This article is an edited excerpt from David Ho’s June 2026 interview on The Land and Climate Podcast, as told to Bertie Harrison-Broninski.
Marine carbon dioxide removal (CDR) initially drew enthusiasm from the private sector, but momentum is slowing down. Mostly, the private sector is interested in making money – and we have a long way to go to develop this technology before it is profitable.
Marine CDR lumps together many different techniques. They all seek to remove excess carbon from the atmosphere by lowering surface ocean partial pressure of carbon dioxide, or pCO2.
Some techniques exploit photosynthesis, for example by adding nutrients like iron to the ocean, to increase phytoplankton productivity. The complication there: if you make something organic in the ocean, something else will want to eat it. If the phytoplankton get consumed before their bodies sink to the deep sea, that organic matter is quickly turned back into CO2. There are also potentially negative effects for ecosystems, such as decreasing oxygen levels in the ocean, which would be bad for organisms with gills.
Alternatively, there are geochemical techniques, such as increasing ocean alkalinity to shift CO2 into dissolved bicarbonates and carbonates. This allows the ocean to absorb more carbon dioxide from the air. People think that this additional CO2 store should last tens to hundreds of thousands of years, and may not be as disruptive as other methods.
The different techniques have different uncertainties, but I wouldn’t say any of them are ready, for lots of reasons. We don’t know how effective they would be, or whether they will have negative environmental impacts.
Some effects can only be seen if you do experiments at very, very large scale, which we will never do. To do marine CDR at scale will cost trillions of dollars – who has that money to waste, when its efficacy is unknown?
On top of that, once you start doing these techniques, you have to keep doing them. Otherwise, when you stop, the end result could be worse than if you had not done anything.
Regulatory issues also need to be worked out. The London Protocol specifically prohibits putting iron in the ocean for CDR, but does not prohibit research. When does research become deployment? People have also proposed other substances to increase alkalinity, but The London Protocol does not say anything about these.
Another question is over who should get credit for the carbon that is removed: the country that deployed it, or where the process happened? This is not only an academic question. One country deploying marine CDR could decrease capacity for another to use the same technique, and it is not clear how it should be accounted in the emissions inventories countries submit to the United Nations.
The more I research marine CDR, the more sceptical I am that we will be able to do a lot of it. Not just for technological, or geophysical, or environmental reasons; the social acceptance, the governance, and the finance is going to be difficult.
Despite this, we see journalists build hype with phrases like ‘magic rock dust’, leading people to believe the problem is solved, and we do not need to decarbonise. That is very far from the truth.
Startups have to sell carbon dioxide removal as a solution today in order to survive. In reality, we are so far from deploying these things that none of the startups that currently exist will be the ones removing carbon in 50 years. They are developing intellectual property to sell.
The most successful carbon removal company is Carbon Engineering, a direct air capture company. They’re successful because they managed to sell themselves to a fossil fuel company for $1.1 billion.
Startups funded by venture capital are not a good way to develop potentially an important climate solution. If we want to scale CDR, it should be government-funded and government-led.
We are not ready to have a methodology for marine carbon dioxide removal; we need a lot more research. Nevertheless, it is a political decision to include one in the upcoming IPCC report on CDR methodologies, so we are forced to do it.
Mitigation deterrence is a real thing: we get too complacent with the idea that new technology can solve our problems, and then overlook the technology that can actually help – like renewable energy, public transport, and electric vehicles.
CDR is something that we are researching, and it is potentially something we will have in the future, many decades from now. It is not a solution we have now, and we might never have it. It is really important we implement the solutions we do have today.
Listen to the full podcast interview with David Ho by clicking here.
David Ho is a professor of oceanography at the University of Hawaiʻi at Mānoa, and a lead author on the upcoming IPCC Methodology Report on Carbon Dioxide Removal Technologies.
