Monday, 15 March 2010

More vinegar on your fish, sir?

Rising greenhouse gas levels are not “just” a threat to the climate, food supplies, habitats etc. Elevated levels of CO2 are dissolving in the oceans and are acidifying them. Normally, the ocean is slightly alkaline but it is getting less so due to our excess emissions. Some might argue that if the seas are absorbing CO2 then  we don’t have to reduce fossil fuel use. The problem is that even with this effect, we are still “gaining” – the Earth’s systems can absorb a certain amount of emissions of CO2 per year but, on top of the natural emissions, we are adding sufficient extra CO2 to overwhelm the Earth’s ability to absorb it – that is why CO2 levels in the atmosphere are steadily rising.

The oceans currently are acting as a partial buffer to our emissions but buffering solutions (seawater in this case) only work for a while before approaching saturation. As this starts to happen, the oceans will slow in their ability to absorb CO2 and, at that point, if we have not reduced our emissions, there will be a steepening rise in the amount of CO2 building up in the atmosphere, leading to an increasing boost (a positive feedback) to the greenhouse effect boost. This won’t be a runaway feedback, because the greenhouse potential of CO2 reduces logarithmically as the concentration increases, but it still won’t be a good thing.

Ocean acidication is an astonishing long term threat that has been getting very little publicity. The professional video at the end of this blog is an attempt to rectify that.  Here’s an article about acidification which paints a worrying picture. Here’s a link to a scientific paper in Nature. Here’s the Wikipedia article about it.

If we continue on our current emissions path without drastically reducing our use of fossil fuels, the oceans will steadily get more acidic over the next couple of hundred years.The problem with this is that many of the smallest organisms in the sea, such as plankton, which form the basis of the oceanic food chain, have shells or other structures that are vulnerable to increased acid in sea water. There are few tipping points known for certain in climate/Earth science.  One of them in prehistory is when CO2 reached about 1000 ppm leading to an “anoxic event”. In the Permian-Triassic era (250 million years ago) mass die off of species, up to 96 percent of all marine species and 70 percent of terrestrial vertebrate species became extinct; it was the only known mass extinction of insects. Fifty-seven percent of all families and 83% of all genera were killed. There are various reasons posited for this event but a strong contender is hypercapnia (too much CO2) which causes anoxic events.

Methane release, from when permafrost melts and releases its stored CO2 and methane, gives a large boost to the greenhouse effect. Methane however is a relatively short lived gas in the atmosphere – it ends up being oxidised to CO2. A worse situation would be the release of methane clathrates from under the sea bed – a so-called “clathrate gun”. Clathrates are “condensed” methane held in a sort of waxy ice which is stable  only because it is cold and under great pressure at the bottom of the sea. Warm it up or remove the pressure and it bubbles up as the powerful greenhouse gas methane. Gas releases from undersea methane clathrate deposits have caused a sudden powerful excess greenhouse effect which was thought to be responsible for mass species extinctions in the past, like those referenced above

Here’s a 21 minute video from the NRDC, narrated by Sigourney Weaver, about the increasing acidification of the oceans - which is happening right now. As I said at the beginning, it’s an under-reported consequence of increasing carbon dioxide levels specifically, as opposed to general greenhouse gases.

It’s worth double clicking on the headline link to go directly to Youtube rather than watching it on the embedded player because the film is quite beautiful too and worth watching large.

Acid Test: The Global Challenge of Ocean Acidification


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