Outcome Advisory Board meeting:�Key research questions/themes

Type #1 - Asymmetry in Earth system responses to emissions vs removal pulses

Type #2 - Activity-driven CDR implementations of IAM-developed scenarios

Type #3 - CO₂ removal effectiveness of individual CDR measures for different climates

Type #4 - CDR in overshoots with and without SRM (not pursuing in CDRMIP)

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Asymmetry in Earth system responses

to emissions vs removal pulses

Tier 1:

• Investigate response of the climate system to large pulse with additions and removals of CO₂
• Disentangle the contribution from the transient disequilibrium
• Provide ESM simulations for the calibration of simple climate models (emulators)

Tier 2:

• Direct ocean vs air removal experiment
• Branching from different climate states

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Tier 1:

• building on C4MIP fast-track esm-flat10-zec
• CDRMIP experiment:
1. 100 years of flat10 (1000PgC emitted) followed by a removal pulse of 500PgC (esm-flat10-rmv500)
2. 100 years of flat10 (1000PgC emitted) followed by a emissions pulse of 500PgC (esm-flat10-emit500)

Asymmetry in Earth system responses

to emissions vs removal pulses

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Tier 2

• building on C4MIP esm-flat10-zec
• CDRMIP experiment:
1. 100 years of flat10 (1000PgC emitted) followed by a removal of 500PgC from the surface ocean (esm-cdrmip-rmv500-actDOR)
2. repeat the emissions and removal pulses for different cumulative carbon emissions budgets (e.g., 750/1500/2000) (esm-cdrmip-emit/rmv500_1000/_750/_2000)

Asymmetry in Earth system responses

to emissions vs removal pulses

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Activity-driven CDR implementations of IAM-developed scenarios

Tier 1:

• Evaluate impacts and uncertainties of resolving activity-driven BECCS in policy-relevant ambitious mitigation scenarios (i.e. ScenarioMIP)
• Quantify CDR mismatch between IAMs & ESMs in a multi-model context
• What is the impact of climate change on yields and BECCS effectiveness?

Tier 2:

• Portfolio implementations of terrestrial CDR and marine CDR

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Activity-driven BECCS in Scenario-MIP experiment

Tier 1 (ScenarioMIP-LN-actBECCS):

• building on ScenarioMIP low to negative (LN) scenario
• CDRMIP experiment:
• emissions-driven & activity-driven BECCS in ScenarioMIP-LN scenario
• activity-driven BECCS implementations in ESM based on energy crops
• yields from BE crops to be stored in a permanent carbon pool (incl. loss terms)
• omit net-negative BECCS emissions from ScenarioMIP-LN in the ESM emission forcing

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Activity-driven OAE in IAM scenario

Tier 2 (RESCUE-2deg-actOAE or ScenarioMIP-LN-REMIND-actOAE):

• expanding the IAM scenario with Ocean Alkalinity Enhancement (OAE)

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• CDRMIP experiments:
1. emissions-driven IAM scenario with activity-driven OAE �(including gross emissions from calcification and spatially �resolved OAE implementation)
2. emissions-driven IAM scenario no-OAE baseline (omit OAE implementation including positive emissions related to the process)
3. concentration-driven no-OAE baseline (CO₂ concentrations �from 1, no OAE implementation)

CDR effectiveness of individual measures for different climates

Tier 1:

• Quantify CDR effectiveness of a given activity-driven CDR implementation under net-zero
• Assess the Earth system responses (incl. biogeophysical) to the CDR implementation
• Bonus: investigate the partitioning of ocean and land carbon sinks under land-use vs no-land-use flat10 experiments

Tier 2:

• further selected CDR options
• test CDR effectiveness under increasing/stable/decreasing atmospheric CO₂

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CDR removal effectiveness under net-zero

Tier 1 (flat10-LUC-zec-act**CDR**, e.g. for A/R):

• all experiments will be concentration-driven prescribed from esm-flat10-zec
• CDRMIP experiment:
1. apply LUH3 from last 100 years of historical land-use

to flat10 and constant thereafter (flat10-LUC & flat10-LUC-zec)

• during zero emissions phase implement global reforestation of all-non-habitated areas �(i.e. all deforested areas)

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CDR removal effectiveness experiments

Tier 1:

• concentration-driven prescribed from esm-flat10-zec
• proposed CDRMIP experiments:
• global deforestation experiment (details see slide #10) (flat10-LUC-zec-actARF-global)
• annually repeating BECCS implementation at maximum scale in most-ambitious BECCS scenario (AIM) (flat10-LUC-zec-actBECCS)
• annually repeating coastal, uniform ocean alkalinity addition at the max scale found in the RESCUE scenarios (flat10-LUC-zec-actOAE)

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CDR removal effectiveness experiments

Tier 2:

• concentration-driven prescribed from esm-flat10-zec
• proposed CDRMIP experiments:
• following LUH wrt to forest from ScenarioMIP

(flat10-LUC-zec-actARF-Scenario)

• annually repeating macroalgae open-ocean mariculture and sinking in defined areas at the max scale

(flat10-LUC-zec-actMOS)

• annually repeating enhanced rock weathering at max theoretical rates (flat10-LUC-zec-actERW)
• annually repeating coastal uniform direct ocean removal at max theoretical rates (flat10-LUC-zec-actDOR)

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esm-flat10-zec

flat10-LUC-zec-ARscen

flat10-LUC-zec-MOS�flat10-LUC-zec-ERW

flat10-LUC-zec-DOR

CDR removal effectiveness under varying �background climate states

Tier 2:

• based on C4MIP esm-flat10
• CDRMIP experiment:
• assess CDR effectiveness under increasing atmospheric CO₂ concentrations: activity-driven CDR experiments with the atmospheric CO₂ concentrations from esm-flat10 (flat10-LUC-act**CDR**)
• assess CDR effectiveness under stable atmospheric CO₂ concentrations: activity-driven CDR experiments using constant CO₂ following esm-flat10 for 100 years (flat10-LUC-stableCO2-act**CDR**)
• diagnose emissions in a noCDR experiment for comparison

esm-flat10-zec

esm-flat10

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