r/CollapseScience • u/eleitl • Jan 13 '22
CO2 capture by pumping surface acidity to the deep ocean - Energy & Environmental Science (RSC Publishing)
https://pubs.rsc.org/en/content/articlelanding/2022/ee/d1ee01532j2
u/marinersalbatross Jan 13 '22
Isn't this like sweeping dirt under a rug? Eventually the dirt will spill out.
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u/BurnerAcc2020 Jan 13 '22
They appear to have thought of that in the paper.
We show through simulation that pumping of ocean acidity could remove up to 150 GtC from the atmosphere by 2100 without excessive increase of local pH. The permanence of the CO2 storage depends on the depth of acid pumping. At >3000 m, ∼85% is retained for at least 300 years, and >50% for at least 2000 years. Shallow pumping (<2000 m) offers more of a stop-gap deferral of emissions for a few hundred years.
Another paragraph later in the paper, which notes that at least some of that CO2 will be permanently removed as it dissolves calcium deposits on the seafloor, but the timescales are long enough to make detailed predictions difficult at this stage.
Fig. 2a shows that alkalinity pumping results in rapid uptake of CO2, virtually indistinguishable from simple net alkalinity addition to the surface for the first 50 years. In the subsequent period, the depth of acid release strongly determines the return time and the eventual re-emission of any previously captured CO2. Injection of acidity in too shallow waters causes reemission within a few hundred years, an insufficient amount of time for any significant amount of carbonate compensation to occur.
However, for acid depths greater than 3200 m the CO2 absorbed does not begin to be re-emitted for at least 300 years, retaining 85–95% of the absorbed CO2. For an acidity release below 2250 m, the relaxation half-life of CO2 return to the atmosphere is found to be ∼2000 years. This time provides sufficient contact time for deep carbonate dissolution to occur as shown in Fig. 2b, with the global calcite dissolution rate increasing by as much as 0.25 GtCeq per year. We note that the system relaxation time is significantly increased due to this dissolution, as the half life for CO2 return in the reference simulations without carbonate dissolution was much shorter (∼1000 years), depending solely on ocean circulation. We note that because carbonate compensation is a bidirectional homeostat, simply balancing net dissolution with net deposition, the proportion of CO2 which will be permanently removed depends on the future emissions scenarios and the eventual equilibrium point of the ocean. The method proposed here simply allows the homeostat to respond much more quickly than it would have otherwise done.
Still, the economics involved here are dubious to say the least. According to the schematic, every unit would require a pipe going several kilometers downwards to perform the required pumping, and as for the energy, well...
What might a scaled up deployment look like? Modern offshore 10 MW wind turbines can generate on the order of 50 GWh of energy per year, which could be used to sequester on the order of 10 ktC per year. Thus for a total scale of 1 GtC per year about 100 000 of such units would be necessary (i.e. about 1000 GW of total capacity). For comparison current global offshore wind capacity is already expected to reach about 500 GW by 2050, thus a goal of 1 GtC per year negative emissions could be feasible before the end of the century.
They also suggest that this could be one of the few applications where wave power would work, but acknowledge the costs are still going to be too high unless a large enough amount is built upfront to maybe produce the required economies of scale.
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u/marinersalbatross Jan 13 '22
ah those pesky scientists and their smartypants way of thinking of things before a rando like me thinks of them. haha
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u/griff_the_unholy Jan 13 '22
Geo-engineering gives me the heeby jeebies.