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Ocean alkalinity enhancement - climate change silver bullet or a future environmental disaster ?

Updated: Sep 22, 2023


What is it?

Ocean alkalinity enhancement (OAE) is a process by which we reduce the concentration of dissolved CO2 in the oceans, allowing them to absorb more C02 from the atmosphere, thereby reducing global warming effect of CO2 emissions, and reducing ocean acidification, killing two birds with one stone so to speak.

To do this, alkaline minerals (those with a pH above 7) including Olivine, an interesting looking, green, volcanic mineral rock, are mined, crushed, transported by ships into the ocean, and finally dropped into the depths. As the Olivine falls, and whilst on the seabed, it reacts with the acidic CO2 in the water, turning into carbonate and bicarbonate. After reacting further, the final form sequesters carbon on the seabed for hundreds to thousands of years, allowing the ocean to absorb more of our CO2 emissions from the atmosphere.

This OAE process is believed by some to be a critical part of our response and mitigation of climate change, by sequestering part of the 1.5 trillion tons of carbon dioxide that we have added to the atmosphere since the industrial revolution, and the millions more we will emit before reaching net zero. If we were to do nothing about climate change, the Earth would rebalance its carbon cycle over a much longer time period, somewhere in the region of thousands of years, through weathering silicate minerals, and sequestering ocean carbon through dissolved alkaline minerals entering the oceans via rivers and runoff. Ocean alkalinity enhancement is just speeding up this process to a decadal scale.

Why is it necessary?

We have added 1.5 trillion tons of CO2 to the atmosphere since industrialization. The oceans of the world are the largest carbon store by a long way, storing 50 times more carbon than the atmosphere, and 20 times more carbon than all land and plants combined. It is therefore clear that the oceans have the lion's share of climate mitigation to undertake. The 6th report from the IPCC in 2022 found that some CO2 emissions will always need to be removed from the atmosphere, as they are relatively unavoidable, even in a net zero world; for example, shipping or mining operations, which will still be required for raw materials. One report from 2019 indicated that by 2050 we will need to effectively sequester 10 gigatons of CO2, around ¼ of our emissions today.

Other forms of carbon sequestration such as terrestrial reforestation, blue carbon storing system restoration, including mangroves, seagrass meadows, and other forms of natural carbon capture such as peatland restoration, will play a large role in sequestering future emissions. But these too need all the help they can get to become viable solutions to our carbon storage requirements.

All these and more are required, AS WELL AS massively cutting our global emissions.

OAE has an additional positive effect, which is that it fights ocean acidification. The acidity of our oceans has increased by 30% since the industrial revolution. This acidification is caused by dissolving CO2 from the atmosphere. In turn, the more acidic ocean has resulted in reduced coral reef accretion and loss of reefs. Additionally, the higher acidity has negative effects on any sea animal with a shell, including blue-carbon storing oyster and mussel reefs. OAE, if applied locally to coral reefs and oyster beds for example, would have a positive effect on their growth and health according to research.

How effective is OAE?

A 2021 paper modelled the effects of dumping 30,000 tons of olivine across the great barrier reef daily for a year. The model indicated that the olivine would mitigate around 10 years of acidification on the reef, as well as sequester around 35,000 tons of CO2 emissions. They also found that the acidity of the water surrounding the reef returns to its original level after only a few weeks, meaning that regular dosing is required for long term improvements in acidity level.

Adding alkaline materials is already practised under some circumstances in shellfish restoration to improve survival and shell accretion.

Potential problems

OAE has garnered much attention in the carbon capture space due to its relative feasibility, cost effectiveness and low to moderate ecological impact. However, there are some potential ecological concerns to prevent if this is to become a scalable and effective reality.

There are concerns that photosynthesis may be reduced at the dumping sites. Additionally, it is thought that silicate mineral deposits could add bioactive elements such as iron and silica, which fertilise the oceans and cause algal blooms, with resulting negative effects on flora and fauna. The olivine also comes from mines, which comes with the traditional negative impacts of pollution in nature areas, and the operation running on fossil fuels.

Finally, measuring the impact of such a project would be very difficult and could result in the benefits of the OAE being under or overestimated.

Conclusion

OAE research is ongoing and growing, and may become part of our long term climate change mitigation efforts if it succeeds at scaled up tests. If it does, it will stand alongside natural mitigation measures including restored mangroves, forests, peatlands and reefs. However, most importantly, these measures will only have a chance of working if we are responsible, and reduce our emissions to net zero as soon as possible. Our future depends upon it!


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