As we count down to the 4th International Conference on Carbon Dioxide Removal in Milano, we are hosting a series of deep-dive discussions on the research that will be shaping our sessions this June! 
This study evaluates the climate response and efficiency of terrestrial and marine CDR by accounting for complex Earth-system feedbacks during a transition to zero and net-negative emissions. 
It serves as a vital foundation for the next phase of the Carbon Dioxide Removal Model Intercomparison Project (CDRMIP), helping to clarify how much CDR can truly compensate for residual emissions in a shifting climate state! 
Full Abstract: Terrestrial and marine CDR under net-zero conditions: Implications for CDRMIP2
Authors: Makcim De Sisto, Justus Perschon, Giang Tran, Nadine Mengis
CDR complements emission reductions during deep decarbonisation, enables net-zero emissions by offsetting residual emissions from hard-to-abate sectors, and allows for net-negative emissions to reverse carbon-budget overshoot beyond 1.5 °C or 2 °C targets. Despite its central role in future ambitious mitigation scenarios, there remains limited knowledge on the impacts and efficacy of different CDR approaches, since most existing assessments rely on simplified representations or integrated assessment models that only partially capture Earth-system feedbacks and climate-state dependence.
To address this uncertainty, the Carbon Dioxide Removal Model Intercomparison Project (CDRMIP) was initiated and endorsed within CMIP6, with a new phase currently under development for CMIP7. As part of the preparation for this next phase, this study builds on an emission-driven simulation following the esmflat-10-zec scenario, with constant CO₂ emissions of 10 PgC yr⁻¹ applied for 100 years, followed by a zero-emissions commitment (ZEC) phase of an additional 100 years. The resulting atmospheric CO₂ concentration trajectory is then prescribed in a suite of concentration-driven experimental simulations that include various large-scale, activity-driven CDR implementations, including reforestation and ocean alkalinity enhancement.
Diagnosed emissions are used to quantify the amount of residual emissions that CDR can compensate for during the net-zero emissions phase, following the first 100 years of simulation. Together, these simulations are designed to quantify the efficiency of activity-driven terrestrial and marine CDR measures, assess the CDR’s carbon and climate responses, the efficiency’s sensitivity to the background state, and inform the extent to which CDR can compensate for residual emissions.
What do you think is the biggest challenge in predicting how the Earth system reacts to large-scale CDR?