A couple of weeks ago, we looked at the quarterly Greenhouse Gas update and found Land Use emissions had remained unchanged for 10 quarters. (Catch up here if you missed it).
We’re going to spend the next couple of briefings looking into that curve.
Let’s get started.
What is Land Use?
One of the hardest things about reporting on climate is the abstruse language that permeates it.
We say ‘Land Use’ as shorthand for Land Use, Land Use Change and Forestry sector, which is often abbreviated to LULUCF.
It refers to the way land is covered (e.g. forests) or used (e.g. growing crops).
Why It Matters
Land Use is the only sector that both adds and removes greenhouse gases (GHG) in the atmosphere.
Because the world is so focused on Net Emissions, the question of how much GHG is removed is, ahem, a hot issue.
The more carbon dioxide the Land Use sector absorbs, the more carbon dioxide other sectors can release — all without disturbing those Net emissions curves.
(A wee reminder that this is why the world needs to pay more attention to Gross emissions, not only Net).
How It's Calculated
There are different ways to calculate carbon emissions and removals from Land Use. Some are more detailed and complicated than others, but they all have the same core steps.
Step 1
Allocate land to a sub-category based on how it's covered or used. These are:
- Forest: woody vegetation that meets certain thresholds (E.g. Tree height must be over two metres).
- Cropland: farmland used for growing crops (might include trees that aren’t quite forests).
- Grassland: everything from wild grasslands, to parks and recreational areas, to farmland used for grazing.
- Wetlands: covered or saturated by water for all or part of the year (includes reservoirs, rivers and lakes).
- Settlements: all developed land, including transport infrastructure and human settlements of any size.
- Other: bare soil, rock, ice, and all unmanaged land areas that don’t fall into the other categories.
Australia has a land area of 769 million hectares. Every piece of it is allocated to one of these sub-categories.
The charts below are sourced from Australia's National Inventory Report 2022 Volume 1. (Don’t miss the tiny Green wedge in between the Lime and Teal).
Step 2
Monitor the land over time and analyse for changes. It will either stay in the same category or move to a different one.
Below is the detailed report on Land Use by sub-sector in Australia’s recent update.
See how the categories in the legend refer to land remaining the same or changing?
(Note: 'Other land' refers to Grassland, Settlements and Wetlands).
Step 3
Next, use the categories to calculate how much carbon would be released or sequestered on that land.
This is done using default values or more sophisticated, localised models. While the latter might sound good, it can also lead to huge inconsistencies in methodologies. We’ll look at that another time.
The point is, changes in Land Use categories lead to changes in carbon emissions and removals.
Back To The Big Picture
Let’s go back to our original question.
The top-level metric for Land Use emissions was -88.4 Mt CO2-e for the year to March 2024.
That means that across the 6 sub-categories, Land Use was a net sink, absorbing 88.4 Mt CO2-e in the year.
(To give that context, Australia’s total transport emissions were 98.6 Mt CO2-e in the same period).
So, why haven’t Land Use emissions changed in 2.5 years?
The DCCEEW* has addressed this, basically saying it’s too much work to do quarterly reports, so the estimates from the annual updates get rolled over. e most recent annual report — and that data is 2.5 years old.
One More Thing
You know how we just spent five minutes talking about how Land Use emissions haven’t changed?
Well, they have changed — but in a different way.
Even though the trend for the last 2.5 years has been flat, the figure that trend sits on has been retrospectively revised.
We’ll look at that issue — Land Use revisions — next week.