26 June 2010

Other Climate Change Indicators

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Other than temperature, there are a few more indicators of climate change that are studied, which I will cover in overview here as promised in one of my earlier blogs.

Firstly, there is sea level rise.  The first thing to say about sea level rise is that the melting of the Arctic Ice Sheet does not increase the sea levels as you are simply replacing the volume of ice with the same of water.  Sea level rise comes mainly from the expansion of the water volume as the temperature of the oceans rises, plus just under half from the melting of land based ice such as on Antarctica or Greenland's glaciers or over North America.  However, while there is definitely sea level rise, it is not that scary being of the order of centimetres rather than metres.  So we have historic sea level rises of 1.7mm to 3mm (after 1993) per annum  during the 20th century, or 20cm over 1900 to 2000, with forecast sea level rises of about 4mm every year reaching a total rise of 22cm to 44cm by 2090 from a base date of 1990. 

There is the remote possibility of a massive ice sheet melt from the Antarctic but this is viewed by the IPCC as a millenium scale event, i.e. really, really unlikely; in fact, increased precipitation is expected to continue with extra snowfall falling onto the Antarctic and so thickening the ice cap on the South Pole!  For a more detailed and easy to understand slide show go to this one on Slideshare.

Next, there is the increasing acidity of the oceans.  As carbon dioxide in the atmosphere increases, so more of this in dissolved in the oceans and waters of the world; other gases like nitrous oxide and sulphur dioxide also dissolve in water creating further acids, but here I am focussing on carbon dioxide.  The oceans act as an important sink or buffer for human activity, having absorbed over 80% of the heat added to the climate system and 30% of the human-derived carbon emissions over the last 200 years.  This point which has passed me by probably goes some way to explaining my earlier query as to why the link between greenhouse gas emissions and global warming is not so direct, i.e. because the water in the oceans, rivers and lakes dampens the impact [pun unitended but I like it] and takes up much of the initial heat and some of the increase in carbon dioxide and other gases. 

The ocean pH is about 0.1 pH units below the pre-industrial averages at around 8.1 and is forecast to fall another 0.4 to 0.4 pH units by 2100.  The impact directly on humans is minimal, however there is concern as to the impact on calcifying organisms that require carbonates to build their shells; a falling pH reduces the availability of carbonate in the water for corals, bivalves, crustaceans and plankton, which would then have implications on marine food webs and ecosystems.  These are simply explained at the following link and then there's more detail on the oceans and coral reefs at the great web site Climate Shifts and on the BBC.

So we have further climate indicators that are showing that man is shaping the earth's climate through his/her agricultural and industrial activity.