What do you mean, not sustainable? Cetacean populations are still well below pre-whaling numbers and are very sustainable. Not only they capture and store vast quantities of carbon in their bodies (and when they die and sink, they take all this stored carbon with them), but they are the only source of important nutrients that are required for the phytoplankton to thrive. Phytoplankton is a super potent and effective carbon capturing system as well.So not only cetaceans help carbon sequestering directly, they also help indirectly by helping phytoplankton to grow. This is a perfect system, it is safe and it is effective, unlike dimming the sunlight and changing the atmosphere.
I mean that unless you're increasing the amount of plankton in the ocean by hundreds of gigatons you're not making a dent compared to the amount currently in the air, let alone what's still being made.
How much CO2 do you think your method can capture?
To achieve net-zero emissions by 2050 we will need to sequester additional 1859 million tons of CO2.(SOURCE: edf.org).
Whales can sequester carbon in 2 ways. First, they store carbon in their bodies. When they die and sink, they take all this carbon with them. One blue whale can directly store 12 tons of CO2, a humpback can store 5.5 tons, a fin whale can store 6.7 tons, etc. In terms of populations, we are nowhere near pre-whaling, stable population numbers. We had 303500 blue whales (now 5400), 307000 humpback ( now 66000), 246000 sei whales (now 49100). Increasing number of whales directly will increase annual carbon capture. Second, whales help to sequester carbon because they are the only organisms on this planet that can fertilize phytoplankton. Only whale transport can bring iron to the surface where the phytoplankton blooms, and in addition to iron, whales also bring a number of other crucial nutrients that are in short supply where phytoplankton lives. Thus by increasing the number of whales (and not losing existing whales via strandings) we can contribute to phytoplankton growth, leading to more carbon capture and sequestration. Right now phytoplankton alone captures 37 billion tons of CO3 yearly. So if we even increase phytoplankton numbers slightly, it could result in large absolute contribution in terms of capturing carbon. Some estimations show that for example just 12000 sperm whales in the Southern Ocean are responsible for the export of 400000 tons of carbon yearly via their direct impact on phytoplankton.
All of the above means we cannot afford to lose whales, have to preserve current populations and increase their numbers. According to our estimates we now lose around 200 great whales and 1000 small delphiniids yearly via live stranding and many of them can be saved with proper interventions , response and adequate resources.
Please note, apart from carbon capture, whales also have additional value in terms what they do for fisheries and ecotourism.
Some data from Chami et al. 2022 was used in this comment.
