ALBERT

Description: Given the clear need to inform societal decision-making on the role marine Carbon Dioxide Removal (mCDR) can play in solving the climate crisis, it is imperative that researchers begin to answer questions about its effectiveness and impacts. Yet overly hasty deployment of new ocean-based climate interventions risks harm to communities and ecosystems and could jeopardize public perception of the field as a whole. In addition, the harms, risks and benefits of mCDR efforts are unlikely to be evenly distributed. Unabated, climate change could have a devastating impact on global ecosystems and human populations, and the impacts of mCDR should be contemplated in this context. This Code of Conduct exclusively applies to mCDR research and does not attempt to put any affiliated risk in the context of the risk of delaying climate action. Its purpose is to ensure that the impacts of mCDR research activities themselves are adequately understood and accounted for as they progress. It provides a roadmap of processes, procedures, and activities that project leads should follow to ensure that decisions regarding whether, when, where, and how to conduct mCDR research are informed by relevant ethical, scientific, economic, environmental, and regulatory considerations.

Description: Carbon dioxide removal (CDR) is discussed for offsetting residual greenhouse gas emissions or even reversing climate change. All emissions scenarios of the Intergovernmental Panel on Climate Change that meet the ‘well below 2 °C’ warming target of the Paris Agreement include CDR. Ocean alkalinity enhancement (OAE) may be one possible CDR where the carbon uptake of the ocean is increased by artificial alkalinity addition. Here, we investigate the effect of OAE on modelled carbon reservoirs and fluxes in two observationally-constrained large perturbed parameter ensembles. OAE is assumed to be technically successful and deployed as an additional CDR in the SSP5-3.4 temperature overshoot scenario. Tradeoffs involving feedbacks with atmospheric CO 2 result in a low efficiency of an alkalinity-driven atmospheric CO 2 reduction of −0.35 [−0.37 to −0.33] mol C per mol alkalinity addition (skill-weighted mean and 68% c.i.). The realized atmospheric CO 2 reduction, and correspondingly the efficiency, is more than two times smaller than the direct alkalinity-driven enhancement of ocean uptake. The alkalinity-driven ocean carbon uptake is partly offset by the release of carbon from the land biosphere and a reduced ocean carbon sink in response to lowered atmospheric CO 2 under OAE. In a second step we use the Bern3D-LPX model in CO 2 peak-decline simulations to address hysteresis and temporal lags of surface air temperature change (ΔSAT) in an idealized scenario where ΔSAT increases to ~2 °C and then declines to ~1.5 °C as result of CDR. ΔSAT lags the decline in CO 2 -forcing by 18 [14–22] years, depending close to linearly on the equilibrium climate sensitivity of the respective ensemble member. These tradeoffs and lags are an inherent feature of the Earth system response to changes in atmospheric CO 2 and will therefore be equally important for other CDR methods.