CDR under the Emissions|CO2|* : is it clear enough where to report removals from different methods ?

[jkikstra]

In the first round of ScenarioMIP submissions (for those involved, link), there was some confusion over where negative emissions should be reported under the CO2 variables.
The AIM team had reported some negative emissions under Emissions|Other, while other teams tend to report it only* under Emissions|CO2|Energy and Industrial Processes

This is not my expertise, so feel free to point towards clear descriptions if they already exist. I just looked at the template.

If we split up Emissions|CO2|Energy and Industrial Processes, looking at 2100 of the "Low Overshoot" scenarios, most modelling teams report most negative emissions under Emissions|CO2|Energy, with only GCAM reporting net-negative emissions also under Emissions|CO2|Industrial Processes (in addition to being net-negative in Emissions|CO2|Energy).
There is now also the new variable Emissions|CO2|Capture and Removal, which wasn't used by any model in the first round. And also Emissions|CO2|Product Use, where I don't think there would be CDR, but I'm not sure about either the modelling of it or the guidance on reporting CDR (CCS yes, but CDR I don't think so).

(Some of) the definitions are now:

variable	description
Emissions|CO2	Emissions of fossil carbon dioxide (CO2)
Emissions|CO2|AFOLU	Emissions of fossil carbon dioxide (CO2) from agriculture, forestry and other land use (IPCC category 3)
Emissions|CO2|Capture and Removal	Capture and removal of atmospheric fossil carbon dioxide (CO2) using net-negative technologies that are not directly linked to an emissions source, e.g., direct air capture (DAC) or enhanced weathering
Emissions|CO2|Energy	Emissions of fossil carbon dioxide (CO2) from energy use, including fugitive emissions from fuels (IPCC category 1A, 1B)
Emissions|CO2|Energy and Industrial Processes	Emissions of fossil carbon dioxide (CO2) from energy use in supply and demand sectors (IPCC category 1A, 1B) and from industrial processes (IPCC categories 2A, B, C, E), including emissions from international bunker fuels, net of negative emissions from bioenergy with CCS (BECCS) in these sectors
Emissions|CO2|Industrial Processes	Emissions of fossil carbon dioxide (CO2) from industrial processes (IPCC categories 2A, B, C, E), net of negative emissions using CCS
Emissions|CO2|Other	Emissions of fossil carbon dioxide (CO2) from other sources
Emissions|CO2|Product Use	Emissions of fossil carbon dioxide (CO2) from product use (IPCC category 2D, 2F and 2G)
Emissions|CO2|Waste	Emissions of fossil carbon dioxide (CO2) from waste (IPCC category 6)

I note that there's:

• no explicit mention of BECCS under Emissions|CO2|Energy
• potential confusion on where to report novel CDR methods like DACCS, EW, OAE (and probably others); should they be under "Energy and Industrial Processes", or not? And under which subcomponent?

The complete, up-to-date description of the emissions variables in the current variable template are here:
https://github.com/IAMconsortium/common-definitions/blob/main/definitions/variable/emissions/emissions.yaml

---

*"Only" here meaning, out of the (presumed additive, and comprehensive) summation set "Emissions|CO2" = "Emissions|CO2|AFOLU" + "Emissions|CO2|Energy and Industrial Processes" + "Emissions|CO2|Other" + "Emissions|CO2|Waste"

[shinichirofujimoriKU]

The description on Emissions|CO2|AFOLU, which is "Emissions of fossil carbon dioxide (CO2) from agriculture, forestry and other land use (IPCC category 3)", is a bit confusing since it is unclear whether only "fossil CO2" is considered or not. I would revise as below.
"Emissions of fossil carbon dioxide (CO2) from agriculture and forestry sectors, and CO2 from land use and land use changes (IPCC category 3)"
Also, we should specify where we should report soil carbon and biochar. I think straightforward classification is Emissions|CO2|AFOLU. However, if the harmonization process uses this AFOLU, then those CDRs could be influenced by the harmonizatoin. So, there are two options. One is including them into AFOLU but have subcategory that specificies these CDRs. In the harmonization process you could deal with them appropriately so that the hamonization only applied to AFOLU emissions exluding biochar and soil carbon. The second option is assign soil carbon and biochar under "Emissions|CO2|Capture and Removal". It is I think easy for harmonization but from the IPCC category and inventory perspective, it may cause confusion. So my proposal is going first option but I am open.

[danielhuppmann]

The description on Emissions|CO2|AFOLU, which is "Emissions of fossil carbon dioxide (CO2) from agriculture, forestry and other land use (IPCC category 3)", is a bit confusing since it is unclear whether only "fossil CO2" is considered or not.

This was a legacy-issue from NAVIGTE and was fixed in #162. CO2 emission variables clearly refer to all emissions, fossil and non-fossil.

[jkikstra]

Also, we should specify where we should report soil carbon and biochar. I think straightforward classification is Emissions|CO2|AFOLU. However, if the harmonization process uses this AFOLU, then those CDRs could be influenced by the harmonizatoin. So, there are two options. One is including them into AFOLU but have subcategory that specificies these CDRs. In the harmonization process you could deal with them appropriately so that the hamonization only applied to AFOLU emissions exluding biochar and soil carbon. The second option is assign soil carbon and biochar under "Emissions|CO2|Capture and Removal". It is I think easy for harmonization but from the IPCC category and inventory perspective, it may cause confusion. So my proposal is going first option but I am open.

Thanks for your input @shinichirofujimoriKU; if it is clear that it should fall under AFOLU (I didn't yet manage to find/get clear guidance) then I agree we should add it there.

For hamonization, if we would have a constant-based offset (as in AR6), it would make no difference to harmonization (with biochar at 0.25 MtCO2/yr currently; not sure how much soil carbon). But with a multiplicative offset, it could indeed matter.

[gidden]

One is including them into AFOLU but have subcategory that specificies these CDRs.

This would be my preferred approach. In the RESCUE project, we split out CDR methods from their "parent" category (so, e.g., DACCS is treated separately from Emissions|CO2|Energy), and would suggest we do the same here. The outcome would be that we have separate emissions (removal) trajectories for AFOLU, biochar, EW, etc. This is also important for the ultimate use in CMIP7, where each CDR method will have different land and removal spatial patterns.

[jkikstra]

So, for being able to split out each CDR method, I assume/hope we can rely on modelling teams reporting CDR by method here: https://github.com/IAMconsortium/common-definitions/blob/main/definitions/variable/emissions/tag_carbon-removal.yaml

But we can update the descriptions for a bit more clarity.
In bold all relevant parts (and some additional updates, following IPCC guidelines).
How is this?

variable	description
Emissions|CO2	Emissions of carbon dioxide (CO2), net of emissions to the atmosphere and carbon dioxide removal
Emissions|CO2|AFOLU	Emissions of carbon dioxide (CO2) from agriculture, forestry and other land use (IPCC category 3), reporting the net of emissions including land-use methods that do not use CCS such as soil carbon sequestration, biochar, forestry, peatland and wetland restoration, and biomass burial
Emissions|CO2|Other Capture and Removal	Capture and removal of atmospheric fossil carbon dioxide (CO2) using other net-negative technologies that are not reported under other variables as they are not directly linked to an emissions source, including direct air carbon capture and storage (DACCS) or enhanced weathering (EW), as well as durable wood products in building elements, mineral products, ocean fertilization, biomass sinking, ocean alkalinity enhancement (OAE), direct ocean capture, and other methods
Emissions|CO2|Energy	Emissions of carbon dioxide (CO2) from energy use, including fugitive emissions from fuels (IPCC category 1A (except manufacturing 1A2 and other unspecified 1A5), 1B), reporting the net of energy emissions and carbon capture and removal using BECCS and other forms of CCS on energy forms such Natural Gas, Oil, and Coal, as well as bio-oil storage
Emissions|CO2|Industrial Processes	Emissions of carbon dioxide (CO2) from industrial processes (IPCC categories 1A2, 1A5, 2A, B, C, E), net of negative emissions using CCS such as from Cement Production
Emissions|CO2|Other	Emissions of carbon dioxide (CO2) from other sources (IPCC category 7, including fossil fuel fires)
Emissions|CO2|Product Use	Emissions of carbon dioxide (CO2) from product use (IPCC category 2D, 2F and 2G)
Emissions|CO2|Waste	Emissions of carbon dioxide (CO2) from waste (IPCC category 6)

N.B. I now added "Fossil Fuel Fires" explicitly under "Other" (see discussions under #165), which would be a change from last time (but nobody reported the variable before anyway).

I tried adding all current options from here, but am not so sure about all, e.g. 'Durable Wood Products'?

N.B. EDITED TO CHANGE to "Other Capture and Removal" AND move "fossil fuel fires" to "Other".

[jkikstra]

Also, should "Emissions|CO2|Capture and Removal" be changed to "Emissions|CO2|Other Capture and Removal", because there is also lots of CDR in other categories?

(just adding #165 as these two issues are very close to each other)

[jayfuhrman]

I concur on both name change to "Emissions|CO2|Other Capture and Removal" as well as most of the suggested definitions in the table above. @gidden @danielhuppmann does this make sense on your end?

One minor issue is regarding this one:

Emissions|CO2|Industrial Processes | Emissions of carbon dioxide (CO2) from industrial processes (IPCC categories 1A2, 1A5, 2A, B, C, E), net of negative emissions using CCS such as from Cement Production

For cement production only the limestone calcination emissions should be reported under Industrial Processes, correct? Any negative emissions from e.g., BECCS for process heat should be reported under Emissions|CO2|Energy. Therefore, I think we should remove the reference to negative emissions from CCS here

[znichollscr]

Hi all, thanks for the comments and work on this thread. I'll add specific suggestions in #188. A general/principle thought (which is basically just a summary of the above, but the summary might help).

In terms of getting this right in a climate model (simple or ESM, I don't think it matters), what you want to know is where did the carbon start and where did it go. I think the proposal by @jkikstra mostly gets us there, but there is the question of whether we want to refine the nomenclature to really capture this, or whether we leave it mostly as is and just clarify things as best we can and live with some of the imperfect parts (which is also ok, getting this really perfect is hard and we can live with some imperfection).

Some specific examples (maybe better discussed in #188)

• DACCS
  • this is obviously a removal from the atmosphere into some permanent storage.
• Afforestation
  • this is obviously a removal from the atmosphere into the land pool.
• BECCS
  • this is effectively a removal from the atmosphere to some storage, but it goes via the land pool. So, the question is, should we split BECCS into its two steps: 1) the removal from growing the plants (where CO2 moves from atmosphere to land) and 2) the removal from the capturing the carbon (where CO2 moves from land to permanent storage). For models that didn't want to report this split, we could just assume it goes straight from atmosphere to storage on the timescale of the reporting timestep (not perfect, but also not a step backwards).
• enhanced weathering
  • removal from the atmosphere into permanent storage? (Or maybe it's into the land pool, but weathering sounds like rocks to me...)
• ocean fertilization
  • removal from the atmosphere into the ocean
• direct ocean capture
  • removal from the ocean pool into storage? (Direct air capture is removal from the air into storage, so I think this definition makes sense but maybe it's something completely different (in which case I would change the name))