Australia’s National Carbon Accounting System (NCAS) is a world-leading system to account for greenhouse gas emissions from land based sectors.
Land based emissions (sources) and removals (sinks) of greenhouse gases form a major part of Australia’s emissions profile. Around 27 per cent of Australia’s human-induced greenhouse gas emissions come from activities such as livestock and crop production, land clearing and forestry. The removal of carbon dioxide from the atmosphere by forests provides an important greenhouse sink. The NCAS accounts for these activities through a highly integrated system that combines:
- remotely sensed land cover change (including mapped information from thousands of satellite images)
- land use and management data
- climate and soil data
- greenhouse gas accounting tools, and
- spatial and temporal ecosystem modelling.
Sources and sinks
Plants, when actively growing and photosynthesising, act as a sink of carbon but when they respire, are destroyed, decay or are burnt, the stored carbon is released into the atmosphere. Carbon is also released into the atmosphere from grazing animals, as they digest food, and from agricultural and soil management practices such as ploughing and fertilizer applications.
Deforestation therefore releases greenhouse gases into the atmosphere as plants decay or are burnt and soils are disturbed. Increasing numbers of livestock also adds to land based emissions, particularly where forests are removed to provide cropping and grazing land. Increasing forest cover, on the other hand, acts as a long-term sink, storing carbon from the atmosphere in the plants and soils.
Emissions from non-CO2 greenhouse gases also contribute to global warming, through forestry (including methane emissions from decomposition and burning; nitrogen emissions from decomposition, burning, fertilization and soil preparation) and agriculture (nitrogen emissions from fertilizer application, animal excrement, soil management, decomposition and burning; methane emissions from decomposition and burning).
Mapping landscape change
Accurate accounting of the stocks and flows of carbon across land systems requires knowledge of all aspects of the carbon cycle - including changes associated with plant growth and life cycles, soils, land cover change, land use and management and climate (both before and after deforestation, and over time).
The NCAS accounts for these activities through a highly integrated digital map-based information system (see emissions modelling). It couples remotely sensed land cover change, land use and management, climate and soils data (including mapped information from thousands of satellite images), with greenhouse accounting and ecosystem modelling to calculate the amount of carbon stock change in a particular area over time.
By mapping landscape change, the NCAS provides a dynamic 30-year perspective on the nature and extent of human-induced change in land systems across the Australian continent over the period since 1970.
System design
The NCAS is being developed over several phases:
- The Initial Phase (from end 1997-1999) - involved establishment of the system and strategic directions;
- Phase 1 (from mid 1999-2002) - involved development of targeted research and capacity building;
- The Transitional Phase (from mid 2002-2003) - aims to strengthen verification requirements; and
- Phase 2 (to commence in mid 2003) - aims to provide complete accounting capability for Kyoto Protocol Articles, updated land cover change assessments and further development of a continuous improvement program, among other activities.
The system design is summarised in Technical Report 1.Setting the Frame and the NCAS Accounting Framework, and fully described in Technical Report 28. The FullCAM Carbon Accounting Model.
International review
The Australian Government encourages regular engagement of the international scientific community to ensure that the NCAS achieves and maintains best practice. In December 1999, the NCAS Implementation Plan was subjected to International review. The review provided independent assessment of the implementation of Phase 1 activities and an understanding of performance against international best practice.
The review was conducted by a panel of leading scientists from a range of countries with expertise in: remote sensing and spatial statistics; soil measurement and modelling; forest modelling and inventory; and an understanding of the UNFCCC and its instruments, including the Kyoto Protocol and draft IPCC Special Report on Land Use, Land Use Change and Forestry.
In a report to the Australian Greenhouse Office in May 2002, Drs Kim Lowell and Darrel Williams reviewed the land cover mapping component of the NCAS and found that, "to the best of their knowledge, NCAS is the most robust continental scale earth observation data set of its type ever assembled" to assess Australia's vegetation cover change for the period 1970 onwards.
This review panel included:
- Dr Kim Lowell - Full Professor, Centre for Research in Geomatics, Laval University, Quebec, Canada. (Remote Sensing)
- Dr Darrel Williams - Associate Chief for Science and Landsat, Project Scientist, Laboratory for Terrestrial Physics, NASA Goddard Space Flight Centre, Greenbelt, Maryland USA.
Programme evaluation (Phase 1)
Like all Commonwealth programs, the NCAS is also subject to periodic audit and review. A recent independent Evaluation of NCAS (Phase 1) in November 2002 by Pat Farrelly and Associates Pty Ltd noted that in developing the NCAS, considerable benefit was gained from using existing datasets and resources to leverage greater accounting capacity in the timeframe and budget specified.
The Evaluation indicated that the data holdings and extensive multi-temporal remote sensing methods of the NCAS could have considerable application to broader natural resource management initiatives (such as native/non-native grassland mapping, biodiversity analysis, urban fringe analysis, water body extent and salt scar mapping).
The Evaluation concluded that Phase 2 of NCAS should proceed and indicated there will be a need to: develop arrangements that efficiently allow broader access to NCAS data for natural resource management purposes; provide tools for private and commercial users (e.g. for measuring forest carbon content and projecting likely growth); and provide capability of other potential Government users to benefit from NCAS activities (such as landcare, forestry, conservation and agricultural initiatives).
