added gross removals in emissions

[flohump]

This PR adds two variables

• Gross Removals|CO2
• Gross Removals|CO2|AFOLU

Together with Gross Emissions|CO2 and Gross Emissions|CO2|AFOLU this allows to understand how net emissions emerge.

This PR is linked to issues #224 and #222

For AFOLU, we could add more subcategories.

[danielhuppmann]

Looks good, may have some suggestions for more concise docs and validation-syntax (net emissions = gross emissions plus gross removals) in a follow-up PR.

[strefler]

Ahhh, I think this was a bit fast! I would much rather have (net) CDR = gross CDR + CDR-related emissions (e.g. from calcination process for OAE). Not sure if that also works for AFOLU, but then net CO2 = gross CO2 + net CDR, not gross CDR

[flohump]

Ahhh, I think this was a bit fast! I would much rather have (net) CDR = gross CDR + CDR-related emissions (e.g. from calcination process for OAE). Not sure if that also works for AFOLU, but then net CO2 = gross CO2 + net CDR, not gross CDR

This PR is about gross removals and not CDR specifically. Of course CDR (as a negative term) is a part of gross removals. But gross removals especially in AFOLU / Land are much broader than intentional CDR.
By adding gross removal variables, this becomes more transparent and improves clarity.

Side note: Your sugested calcuation (net) CDR = gross CDR + CDR-related emissions does not work because CDR is defined as positive.

[merfort]

So in order for "Emissions|CO2" = "Gross Emissions|CO2" + "Gross Removals|CO2" to be true, that would mean that all positive emissions (such as the emissions from calcination for OAE) would need to be part of Gross Emissions|CO2, right?

[strefler]

Ahhh, I think this was a bit fast! I would much rather have (net) CDR = gross CDR + CDR-related emissions (e.g. from calcination process for OAE). Not sure if that also works for AFOLU, but then net CO2 = gross CO2 + net CDR, not gross CDR

This PR is about gross removals and not CDR specifically. Of course CDR (as a negative term) is a part of gross removals. But gross removals especially in AFOLU / Land are much broader than intentional CDR. By adding gross removal variables, this becomes more transparent and improves clarity.

I fully support having gross removals as a variable, especially for AFOLU. I'm just questioning the naming. I'm not sure a new category "Gross removals" is the right way forward, though I have to admit that I haven't thought it through yet. Maybe a disaggregation as part of Emissions|CO2|AFOLU could work, but I'm not sure. I think we would have to discuss this in the emissions subgroup.

[flohump]

Gross removals is in line with the terminology used in GCB 2024
https://essd.copernicus.org/preprints/essd-2024-519/

Let me know if you need me in the discussions with @IAMconsortium/common-definitions-emissions