Direct cooling effect of artificial upwelling dominates over its marine carbon dioxide removal potential

Abstract Artificial upwelling (AU) is investigated as a marine carbon dioxide removal (CDR) method with a strong focus on its potential impact on Earth’s carbon cycle, in particular enhanced air-sea CO 2 flux. The overarching goal of marine CDR methods is to contribute to offsetting remaining CO 2 emissions as a means to stabilize global mean surface air temperature (SAT). However, AU also directly affects ocean heat uptake (OHU) through the upwelling of cold ocean interior water to the surface and the simultaneous backflow of warm surface water into the ocean interior. In this study, we challenge the carbon centered perception of AU. We simulate large-scale AU in an Earth system model of intermediate complexity between the years 2025 and 2100 with and without its direct impact on OHU under low, medium and high future CO 2 emission scenarios. Thus, we can quantify the individual contributions of AU-induced carbon and heat effects to changes in global mean SAT. We find the direct impact of AU on OHU to be key for a significant reduction in global mean SAT and the atmosphere’s CO 2 concentration under all simulated future CO 2 emission pathways. If AU directly impacts OHU, we can attribute only 17% under RCP 2.6 to 27% under RCP 8.5 of the reduction in global mean SAT (−0.17 to −0.27 °C) until the end of the century to the reduction in the atmosphere’s CO 2 inventory (−5.9 to −31.2 Pg C). Our findings lead us to challenge the classical view of AU as primarily a marine CDR method. Instead, we propose to consider AU as a method to enhance OHU and thereby reduce global mean SAT, with secondary effects on the carbon cycle that result in some CDR.