If you want to know how much Australia contributes to the amount of carbon dioxide (CO₂) in the atmosphere, you must study all the “sources” and “sinks”.
Sources release CO₂ into the atmosphere, while sinks take it out. There are sources from human activities, such as burning fossil fuels, and there are natural sinks such as plants absorbing CO₂. You can tally it all up on a balance sheet to find the net result. Are we adding to CO₂ levels in the atmosphere, overall? And if so, by how much?
It’s an enormous undertaking, but not impossible. We have just published the most comprehensive assessment of Australian CO₂ sources and sinks. It covers the decade from 2010 to 2019, and it reveals some surprising features.
Astonishingly, we found the net annual carbon balance of the entire continent switches from year to year. Australia can be a large net source of CO₂ one year and a large net CO₂ sink the next, in response to our increasingly variable climate. That makes it harder to detect long-term trends and understand whether our natural carbon sinks are growing or decreasing.
Our research reveals what we call the “contemporary carbon budget” for Australia.
We constructed the contemporary budget using a wide variety of data and modelling approaches. We needed to estimate the carbon “fluxes” (sources and sinks) of land-based ecosystems, freshwater bodies, and of human activities such as the combustion of fossil fuels and changes in land clearing and revegetation.
We also used global assessments, Australia’s National Greenhouse Gas Inventory, and trade statistics. As well as atmospheric and satellite CO₂ information to help determine the Australian carbon balance, as well as other satellite-based data to estimate Australia’s fire emissions.
When we put all the land-based CO₂ sources and sinks together, overall Australia was a net source to the atmosphere of 200 million tonnes of CO₂ a year during 2010-19. This drops to 140 million tonnes of CO₂ a year if we count the sinks from coastal ecosystems.
This means CO₂ sinks are partially offsetting fossil fuel emissions. This is something we have also estimated at the global scale, where about one-third of global fossil fuel emissions are removed by terrestrial land-based CO₂ sinks.
While this highlights the important role natural CO₂ sinks play in slowing climate change, it does not imply we have less work to do to reach the net zero emissions target.
Please join our webinar on 21 February Emissions reduction in the boom and bust of Australia’s carbon budget – the challenge and the opportunity. Registration details are below.
Dr Pep Canadell
Chief Research Scientist, CSIRO
Executive Director, Global Carbon Project, CSIRO
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