By John Mauer
Today, every news show seems to talk about carbon dioxide (CO2), but usually with very little reference to actual data. Much of the news is dominated by political scare tactics or abject rejection of all science. So, here we describe, in a series of articles, the actual data as available on-line with references and some added science discussion.
However, before we get started, let’s separate science from conjecture and politics. Scientists rarely use the word believe. Those that do are usually theorists, including modelers, and use the word believe because they don’t have the data to back up their statements. Second, scientists never use the word consensus, ever. There are also several substitute words that fall into this category, like incontrovertible and high agreement. Those that use these words are not real scientists, or have left science for another calling. In general, follow the data, and keep an open mind.
And there is a reasonable amount of data. To start, take a look at the air around us, with water vapor excluded for the moment. Most of the air is nitrogen, followed by oxygen and an inert gas, argon. Carbon dioxide, CO2, is just 0.035% or 350 parts per million by volume (ppmv) on average. Water vapor, H2O, is not shown here because it varies so widely over the whole earth.[1]
Indeed, water vapor can vary from near zero to over 3%, depending on the temperature. Of course that is because water has both liquid and solid phases (ice) as well. The temperature determines the dominance of each phase. By the time the temperature reaches -60 degrees C near the poles, water vapor is negligible. Over the surface of the earth, however, water vapor averages about 1% or 1000 ppmv, 3 times CO2.
Although water vapor dominates any science of radiation heating (or cooling), the main trace molecules, carbon dioxide and methane, dominate discussions. Carbon dioxide, in particular, has been studied for some time now and is increasing as a minor constituent in the atmosphere. Methane depends on where you look. Because its main sources are on the surface, its concentration falls off rapidly with height.
The most complete data set for carbon dioxide comes from the Mauna Loa site, located at over 11,000 feet near a volcano in Hawaii.[2] These measurements of the CO2 concentration in air have been made continuously since 1958. They show a continuous increase with a yearly cycle.
Of course, the growth of CO2 concentration did not start in 1958; it has been going on for some time. For instance, using ice core data, the concentration has been growing since 1744. Ice core data are the measurements of air constituents in tapped bubbles in layered ice, generally from Antarctica. Recent data in the last three centuries are from the Siplo station.[3]
So the increase in CO2 concentration has been going on for centuries. In fact, using ice core data from the end of the last ice age, about 13,000 years ago, the concentration of CO2 has been increasing gradually for some time. The concern is the rapid increase in the last half of a century. (Note the suppressed zero which exaggerates the increase.)
All this data begs the question: what will happen in the future? Hofmann, from the NOAA Earth System Research Laboratory in Boulder, Colorado, has fit the Mauna Loa data to an exponential curve and, thus, projects that the total CO2 will double by the year 2050 to 580 ppmv. He also notes that the concentration growth tracks the population growth, which, if continued would indicate a maximum CO2 level of 430 ppmv, using the population projections of the United Nations.[4]
While this seems enormous, it is in line with the projections of the Intergovernmental Panel on Climate Change[5] (IPCC) whose report shows the CO2 concentration, for various scenarios, reaching 475 – 525 ppmv in 2050, and then keep going. And this report is being used to drive governmental change in energy production.
Of course, when projections such as these are used with such dire consequences, one must always ask whether they are properly done. All models must meet at least two criteria: fit all the data not just some and be physically reasonable. And the exponential fit is erroneous for those two very obvious reasons.
First, if the Siplo ice core data is added to the Mauna Loa data, the exponential doesn’t fit any longer. The projections of the fit to the earlier data are poor. Second, the exponential fit is not bounded for future projection, but goes to infinity, a very unphysical situation.
So, what happens if we include the physical processes into the problem, and demand that the fitted curve that we use for projections is bounded and be validated by the earlier data? In that case, we can get an estimate of the upper limit, along with a time frame for its occurrence.[6]
The method is straightforward; the type of mathematical curve is called a growth curve. It is frequently used to describe complex situations in which the growth is the sum of many complex processes. In this case the curve saturates at about 400 ppmv in 2028. (Error bars have been placed about the ice core data.)
Can such a curve be used for projections? Somewhat, but with caution. However, this projection is far better than the projections given by Hofmann and IPCC; at least the actual processes over time are described and the upper limits brought into play.
Now, what does this mean to the climate? None of this data or analysis ties CO2 concentration to world-wide temperature growth. None of the data even indicates the source of the CO2. This merely indicates the potential for the CO2 change in the near term. Thus, conclusions about the meaning of this data must be deferred to another discussion with more pertinent data.
1. The data here is from NASA Earth Fact Sheet modified to reflect the year 1987
2. C. D. Keeling, S. C. Piper, R. B. Bacastow, M. Wahlen, T. P. Whorf, M. Heimann, and H. A. Meijer, Exchanges of atmospheric CO2 and 13CO2 with the terrestrial biosphere and oceans from 1978 to 2000. I. Global aspects, SIO Reference Series, No. 01-06, Scripps Institution of Oceanography, San Diego, 88 pages, 2001.
3. Neftel, A., E. Moor, H. Oeschger, and B. Stauffer. 1985. Evidence from polar ice cores for the increase in atmospheric CO2 in the past two centuries. Nature 315:45-47.
4. World Population Prospects, 2007. The 2006 Revision, Highlights, Working Paper No. ESA/P/WP.202, United Nations, Department of Economic and Social Affairs, Population Division, New York.
5. IPCC, Climate Change 2007: Synthesis Report
6. For the mathematically curious, the analytical expression used is the Loglogisic distribution with a reversed axis. The parameter estimates were done using Maximum Likelihood Estimation, and converged quickly using Gauss-Newton. The curve has a negative skewness demanded by the data; curves with positive skewness did not fit because of the Siplo data.
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