Last week, we looked at the making of the Land Use sausage. That is, how emissions and removals of greenhouse gases in the land sector are calculated. (Catch up here if you missed it).
The DCCEEW updates Land Use emissions data annually.
But the quarterly figures change in another way — they get retrospectively revised.
Let’s take a closer look.
Credit to Ketan
First, the topic of Land Use revisions was inspired by Ketan Joshi, an author and communications consultant who focuses on climate and has been monitoring Australia’s Land Use revisions for a few years. Ketan in turn credits others, which you can read about at his blog. The chart concepts below also come from him.
The Revisions
Let’s start with a chart that you’ve seen a few times.
In the year to March 2024, net emissions from the Land Use sector were ‑88.4 Mt CO2-e.
That means 88.4 million tonnes of carbon dioxide were removed from the atmosphere.
To put that in context, it’s nearly enough to remove all of Australia’s transport emissions that year.
Let’s look at the same data in a different way.
The chart below is the identical curve, but the legend shows when the data was published.
In the March 2024 and December 2023 updates, Land Use emissions were reported as ‑88.4 Mt CO2-e and had flatlined since June 2021.
Now, let’s add the same data from an earlier report.
In the December 2022 update, Land Use emissions for the same period were reported as -63.9 Mt CO2-e.
Let’s do it again.
In the December 2021 update, the same emissions were reported as -39.5 Mt CO2-e.
And the further back we go in reports, the more the emissions change.
Upshot
Each time Australia’s Land Use emissions are reported, they get lower. Recalculations have removed an extra 48.9 Mt CO2-e each year since June 2021.
To put that in context:
- Annual emissions from Australia’s 13 biggest polluting facilities* are 47.5 Mt CO2-e.
- Annual emissions from Australia’s two biggest corporate polluters (AGL and Stanwell) are 53.6 Mt CO2-e.
Reality Check
The danger with data, is it all sounds so factual and specific. It has decimal points, so it must be true!
But let’s remind ourselves of what these figures actually represent — the amount of carbon dioxide being sucked up or burped out by land and vegetation across the country.
Australia is the sixth largest country on the planet. That’s an awful lot of trees, grass, soil, crops, mangroves, desert shrubs, seagrass, wetlands and peatlands to monitor. It grows quickly, grows slowly, shrinks, decays, rots, burns and gets cut down.
We’re not measuring the amount of carbon dioxide being released or absorbed; we’re modelling it.
The calculator used to model Australia’s greenhouse gas emissions from the land sector is called the Full Carbon Accounting Model (FullCAM).
As with all models, if you change the input data, you get different output data. Garbage in, garbage out, as they say (not that we’re calling the inputs garbage!).
The Reasons
DCCEEW* has addressed these recalculations and changes in the FullCAM model. Here is a rough and unquestioning summary of the latest changes:
- Crops and grass: More localised models for croplands and grasslands to better reflect local climate, especially rainfall.
- La Niña and rainfall: More rain during La Niña boosted tree growth and soil carbon storage. But wetter conditions can also increase emissions from soil decay in mature forests.
- Forests in Queensland: Queensland now uses a spatial model like Victoria, NSW, and Tasmania to improve the accuracy of carbon tracking in public forests, based on field data and forest regrowth patterns.
- Climate impacts on forests: The new model accounts for seasonal climate, bushfires, and regrowth after forest harvesting using satellite imagery.
- Farm dams: Estimations of methane emissions from farm dams were updated, using machine learning to link emissions with climate factors.
But why does past data get changed? Because when new modelling methods are introduced, the change is applied to the full time series.
DCCEEW said, “In accordance with Paris Agreement rules, improvements are applied across the full time series where appropriate to ensure consistency and comparability.’
New Revisions Dashboard
Whatever you think about these revisions (and note, they don't only happen in Land Use, but across all sectors), our goal is to make them more visible.
You can now track them at our new Emissions Revisions dashboard.
Data notes
- DCCEEW = Department of Climate Change, Energy, the Environment and Water
- Facilities included in calculation of annual emissions from Australia’s 13 biggest polluting facilities via Clean Energy Regulator: Gorgon Operations; Start up and Operations of the Ichthys LNG Project; Port Kembla Steelworks; Wheatstone Operations; WOR01; Queensland Alumina Limited Refinery; Qantas Airways Limited National Transport Facility; Moomba Plant; Liberty Primary Steel Whyalla Steelworks; APLNG Facility; Rio Tinto Yarwun; Moranbah North Mine; Capcoal Mine.