Photo by Matt Hardy on Unsplash

Is Fertilizing the Ocean the Key to Solving Climate Change?

No, it’s not.

TL;DR

Phytoplankton absorb carbon. When they die, they sink to the bottom of the ocean (along with the absorbed carbon) and we never see it again until centuries later. We can capture carbon from the atmosphere and store at the bottom of the ocean using phytoplankton fertilized by iron. Iron fertilization isn’t really considered a viable method of carbon sequestration these days, because it has unpredictable effects on the complex interactions in ocean ecosystems. It was pretty hyped up in the 90s and 2000s, but the results turned out to be pretty subpar. We’ll go over the main principles behind iron fertilization and why it’s probably not going to be the technology that solves climate change.

The oceans are the perfect place to store our carbon, right?

Photo by Patrick Hendry on Unsplash

There’s a lot of carbon in the atmosphere, trapping heat and warming the planet. But you already know that. So how do we get rid of that carbon?

Well, the oceans already absorb much more carbon dioxide (CO2) than you think. The amount of carbon that is stored in the oceans is 10x more than that stored underground, so that’s good, right?

Not necessarily. When CO2 mixes with water, it produces carbonic acid (H2CO3), turning the oceans into a big pool of acid, killing marine life and the like. So is there a way to move the carbon from the atmosphere to the ocean without acidifying the oceans?

Enter Ocean Fertilization

The oceans can store a lot of carbon in them. 38,000 billion tons, which is pretty good when you compare it to the 37 billion tons in carbon emissions we put out annually.

There are two ways we can move that carbon from the atmosphere to the ocean. The first way is to directly capture the CO2 from the air and inject it deep into the ocean using a system of pipes. But the method that’s been more popular with researchers is to accelerate the natural mechanisms that already move carbon to the ocean.

The Marine Biological Pump

Carbon dioxide from the air dissolves into the upper layer of the ocean, where the waves are. Phytoplankton at the surface absorb that carbon dioxide, along with any other nutrients and sunlight. This causes them to form algal blooms. You may have heard of those in the news. If they get out of control and start poisoning stuff, they can be referred to as a ‘red tide’ that depletes oxygen from the water and kills everything.

It looks like there’s a dead fish near the bottom of the picture but I’m not sure.

Phytoplankton blooms (of the nontoxic variety) can be beneficial in absorbing the carbon dioxide from the atmosphere, because when they die, they sink to the bottom, along with the carbon that they captured.

But that’s not always the case. Most of the time, those phytoplankton are taken up by various decomposers, and the carbon is oxidized into CO2 again and returned to the surface of the ocean by the currents.

If we’re lucky, the phytoplankton can be eaten by other organisms, and their carbon-rich poop can sink to the bottom of the ocean. So does that captured carbon just stay at the bottom of the ocean forever? No, it doesn’t, but it won’t come back up within your lifetime. Over very long periods of time, deep ocean currents will eventually come back up to the surface and release that CO2. But that takes centuries, because those currents move really slowly.

So that’s the biological pump. Carbon from the air gets “pumped” down to the bottom of the ocean through biological processes. Can we increase the rate of pumping? Well, because it’s a biological pump, we can increase the rate of pumping by increasing the amount of organic material created at the surface of the ocean.

Phytoplankton are Basically Really Tiny Plants, so they can also be Fertilized like Plants

Bodybuilders take supplements, because the lack of some particular nutrient is preventing them from obtaining maximum swoleness. Farmers fertilize their crops if they’re missing nutrients like nitrogen or phosphorus.

As it turns out, there are some areas of the ocean where iron is the limiting nutrient. A shortage of iron will limit phytoplankton growth, so if we just fertilize those plankton with iron, it should cause them to grow and stimulate algal blooms, which speeds up the rate of the biological pump.

Great. So what type of plankton should we fertilize?

Skeletonema are my favorite genus of diatoms, because they can link together and form long chains.

Diatoms are the ideal carbon sequestration phytoplankton. They have hard shells made of silicon, and those shells mean that they have few natural predators. And if they are eaten, it can be a good thing, too.

A String of Salps

A salp is a weird jelly-like organism that can eat diatoms. The good thing about salps is their poop. Salp poop sinks to the bottom of the ocean faster than dead phytoplankton. That means it’s less likely for that carbon to get returned to the surface. Some researchers have suggested combining fertilization with salp colonies.

Algal blooms also release dimethyl sulfide gas into the atmosphere, which influences cloud formation by increasing cloud formation while also making the clouds more reflective, or “whiter”, giving the added benefit of cooling the planet.

It’s Easy and Effective, Right?

At first, researchers estimated that about 1 ton of iron could capture as much as 30,000 to 110,000 tons of carbon. All we need to do is just get a boat and dump some iron into the ocean. Climate change solved. That’s great, but also not true in practice. It’s only about 50% effective at best if it’s used in one area of the ocean.

We tried it in the 1990s and 2000s, and the results were bad enough that research in that area pretty much died out. One expedition in fertilizing the oceans with iron only captured about 200 tons of carbon per ton of iron. That’s 109,800 tons less than expected.

It’ll Probably Ruin our Ecosystems

Photo by Patrick Hendry on Unsplash

Algal blooms steal nutrients from other parts of the ocean, so even if we get an increase in ocean productivity in one region, other regions would be less “green”, so our net productivity is probably still going to be close to zero.

Because the water is covered in tiny plants, it becomes less reflective and actually absorbs more heat from the sun, which warms the seas. But what about the dimethyl sulfide? Maybe it’ll cancel out the warming effect, but we don’t know enough about the complex interactions between all of the ocean, atmosphere, and cloud systems to accurately predict what’s going to happen.

Let’s say we have no other choice and we go with fertilization(in real life, we have many better choices, by the way).

If Ocean Fertilization Worked Perfectly, Could We Solve Climate Change?

Photo by Shaah Shahidh on Unsplash

Pretend the entire world decides to undertake a large committed effort to go fertilize the entire ocean. Will it be enough to solve climate change?

It’ll take over 100 years to capture 25–75 billion tons of carbon using fertilization alone. We’re putting out 37 billion tons of carbon annually, as of 2018. So it might be able to offset the annual emissions.

But remember that we still have all of that carbon stored in the atmosphere from the Industrial Revolution. It hasn’t gone away yet. And because it hasn’t gone away, ocean acidification will continue, and global temperatures will continue to rise. A hot, acidic ocean is not the perfect place to grow phytoplankton, so our ocean fertilization project will pretty much be worthless. So it’s not going to be that effective unless we decide to cut out all carbon emissions.

Basically, ocean fertilization will bring about large changes to the oceans. Maybe they’re good changes and they remove some carbon from the atmosphere. However, those changes have unpredictable effects on ocean communities and ecosystems, so it’s better to shift research to areas such as enhanced weathering or direct air capture.

This post was based on a chapter from Clive Hamilton’s 2013 book Earthmasters: The Dawn of the Age of Climate Engineering. It’s a light easy read that you would probably enjoy if you got this far through this blog post. If you feel reading this was helpful or at least a good use of your time, let me know.