Saturday, August 21, 2010

Hey, kids! Let's do some math...just for fun.

This month's issue of Geology has an article with the rather arcane title of "Covariability of the Southern Westerlies and atmospheric CO2 during the Holocene."  As I was reading it - yes, yes, yes, I do read this kind of stuff for "fun" and I don't have a life and I do need to get out more, but let's focus for the moment - I started to wonder how much CO2 is dissolved in the ocean.  Okay, so here is where the math comes in...I'll go slow.

Carbon dioxide can exist in water either as a dissolved gas, as it is in club soda or, more importantly, beer, or it can react with a water molecule to form a bicarbonate ion.  So the total amount of CO2 in the ocean is going to be the sum of the amount of dissolved gas and the amount tied up as bicarbonate ions.  A few minutes Googling will give you these numbers which are 90 milligrams of CO2 per kilogram of seawater and 104.6 milligrams of CO2 as bicarbonate per kilogram of seawater.  Keep in mind that the salinity of the ocean varies with temperature, location, and depth, so these are rough numbers, but we're going for order of magnitude here.  A little more Googling tells me that there are 1.37 million trillion metric tons of water in the world's oceans...again, this is a rough number, the CRC Handbook gives a number 20% higher.  Punching a few buttons on a calculator reveals that there are an estimated 2.67 hundred trillion metric tons of carbon dioxide in ocean waters right now.  Keep in mind also that this is just the "free" carbon dioxide available in sea water.  If all this CO2 were magically removed, it would be replenished by the dissolution of the calcium and magnesium carbonates that make up the bulk of sea floor sediments.  Consequently, it can be assumed that the levels of free CO2 in the ocean are more or less constant and that sea water represents an inexhaustible source of carbon dioxide.

How big are these numbers compared with what is bandied about by the anthropogenic global warmng types.  I will quote the estimable Department of Energy's numbers for annual fossil fuel derived carbon emissions:  averaging 26 billion metric tons of carbon dioxide per year between 2000 and 2006.  One suspects that these numbers are as inflated as James Hansen's temperature measurements, but let's just go with these for the moment.  What these numbers tell us is that it would take a hundred years of coal-burning, SUV-driving, natural gas-heating, airplane-flying carbon emissions at the present record-high levels to amount to one percent of the carbon dioxide reserve in the ocean.

Let me further point out that the solubility of carbon dioxide goes down sharply as the temperature goes up, which is why it is never a good idea to open a warm can of soda.  Between 0 deg C and 20 deg C (roughly the range of ocean temperatures these days) the solubility of carbon dioxide in water decreases about 5% for every degree of temperature increase.  Consequently, if the average temperature of the ocean increased one degree, that would have the potential for releasing 13 trillion tons of carbon dioxide into the atmosphere - the equivalent of 500 years of current levels of fossil fuel-based emissions.

Which brings me back to the Geology article I mentioned earlier.  Without boring you with the grisly details, the authors discovered that there was a direct correlation between the level of atmospheric carbon dioxide (as determined from Antarctic ice cores) and how hard the Southern Westerly winds were blowing (as inferred from pollen populations taken from South American lake sediment samples).  These winds, to quote the authors, “…constitute the major driver of the Antarctic Circumpolar Current, the formation and overturning of North Atlantic Deep Water, and the up-welling of CO2-rich deep water.”  In other words, 14,000 years ago, strong winds in the Southern Hemisphere drove ocean currents that caused CO2-rich water in deep ocean basins to rise to the warmer surface where it devolved carbon dioxide to the atmosphere.

This combination of westerly winds and ocean currents seems to have been operating for at least the past 800,000 years and, arguably, since the opening of the Atlantic Ocean about 40 million years ago.  The correlation between the Southern Westerlies and atmospheric carbon dioxide described in the Geology article would suggest that this has been the dominant mechanism for fixing carbon dioxide levels in the atmosphere for the past 14,000 years.

The take-away here:  The world's oceans represent a very large and temperature sensitive reservoir of CO and air and ocean currents provide a mechanism for the exchange of CO2 between the ocean and the atmosphere.  In the geologically recent past, this exchange has been the primary mechanism for fixing carbon dioxide levels in the atmosphere.  This begs the question that has been dodged and ignored by the Jame Hansen/Phil Jones/Michael Mann crowd:  Are the present high levels of atmospheric CO2 an artifact of rising global temperatures as opposed to the cause of them?  

1 comment:

  1. You know what? I'm going to use this for class. Because the guy who wrote the curriculum I'm following is freaking obsessed with every-day examples and how chemistry relates to global warming and various worldly matters.