| Summary: | To date the global community has failed to effectively curtail growth in anthropogenic emissions of carbon dioxide, in the year 2016 we continue to track the IPCC 2005 ‘business as usual’ projection of annual emissions. The bleak outlook for stabilising the planets rising temperature by reducing reliance on fossil fuel energy has led to recent renewed calls for research into technological solutions. Only geoengineering to remove carbon dioxide from the atmosphere or a dramatic reduction in emissions can address the build-up of carbon dioxide in the atmosphere, and also act to alleviate the associated problem of increasing ocean acidification. Ocean fertilisation is one such technology which offers the prospect of partially addressing two pressing problems, that of rising atmospheric carbon dioxide levels and global food security. The potential of ocean fertilisation is examined here in terms of efficiency of carbon storage, potential benefits, implementation, environmental risk, cost, and societal values. Iron fertilisation was found to be less efficient (carbon stored / carbon fixed) and more expensive than macronutrient fertilisation, while both technologies have sequestration capacities of 1-1.5 Gt C yr-1 (10-15% of current emissions). Experimental studies on the response of plankton communities to macronutrient enrichment suggest that speculation of large ecological risk by encouraging harmful forms of phytoplankton appear to be overstated. The risks need to be compared to the costs of not acting to mitigate climate change, and to the environmental risk of increasing food production on the land to cope with a rising global population. It is found that ocean fertilisation has the potential to make a significant contribution to efforts aimed at mitigating climate change and also potential to contribute to improved food security, however the environmental and ecological implications of such a large scale intervention are poorly understood at this time.
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