Ocean Acidification - what is it about?

 Bednarsek (2012).  

Ocean acidification is sometimes described as global warming's evil twin.

About 30-40% of the CO2 we have put out since the Industrial Revolution (~1750AD) has dissolved into the world's oceans. Which is helpful as far as greenhouse warming goes, but not good for the ocean, as it makes it less alkaline.


Before 1750 the sea water was at pH 8.25. It is now 8.14 - still alkaline, but the drop represents a 30% increase in the concentration of free protons in seawater. pH is a measure of acidity and alkalinity. 7 is neutral, above 7 is alkaline, below 7 is acid. It is a log scale, so a small change of pH represents a big change in the amount of acidic H+ ions (protons) floating about.

It is the rate of change that is the major concern. Sea water is in fact now at a more alkaline pH than it has been for some 300 millions of years. 110 million years ago it sea water was acidic, at a pH of 7.5, so it is not the case, as some have mistakenly said, that sea water is more acidic than in the last 300 million years, but it is the case that the pH changing more rapidly than at any time in many, possibly 300, millions of years.

What are the dangers of this rapid acidification?

First and most obvious is that marine creatures that rely on calcification for shells or structure are going to struggle.

Both zooplankton and some phytoplankton rely on calcification. Since they are at the beginning of the food chain, their difficulties will feed back to the rest of marine life.

Coral reefs are at risk, which is the primary problem, because they are to the sea what forests are to land. They support vast numbers of marine species, and their decay or loss puts pressure on marine biodiversity and the livelihoods of up to 500 million people. Corals are also stressed by warm water and nutrient runoff from human pollution. It is thought that coral growth rates are already slowing. Warm seas cause coral bleaching episodes. Sometimes coral does not recover from prolonged bleaching episodes. It is thought that 450 ppm of CO2 in the air, and +2C temperature rise, could render coral extinct.

Squid and other organisms could also be affected directly by acidification.

Although the changes we see now are small, we must keep in mind that acidification will continue long after we have stopped putting fossil CO2 into the air, and so we are committed to worsening effects throughout the rest of this century. It is vital therefore that we address decarbonisation with more enthusiasm.

Acidification is made more serious because of other man-made changes in the oceans, namely

• warming
• overfishing
• pollution, especially that which causes deoxygenation of the water.

It is both difficult and pointless to try to separate these synergistic effects. Marine ecosystems are stressed and if these stresses continue, the results will be severe. The International Programme on the State of the Ocean (IPSO) warned in June 2011 that we are at risk of a mass extinction event in the ocean unless we change course. In their latest press release, they say at CO2 concentrations of 450-500 ppm (projected in 2030-2050) erosion will exceed calcification in the coral reef building process, resulting in the extinction of some species and decline in biodiversity overall. 

Here is their 2013 report

IPSO's policy recommendations are worth noting:

As a matter of urgency, the marine scientists say that world governments must: 

• Reduce global C02 emissions to limit temperature rise to less than 2C, or 
below 450 CO2e. Current targets for carbon emission reductions are 
insufficient in terms of ensuring coral reef survival and other biological effects 
of acidification, especially as there is a time lag of several decades between 
atmospheric CO2 and CO2 dissolved in the ocean. Potential knock-on effects 

of climate change in the ocean, such as methane release from melting 

permafrost, and coral dieback, mean the consequences for human and ocean 

life could be even worse than presently calculated.

 

• Ensure effective implementation of community- and ecosystem-based 

management, favouring small-scale fisheries. Examples of broad-scale 

measures include introducing true co-management with resource adjacent 

communities, eliminating harmful subsidies that drive overcapacity, protection 

of vulnerable marine ecosystems, banning the most destructive fishing gear, 

and combating IUU fishing. 

 

• Build a global infrastructure for high seas governance that is fit-for-purpose. 

Most importantly, secure a new implementing agreement for the conservation 

and sustainable use of biodiversity in areas beyond national jurisdiction under 

the auspices of UNCLOS. 

The problem with the sea is (a) that it is very big, which causes nervous land based life forms to think that nothing could harm it, and (b) nobody owns it, so no politician feels directly responsible for its health and well-being. This has to change.  I am hopeful that in coming years the realisation will hit that humans are social animals, not solitary animals, and that we will have to work together to protect our common living space.

The one chink of light in this picture is that warmer seas will be slower to dissolve CO2. However, this in turn means that atmospheric CO2 levels will increase.

Ocean acidification is sufficiently serious that in a rational world it alone should cause us to decarbonise our energy sources. In tandem with the other effects of carbon use, and the fact that carbon resources are finite, the case for decarbonisation is overwhelming.

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There is a very helpful brief summary of the science here

Here is the 2005 Royal Society report on acidification

Needless to say, the carbon industry's denial machine is trying to start itself up. Cliff Ollier has a string of anecdotal accounts which will, in the minds of assorted oil industry schills, libertarians and free marketeers, be more convincing than pages and pages of peer-reviewed science.