Carbon is arguably the most important element; the universal building block for life as we know it. However, carbon dioxide is the primary greenhouse gas produced across the world from human activities, posing a major threat to ecosystems across the world via global warming. Curbing the release of carbon dioxide is vital, to slow the rate of global warming and prevent ecosystem degradation.
Across the globe there is an international effort to find and better utilise ‘carbon sinks’ (reservoirs that accumulate and store carbon) to promote the natural sequestration of carbon dioxide. Carbon sequestration is the long-term removal or capture of carbon dioxide from the atmosphere to slow or reverse atmospheric carbon pollution and help mitigate climate change. The ocean is one of the largest carbon sinks, with the term ‘blue carbon’ describing carbon sequestration into ocean ecosystems.
Mitigation strategies typically target the protection of highly efficient carbon sinks found around coastal areas, such as kelp forests, mangroves, and salt marshes. These ecosystems are under increasing pressure from human activity such as coastal clearing and urban expansion. Every year 2% of mangrove forests, 1-2% of tidal marshes and 1.5% of seagrass ecosystems are being lost. Research suggests that the degradation of these coastal ‘blue carbon’ ecosystems has a societal cost of up to $US 42 billion per year as billions of tonnes of previously sequestered carbon is released into the atmosphere. These emissions are equivalent to 3-19% of those from global deforestation. Thus, the conservation of these coastal ecosystems is vital not only to ensure high rates of annual carbon sequestration but to also prevent the release of pre-sequestrated carbon entering our atmosphere.
There is increasing interest in the conservation of these incredibly diverse and valuable ecosystems, as well as in promoting the efficiency of blue carbon in other areas of the ocean. One artificial method of promoting ‘blue carbon’ sequestration involves the addition of nutrients to surface water which instigates the growth of marine phytoplankton. Phytoplankton produce organic matter through the process of photosynthesis, this biological carbon pump plays a vital role in the net transfer of CO2 from the atmosphere to the oceans and then to the sediments, where it is concentrated and sequestered for centuries.
Worldwide, this ‘biological carbon pump’ transfers about 10 billion tonnes of carbon from the atmosphere to the deep ocean each year. Using an estimated social cost of carbon of £86/tonne, this results in a yearly societal benefit of £0.86 trillion, in terms of avoided carbon. This indicates the significance and value of phytoplankton within the ocean sink, therefore, improving the capacity and efficacy of this is a priority for sustainability and conservation.
So, how can these benefits help in the fight against climate change? Research has explored the potential to use phytoplankton in a process called ocean fertilization – a type of climate engineering based on the purposeful introduction of nutrients to the upper ocean to increase phytoplankton production and to remove carbon dioxide from the atmosphere.
While numerous studies have found ocean fertilization to be a cost-efficient method of removing carbon from the atmosphere: with estimates of cost ranging from £1.50/tonne of carbon (iron fertilisation) to £33/tonne (phosphorous fertilisation), other studies have found that these costs increase to as high as £330/tonne when considering distribution costs and phytoplankton population dynamics – making ocean fertilization unviable as a mitigation technique.
It is also essential to explore any potential environmental impacts associated with ocean fertilisation, including the risk of eutrophication – the over nourishment of a water body. The key features of eutrophication include reductions in oxygen levels, changes in phytoplankton species including development of harmful algal blooms and a lowering of biological diversity. Furthermore, the bacteria that decompose phytoplankton release methane, a more potent greenhouse gas than CO2, which can potentially have greater adverse impacts on the environment. Little research has been performed to investigate or quantify these consequences and further research will be needed to analyse whether ocean fertilisation is a viable strategy economically.
Economic valuation methods allow us to understand the impacts of our actions across all capitals: Human, Intellectual, Natural, Manufactured and Social. Route2 can provide cost-benefit analysis using our Value2Society tool – revealing insightful information on the overall value of projects, such as ocean fertilisation schemes, by contrasting the operations cost and local ecosystem damage with the wider societal benefit of carbon sequestration. With anthropogenic emissions driving a rise in global temperatures, ensuring conservation efforts are effective and sustainable is an imperative.