Wednesday, June 8, 2011

Its the bubbles of nothing that make it something…

What is ocean acidification and how is it related to carbon dioxide in the atmosphere?

Alan Jones recently claimed that CO2 is nothing, or as the SMH characterized it a bit of fizz that enlivens the brew.

The following simplified explanation is straight from the evil genius of  global warming swindler strongholds The Royal Society and The Annual Reviews of Marine Science.

Below is an equation and accompanying graph that describe the interaction of CO2 and water. From the left, the equation shows CO2 in the atmosphere in a dynamic equilibrium with CO2 dissolved in water. This CO2 then interacts with water to form carbonic acid which then dissociates (ie “breaks up”) releasing hydrogen ions (ie H+, ie acid) in two steps. Each of the double arrows means that the reaction proceeds in both the forward and reverse direction until an equilibrium is achieved (in theory). In practice an equilibrium may not be achieved (ie concentrations of all species may fluctuate slightly).


image The graph depicts the relative concentrations of the three forms of inorganic carbon as a function of pH. The pH range for seawater is shown, which depends on the concentration of CO2 over the ocean and the temperature of the water (among other factors). Another way of thinking about this diagram is to ask ;

“What happens if the concentration of CO2 over the water increases?”

Mauno Loa is the atmospheric station with the longest continuous CO2 record. Since 1990 pH in the ocean nearby has also been recorded and a strong correlation is seen between these adjacent sites. Note, these are not the longest time series measurements of pH.


Returning to the equation, if the CO2(atmosphere) (on the left)  increases this will have the effect of “driving” the reaction to the right, first increasing the CO2 dissolved in the water then the carbonic acid (H2CO3) then the bicarbonate etc… It should be clear from this equation that as the equilibrium is pushed to the right, the concentration of H+  and therefore the acidity increases. This shows up as a decrease in the value of pH. Note in passing that pH is a log scale (ie pH = –log[H+] where [ ] means concentration). The important point to note is that like the Richter scale a change of one unit represents an absolute change of 10 times magnitude (in this case in concentration).

In school we are all taught that pH 7 is “neutral” and that anything below this is acidic. The use of the word neutral does not mean “no effect”. It just means that at this pH the concentration of H+ and OH- are equal. The solubility of carbonate species begins to increase before the pH reaches or drops below 7. In the figure below at a pH of ~8 the concentration of Ca ions (from CaCO3 in water) is “only” ~ 120 mg/L but at pH ~ 7 this has increased to ~ 12 g/L (eyeballing this graph it is – if I’ve remembered right!).

image The species each side of a double arrow can be further considered in detail, and each represents a process that can be related to a constant – the solubility product (Ksp) – which is mostly dependant on temperature. These constants are not affected by how people feel about them or who they vote for. All of the other chemical reactions/equilibria in the ocean can be described with similar equations. The practical upshot being that given accurate measurements of the current concentrations of the important chemical species, it is relatively simple to project the consequences of increased CO2 concentrations on oceanic pH. There are far fewer uncertainties than experienced with atmospheric modeling.


This figure is the projected effect on the ocean for the next 1000 years as the oceans absorb a substantial amount of the CO2 released by burning fossil fuels. Note that this is a simple box model representation of the whole ocean (ie global average effect). Local extremes in pH outside of the ranges shown here will occur.

image What does this mean? The acidity of the ocean affects the formation of shells by interfering with the formation of Ca minerals used by many marine species. Corals and other organisms that use aragonite (a form of carbonate mineral with a higher solubility) are more susceptible to stress as a result. The reefs of the world in turn support numerous diverse species. In purely economic terms, they are an important fishery and recreational area. For example,

The World Resources Institute (Burke et al 2004) has estimated that in 2000, Caribbean coral reefs alone ‘provided annual net benefits in terms of fisheries, dive tourism, and shoreline protection services with an estimated value between US$3.1 billion and US$4.6 billion’ (about £2 000 million and £3 000 million, using the exchange rate in May 2005); and that the loss of income by 2015 from these degraded reefs may be several hundred million dollars per annum.


Coastal reefs in Hawaii have been estimated to generate almost US$364 million each year in added value (Cesar et al 2002).


See a more detailed graphical version here.

There are winners and losers in this race - mostly losers - and what is not captured is the flow on affects as species abundances change. These stresses are on top of the stresses due to the already observed changes in ocean temperature.

One of the important debating reasons for being aware of ocean pH is that it is an independent effect of CO2 that can not be accounted for by alternative global warming theories. IE, the anthropogenic global warming due to atmospheric CO2 release model accounts for both temperature rise and pH changes. Alternative views (ie the sun did it) have to separately account for the pH changes.

I prefer Occam's Razor.

Ocean Acidification: The Other CO2 Problem, Annual Reviews of Marine Science.

Ocean acidification due to increasing atmospheric carbon dioxide, The Royal Society.

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