In a paper published today in Environmental Research Letters, Manon Berger, Lester Kwiatkowski, Laurent Bopp, and I used a high-resolution ocean biogeochemical model (NEMO-PISCES) to examine the efficacy and efficiency of #kelp-based ocean CO₂ removal (#CDR). 1/n
https://iopscience.iop.org/article/10.1088/1748-9326/acb06e/meta
We grew kelp in all the Exclusive Economic Zones (EEZs) where kelp would grow — regions free of seasonal sea ice; mean sea surface temperature between 0 and 35°C; average nitrogen to phosphorus ratio between 4:1 and 80:1 in the upper 100 m — and harvested 100% of the kelp (this is an unrealistic scenario so it represents an upper limit of kelp-based CDR).
We found that averaged globally, only 58% of CO₂ removed was replaced by atmospheric CO₂. We call this CDR efficiency. 2/n
The CDR efficiency is widely variable at regional scales — ranging from -14% to 85% — meaning that growing kelp for CDR can even result in a reduction of the ocean carbon sink in some regions.
Only 0.3 out of 73 million km² suitable for kelp growth have a CDR efficiency greater than 80%, highlighting the importance of choosing the right location; eastern boundary upwelling systems, the Northeast Pacific, and the Southern Ocean are potentially promising regions. 3/n
David Ho