GALCIT Colloquium

Since the preindustrial era, the ocean has removed about 40% of fossil CO2 from the atmosphere, and it will eventually absorb at least 80% of human CO2 emissions. To manage the climate system, we must manage the global carbon cycle, and the ocean plays a critical role in this.

At the global scale, three independent approaches allow for quantification of ocean carbon sink to within ~15% uncertainty. I show with theory, observations, and models that strong forcing from the variable growth rate of atmospheric pCO2 drives about half of the globally integrated interannual variability. Climate processes, both internal and externally-forced by Mt Pinatubo, have driven the other half of the global variability in recent decades.

Given the outsized role of the ocean in mitigating anthropogenic CO2 emissions, there has been a recent boom of proposed engineering efforts to remove additional carbon from the ocean. For a marine Carbon Dioxide Removal (mCDR) project to be demonstrated successful, the carbon it sequesters in the ocean must be "additional" to what would have occurred without intervention. This is a challenge for which current ocean carbon sink quantification approaches are insufficient. We use machine learning with sparse surface ocean observations to assess current ocean models' biases and to identify optimal observing strategies.