UK United Kingdom

Ocean acidification is chemistry, not conjecture

As a scientist working on the impact of climate change on marine ecosystems, one of my duties is to communicate my work. My main goal is to convince students, citizens, economists and politicians that…

Coral are among the sea organisms susceptible to small changes in acidity. NOAA/David Burdick

As a scientist working on the impact of climate change on marine ecosystems, one of my duties is to communicate my work. My main goal is to convince students, citizens, economists and politicians that we need to take urgent action to reduce our carbon dioxide emissions. This is not an easy task and I often face very difficult questions. Are we really warming the planet? Is there really a link to our carbon dioxide emissions?

I am not a climate scientist and I do not have the expertise to judge the quality of the science behind global warming. But while I’m not a chemist either, I can understand that if carbon dioxide (CO2) is dissolved in water (H2O), it turns into carbonic acid (H2CO3). This is such a simple relationship that there is no place for controversy.

The amount of carbon dioxide released into the atmosphere by human activities is so large that it is changing the whole ocean. Every year, humans are releasing nine petagrams (1015) of carbon in the atmosphere and a quarter of these nine billion tons are absorbed by the ocean. This carbon dioxide turns into carbonic acid which makes the ocean more acidic, a phenomenon known as ocean acidification.

Since the beginning of the industrial revolution, the average surface ocean acidity has increased by 30% and it is predicted that acidity may double again by the end of this century.

This is not without consequences for marine species and ecosystems. Many laboratories around the world have demonstrated that if we do not drastically cut carbon dioxide emissions, many species and ecosystems potentially face extinction within decades. For example, the brittlestar Ophiothrix fragilis - a close relative to starfish - is a key species on the west coast of Europe. It is not unusual to find hundreds of individuals per square metre and these beds of brittlestars constitute a habitat for dozens of other species. When we raised Ophiothrix larvae in ocean conditions that could be expected within a few decades, we found they were unable to develop normally and all died within a few days. Perhaps you may not care if this brittlestar goes extinct - but if it does it will have a huge impact on the many species associated with it, including fish.

When raised in ocean acidification conditions (right), brittlestar are unable to form their delicate pluteus larvae (left) and die within a few days.

Ocean acidification is not something that will happen in a distant future. We can monitor chemical changes and the first biological signs are already visible today - some massive oyster declines on the west coast of the USA have been attributed to ocean acidification, as has been linked to coral bleaching.

Of course many uncertainties remain. More information is needed if we want to fully understand the impact of ocean acidification on the oceans, as advocated in a piece that we published in the scientific journal Nature today. Today, we know that to capture the potential impacts of ocean acidification on marine ecosystems, we need to perform longer term experiments, and expand from studying single species to whole ecosystems to capture the environment’s complexity. Ocean acidification is happening together with other global changes such as warming, deoxygenation and freshning (de-salination from mixing with fresh glacial meltwater). On top of this, you have local pressures on ecosystems, such as pollution or over-fishing.

55m3 mesocosms in use, studying the impact of ocean acidification on the pelagic ecosystem over five months in the Gullmarsford, Sweden.

However, uncertainty is not an excuse for inaction. We do know enough to claim that ocean acidification may lead to major changes in marine ecosystems, including reduction in biodiversity and impacts on seafood and other ecosystem services.

So what can we do? The obvious answer is that we need to reduce our carbon dioxide emissions. There is no other serious alternative at the moment. We know that this may be a long and difficult process, so we need to buy some time.

This can be achieved in various ways. We can reduce other pressures such as pollution or over-fishing on a marine ecosystem suffering acidification so as to improve its ability to help itself, increasing its resilience to other factors. We can also make use of the oceans' diversity to select some strains of important species, for example those important to food fisheries, that are more tolerant of environmental changes. Some species of oysters, for example, have been shown to be less sensitive to ocean acidification than others .

Ocean acidification is chemistry, not conjecture - it is as real as water making you wet. It is one of the major threats on the marine realm, and it is essential to act now and reduce carbon dioxide emissions if we are to keep a diverse and productive ocean.

Sign in to Favourite

Join the conversation

7 Comments sorted by

  1. Paul Richards

    integral operating system

    Sam Dupont wrote" ... while I’m not a chemist either, I can understand that if carbon dioxide (CO2) is dissolved in water (H2O), it turns into carbonic acid (H2CO3)." This reminds me of the cryoconite issue on glaciers and irreversible rapid melting trend. These two issues together put global warming beyond doubt and are easily understood with common sense. Thank you for the article.
    The method and range of the EIS;

    1. Ryan Beall

      pdo / student

      In reply to Paul Richards

      This is the most ridiculous thing I have ever read. That reaction would occur with pure h2o and co2. But in the ocean it is very different. You are knowingly ignoring salts and heavy metals which prevent acid from forming. The ocean produces oxygen from co2. Coral grows from this very process. If h2co3 was formed no plant or coral or algae would exist in any body of water anywhere in the world. It is no wonder you have a hard time convincing people.

    2. Paul Richards

      integral operating system

      In reply to Ryan Beall

      Ryan Beall wrote; "It is no wonder you have a hard time convincing people." This comment is subjective, as is the depth of comment on CO2.
      As for convincing people; When presenting information, acceptance has far more to do with individual development, people convince themselves.
      It is their value system, the stage of development and tier reached that creates an open mind allowing genuine critical thinking. Adults need to take full responsibility for educating themselves, regardless of information, read, seen or heard.

    3. Sam Dupont

      Researcher, Ocean Acidification Infrastructure Facility co-ordinator at University of Gothenburg, Sweden

      In reply to Ryan Beall

      Dear Paul,

      Thanks for giving me the space to explain more in details the carbonate chemistry. I did not have the space in this short text to go into more details.


      he details of the reactions look like this:

      When CO2 dissolves in seawater, carbonic acid. This carbonic acid dissociates in the water, releasing hydrogen ions and bicarbonate (H+ and HCO3-). The increase in the hydrogen ion concentration causes an increase in acidity. One result of the release of…

      Read more
    4. Paul Richards

      integral operating system

      In reply to Sam Dupont

      Firstly Sam I agree with your premise and logic stream.
      You wrote; "In a way, you are right. The ocean has the ability to buffer changes in acidity... " This is not the only issue that is counter intuitive, part of the dilema in earth science and cause for great misunderstanding. On the other side it leaves room for new thinking and great opportunity.
      George Monbiot covers counter intuitive science in a talk this month at the RSA. There is a reference your area of interest during the talk. I might not hold his values regarding IV Gen nuclear reactors, but he is a great communicator and thinker.
      Recommend saving the video or the podcast of the event if you are interested as it was on 6th Jun 2013 with links live for next ten days;
      This video may last longer than 10 days;

  2. Barry Woods

    logged in via Twitter

    immediate comment would be that pH is measured on a logarithmic scale (pH = -log (10)[H+])

    In this context a 30% change is very small, as you have to increase the hydrogen ion (H+) concentration by a factor of 10 to get a decrease in pH of 1.

    Doubling 30% is 60%- still a small fraction of total (H+).

    using these %age figures in this way is imho very misleading and even scaremongering for the general public (and journalists/politicians ;-) )

    second concern is changing pH by such a degree in a few days in the experiments, vs, a long term gradual change of pH which is expected over very many years.
    a sudden abrubt change may cause harm in a very short time (days) , but this is not what is going to happen to the oceans

    1. Sam Dupont

      Researcher, Ocean Acidification Infrastructure Facility co-ordinator at University of Gothenburg, Sweden

      In reply to Barry Woods

      Dear Barry,

      Thansks for you remark.

      1. PH vs ACIDITY

      You are right, pH scale is used as a measure of acidity and is a log scale. The observed changes si since 1850 are about a decrease of 0.1 pH unit (a 30% increase in H+ concentration) and expected changes by the end of the century are about 0.4 pH changes (doubling/trippling in H+ or increase in acidity).

      These are scenario for average open ocean.

      It sounds small (0.4 pH unit) but the average pH of the ocean was very stable over…

      Read more