - wastewater handling N2O 153.5 183.8 0 1200 1200.0 2.0 0.0001 0.0019 0.1205 0.0000 0.1 D R 4.16472939 0.0145172
CRF6C - waste incineration N2O 1.6 1.3 10 100 100.5 0.0 0.0000 0.0000 -0.0006 0.0002 0.0 D D 1.406E-06 4.0142E-07
CRF2F HFCs 0.0 812.5 0 26 25.9 0.2 0.0085 0.0085 0.2213 0.0000 0.2   R 0.03798484 0.04896241
CRF2C PFCs 629.9 38.8 0 30 30.0 0.0 -0.0071 0.0004 -0.2131 0.0000 0.2 M M 0.00011627 0.04541992
CRF2F SF6 15.2 14.5 0 24 24.0 0.0 0.0000 0.0002 -0.0007 0.0000 0.0 R R 1.0427E-05 4.6896E-07
                                 
Total emissions/removals   95,190.0 108,073.1   Uncertainty in the year 9.5%   Uncertainty in the trend 3.8%     89.665914 14.407612

Table A7.2 The uncertainty calculation (excluding LULUCF) for New Zealand’s Greenhouse Gas Inventory 1990–2008 (IPCC Tier 1)

Table A7.2 The uncertainty calculation (excluding LULUCF) for New Zealand’s Greenhouse Gas Inventory 1990–2008 (IPCC Tier 1)
IPCC source category Gas Base year emissions  Year t emissions Activity data uncertainty Emission factor uncertainty Combined uncertainty Combined uncertainty as a % of the total emissions in year t Type A sensitivity Type B sensitvity Uncertainty in the trend in national totals introduced by emission factor uncertainty Uncertainty in trend in national total introduced by activity data uncertainty Uncertainty introduced into the trend in total emissions Emission /removal factor quality indicator Activity data quality indicator column H^2 (Year t) column M^2 (Trend)
Energy sector CO2 22,139.7 32,636.2 5 0 5 2.2 0.0892 0.5370 0.0000 3.7973 3.8 M R 4.77724439 14.4191128
Industrial processes sector CO2 2,740.7 3,426.0 5 0 5 0.2 0.0010 0.0564 0.0000 0.3986 0.4 M R 0.05264603 0.15890102
CRF6C - waste incineration CO2 12.9 0.9 10 40 41 0.0 -0.0002 0.0000 -0.0098 0.0002 0.0 D D 2.5814E-07 9.6787E-05
Energy sector CH4 745.8 939.4 5 50 50 0.6 0.0004 0.0155 0.0191 0.1093 0.1 D R 0.39974321 0.01231022
CRF2A - mineral products CH4 0.0 0.0 0 0 0 0.0 0.0000 0.0000 0.0000 0.0000 0.0     0 0
CRF2B - chemical industry CH4 0.0 0.0 0 0 0 0.0 0.0000 0.0000 0.0000 0.0000 0.0 D R 0 0
CRF4A - enteric fermentation CH4 21,837.2 22,657.5 0 16 16 4.9 -0.0684 0.3728 -1.0936 0.0000 1.1 M M 23.5777328 1.19604509
CRF4B - manure management CH4 579.1 719.5 5 100 100 1.0 0.0001 0.0118 0.0132 0.0837 0.1 M M 0.93094674 0.00718144
CRF4E - prescribed burning CH4 2.7 0.9 20 60 63 0.0 0.0000 0.0000 -0.0025 0.0004 0.0 D R 5.4963E-07 6.1812E-06
CRF4F - burning of residues CH4 21.4 14.3 0 40 40 0.0 -0.0002 0.0002 -0.0078 0.0000 0.0 D R 5.9107E-05 6.1492E-05
CRF 6A - solid waste disposal CH4 2,063.2 1,278.4 0 40 40 0.7 -0.0207 0.0210 -0.8265 0.0000 0.8 M R 0.4691627 0.68308507
CRF 6B - wastewater handling CH4 207.0 206.3 0 20 20 0.1 -0.0008 0.0034 -0.0158 0.0000 0.0 D R 0.00305275 0.00024937
CRF6C - waste incineration CH4 0.0 0.0 10 100 100 0.0 0.0000 0.0000 0.0000 0.0000 0.0 D D 2.3469E-12 2.6482E-10
Energy sector N2O 157.3 263.2 5 50 50 0.2 0.0012 0.0043 0.0576 0.0306 0.1 D R 0.03138505 0.0042555
Solvents - N2O use N2O 41.5 31.0 10 0 10 0.0 -0.0003 0.0005 0.0000 0.0072 0.0     1.7241E-05 5.2038E-05
CRF4D - agricultural soils N2O 9,379.0 11,372.3 0 74 74 11.3 -0.0025 0.1871 -0.1818 0.0000 0.2 M M 127.057976 0.03305271
CRF4B - manure management N2O 38.1 56.9 5 100 100 0.1 0.0002 0.0009 0.0166 0.0066 0.0 R R 0.00581965 0.00032073
CRF4E- prescribed burning N2O 0.5 0.2 20 60 63 0.0 0.0000 0.0000 -0.0004 0.0001 0.0 D R 1.8342E-08 2.0627E-07
CRF4F - burning of residues N2O 7.4 4.7 0 40 40 0.0 -0.0001 0.0001 -0.0028 0.0000 0.0 D R 6.4661E-06 7.9827E-06
CRF6B - wastewater handling N2O 153.5 183.8 0 1200 1200 3.0 -0.0001 0.0030 -0.0935 0.0000 0.1 D R 8.72691555 0.00873976
CRF6C - waste incineration N2O 1.6 1.3 10 100 100 0.0 0.0000 0.0000 -0.0012 0.0003 0.0 D D 2.9461E-06 1.5203E-06
CRF2F HFCs 0.0 812.5 0 26 26 0.3 0.0134 0.0134 0.3466 0.0000 0.3   R 0.07959472 0.12012001
CRF2C PFCs 629.9 38.8 0 30 30 0.0 -0.0121 0.0006 -0.3628 0.0000 0.4 M M 0.00024363 0.13158884
CRF2F SF6 15.2 14.5 0 24 24 0.0 -0.0001 0.0002 -0.0016 0.0000 0.0 R R 2.1849E-05 2.6622E-06
                                 
Total emissions/removals   60,773.6 74,658.7   Uncertainty in the year 12.9%   Uncertainty in the trend 4.1%     166.11257 16.775191