You may have heard that after revisions to land-use change emissions, total global CO₂ emissions are approximately flat over the last decade (black line).
But, how much do we revise carbon budget components each year?
Let's have a look...
1/
Fossil CO₂ emissions are revised each year, particularly the last decades. We update data & improve methods. Chinese data has had major revisions & cement was completely revised in 2018, plus lots of smaller improvements.
More details: zenodo.org/record/5569235
2/
Land-use change (LUC) emissions are much more uncertain:
* 2014-2015: one bookkeeping model used
* 2016-2019: two bookkeeping models used
* 2020-2021: three bookkeeping models used
* 2021: major update of land-use forcing (change) datasets
Uncertainty remains high! Beware!
3/
The land sink (outside of areas considered LUC) is mainly due to CO₂ fertilization & climate effects:
* 2014-2016: estimated as a residual from the budget balance
* 2017-2021: estimated independently using models (leading to a budget imbalance, see below)
4/
The ocean estimates show more revisions as methods have changed:
* 2014-2016: models were scaled to match an estimate of the ocean sink in the 1990s
* 2017-2020: average of models
* 2021: average of models & data products (which have a greater sink
5/
A side note: From 2020 we have included a CO₂ sink from cement carbonation, where CO₂ is slowly taken up over time in concrete structures.
An open question is whether to aggregate the sink to fossil emissions or keep separated.
6/
The atmospheric CO₂ concentration is the best constrained & revisions are small & usually the final year.
The carbon budget should close due to mass balance:
Fossil + LUC = Sinks (land + ocean) + atmospheric increase.
But, we measure these all independently...
7/
Because we estimate each budget component independently, & the budget must close, we get a 'budget imbalance' (BIM), which is how far we were from closing the budget.
Our goal is to get this as close to zero as possible... We started doing this in 2017.
8/
This year there was a major revision in LUC (lower) & the ocean sink method was changed (bigger sink), compounding the BIM.
We now have a larger drift in the BIM in the last decade & now our task is to understand why...
Read more: essd.copernicus.org/preprints/essd…
9/9
A small error spotted. I did not have the latest version of the 2020 dataset loaded, affecting mainly the land sink and BIM...
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