As we count down to the 4th International Conference on Carbon Dioxide Removal in Milano, we are hosting a series of discussions on the research that will be shaping our sessions this June! 
This research evaluates socio-economically consistent deployment scenarios 
of Ocean Alkalinity Enhancement using coupled Earth System Model simulations, moving beyond idealised assumptions to an “activity-driven” framework 
where alkalinity is explicitly added to the ocean. 
The authors show that integrated assessment model estimates of OAE efficiency are broadly reliable, while also highlighting how OAE deployment could successfully reduce ocean acidification but produce regionally variable environmental impacts and deep monitoring challenges 
due to intense natural ocean variability! 
Full Abstract: Investigating ocean alkalinity enhancement in activity-driven Earth system model simulations of deep mitigation scenarios
Authors: Jörg Schwinger, Leon Merfort, Nico Bauer, Nadine Goris, Timothée Bourgeois
So far, Ocean alkalinity enhancement (OAE) has been mostly investigated using model simulations of idealized deployment, but socio-economically consistent scenarios of OAE deployment have been missing. Recently, OAE has been added as a CDR option in the Integrated Assessment Model REMIND-MAgPIE, and deep mitigation scenarios that include coastal ocean liming have been created. Here, we present Earth System Model (ESM) simulations of these scenarios, where OAE is simulated in an ‘activity-driven’ fashion. In activity-driven mode, alkalinity is added to the surface ocean of the ESM, rather than prescribing the carbon removal estimated by the IAM as a negative emission flux.
In addition, baseline simulations without CDR have been performed to estimate the carbon removal efficiency of OAE in the ESM. Thereby, we can use the ESM simulations to confirm that the relatively simple IAM assumptions regarding the CO2 sequestration efficiency of OAE are reasonably accurate, and we recommend principles for the IAM-ESM data flow related to OAE. We further investigate monitoring aspects, specifically the emergence of OAE signals in these scenarios from the background of natural variability in commonly observed ocean variables. We quantify environmental co-benefits, i.e. the reduction of surface ocean acidification, and we identify regions where OAE leads to the exceedance of environmental thresholds in our ESM simulations.
How should we balance the global benefits of fighting climate change against the local environmental risks of modifying our oceans? 
