In the first part of this article I presented a broad overview of the carbon cycle. What it shows is that no matter how the data is analyzed, the human contribution to the flow of carbon into the atmosphere is relatively small (~4%) part of the total. This also means that the contribution to the ‘acidification’ of the oceans must be even smaller than the atmospheric contribution. The available papers on the subject estimate the human contribution at ~2%. In this article I am going to spend more time looking at each carbon flow shown in the overall diagram.
I will start by showing the most well understood flow which is the human contribution. I will use the UN data as the source. This is also a good example of how difficult it is to compare the data from different sources. The units in the above diagram are for billion metric tons (Gt) of carbon. That is different than tons of carbon dioxide. The numbers used by the UN are in thousands of tons of carbon dioxide. Since CO2 has a total molecular weight of 44 and carbon is 12, then only 27.3% of the weight of carbon dioxide is carbon. So only that ratio of the emissions counts for the above carbon balance.
So in 2008 (latest year of full data) the total CO2 emissions were ~30 Gt, but that counts for almost 8Gt of actual carbon. It is this difference in carbon and carbon dioxide that makes looking at numbers from different sources confusing. Like many things, which numbers are used is determined by the appearance that one side would like to give. This difference can lead to confusion and I myself have missed it before.
Conversely, it is possible to multiply the values above by 3.67 to show how much carbon dioxide is emitted by each source. For instance plants absorb ~120 Gt of carbon each year, which is 440 Gt of carbon dioxide. So the direct comparison is that plants take in about 15x the amount of carbon dioxide that is emitted by mankind each year.
This difference between units needed to be clarified because otherwise none of it makes sense or adds up. The following chart shows human carbon emissions per year since 1990.
So by the official numbers the 9 Gt that show as emissions are a little optimistic, but only by a few years and it might be even be accurate for 2012 so I won’t argue the point.
Now lets consider the scale of carbon into the atmosphere in the past.
So here is where it gets interesting. One of the comments to the previous post stated that it isn’t the relative amount of CO2 that is the worry, but that what we are doing is disrupting the balance. My response is, at what point on this chart did the balance start to get disrupted?
Up until about 1950 the total carbon was about 1 Gt/year. That is ~0.4% of the annual flow to and from the atmosphere. It is also obvious from reading the papers that the error in our understanding is much greater than the amount of carbon that was being emitted prior to 1950. We know that the natural flow is ~210 Gt/year. We also know that in ENSO years will cause variations in the natural carbon flow of at least 2 Gt/yr. Droughts are thought to cause significant reductions in CO2 removal as well. So there are many natural factors that will cause variations that are larger than the human influence.
Certainly the Earth normally deals with natural variations on a regular basis. The seasons, droughts, floods are all natural variations that can easily exceed 10% of the average. Since we know that the Earth will naturally have a 2 Gt variation based on ENSO without any problem, it should be clear that emissions under 2 Gt are not a problem for the Earth. That demonstrates that a 1% human contribution is very unlikely to be significant.
At 4% I would agree that human emissions are reaching the point of being able to influence the total amount of CO2 in the atmosphere for a short while. What that means is that if we stopped, the natural equilibrium would be reached again in a few years. What impact the CO2 in the atmosphere would have is NOT the point of this article, so lets not go there. The point of this article is to go over the carbon cycle and look at the influence mankind may be having on it.
The one great flaw in the debate about the human influence is that we don’t have accurate measurements for CO2 over the past 10,000 years. What we have are air bubbles trapped in ice cores. No matter what anyone says, using ice cores bubbles is not an apples to apples comparison. Not only that, only ice cores from Antarctica are used. This is because the ice cores from the Northern Hemisphere show much greater variation than the ones in the Southern Hemisphere.
It is also interesting that each year, a similar difference in the variation takes place at different places on the Earth.
It is pointless to argue that there is not a regional dependence on the CO2 level and that each region will have a different CO2 level based on the time of the year. It would make sense that ice cores from the Northern Hemisphere would reflect this and in fact they do, but because they show greater variation, they are considered unreliable and ignored because the argument is accepted that CO2 is added into the air bubbles in the Northern Hemisphere, but not the Southern Hemisphere.
As a result the inconvenient data is safely ignored, even though it more accurately reflects what is taking place in the world today. If the Greenland Ice Cores were the accepted ones, then the argument about CO2 level would be very different today.
So the only thing that is clearly known with accuracy and precision today is that the CO2 level has increased over the past 100 years. It is likely that mankind’s emissions have contributed to this increase, but only after the 1950’s and just how much cannot be known precisely. What is known is that the human contribution is comparable in size to yearly natural variations in the the flow of carbon to and from the atmosphere. It is also known that where and when the CO2 level is measured makes a big difference in the results that are obtained.
In the next and final part of this, I will delve into the carbon flow of the oceans and deal with the entire acidification aspect of the debate.