Curious whether artificial upwelling can really remove carbon? Not at climate scale, on present evidence: models show modest potential, no field trial has shown net removal, and the side effects are poorly understood.
This page is part of a broader look at ocean climate solutions, where artificial upwelling sits alongside other approaches.
| Item | Value |
|---|---|
| Modelled maximum removal, microalgae | Did not exceed 0.66 tons of carbon dioxide per square kilometer per year |
| Modelled maximum removal, macroalgae | Did not exceed 0.85 tons of carbon dioxide per square kilometer per year |
| Global potential with microalgae | Less than 50 megatons of carbon dioxide per year |
| Global potential with macroalgae | About 100 megatons of carbon dioxide per year |
| Carbon returned to the surface ocean in some research | More than 70% within 50 years |
| Project Drawdown rating | “Not Recommended” |
The figures come from a 2022 modelling study in Frontiers in Marine Science and Project Drawdown’s assessment. They can change as research moves on, so check the sources before you rely on them.
How artificial upwelling is meant to work
Artificial upwelling uses pumps or other devices to bring deep, nutrient-rich seawater up to the sunlit surface. The extra nutrients are meant to boost phytoplankton growth through photosynthesis, which removes carbon dioxide from seawater and lets the ocean absorb more from the air, according to Project Drawdown.
The idea borrows from natural upwelling, which Geoengineering Monitor describes as caused by winds and the rotation of the earth. Deep water is often rich in nutrients, so it can raise growth in the upper layers that receive sunlight.
Engineers have described several ways to lift the water. Project Drawdown lists these device types:
- Air-lift pumps
- Gravity wave devices
- Air bubble systems
- Electrical pumps
- Wave-based pumps
Cost shapes the choice. Geoengineering Monitor reports that electrical pumps are considered too expensive, and that using temperature or salinity gradients is considered too inefficient.
How much carbon could it remove?
A 2022 study in Frontiers in Marine Science tested the question with a simple model of upper and deep ocean properties. It explored a range of carbon-to-nutrient ratios for microalgae and macroalgae, so the estimates do not hinge on one assumed value.
Across the tropical-to-subpolar ocean, simulated removal did not exceed 0.66 tons of carbon dioxide per square kilometer per year for microalgae. For macroalgae the ceiling was 0.85 tons per square kilometer per year, as reported by the same study.
Scaled up with present technology, the global estimate was less than 50 megatons (0.05 gigatons) of carbon dioxide a year with microalgae. With macroalgae it was approximately 100 megatons (0.1 gigatons) a year, and the author concluded that artificial upwelling is unlikely to reach one gigaton a year, per the study.
The same paper says controlled field trials are needed to validate or invalidate its findings. Treat the numbers as a model-based ceiling, not a measurement.
There is a further drag on any gain. Project Drawdown notes that upwelled deep water often holds high concentrations of dissolved inorganic carbon, so extra carbon dioxide could escape to the air, and some research suggests more than 70% of carbon returns to the surface ocean within 50 years.
What field trials have shown
Researchers have tested the hardware many times. Geoengineering Monitor reports at least 20 outdoor trials in recent decades, and says their stated aims have not been met.
The more important gap is carbon accounting. Project Drawdown states that some efforts have shown they can bring deep water to the surface, but no proof-of-concept field trials have demonstrated net carbon removal, and even short deployments have operationally failed.
Examples of trial work reported in the sources include:
- Canary Islands: the European Ocean artUp project, coordinated by the German GEOMAR Helmholtz Centre for Ocean Research, ran from 2017 to 2021 and included open-ocean trials in Taliarte harbor, per Geoengineering Monitor.
- Shandong, China: from November 2018 to May 2019, a trial in a coastal kelp farm in Aoshan Bay used offshore solar energy and rising air bubbles, according to a 2019 Geoengineering Monitor article.
- Pipe depth: the same article says earlier outdoor trials used pipes to lift water from depths of up to about 300 m.
That 2019 article also reports the conclusion of GESAMP, a body advising the United Nations, that field studies to that point did not provide evidence that artificial upwelling can sequester carbon on a larger scale.
One commercial use is different in kind. Geoengineering Monitor cites UK-based Brilliant Planet Ltd, which pumps nutrient-rich deep-sea water into on-shore ponds to feed microalgae, and reports that it has built three hectares of raceway ponds in Morocco.
Risks and side effects to weigh
Scale is the first problem. Project Drawdown estimates that large-scale deployment could require millions to hundreds of millions of pumps, and says energy needs and costs remain unclear.
The GESAMP review, as summarised in the 2019 Geoengineering Monitor article, names these risks:
- Termination effect: colder deep water increases heat absorption, and when upwelling stops the absorbed heat would be released into the air, causing additional warming.
- Transboundary effects: changes in weather patterns such as rainfall could affect agricultural production.
- Gas composition: extra carbon uptake may worsen ocean acidification, deep water may release additional carbon dioxide, and enhanced production can deplete oxygen in the upper ocean.
Ecological effects are also hard to bound. Project Drawdown says artificial upwelling shares ecological risks with ocean fertilization, and that some models suggest large-scale deployment might increase ocean heat uptake and alter ocean circulation.
Marine life could also be affected by hardware itself. Geoengineering Monitor says large structures could cause issues for marine life, shipping and fisheries, and that data on device lifetime and maintenance costs are incomplete or unavailable.
Possible benefits and how to read the evidence
Supporters point to side benefits. Project Drawdown notes that bringing up deep water could lower surface temperature, which may benefit some marine organisms, and that it could be coupled with aquaculture in nutrient-poor regions.
Weigh the sources by their stance. Geoengineering Monitor is a campaign site that lists its Key Reasons to Oppose geoengineering, so read it alongside the modelling study and the Drawdown assessment, which reach similar conclusions on carbon removal.
For another approach to compare, see the explainer on ocean alkalinity enhancement. Options based on coastal ecosystems are covered in the guide to blue carbon.
Frequently asked questions
Is artificial upwelling the same as natural upwelling?
Show answer
No. Natural upwelling is caused by winds and the rotation of the earth, while artificial upwelling relies on pumps or other devices, according to Geoengineering Monitor. Project Drawdown adds that the biology rests on well-understood natural processes, but net carbon removal from the engineered version is unproven.
Could artificial upwelling remove a gigaton of carbon dioxide a year?
Show answer
The 2022 modelling study suggests it is unlikely. Its estimates were about 0.1 gigatons a year with macroalgae and 0.05 gigatons or less with microalgae, as reported in Frontiers in Marine Science.
Has any field trial proven it removes carbon?
Show answer
Not according to Project Drawdown, which says no proof-of-concept field trials have demonstrated net carbon removal. Carbon uptake by phytoplankton and long-term storage in the deep ocean both remain largely unexplored for this method.
Why could upwelling add carbon dioxide to the air?
Show answer
Deep water often contains high concentrations of dissolved inorganic carbon and low oxygen, per Project Drawdown. If the upwelled water releases more carbon than the algae remove, the net effect could be more carbon dioxide in the atmosphere.
