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There's a mechanism by which the southern ocean sequesters carbon from the atmosphere. It happens when strong winds displace a large slab of surface water, accumulating in a specific region where the localised excess water in the surface layer gets injected downward into the ocean's interior. This makes the ocean's absorb about 25% of annual man-made $CO_2$ emissions.

Are any geophysicists and engineers working on developing a man-made mechanism by which we can make the ocean's absorb more carbon and therefore reduce climate change? Is it humanly possible?

NOTE: I read an article on the phenomenon in Physics World magazine, and it didn't mention anything about scientists looking to make it happen more.

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If you allow bio-engineering, you can probably seed the ocean with microorganisms which are engineered to photosynthesize more. The unintented consequences are probably worse than the CO2. I think the only real solution is to dump less CO2, unfortunately, but I am not so imaginative about this, and perhaps there is a way, so +1 on the question, and I don't have an answer. –  Ron Maimon Sep 4 '12 at 4:47
@RonMaimon Indeed, what you mention represents a certain category of these proposals. The "simple" concept I've heard is to sprinkle iron over some of the ocean, which phytoplankton need. Indeed, there is much less photosynthesis happening that what physically could, evidenced by the fact our ocean isn't green. Of course, my physics knowledge is useless here. That all said, I'm not sure if this is a well-defined question. –  Alan Rominger Oct 22 '12 at 16:11
A more reasonable geoengineering proposal is to increase the albedo thus compensate for the excess CO2 ( assuming it is doing what the GCM models are saying). It has the advantage that water already exists in the atmosphere and the project can be stopped on a dime.… –  anna v Oct 22 '12 at 16:50
@annav Atmospheric albedo approaches are usually not associated with the ocean, although you link does present an interesting hybrid. One major lacking of those approaches is that the CO2 concentration itself has an effect on life and is unchanged. One could imagine a series of measures, the first line focused only on surface temperature, and the later more expensive and dramatic measures to reduce CO2. Temperature vs CO2 concentration is a mouse vs a dragon. Of course, it should be decades before the rest of human kind starts talking seriously about this. –  Alan Rominger Oct 22 '12 at 20:52
@AlanSE Hmm. CO2 is what makes life possible and the official limits of concentrations before harm appears is 8000ppm. In real greenhouses they raise CO2 artificially in order to improve growth and reduce water needs ( stomata of leaves close when there is plenty of CO2). There is nothing harmful in CO2 to plant and animal life until huge concentrations that will never be reached. A sunshade like in the link can control incoming temperatures and be reversible in short time, which is not the case with aerosols. What if they release aerosols and a major cracatao like volcanic eruption happens? –  anna v Oct 23 '12 at 5:01

2 Answers 2

up vote 2 down vote accepted

Another proposal involves putting large pipes into the middle of the oceans (tropical regions) and pumping cold water from the depths to the surface. Here is one paper that analyzes it.

I will try to summarize. This is a very multifaceted idea, so I'm going to try to keep to pure physics as well as I can.

Firstly, what is the engineering involved with this? In order to pipe cold water from deep down to the surface we would have to pump it against the density gradient. Hot water in this temperature range is less dense, so it naturally hangs around the surface. This would take energy and very large pipes. The good news, however, is that the conditions in the ocean make this a little easier in several ways. The construction and placement of mile-long (or so) pipes wouldn't be that impractical, as you would have a floating thing holding them up and they would just hang there. The pumping could actually be done by the waves themselves, and it moves the pipe up and down. For this deployment, you would mainly require some one-way valve that allows the water to travel up the pipe but not down. This wouldn't be all that difficult. So we've established we can engineer and build these things that would make the ocean surface cooler. Studies also seem to indicate that the capital cost wouldn't be prohibitive. Ask it of your engineers and they should be able to make it.

Next, how would this affect climate? Several ways.

  • The decreased surface temperature of the ocean would cause it to be a large Carbon sink. The ocean has already demonstrated a measurable increase in pH and a decrease rate of CO2 absorption, which is a natural consequence of increasing concentration. Decreasing the temperature would cause it to suck up more.
  • The decreased surface temperature would reduce atmospheric temperature. This is a pretty obvious impact, and the paper I reference notes that this could be the most major immediate effect.
  • I would change the ocean life dramatically. Obviously, since phytoplankton are one of the most major photosynthesizers in the world, changing their environment would change the rate of CO2 capture by the environment. How? I have no idea.

I'm not sure the context or motivations in which researchers propose and discuss such ideas, but I've heard some arguments for geo-engineering proposals in general, of which this proposal is one. For one, the idea is entirely doable as I've argued. It could decrease the temperature of the Earth and it could be done with our resources today. If the situation on Earth became so perilous to human life, it's likely that politicians would order such a thing. With that established, the motivations become awfully warped. Many people argue that quantifying the effect of geo-engineering in the future could motivate current negotiations for emissions mitigation to take the necessary steps. Almost all geo-engineering proposals have a temporary effect, so after implemented, they risk a return to an even hotter climate, and possibly deleterious effects due to the solution itself that could be even worse than global warming itself. To add my own personal thinking, it's obvious that we're not reducing emissions today and won't in the conceivable future, so if one believes climate change will significantly impact life, then it's very likely that some form of this geo-engineering will be the future, whether we like it or not.

Here is a picture: (illustration credit to Graham Murdoch of Popular Science, believed to be fair use)

the idea in an image

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changing ocean pH is already becoming an issue - increased acidity decreases the stability of calcium carbonate used by many forms of marine life to form vital structures. It also can affect the bioavailability of iron in the water. –  user2963 Oct 22 '12 at 16:15

It is possible for geoengineers to trap carbon dioxide in the oceans through a process called ocean fertilisation. The principle behind ocean fertilisation is that by dumping nutrients into the ocean we can encourage the growth of phytoplankton which absorb carbon dioxide in the atmosphere. When the phytoplankton die, they'll sink to the bottom of the ocean and lock up some of the carbon dioxide that was inside of them when they were alive, taking it out of the atmosphere. There are a couple of nutrients that could be used to encourage phytoplankton growth however the most favourable would be iron since this has been shown to produce large quantities of phytoplankton using only small amounts of iron.

Since the amount of carbon dioxide each phytoplankton absorbs is quite small, this process still takes thousands of years to have any effects on global carbon dioxide levels so there isn't much in the way of firm evidence that this process will work. We do, however, have evidence that fertilising oceans with iron does produce blooms in phytoplankton populations as several experiments have been performed where iron was dumped into the ocean and phytoplankton populations grew greatly in the area. A recent (illegal) experiment, for example, where 100 tonnes of iron sulphate was dumped into the Pacific Ocean, produced a plankton bloom around 10,000km2 in area. The problem with all of the experiments that have been performed to date is that they are very short-lived as the plankton either die out or are eaten by predators before any effects on carbon dioxide levels can be measured.

Assuming iron fertilisation is effective at reducing carbon dioxide levels, carrying out the process on a global scale will likely be impossible due to the cost of such a project. It would cost billions of dollars every year to provide the necessary nutrients to maintain a large population of phytoplankton and to replace the phytoplankton lost to predators.

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Not to mention that fish are the main staple for billions and if the oceans are clogged with plankton fish will die. All these geoengineering proposals remind me of "the sorcerer's apprentice" . Problem is once the processes start there is no sorcerer to stop them ( except the proposal with the albedo ships, which can be stopped on a penny and it is only water). The holocene has lasted longer than the average interglacial and what will happen if we fall into the next ice age and these projects are just a trigger for it to happen earlier? –  anna v Oct 22 '12 at 15:23
@annav: Huh? I thought that fish eat plankton. Wouldn't more plankton lead to more or bigger fish (or both)? –  David Cary Oct 22 '12 at 18:09
@DavidCary Like all things in nature, balance is important. A few years ago the Adriatic sea from the fertilizers flowing in the rivers generated a lot of plankton down to the Cretan seas. It was considered unhealthy and no great boon to fisheries. Plankton if it covers a whole area can block the exchange of oxygen with the water so necessary for the fish. –  anna v Oct 22 '12 at 18:42
@DavidCary for ponds . The oceans will turn into a giant pond in order to sequester that much CO2 –  anna v Oct 22 '12 at 18:47

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