The idea of fertilizing the ocean with iron to capture carbon is one of the more colorful ideas to arise directly from a basic understanding of biogeochemistry. Ocean phytoplankton are iron-limited and alleviating that iron limitation makes them grow enough to cause some of the fixed carbon to get locked away in the deep ocean. There was substantial debate about a decade ago about the feasibility of this idea for fighting climate change and I seem to remember that most of the scientists involved decided that it was an interesting but not practical idea.<\/p>\n
A re-promotion of the idea was making the internet rounds today due to this profile<\/a> of a prominent advocate\u2014practicioner even\u2014of iron fertilization. I had forgotten the details of the debate so it was fun to revisit them. The profile is written in such a way to make it seem like iron fertilization is a great idea that is being held back only by environmentalists scared of geo-engineering. Unfortunately for the author–or perhaps to their credit in being objective–the counterarguments to this viewpoint are apparent in the article itself. The author writes:<\/p>\n iron fertilisation could potentially sequester as much as 1 billion metric tons of carbon dioxide annually, and keep it deep in the ocean for centuries. That is slightly more than the CO2<\/sub>\u00a0output of the German economy, and roughly one-eighth of humanity\u2019s entire greenhouse gas output.<\/p><\/blockquote>\n This sounds good until it is put to a simple cost benefit analysis. The one-eighth figure likely comes from a modeling study, and is also discussed in an editorial<\/a>\u00a0in Nature\u00a0<\/em>arguing against iron fertilization back in 2009. (I note that the authors here are better described as ‘scientists’ than ‘environmentalists.’ ) In that editorial they write:<\/p>\n A model published in 2008 (K. Zahariev\u00a0et al<\/em>.\u00a0Prog. Oceanogr.\u00a077, 56\u201382; 2008<\/a>), which is as convincing as any available, found that even if the entire Southern Ocean were fertilized forever with iron sufficient to eliminate its limitation of phytoplankton production, less than 1 gigatonne of carbon a year of CO2<\/sub>\u00a0of probable future emissions (currently about 8 gigatonnes a year) would be sequestered, and that amount for only a few years at best.<\/p><\/blockquote>\n So there you have the cost and the benefit. The benefit: we may reduce 1\/8th of our emissions, a substantial and impressive amount, but nowhere near enough to stop global warming. The cost: we risk fucking up an entire ocean. The ‘environmentalists’ were ridiculed in the the pro-fertilization piece for having that attitude, but it hardly seems outrageous to worry that fertilizing an entire ocean to stop 1\/8th of our emissions could have unintended consequences, and the Nature<\/em> editorial shows that scientists, myself included feel the same way.<\/p>\n There are too many examples of fragile food webs tied together as trophic cascades<\/a>\u00a0and\u00a0biocontrol agents gone wrong<\/a> to not worry about unintended consequences of a vast ecological manipulation in a system that is not totally understood. We are still barely getting a handle on the consequences of doubling carbon in the atmosphere. Is it wise to perform a similar experiment with another element in the ocean? The pro-fertilization piece crescendos toward this point at the end:<\/p>\n The ocean is no longer a vast, unknowable wilderness, whose mysterious gods must be placated before it can be crossed. Instead, it\u2019s become the first viable arena for large-scale manipulation of the planetary environment.<\/p><\/blockquote>\n What could possibly go wrong?<\/p>\n","protected":false},"excerpt":{"rendered":" The idea of fertilizing the ocean with iron to capture carbon is one of the more colorful ideas to arise directly from a basic understanding of biogeochemistry. Ocean phytoplankton are iron-limited and alleviating that iron limitation makes them grow enough to cause some of the fixed carbon to get locked away in the deep ocean. 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