That Ocean Fertilization Idea

If you’re an avid follower of the news, you may have heard of a company called Planktos that’s trying to fight global warming and make a profit at the same time through a process called "ocean fertilization".

The concept is simple: phytoplankton (tiny one-celled algae) take up carbon dioxide (CO₂) during photosynthesis. Fertilizing the ocean encourages growth of phytoplankton, and increases the rate at which CO₂ is consumed – presumably leading to less CO₂ in the atmosphere. Since ocean photosynthesis is often limited by lack of iron, the idea is to dump iron into the ocean and watch the phytoplankton bloom. Planktos sees this as an economic opportunity: Increase CO₂ uptake in the ocean, and sell it as an offset to carbon emitters. (I talked more about how offsets work in a previous post on land-based offsets.)

Ocean fertilization may sound like a good idea, but it has some very serious problems. Here’s why.

Scientists have been looking at ocean fertilization for a while, and so far the results have been very mixed, and often discouraging. After reviewing many studies, the latest IPCC report [PDF] concluded that "Geo-engineering options, such as ocean fertilization to remove CO₂ directly from the atmosphere… remain largely speculative and unproven, and with the risk of unknown side-effects."

Ocean fertilization is dangerous due to the threat of unintended consequences (see my geo-engineering post). Not all phytoplankton are alike; some need iron more than others. So when you add iron to the ocean, you are favoring one species over another. That can have profound consequences, since phytoplankton are at the bottom of the food chain.

• One possibility is that ocean fertilization will encourage the spread of so-called "de-nitrifiers" – critters that produce nitrous oxide. Many of us know of nitrous oxide as laughing gas, but when it gets into the atmosphere it’s no laughing matter. Nitrous oxide is 120 times more potent as a greenhouse gas than CO₂. If this happened, ocean fertilization could turn out to be a net global warmer rather than a global cooler.

There are also problems with ocean fertilization as an offset. For a carbon offset to be credible, the quantity of CO₂ that has been removed by the project must be accurately quantified. This is a major hurdle for an ocean fertilization project.

• Just because phytoplankton consume CO₂ during photosynthesis doesn’t mean that CO₂ has been removed from the climate system. The vast majority of phytoplankton are eaten by other critters in the surface ocean that, through respiration, release the CO₂ back into the system. As much as 10 percent of the phytoplankton die and sink into the deep ocean before they are consumed. Only the carbon that accompanies that small fraction of phytoplankton qualifies as an offset, because that’s the only carbon that’s permanently removed from the system.
• Now imagine how difficult it would be to measure the amount of carbon that sinks into the deep ocean. You’d have to contend with crosscurrents bringing unfertilized waters into your project area while moving your fertilized waters away. And there are also vertical eddies, bringing deep water up to your area, that may or may not contain some of your recently fertilized but now dead phytoplankton. Upwelling can bring carbon up from the deep ocean, releasing more CO₂ into the atmosphere than what’s taken out. In short, it’s a mess.

And that is why ocean fertilization isn’t cool in my book. Let me know if you hear of any other too-good-to-be-true fixes to climate change, and we can take a look at them.