Climate change and ocean acidification

The topic of climate change is controversial, especially when it concerns changing weather patterns. At sea, however, it’s quite different. We know that sea temperatures are rising slowly and we also know that as carbon dioxide (CO2) dissolves in seawater it becomes more acidic.

We know because we have long time series of measurements, these things really are happening.

Nearly all fish species have their own ‘comfort zone’ – a fairly narrow temperature range of the water in which they live. Most could actually exist outside this range but very often they are programmed to adopt it because it sets the conditions for where their prey is. A very good example of this is cod. They can tolerate quite a wide range of temperatures – from almost freezing to nearly 20oC – but as small fish they need to feed on particular species of plankton that are very nutritious. The plankton bloom when light and temperature conditions are just right so, if they change their seasonality or their distribution, the bloom may not coincide with the appearance of the tiny cod. If the cod can’t get the right food at the right time they don’t grow fast enough and they get eaten by another species – maybe haddock or whiting. Small changes can have big impacts – a whole ‘year class’ of a species can be very strong, or very weak, depending on tiny temperature changes.

The populations of many fish species are tending to move very slowly towards the polar regions. In the British Isles we are now seeing many fish that were previously associated with Spain, Portugal or the Mediterranean – fish like red mullet along with octopus and squid – so opportunities for fishermen are changing.

Acidification is a far more serious matter. Each year the oceans absorb over 25% of all the CO2 we emit. The acidity of sea water does vary naturally across the oceans but creatures have adapted to these differing, but fairly stable, conditions. Ocean acidity has increased by 30% since the beginning of the Industrial Revolution and the rate of change will accelerate in the coming decades. This rate of change is faster than anything in the last 50 million years plus.

Very many animals and plants in the sea have calcium carbonate skeletons or shells, are at the base of the food web, produce oxygen by respiration and ‘bury’ carbon when they die, sink, and form sedimentary rock. Some that are especially sensitive to acidification are already being affected. Very few, if any, can adapt quickly enough to keep pace with what’s happening.

The impact of ocean acidification will be profound. As it affects marine species, food webs will be damaged and result in major economic impacts as well as putting at risk food security in regions that are particularly dependent on seafood protein.

Coral reefs are being affected by a combination of temperature increase and acidification. They are important for biodiversity but they also play a key role in protecting low-lying land.

So ocean acidification is happening, we can measure it and it’s creating potentially huge risks. It may be the strongest argument we have for introducing aggressive and immediate cuts in CO2 emissions.

You can learn more about ocean acidification from the European Project on Ocean Acidification.

The MCCIP website has recently been updated with new marine climate change news and events.

SEAFISH, Web site.

1 Response to “Climate change and ocean acidification”


  1. 1 Joe Earth 8 February 2011 at 15:48

    I think the best way to get a response to this would be to estimate how ocean acidification would affect fishing industries in the near future.


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