By Phil Williamson University of East Anglia (Eds. EMBARGO: 02:07 IST 02/02/2022 London, Jan 31 (360info). Carbon dioxide can be removed from our atmosphere by using the deep ocean. These are the risks, opportunities and constraints.
The ocean is inextricably connected to the climate. More than 90 percent of the extra heat from global heating has gone into deep blue oceans. The associated climate-driven changes have decreased productivity of fisheries and threatened more than 600 million people by increasing sea level rise.
The ocean is a source of potential solutions, not just a victim to climate change. One possibility is to increase the oceans carbon dioxide (CO2) uptake from the atmosphere and store it in the deep. This would help achieve the Paris Climate Change Agreement’s net zero goal. It is necessary to consider other factors than the US$2.5 billion research and development costs.
You could use biology or chemistry to remove carbon dioxide in the atmosphere and store it under the sea. The most straightforward solution is one that is nature-based. This involves restoring the natural functions, and processes, provided by our environment.
Protecting marine ecosystems through ending overfishing and other conservation measures can restore the role of top predators within marine food webs. This is especially true for deep oceans that extend beyond 200 metres.
The increase in the number of larger organisms such as fish or whales would transfer organic matter from the surface to deeper layers via feces and deadfall, slowing down the return of carbon to the atmosphere. UN Sustainable Development Goal 14 recognizes the need to reduce overfishing and improve ocean protection. This goal is also associated with the Convention for Biological Diversity (CBD), and the World Parks Congress.
This approach to climate mitigation has one major problem: the amount of carbon that is removed from the atmosphere over the long-term is likely to be very small. It cannot also be easily attributed to any one country.
Ocean ecosystem restoration is a worthwhile endeavor for its many non-climatic advantages. However, signatories to Paris Climate Change Agreement are required by the Paris Climate Change Agreement to share their emission reduction strategies and quantify national contributions. The theory is that a greater CO2 drawdown can be achieved if marine phytoplankton (microscopic floating alga) is grown. This is especially true for areas of the ocean where dissolved minerals in seawater are scarce.
Directly adding relatively small amounts of biologically-available iron, or larger amounts of nitrogen and phosphorus, would stimulate phytoplankton blooms, converting inorganic carbon dioxide to plant biomass. Artificial upwelling, which is also known as pumping up nutrients from deep water using underwater pipes, could also be used for the same effect. These ideas were first proposed in the early 1990s. They have been tested using patch-scale field experiments as well as modelling studies. However, there are many key issues that remain unresolved.
These include: whether fisheries may benefit or not from increased ocean productivity; whether there might other detrimental side effects; for instance, reducing productivity elsewhere that is potentially many thousands of kilometers away (linked via ocean circulation patterns); and the uncertain rate in which CO2 will return to the atmosphere over the next 50-100 year.
The Essential Context In 2008, there was a non-binding moratorium against ocean fertilisation. This was followed by a more detailed regulation of marine geology. Marine geoengineering is defined as “deliberate intervention in marine environment to modify natural processes, including to counteract anthropogenic global warming and/or its effects. It has the potential for deleterious effects, particularly where they may be severe, long-lasting, or widespread.” The Convention on the Prevention of Marine Pollution by Dumping of Other Matter (LC/LP) restricts marine geoengineering to strictly controlled research.
Further restrictions apply to the Southern Ocean where iron additions could have the greatest climate-friendly effect under various agreements.
Another biological option for ocean-based climate mitigation is large-scale seaweed cultivation (macroalgae). Seaweed photosynthesis would remove carbon dioxide in seawater and then it would be followed by long-term, managed storage of carbon in its biomass.
This method would work best in shallow water, scaling up the cultivation and harvesting of existing seaweed farmers, widely used in Japan, South Korea, China and South Korea. Cultivation in deeper water has also been proposed, but requires a very large area (of around 10 million square kilometre or more than 40 per cent of global shelf seas) for climatically-significant carbon removal. Carbon storage could be achieved by deliberately sinking the seaweed harvested to the deep ocean floor. According to a model study currently under review, large-scale open ocean seaweed cultivation and its sinking could have significant climate mitigation potential.
Because the seaweed could be physically moved to seafloor (for instance, by baling up and adding ballast), there would be more management control and less uncertainty than nutrient based ocean fertilisation.
Yet there would also be adverse environmental impacts and climatically-important feedback effects, both in the water column, as a result of seaweed cultivation, and on the seafloor, as a result of storage. In the upper ocean, shade and nutrient competition would reduce the natural productivity and CO2 removal of phytoplankton and increase the number of marine calcifiers such as molluscs. This would also release CO2.
The seaweed at the seafloor would directly smother all other organisms there; its breakdown would also reduce oxygen levels over larger areas and affect many more deep-sea creatures.
Although the LC/LP regulation doesn’t cover seaweed cultivation, it would be included under ocean disposal by deliberately counteracting anthropogenicclimate change. Ocean climate mitigation is based on chemistry-only methods. These include adding large quantities of silicate or calcium compounds to open ocean waters or coastal waters to increase ocean alkalinity. This will convert CO2 dissolved into seawater to bicarbonate ions and carbonate. This process could theoretically be very effective in removing carbon dioxide from the atmosphere.
The extra CO2 entering the ocean would not be easily quantified with the naturally variable water chemistry and air exchanges of CO2. As noted by the United States National Academies of Sciences, Engineering and Medicine, (NASEM), mining, industrial transformation, pulverising, and transporting of minerals requires careful consideration. Alkaline compounds could be added to the ocean to counter acidification caused by extra CO2 in the atmosphere or ocean.
Depending on the specific mineral elements used, adding alkalinity might have other effects.
High silica could cause significant changes in phytoplankton species composition, productivity, and the strongest effects would be closest to areas where alkalinity rises.
The governance of ocean acidity enhancement is also likely problematic. It is constrained under LC/LP regulation, and strongly opposed by NGOs who reject climate interventions as being harmful to nature.
Mineral dissolution in the sea is undoubtedly a natural phenomenon. However, there is much more debate about where the boundary should be drawn between natural solutions to climate change (generally accepted) and technological solutions (widely rejected). The distinction is arbitrary from a scientific perspective.
The ocean has enormous potential to provide renewable energy. However, the deep sea seems unlikely to offer a solution to climate change via carbon removal.
While some approaches may be considered low regret or no regret because of the wide range they are expected to offer, most remain at the conceptual stage. They are too risky and uncertain to be included in current policies. (360info.org/CPS
(This story is not edited by Devdiscourse staff.
