Tubes: they’re not just for the internet anymore. A series of giant ocean tubes has been proposed as a solution to global warming. The tubes are supposed to pump up nutrient-rich water from the depths, which will foster phytoplankton growth, which will soak up carbon dioxide, which will then sink back into the deep as the phytoplankton die.
Now, I am just a baby biological oceanographer, but I think this is unlikely to work. It’s a very similar idea to that of iron fertilization – vast areas of the ocean have plenty of nitrogen and phospheros but are limited in plant growth because of lack of iron. The whole iron-fertilization thing came to a head when oceanographer John Martin famously said, “Give me a half tanker of iron, and I will give you an ice age.” Sadly, no woolly-mammoth-rampaging was forthcoming, due to these problems:
1 ) Just because phytoplankton are growing doesn’t mean that they’re sucking CO2 out of the atmosphere. There is lots of carbon already dissolved in the ocean. A recent study estimates that only 8% of the total carbon incorporated into living tissue comes from the atmosphere.
2) Even assuming phytoplankton will suck CO2 out of the atmosphere, can they remove out enough to make a difference in global climate? Iron fertilization experiments suggest no. One study found that fertilizing the entire ocean for 100 years would only result in a 33 part-per-million reduction in CO2. Since CO2 is estimated to increase by 300 ppm in the next 25 years, this unlikely to make a difference to global temperature.
3) OK, so assume that phytoplankton are able to suck out huge quantities of atmospheric CO2. Will this carbon actually be stored in the deep ocean? Well, maybe some carbon would actually make it down, but a lot is going to leak out. Very, very little carbon actually makes it to the seafloor. 1% would be a very generous estimate.
There’s entire ecosystems down there that make a living off sinking food, and a lot of them have contact with the surface. For example, as this magical carbon-soaked phytoplankton is sinking, it will be eaten by scavenging zooplankton which is eaten by tiny crustaceans which are eaten by fish which are eaten by squid which are eaten by a sperm whale. Then the sperm whale takes a dump on the surface. Poof! There goes your carbon storage!
4) Finally, fertilizing the ocean could have a really nasty effect on the ocean’s ecosystems. We’ve already done a lot of ocean fertilizing in coastal areas – most famously, the Gulf of Mexico Dead Zone. That kind of fertilizing sucks the oxygen out of the water column, killing or driving out everything but bacteria and jellyfish. So maybe there’s carbon sequestration there, but I hope that’s not the kind of ocean that we want.
To make matters worse, fertilization stimulates the growth of poisonous phytoplankton over the usual harmless varieties. For example, the diatom Pseudo-nitzschia produces domoic acid, a hugely potent neurotoxin that causes amesiac shellfish poisoning in people and all kinds of terrible effects in marine mammals.
I want a quick fix to global warming as much as the next person-who-loves-the-earth-and-not-in-that-soggy-hippy-way-because-my-
heart-is-cold-and-dark person. But I don’t think it’s going to happen. There’s going to have to be action on a LOT of fronts, from autos to industry to cow farts.