Cake
• If filtering CO2 from the air itself isn't feasible, I wonder if at least stabilizing the oceans' acidity through chemicals or technical means (large-scale electrolysis platforms on the oceans?) would allow them to act as a buffer for a longer period, even if that wouldn't solve the problem the ocean itself faces. Is there any research going on in that regard?

One constraint of an ocean platform electrolysis system is the amount of energy required and the pollution caused. I’ve seen videos of power systems that generate energy through wave movement. Wind, wave and solar perhaps to power it?

• Here's what bugs me: most carbon is coming from beneath the surface: we dig it up as coal or suck it up as oil & gas. Then we burn it, which atomizes it into the atmosphere. Some gets put in the atmosphere by cutting down forests and burning them, because carbon is in the trees.

You and apm are math wizards. If you do the math on the amount of carbon coming out of the ground, you get an estimate of how much we have to pull from the atmosphere. Then we have to figure out where to put it. The volume boggles the mind. Think of the energy and machinery required.

The sad thing is that the math is actually quite simple:

1. Growing plants capture carbon.
2. Decaying plants release carbon.
3. Fossil fuels are ancient plants that haven't decayed yet.

It immediately follows from this that increasing the amount of non-decaying biomass (as in living trees, or at least plant matter that isn't burned for energy or fun) is a good thing, while deforestation is a bad thing, and digging millions of years worth of non-decayed biomass from the earth to add its carbon equivalent to the atmosphere is an absolutely crazy thing.

It also follows that, to balance this, one would need to store away about as much mass and volume as has been dug out in form of coal and petroleum in the last 150 years.

Doing so would be a huge endeavour, yes - but it's not as if digging out all that stuff was an easy undertaking in the first place:

If people manage to create holes like this in the ground, one would think they are also able to fill them with something else than just water if they really want to.

• One constraint of an ocean platform electrolysis system is the amount of energy required and the pollution caused. I’ve seen videos of power systems that generate energy through wave movement. Wind, wave and solar perhaps to power it?

Chemistry really isn't my strong suit, so I'm mostly just asking questions here. In the end, what all of this boils down to is that these problems (like CO2 in the atmosphere, ocean acidity, ...) all are the result of various processes to make energy available for human consumption. To solve these problems, we'd absolutely need to use "free" sources of energy and basically store the energy away by reverting the processes that released energy in the first place.

One such process is burning fossil fuels - taking Carbon and oxidizing it to form CO2 while gaining some amount of energy to consume. Its reverse process would be any form of photosynthesis, whether naturally occurring or artificial - energy is used to split CO2 into its components, storing or releasing them individually.

Another process that uses energy to split something into its components is electrolysis (of water into Hydrogen and Oxygen) - and this process at the same time leads to some parts of the remaining water becoming more basic (near the cathode) while the other becomes more acidic (near the anode). What I wonder here is if this process of electrolysis can be combined with something else that prevents the acidic part from spreading into the water, so that the remaining basic part counteracts the increasing ocean acidity. Very roughly speaking, the magic formula here would be the following:

(acidic ocean) + (solar/wind/wave energy) + (water) -> (less acidic ocean) + (some mysterious type of acid being removed from the water) + hydrogen + oxygen

Here, my lack of chemistry knowledge leaves me stranded... :)

• The chemistry of carbon dioxide and ocean water is, without writing a bunch of chemical formulas, something like this: carbon dioxide and water combine to form carbonic acid (H2CO3). It is a weak acid so it doesn't make the ocean super corrosive or anything. But it does shift a giant chemical equilibrium that exists in the ocean. The carbonic acid molecule is in equilibrium with bicarbonate ion (HCO3-) which is in turn in equilibrium with carbonate ion (CO3-2). That series of equilibria is called the "carbonate buffer system". The carbonate ions are in equilibrium with solid carbonate minerals - most notably limestone and coral, but also a good bit of Mollusca shells. As more carbon dioxide enters the ocean, it causes all the reactions to shift to undo the change caused by adding the carbon dioxide. So there are more bicarbonate ions and more carbonate ions in the ocean, and at each stage of the reaction shift, hydrogen ions are released and cause the pH of the ocean to drop.

In today's ocean almost all of the carbon in solution is in the form of bicarbonate ions. The equilibrium point for bicarbonate to be the preferred ion is just over a pH of 8. But as more hydrogen ions are produced and the pH shifts lower, the amount of bicarbonate is less and the amount of carbonic acid is greater. The carbonate buffer system resists changes to pH and in the ocean this happens by ocean water dissolving more carbonate minerals: as the carbon dioxide dissolves into the ocean from the atmosphere, the ocean in turn dissolves solid carbonates so the ocean pH doesn't change too much.

We'd be perfectly content if the ocean simply dissolve a bunch of limestone and the carbon dioxide stayed dissolved in the ocean forever. But the ocean has much better contact with the shells of those Mollusca and the coral reefs than it does with limestone rocks, so the shells and reefs tend to dissolve first. The mollusks and the reefs are the basis of much of the ocean food chain. Acidifying the ocean with carbon dioxide is a really bad idea.

But there is lots of limestone around. Maybe we could just react carbon dioxide directly with the limestone and leave the mollusks and corals out of it? That is the basis of acid scrubbers on fossil fuel power plant stacks. The scrubber is a tank full of crushed limestone with water trickling over it and the gases go through. The acidic stuff in the gas dissolves in the water and the acidified water dissolves some of the limestone. Instead of calcium carbonate rock, it becomes calcium bicarbonate solution. Sadly, when one tries to dry out the solid calcium bicarbonate, it perversely gives up a carbon dioxide molecule and turns back into calcium carbonate.

This feature of carbon dioxide stubbornly reappearing is common to various scrubbing technologies: the carbon dioxide is captured but it remains as carbon dioxide. It is a quite energetically stable molecule so it does not have a lot of beneficial above-ground chemical industrial sorts of uses (basically, none). If we are not allowed to vent it into the atmosphere, what are we to do with it? The most common solution appears to derive from the concept that it came out of the ground, so let's put it back. Carbon dioxide can be injected into the ground where it will stay for a long time. The oil industry volunteers that they can use it to extract more oil! They are not helping.

I think back in the ground is the best solution for now. Maybe in the future we will be able to do like plants and convert carbon dioxide and water and sunlight into cellulose. We can't do that yet except by planting more trees.

• Great explanation, Cade. It’s similar to the mechanism for acid rain that have been dissolving the limestone cathedrals in Europe, no?

I am very glad activists in the 1800s were able to preserve some of the giant redwoods and sequoias from the rush to cut them down for their timber. Those beasts store a lot of carbon.