Posted by Mark Halper


Just add limestone. Molten salt reactors could process limestone and dolomite into a substance that would help neutralize ocean acid, says Alex Cannara.

Ask anyone to identify the consequences of CO2 emissions, and the answer that most people who are not climate change skeptics will give is “global warming.”

It’s a good reply. Rising concentration of atmospheric CO2 is heating up the planet to temperatures that could have broad, catastrophic climate consequences by 2050.

But while global warming rightly receives plenty of attention, there’s another ongoing and lesser known CO2 scourge that could be even more disastrous: ocean acidification.

Simply put, up to half of the world’s man-made CO2 emissions land in the ocean, where it forms carbonic acid which will eventually wreak havoc if not stopped according to the United Nations-backed Ocean Acidification Network and other groups.

Scientists say that the oceans’ average acidity managed to remain constant for 300 million years until the Industrial Revolution came along. Over the last two centuries, it has increased by about 30 percent. In technical terms, the pH level has dropped from an average of around 8.2 to 8.1.

The ocean is not acidic per se, but on the 0-to-14 pH scale where anything over 7 is “alkaline” and under 7 is “acidic”, the needle has moved dangerously down. pH measurement is one of those logarithmic things like the Richter scale where progressions are much bigger than their numbers outwardly suggest, so a 0.1 drop in pH indicates a signifiant move toward acidity. If any of you humans suffer a 0.1 drop in blood pH, for instance, hold on for a seizure or a coma.


A more acidic ocean threatens the existence of anything in the waters that has a shell or a skeleton. Translation: let the acidification continue, and before long, oops, there goes the fish, crustaceans, molluscs, coral and more. As oceanic CO2 levels rise and form carbonic acid with a “CO3” molecule (H2CO3), it will increasingly deprive marine creatures of the carbonates – CO3 – that they need to combine with calcium to build strong bones and shells.

Ocean acidification is even undermining certain plankton, the foundation of the ocean’s food chain. So the carbonic acid that’s not directly weakening the bigger creatures could eventually starve them.

Exactly how long this pH decline can continue before real trouble starts is a matter of debate, but some experts believe that if we don’t raise the pH, we’ll hit a tipping point before 2050 and as early as 2035, when the ocean will lose its ability to recycle carbon into living creatures.

As the U.S. National Oceanic and Atmospheric Administration (NOAA) notes:

“Fundamental physiological processes such as respiration, calcification (shell/skeleton building), photosynthesis, and reproduction have been shown to respond to the magnitude of changes in CO2 concentrations in seawater, along with the resultant changes in pH and carbonate ion concentrations that are expected over the next century.

“This change is more rapid than any change documented over the last 300 million years, so organisms that have evolved tolerance to a certain range of conditions may encounter increasingly stressful, or even lethal, conditions in the coming decades.”

The implications of that are staggering. NOAA points out that over a billion people in the world rely on the ocean as their primary source of food protein. Then there’s the hit to the global fishing industry, which employs hundreds of millions of people.

Alex Cannara Ocean Slide

Acid attack. A slide from Alex Cannara’s presentation shows that carbonic acid could cause “big trouble” for sea life as soon as 2035.

What can be done?

Alex Cannara is glad we asked.

Dr. Cannara, an engineering and environmental consultant based in Menlo Park, Calif., says that molten salt reactors (MSRs) can come to the rescue in a multi-pronged assault on acidification.

As regular readers of this blog will know, MSRs are small nuclear reactors that use liquid fuel and operate at much higher temperatures than today’s solid-fuel reactors, over which they offer operational, safety and economic advantages. As such, they have huge potential as CO2-free energy generators for the future (nuclear reactors do not emit CO2 during electricity and heat production; their lifecycle entails some CO2 emissions during stages including manufacturing and mining).


Just like MSRs could be a key weapon in the fight against CO2-induced global warming, the same CO2 reduction would help reverse the toxic build-up in the world’s seawaters, notes Cannara, speaking at the recent Thorium Energy Alliance Conference in Chicago (some MSR developers believe the reactors would work best using thorium rather than uranium).

That’s good, but you could say that the reduction in CO2 emissions is just a warm-up act to a direct MSR-based scheme (a substantial warm up act that is – a bit like Santana opening for the Rolling Stones, which they used to do).

In Cannara’s vision, heat from MSRs could process limestone and dolomite (both are carbonate minerals) into a residue that, when dumped in seawaters, would raise the pH level. As Cannara explained in a letter to anti-global warming campaigner and former U.S vice president Al Gore earlier this year:

“One path is to process billions of tons of dolomite/dolostone (calcium-magnesium carbonate) so that it can be distributed in seas to neutralize the carbonic acid created by our emitted, then dissolved, CO2 and thus to precipitate that carbon as new seafloor carbonates. Similarly, calcium oxide (quicklime) can be used — again derived from limestone and similar rock.”

The process mimics the production of cement, in which fossil-fuel fired kilns heat limestone (calcium carbonate) and break it down into quicklime that blends into a “clinker” that becomes cement.

“Basically, you’re doing a cement plant that’s not making cement,” Cannara told me when I spoke with him after the Chicago conference. “You don’t ship it for cement, you ship it for the ocean. It would suck carbonic acid from the water – it’s just like putting a Tums in your stomach. It neutralizes some of the acid.” (Tums is an over-the-counter indigestion tablet).

It’s a grand vision, but it comes with a few major challenges. As Cannara acknowledges, it will require an immense amount of ground-up rock to make a difference, requiring a sizeable fleet of MSRs. “We would be talking about doubling the amount of processing that’s done for cement,” he said.


On the technical side, I also wonder if MSRs can operate at a hot enough temperature. Even at, say, 800 or 900 degrees C, which MSR developers are targeting, an MSR would still be short of the 1,450 degrees C of today’s cement kilns.

That aside, in a virtuous circle, once MSRs are enlisted for grinding limestone and dolomite in the fight against ocean acidification, they could also go to work replacing CO2-spewing fossil fuels as a heat source for cement production. As Cannara noted when I spoke with him, “You could make cement without combusting things.”

There’s more to this MSR campaign too: Cannara notes that in the MSR process, CO2 that naturally breaks off from the limestone and dolomite could be captured and combined with hydrogen to form synthetic fuels. Where would the hydrogen come from? It would be extracted from water in a process that would be powered, again, by an MSR. As an added benefit, the water’s oxygen would be released into the air.

But the focus of Cannara’s plan is to reverse the decline in ocean pH.

“We have to neutralize at least everything that’s currently being emitted, and that’s a lot of carbon,” says Cannara. “The problem is so immense. It’s non-linear. It’s a true tipping point problem, because once you turn off the ocean’s natural recycling of carbon to the life forms that live in the ocean, you’re not going to get that back. What you’ve done is a massive extinction. We need massive amounts of clean power through MSRs, not only to eliminate combustion power, but also to deal with the issue of how to ameliorate the ocean chemistry problem.”

In other words, now’s the time to recruit MSRs in the environmental fight against catastrophic CO2 emissions on all fronts – land, air and sea.

Photo of Alex Cannara presenting in Chicago is from Mark Halper. Slide is from Alex Cannara.


  1. Robert Hargraves says:

    The high temperature 1450 C can be achieved with an electric plasma arc driven by electric power from the LFTR.

    About how much limestone would be needed? How many GW of LFTR power?

  2. John Preedy says:

    Isn’t there a problem here? When you heat calcium carbonate to create calcium oxide (quicklime) you drive off CO2. If you add quicklime to seawater to lower the pH you will absorb both carbonate and sulphate ions and they will precipitate out in the ocean as calcium carbonate and calcium sulphate. But, because of the presence of sulphate ions in sea water, you will take out less carbon dioxide from the ocean (in the form of carbonate ions) than you have already added to the atmosphere. This will then be reabsorbed by the oceans and once again contribute to increased acidity. So the author proposes to capture the carbon dioxide released by processing calcium carbonate, in order to turn it into something else to avoid contributing to atmospheric CO2 concentrations. But he suggests using it to make synthetic fuels, which when burnt would release carbon dioxide again!
    Someone with more knowledge of chemistry and sea water composition than me needs to review this article.

    • Dr. A. Cannara says:

      ” If you add quicklime to seawater to lower the pH” — remember your HS chemistry? Alkalis raise pH. Lime is an alkali.

      “suggests using it to make synthetic fuels, which when burnt would release carbon dioxide again!” — indeed, but the point is that no CO2 is added net for essential combustion, as for aircraft. If you invent a non-emitting aircraft propulsion system, even MSR, write!

      The point is that the vast majority of the CO2 from limestone will be sequestered as C-H molecules of benign sorts (waxws…) and injected back to geologic storage (oil wells) where the C originally came from.

    • Janodin says:

      I have come to think that maybe a fast spectrum MSR would be the best iaiitnl and perhaps longterm approach. Although less further along developmentally I think they would have advantages in cost and scaling. The S-Prism and pyro-processing seem to be the next most probable new nuclear tech to see commercial deployment. Fast spectrum MSRs would be directly competitive and offer significant advantages and could likely be coupled with pyro-processing in a limited ad-hoc way to lower costs and risk.

  3. George Fleming says:

    Excellent comment. Why has there been no reply from Dr. Cannara or Mark Halper?

    All advocates of nuclear power of any kind who are not merely industry shills are fantasists. Many of them ignore the inevitability of nuclear accidents at existing nuclear power plants, which will be operating for decades to come. Or they think that the money and the resources will be available to recover from those accidents. All of them believe that, despite the absence of sufficient resources and the political will, they can completely transform industrial civilization to their specifications. They ignore the fact that there is no solution to the problems that nuclear power has already created, which cannot be solved by a new generation of reactors which the nuclear fantasists are trying to dream into existence.

    Dr. Cannara is certainly right that we are destroying the oceans, along with the rest of nature as we know it. It might be much worse than we thought:

    “How could jellyfish take over the ocean? ‘One bite at a time’ Gershwin says. And there may be no way back. A new balance may be struck, one in which jellyfish rule:

    ‘We are creating a world more like the late Precambrian than the late 1800s—a world where jellyfish ruled the seas and organisms with shells didn’t exist. We are creating a world where we humans may soon be unable to survive, or want to.'”

    Dr. Cannara, you are right about the dangers we face, but I do not believe you know how to meet them.

    • John Preedy says:

      thanks for the compliment but don’t get me wrong. I am only trying to ensure that ideas put forward to help the environment are properly thought through. I actually believe that investing heavily in fourth generation nuclear power is the only way to reduce CO2 emissions worldwide because I can’t see how intermittent sources of renewable energy i.e. wind and solar can satisfy the continuous base load requirement for energy.
      Furthermore we in the West can’t say to developing countries that they should use less energy and sacrifice their economic development for the environment. We can suggest that they should be rapidly improving their energy efficiency and developing safe emission free technologies, including nuclear, which China is already doing.

      • George Fleming says:

        John, I hope the author of the article and Dr. Cannara will respond to your questions. We ought to know whether “tums for the ocean” would work before we try it.

        But it seems to me that the hopes and plans of the nuclear power advocates are merely academic.

        Suppose there is a safe reactor, the widespread use of which could reduce the quantity of greenhouse gases in the atmosphere and the oceans to a safe level. Set aside the political impossibility of building such a fleet and consider only these questions: How long would it take to build enough of them to make a difference? How much would it cost?

        An honest answer to these questions would show the futility of placing any hope in such a plan. The point of no return, after which global heating will accelerate beyond control, will occur long before these plants could come into operation. As for the cost, it would require stringent sacrifice by everyone. But there are too many of us who are getting rich by destroying the planet to permit a sacrifice of this magnitude.

        There were those who predicted long before the American Civil War that it would happen. Others doubted it until the Confederates attacked Fort Sumter. I predict climate catastrophe and the end of civilization, along with most of the life forms on this planet. Because of human nature, this is inevitable. Others think we can avoid it. I think they are dreaming.

        Nonetheless, as a mechanical engineer with several decades of experience in the fossil fuel power industry, I think your questions are excellent. Dr. Cannara should reply. The discussion would be interesting, even though it is just academic.

        • John Preedy says:

          I think you make good points concerning the lack of political will, the cost and the timescale necessary to urgently address the issue of climate change. Politicians in the West are locked into election cycles and frequently take decisions with the next election in mind and not long term policy. Unfortunately changing the future of energy generation and consumption is a long term matter.
          Unlike some of my acquaintances I don’t believe that mankind is incapable of addressing these issues. It will require political will, radical innovation and some social changes but there are already indications that these are possible. Almost everybody thinks that subsidizing wind and solar power is a good idea but since Chernobyl and Fukushima there are few supporters of nuclear power in political circles. There are nonetheless a growing number of technically aware environmentalists who, like James Lovelock, see nuclear power as the best option to combat climate change. However, it just doesn’t have any votes behind it and yet it’s a proven technology which has a much better safety record than, for example, coal mining. If there was the political will the existing forty or fifty year old nuclear power plants could be replaced with inherently safe designs, producing orders of magnitude less waste, which cannot explode even in the event of total power failure.
          But the challenge for the supporters of nuclear power is, not only to persuade the public that it’s a safe and viable option, but also to get the cost down to levels which can compete with fossil fuels. I think that this is possible and the country most likely to lead the way is China. They have already started a programme to reproduce the pioneering work on Molten Salt Reactors done at Oak Ridge National Nuclear Laboratory in the late sixties under Alvin Weinberg’s leadership. I wish them every success.

    • Dr. A. Cannara says:

      “Why has there been no reply from Dr. Cannara or Mark Halper?” — maybe because I got no notice of any comment — ok with you, George?
      As to your nati-nuclear stance — it appeasr to be uninformed, in relation to scientists like Hansen, Caldeira… Nobellists like Richter, Blix, Rubbia… and even the Dalai Lama…

      If you want to learn why nuclear power has been the safest form of generation for uts entire history, mabye read things like: “Atomic Accidents” by MAhaffey, or look at the ststs here… (1998) (2nd video graphic)

      And if you don’t get why both Chernobyl and Fukushima demonstrate western nuclear-power’s safety, then…
      AAAS Science, Vol 340, p678, 10 May 2013 (2013 Fukushima)
      Chernobyl’s RBMK reactors were/are illegal outside the old Soviet Union, and one of the physicists involved committed suicide because he felt he hadn’t bucked the Russian bureaucracy enough in warning about the RBMK’s instabilities. But hey, Caldicott & others have made good $ on books and lectures slyly implying Chernobyl is related to all nuclear power.

  4. Paul Wick says:

    George, who is entertaining fantasies here? You proclaim the inevitability of nuclear accidents at existing nuclear plants. Have you investigated the work at MIT and elsewhere on silicon dioxide clad uranium/beryllium oxide fuel? Have you investigated the new metallic fuel rod technology being developed by Lightbridge Corp.? Of course not, or you probably would not have made your uninformed proclamations. As well, if I were to balance a fear of another possible nuclear accident with the certainty that we will destroy the oceanic food chain if we continue to burn fossil fuels, only an very uninformed person would fear the meltdown more. After all, TMI killed not a living soul, nor even injured anyone. The Fukushima meltdowns had the same death toll, i.e. zero. The Chernobyl death toll, by UN figures is about 57, and the long term cancer prognosis is indistinguishable from statistical noise. As well, the Chernobyl plant design was preposterous and is no longer in use. Fear-mongering about existing nuclear technology to scare people away from all nuclear technology seems to be your intent. I would advise you to reconsider. We need a healthy ocean.

  5. Robert Bernal says:

    I have came across a pdf about the mining and crushing of olivine. They say it would take mining somewhere on the order of existing coal mining. The “carbon tax” should be applied to subsidize this kind of research and effort, instead of advancing (possibly) dangerous CCS. It should, of course, also be used to re-develop the MSR into the commercial and modular stage.

    • Dr. A. Cannara says:

      Relevance, Robert? We have enough spent fuel from LWRs and more enrichment-waste Uranium than needed for hundreds of years operating advanced reactors. Then there’s seawater UO2 and all the Thorium all over the place — even your back yard. Maybe time to study before speaking in public?
      ;] (the French, p7 & 21 on)

  6. John Doyle says:
    Watch this 2011 video.
    Nothing said here matches the severity of the collapse we are engineering for ourselves!!!

  7. praos says:

    In cement-making more than half of energy is used for CaCO3 decomposition at 900 C, and about 2/3 of the another half, used for heating (with no recuperation), is spent up to that temperature, meaning that direct use of MSR could cover at least 5/6 of the energy. Recuperation, as well as exothermal silicate reactions taking place at over 900 C could possibly reduce the use of non-nuclear heat to less than 10%.

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