Atmosphere Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Dr Peter Manins, Environmental Consulting and Research Unit, CSIRO Atmospheric Research, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06746 9
Climate Variability and Change (continued)
Development of carbon sinks and forest regrowth [A Indicator 1.20]
Australia is committed to performing carbon accounting as part of its international obligations. Carbon accounting refers to the estimation of carbon dioxide emitted to, and removed from, the atmosphere as a result of land use change and forestry activities.
Carbon dioxide emissions from land use change arise from above-ground burning and decay of vegetation following clearing. Below-ground release of soil carbon is due to soil disturbance resulting from vegetation clearing and decay of roots. Forestry contributes to carbon emissions through the decay of harvested timber products and slash and burn practices, as well as emissions from soil.
Development of carbon sinks includes the growth of commercial and other managed forests, regrowth of cleared vegetation, and build up of soil carbon resulting from management practices such as pasture improvement and minimum tillage.
An estimated net 39.5 Mt of CO2-e emissions were produced from the land use change and forestry sector in 1998. The current best estimate of total gross emissions from the land use change and forestry sector is 134.7 Mt CO2-e. Emissions are made up of 37.6 Mt CO2-e from burning of cleared vegetation, 4.5 Mt CO2-e from the decay of debris not burned, 39.4 Mt from soil disturbed in the clearing process, 51.8 Mt CO2-e from the harvesting of forestry timber and 1.4 Mt CO2-e from trace gases emitted from prescribed burning and bushfires. However, further investigations are needed to estimate carbon dioxide emissions from the burning-off by Indigenous peoples in northern Australia and also from sugar cane burning.
Total removals in 1998 were estimated to be 95.2 Mt CO2-e. Removals are made up of 73.4 Mt CO2-e from forest growth, 17.5 Mt CO2-e from regrowth associated with land clearing and 4.2 Mt CO2-e from pasture improvement and minimum tillage practices. Table 9 shows the year-to-year values of emissions and sinks under different categories and their changes between 1990 and 1998.
| Sources and sinks | CO2 equivalent emissions (Mt) | Change 1990 to 1998 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | CO2-e Mt | Change (%) | |
| Emissions | |||||||||||
| Burning | 61.6 | 32.1 | 32.1 | 32.1 | 32.1 | 33.5 | 37.7 | 37.7 | 37.6 | -24.0 | -39.0 |
| Decay of slash | 5.8 | 5.6 | 5.4 | 5.2 | 5.1 | 5.0 | 4.9 | 4.8 | 4.5 | -1.2 | -21.6 |
| Below ground | 57.6 | 55.3 | 52.1 | 49.2 | 46.6 | 44.3 | 42.7 | 41.2 | 39.4 | -18.1 | -31.5 |
| Prescribed burning | 1.4 | 1.6 | 1.5 | 1.5 | 1.4 | 1.4 | 1.3 | 1.4 | 1.4 | -1.1 | -74.8 |
| Forest harvesting | 46.9 | 47.3 | 47.0 | 47.4 | 48.3 | 49.4 | 50.4 | 51.2 | 51.8 | 4.9 | 10.4 |
| Total emissions | 173.3 | 141.8 | 138.0 | 135.3 | 133.5 | 133.6 | 137.0 | 136.2 | 134.7 | -38.6 | -22.3 |
| Sinks | |||||||||||
| Regrowth | 21.4 | 18.7 | 18.5 | 18.3 | 18.1 | 18.1 | 18.2 | 18.2 | 17.5 | -3.9 | -18.2 |
| Forest growth | 71.3 | 71.3 | 71.3 | 71.3 | 71.3 | 71.9 | 72.4 | 72.9 | 73.4 | 2.1 | 2.9 |
| Pasture improvement and min. tillage | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 0.0 | 0.0 |
| Total sinks | 97.0 | 94.3 | 94.1 | 93.9 | 93.7 | 94.2 | 94.7 | 95.3 | 95.2 | -1.8 | -1.9 |
| Net emissions | 76.3 | 47.6 | 44.0 | 41.5 | 39.8 | 39.4 | 42.3 | 40.9 | 39.5 | -36.8 | -48.2 |
Source: AGO (2000b).
Estimated emissions from forest harvesting show a small increase from 46.9 to 51.8 Mt CO2-e between 1990 and 1998. The sink associated with forest regrowth is estimated to have increased from 71.3 to 73.4 Mt CO2-e. The estimated net sink is 2.8 Mt CO2-e (Table 10).
| Sources and sinks | CO2-e emissions (Mt) | Change 1990 to 1998 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | CO2-e Mt | Change (%) | |
| Emissions | |||||||||||
| Forestry harvesting (a) | 46.9 | 47.3 | 47.0 | 47.4 | 48.3 | 49.4 | 50.4 | 51.2 | 51.8 | 4.9 | 10.4 |
| Other (b) | 1.4 | 1.6 | 1.5 | 1.5 | 1.4 | 1.4 | 1.3 | 1.4 | 1.4 | 0 | 0 |
| Below ground | 57.6 | 55.3 | 52.1 | 49.2 | 46.6 | 44.3 | 42.7 | 41.2 | 39.4 | -18.1 | -31.5 |
| Total emissions (a) + (b) | 48.3 | 48.9 | 48.5 | 48.9 | 49.7 | 50.8 | 51.7 | 52.6 | 53.2 | 4.9 | 8.8 |
| Sinks | |||||||||||
| Forest growth (c) | 71.3 | 71.3 | 71.3 | 71.3 | 71.3 | 71.9 | 72.4 | 72.9 | 73.4 | 2.1 | 2.9 |
| Other (d) | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 4.2 | 0.0 | 0.0 |
| Total sinks (c) + (d) | 75.6 | 75.6 | 75.6 | 75.6 | 75.6 | 76.1 | 76.6 | 77.1 | 77.7 | 2.1 | 2.8 |
| Net forest sink (c) - (a) | 24.4 | 24.1 | 24.4 | 24.0 | 23.0 | 22.4 | 22.0 | 21.7 | 21.6 | -2.8 | -11.4 |
| Net other sink (d) - (b) | 2.8 | 2.6 | 2.7 | 2.7 | 2.8 | 2.8 | 2.9 | 2.9 | 2.8 | 0 | 0 |
| Net forest and other sinks (c) + (d) - (a) - (b) | 27.2 | 26.7 | 27.1 | 26.7 | 25.8 | 25.3 | 24.9 | 24.6 | 24.4 | -2.8 | -10.3 |
A Forest = forest and other woody biomass stocks.
B Other = minimum tillage and pasture improvement practices and non-CO2 gas emissions from prescribed burning and wildfires.
Source: AGO (2000b).
Forest and grassland conversion (land clearing) shows an estimated decrease in net emissions of 39.5 Mt CO2-e between 1990 and 1998 (Table 11). Net emissions from land clearing decreased from 103.5 Mt CO2-e in 1990 to 64.0 Mt CO2-e in 1998 (Table 11). The AGO (2000b) states that only low confidence can be placed upon these trend estimates. The uncertainty associated with the estimates of emissions and removals from forest and grassland conversion remains high. This uncertainty is largely as a result of the use of incomplete data, preliminary rates of land clearing for some states and some years, inadequate methodology for calculation of regrowth sequestration, use of averaged preclearing biomass and soil carbon estimates not spatially linked to where clearing is occurring, and the use of default conversion factors for soil carbon change following clearing.
| Sources and sinks | CO2-e emissions (Mt) | Change (1990-1998) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | CO2-e Mt | Change (%) | |
| Emissions (Clearing of vegetation) | |||||||||||
| Burning | 61.6 | 32.1 | 32.1 | 32.1 | 32.1 | 33.5 | 37.7 | 37.7 | 37.6 | -24.0 | -39.0 |
| Decay of slash | 5.8 | 5.6 | 5.4 | 5.2 | 5.1 | 5.0 | 4.9 | 4.8 | 4.5 | -1.2 | -21.6 |
| Below ground | 57.6 | 55.3 | 52.1 | 49.2 | 46.6 | 44.3 | 42.7 | 41.2 | 39.4 | -18.1 | -31.5 |
| Total emissions | 124.9 | 93.0 | 89.6 | 86.5 | 83.8 | 82.7 | 85.3 | 83.7 | 81.5 | -43.4 | -34.8 |
| Sinks | |||||||||||
| Regrowth | 21.4 | 18.7 | 18.5 | 18.3 | 18.1 | 18.1 | 18.2 | 18.2 | 17.5 | -3.9 | -18.2 |
| Total sinks | 21.4 | 18.7 | 18.5 | 18.3 | 18.1 | 18.1 | 18.2 | 18.2 | 17.5 | -3.9 | -18.2 |
| Net emissions | 103.5 | 74.2 | 71.0 | 68.2 | 65.6 | 4.6 | 67.1 | 65.4 | 64.0 | -39.5 | -38.2 |
A Forest and grassland conversion = emissions from above ground (burning, decay of slash) and below ground, and sinks from regrown associated with land clearing.
Source: AGO (2000b).
Implications
The data used to calculate the effect of carbon sinks and forest regrowth on the total greenhouse gas budget needs to be improved. Although existing data shows decreases in net emissions from land clearing during 1990 to 1998, confidence in these figures is low.