Geo-engineering schemes to reduce levels of the greenhouse gas carbon dioxide in the atmosphere and so reduce the risk of global warming and climate change keep cropping up. Ocean fertilization is one such. This involves dispersing large quantities of iron salts in the oceans to fertilize otherwise barren parts of the sea and trigger the growth of algal blooms and other photosynthesizing marine life. Photosynthesis requires carbon dioxide as its feedstock and when the algae die they will sink to the bottom of the sea taking the locked in carbon with them.
But there are so many aspects of marine dynamics which come into play and which we do not still understand. This has been the warning issued by many experts.
According to Daniel Harrison of the University of Sydney Institute of Marine Science, NSW who calculated the impact of iron seeding schemes in terms of the efficiency of spreading the iron, the impact it will most likely have on algal growth is low. The tonnage of carbon dioxide per square kilometer of ocean surface that will be actually absorbed compared to the hypothetical figures suggested by advocates of the approach is lower. In essence it is going to be a very costly affair!
His calculations take into account not only the carbon dioxide that will be certainly be sequestered permanently to the deep ocean but also subtracts the many losses due to ventilation, nutrient stealing, greenhouse gas production and the carbon dioxide emitted by the burning of fossil fuels to produce the iron salts and to power their transportation and distribution at sea. His calculations suggest that on average, a single ocean iron fertilization will result in a net sequestration of just 10 tonnes of carbon per square kilometer sequestered for a century or more at a cost of almost US$500 per tonne of carbon dioxide.
Now, it is a good question if money should be the deterrent to a good cause. But when you look at all the iron needed to make a significant difference, and all the unknown factors in the equation, it is dicey!