I'm confused about how increased $\ce{CO2}$ concentration in the atmosphere affects the pH of the ocean.

The increase in $\ce{CO2}$ concentration means the pH of the ocean will decrease (by several chemical reactions). However, as there is more $\ce{CO2}$ in the atmosphere, ocean temperatures will rise meaning the ocean will absorb less $\ce{CO2}$, likely slowing down ocean acidification.

In short, the rise in $\ce{CO2}$ seems to have two contrasting effects on the pH of the ocean. Am I interpreting this correctly? If so, how is ocean acidification a problem?

For reference, the article I read is Barker and Ridgwell (2012), Ocean Acidification, Nature Education Knowledge.

  • $\begingroup$ I'm voting to close this question as off-topic because it is about mechanisms in earth or environmental science rather than biology itself. $\endgroup$
    – David
    Feb 25, 2020 at 8:17
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    $\begingroup$ Best move this to Earth Science stack its a classic environmental science question of global economic processes. $\endgroup$ Feb 25, 2020 at 9:02
  • $\begingroup$ CO2 acidifies sea water. I had a saltwater tank ( 75 gal) with a large amount of green plants ( calurpa). Water parameters were correct for sea water ( alkalinity , etc). The pH would drop ( 8.2) when the lights were off and rise ( 8.5) when the lights were on and the calurpa was absorbing CO2 and making O2. The numbers are from memory; My log book is not presently handy . I found the pH shift surprising because as ,with all salt tanks, it had substantial water movement facilitating exchange with air. $\endgroup$ Feb 25, 2020 at 17:32
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    $\begingroup$ I think this is a reasonable question ... the answer, I believe (see below), hangs on an understanding of the solubility of CO2 in the oceans and the fact that they are not currently saturated. This is a really important issue in climate research. $\endgroup$
    – M Juckes
    Feb 25, 2020 at 18:36
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    $\begingroup$ Being aware of the rate of the processes would help you. There are essentially thousands of processes having opposite effect in any complex system. $\endgroup$
    – y chung
    Feb 26, 2020 at 23:32

1 Answer 1


Increasing CO2 concentration in the atmosphere is leading to an increasing concentration of dissolved CO2 in sea-water. The dissolved CO2 then reacts with the water to create carbonic acid, decreasing the pH as recognised in the question.

The solubility of CO2 in water does decrease with increasing temperatures, so the maximum amount of CO2 that can be dissolved is being decreased as global temperatures rise, but the oceans are not yet saturated. There is a some further discussion and references om this page by NASA: The Oceans Carbon Balance.

Should global temperatures reach a point at which the oceans are saturated and start to release CO2 that they have been absorbing since the start of the industrial revolution, there would be very serious consequences for us all. This is, naturally, the subject of much ongoing research, e.g. Ocean-Atmosphere CO2 Exchange.

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    $\begingroup$ hot water can hold less of all the atmospheric gasses not only CO2 but O2 and CH4.if the O2 level drop life in the oceans will struggle to survive. $\endgroup$ Feb 25, 2020 at 18:41

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