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The Carbon Cycle And The ‘Acidification’ Of The Ocean

One of the few things that I have not covered before in depth is the carbon cycle.  That is the path that carbon takes in and out of the atmosphere.  For example, plants absorb CO2 from the atmosphere, but eventually that carbon will make it’s way back into the atmosphere.  The flow of carbon from one place to another is the carbon cycle.  I have been waiting for the right time to get to this topic and that has finally arrived.

Why now you ask?  Well there is a new paper that is in the news which plays on peoples lack of perspective about the carbon cycle.  It has been all over the news in the past week and it is an amazing piece of FUD.  The claim that the paper makes is that the oceans are experiencing the fastest rate of ocean acidification that has happened in the past 300 million years.  Even more disturbing is the claim that they can’t go back farther than that so what is left implied is that the Earth is currently experiencing the greatest rate of ocean acidification ever.  In addition they tie such changes to the oceans acidification to mass extinctions.  So to sum it up, the paper is saying that the Earth is potentially heading to the greatest mass extinction of life because of CO2 emissions.

Carbon Cycle Overview

The Inconvenient Skeptic

Overview of the “fast” carbon cycle. (Yellow) Natural Carbon Flows, (Red) Human Carbon Flows

I will use the NASA Earth Observatory as the source of graphics and in general I will use the numbers from them for this article.  I will specify if I am not using their numbers.

Flows to the Atmosphere:

There are three natural flows of CO2 to the atmosphere and then there are human emissions.

Ocean Exchange:      90

Plant Respiration:     60

Decomposition:        60

Human Emissions:    9


Total CO2 into atmosphere:   219

Human Contribution:            4%

So all of the human activity accounts for only 4% of the total flow into the atmosphere.  It is also the only quantity that is accurately known.  If I assume that we know the other values to within 10% accuracy, then it would be accurate to say that the natural flow of CO2 into the atmosphere is 210 +/- 21 carbon units.  Even the uncertainty in the natural flows is larger than what is known to be human caused.

This should be a very clear indicator that while mankind does indeed introduce a measurable amount of CO2 into the natural cycle, the natural portions of the cycle dwarf the human contribution.  The small scale of the mankinds contribution is tied to questions about the reliability of the past CO2 levels as I previously discussed here.  The ice cores in Greenland show a very different history than the ice cores from Antarctica.

The Inconvenient Skeptic

GISP2 CO2 ppmv data by ice core depth. The depths associated are: 1900m ~= 19,000 YPB, 1650m ~= 11,100 YBP

The records from Greenland show many times in the past when the CO2 level cycled rapidly over the course of a few hundred years by as much as 100 ppm.  This provides some evidence that such rapid cycles of CO2 change are in fact natural in origin.  Considering the scale of mankinds contribution, I consider this a realistic probability.

Flows to the Atmosphere

There are only two paths by which CO2 exits the atmosphere.

Ocean Exchange:        92   (2 anthropogenic)

Photosynthesis:         123  (3 anthropogenic)


Total CO2 from atmosphere:   215  (5 anthropogenic)

Human Contribution:            2%

The scope of the uncertainty is equal for the amount of CO2 leaving the atmosphere at +/- 21 units, but there is also some uncertainty about the anthropogenic values, but for arguments sake I will accept these values as reasonable.  If this is the case, then the human contribution to the ocean exchange is ~2% of the natural value.

In both of these cases I have only dealt with the flows of carbon to and from the atmospheric system.  The amounts of carbon that exist in some of the systems is enormous.  The ocean surface is listed as having 1,000 units of carbon already.  Of course it only takes 11 years for the entire ocean surface to completely turn over the carbon with the atmosphere (1,000 units at 90 units per year).  While this is not quite the same as having the sprinklers on during a thunderstorm, it is pretty close.  Human contribution to the carbon cycle is little more than rounding error for the natural cycle.

It also shows the problem of treating CO2 as a pollutant.  Natural decomposition of plant material contributes more than 6 times as much CO2 to the atmosphere as all of the activity that mankind does.  The science does not support the idea that CO2emissions are a pollutant.  The next part of the article will discuss the specifics of ocean acidification.  That mankind is at most a 2% contributor to the amount of carbon that is entering the ocean should give the reader a pretty good idea of how that will go.

see also Part II