Australasian Science: Australia's authority on science since 1938

Rethinking Australia’s Carbon Abatement Contracts

By Bill Burrows

Australia’s total net CO2 emissions are much lower than are implied by published numbers.

Australia is often described as one of the world’s leading emitters of carbon dioxide (CO2) – a consequence of our small population, advanced economy and relatively large land area.

Crucially, Australia’s poor ranking is a consequence of sources and sinks from the land use and forestry sectors being included or excluded from the National Greenhouse Gas Inventory. A carbon sink is anything that absorbs more carbon than it releases, while a carbon source is anything that releases more carbon than it absorbs. Forests, soils, oceans and the atmosphere all store carbon, which moves between them in a continuous cycle.

However, huge areas of native vegetation have not been taken into account when compiling Australia’s carbon budgets. The nation has essentially reported CO2 emissions that have been “measured” and directly identified with human activities – rather than those that mirror Australia’s true input to CO2 content in the global atmosphere.

A less selective and more meaningful analysis of CO2 fluxes would report net emissions –when all known sinks (sequestered amounts) of CO2 are subtracted from all known sources.

Satellite-based spectral sensors now enable net CO2 emissions to be measured with accuracy and precision. The fact that we are an island continent adds to the integrity of the values reported (compared with countries in Europe, for example, where a nation’s air mass can cross borders at daily – or even shorter – time intervals).

Two such satellites monitor CO2 in the atmosphere today: Japan’s GOSAT and NASA’s OCO-2, which both record CO2 from the top of the Earth’s atmosphere to its surface. The satellites’ sensors integrate the net atmospheric contributions from all CO2 sources and sinks, with no distinction made as to whether the recorded gas is anthropogenic or naturally occurring. Clearly the concentration of CO2 in the atmosphere, rather than its origin, is of most interest when monitoring it.

Prior to these space-based observations, carbon fluxes derived from ground-based measurements were problematic. This notably applied to observations made for the land use and forestry sectors. To determine carbon fluxes in vegetation from field data it is necessary to obtain sequential recordings of carbon stocks in the above-ground and below-ground components of the vegetation, as well as in the soil supporting it.

Sampling problems are immense, particularly in native plant communities. At any time weather patterns, vegetation age and disturbances such as clearing, harvesting, fire and grazing can impact the flux being estimated.

Only space-based measurements can provide the robustness, spatial coverage and sampling density and frequency, as well as the accuracy and precision necessary, to determine the Australia-wide flux of CO2.

Results from GOSAT and OCO-2 missions have been slow to be published, but two recent data sets suggest that Australia would be wise to embrace the technology and its outputs, especially given the significant budget allocations set aside by the Australian government to buy carbon abatement contracts.

Why has the government committed up to $2.5 billion to purchase these contracts? The first two offer rounds appear to be mostly based on modelling of native vegetation systems, with questionable accuracy and precision surrounding the inputs.

Published GOSAT measurements, along with OCO-2 sensor data, suggest that Australia’s total net CO2 emissions are much lower than has been implied by the National Greenhouse Gas Inventory. Averaged across years we are very likely to act as a net sink. These conclusions are supported by convincing evidence of increases in woody plant cover in Australia’s intact woodlands and shrublands.

Why pay $2 billion or more for carbon abatement contracts with greatly limited land coverage when a spatially comprehensive, accurate and precise accounting of net CO2 fluxes for all of the Australian continent can be derived from satellite sensors at minimal cost to Australia’s budget?

Dr Bill Burrows FTSE is a retired Senior Principal Scientist in the Queensland Department of Primary Industries, where he studied the ecology and management of Queensland’s grazed woodland communities.