Additional CDR Variables

[gidden]

For our SoCDR work, the MESSAGE model would like to explicitly report Biomass Burial and non-land-based Biochar applications. It sounds like this is also needed for UPTAKE. The current variable definitions do not support this. Further, there seems to be an inconsistency in the Carbon Removal Tree where the definition logic is Carbon Removal | {Where CO₂ is Stored or applied} | {Method} - but ERW in particular does not follow this (it is just Carbon Removal|ERW)

My suggestion would be to expand the Other category more explicitly, including:

• Carbon Removal|Land Use|ERW (erw on agricultural lands to enhance crop yields) [this is open for discussion, we can just use the Other version below if this is confusing/not helpful]
• Carbon Removal|Other|ERW (non-land-based ERW)
• Carbon Removal|Other|Biomass Burial
• Carbon Removal|Other|Biochar (non-land-based biochar)

@strefler @jayfuhrman @ywpratama @danielhuppmann @CandeBergero

[danielhuppmann]

Maybe naive comment, but as "not-a-CDR-expert", I find it strange to separate EWR into two subcategories when a lot of public discourse treats it as one.

I'm also skeptical of grouping several diverse (and potentially substantial) methods into an "Other" category.

[ywpratama]

In addition to those variables, I would also suggest to separate Direct Ocean Capture, which currently falls under Ocean (i.e., Carbon Removal|Ocean|Direct Ocean Capture) into two variables:

• Carbon Removal|Ocean|Direct Ocean Capture and
• Carbon Removal|Geological Storage|Direct Ocean Capture

[gidden]

Maybe naive comment, but as "not-a-CDR-expert", I find it strange to separate EWR into two subcategories when a lot of public discourse treats it as one.

I'm also skeptical of grouping several diverse (and potentially substantial) methods into an "Other" category.

There are different ways to deploy ERW. The most discussed is on agricultural fields. But there is also discussion of riverine ERW, etc. So it goes back to how we want to define the variables (is it by application like on land, etc.). Water-based ERW would not fit in "Carbon Removal|Land Use".

[gidden]

Note this issue is related with #403

[strefler]

We've had this discussion last year around the IAMC, and decided to move biochar and enhanced weathering out of the "land" category. I also don't see the need for grouping them into the "other" category, I think that one should not have subcategories, but rather be reserved for anything that is not explicitly included. So based on what we discussed, I suggest to have
Carbon Removal|Enhanced Weathering
Carbon Removal|Biochar
Carbon Removal|Biomass Burial.

[strefler]

In addition to those variables, I would also suggest to separate Direct Ocean Capture, which currently falls under Ocean (i.e., Carbon Removal|Ocean|Direct Ocean Capture) into two variables:

* `Carbon Removal|Ocean|Direct Ocean Capture` and

* `Carbon Removal|Geological Storage|Direct Ocean Capture`

As these subcategories add up, every method should go only in one. As the carbon removal happens in the ocean, I would only include Carbon Removal|Ocean|Direct Ocean Capture, analogous to how we report OAE

[gidden]

DOC also has a gross/net issue which we should discuss how to address. Namely, for every 1 unit of CO2 removed by DOC, current modelling studies suggest roughly 0.6-0.7 units of CO2 is taken back up by the ocean. So there is an efficiency loss not captured by only accounting for the quantity removed (and geologically stored).

I agree, there should only be one variable. But if we are being consistent with the current tree (based on storage location over activity location), then DOC should be in Geological Storage. The way I read the current tree is that OAE is in ocean because the carbon stored is ultimately in the ocean (i.e. through DIC and downwelling).