Foreword: This is the final entry in a four part series by Fedinand Engelbeen. While the narrative is contrary to the views of many of our readers, it is within the framework of WUWT’s goal of providing discussion on the issues. You won’t find guest posts like this on RC, Climate Progress, Open Mind (Tamino), or Skeptical Science where a guest narrative contrary to the blog owner(s) view is not allowed, much less encouraged in a four part series.
That said, I expect this final entry to be quite contentious for two reasons. 1) The content itself. 2) The references to the work of Ernst Georg Beck, recently deceased.
As Engelbeen mentions below, this part was written weeks before, and readers should not get the impression that this is some sort of “hit piece” on him. Unfortunately, it simply worked out that the appearance of part 4 happens after his death, since I had been running each part about once a week. I had considered not running it, but I’m sure he would invite the discussion, and we’d have a lively debate. It is our loss that he will not be able to. For that reason, I’d appreciate readers maintaining a civil tone in comments. Moderators, don’t be shy about enforcing this. My thanks to Ferdinand Englebeen for his hard work in producing this four part series. – Anthony
About background levels, historical measurements and stomata proxies…
1. Where to measure? The concept of “background” CO2 levels.
Although there were already some hints of a “global” background CO2 level of around 300 ppmv in previous years, the concept was launched by C.D. Keeling in the fifties of last century, when he made several series of measurements in the USA. He found widely varying CO2 levels, sometimes in samples taken as short as 15 minutes from each other. He also noticed that values in widely different places, far away from each other, but taken in the afternoon, were much lower and much closer resembling each other. He thought that this was because in the afternoon, there was more turbulence and the production of CO2 by decaying vegetation and/or emissions was more readily mixed with the overlying air. Fortunately, from the first series on, he also measured 13C/12C ratios of the same samples, which did prove that the diurnal variation was from vegetation decay at night, while during the day photosynthesis at one side and turbulence at the other side increased the 13C/12C ratio back to maximum values.
Keeling’s first series of samples, taken at Big Sur State Park, showing the diurnal CO2 and d13C cycle, was published in http://www.icsu-scope.org/downloadpubs/scope13/chapter03.html , original data (of other series too) can be found in http://www.biokurs.de/treibhaus/literatur/keeling/Keeling_1955.doc :
Several others measured CO2 levels/d13C ratios of their own samples too. This happened at several places in Germany (Heidelberg, Schauinsland, Nord Rhine Westphalia). This confirmed that local production was the origin of the high CO2 levels. The smallest CO2/d13C variations were found in mountain ranges, deserts and on or near the oceans. The largest in forests, crop fields, urban neighborhoods and non-urban, but heavily industrialized neighborhoods. When the reciprocal of CO2 levels were plotted against d13C ratios, this showed a clear relationship between the two. Again from http://www.icsu-scope.org/downloadpubs/scope13/chapter03.html :
Figure 2. Relation between carbon isotope ratio and concentration of atmospheric CO2 in different air types from measurements summarized in Table 3.4
(Keeling, 1958, 1961: full squares; Esser, 1975: open circles; Freyer and Wiesberg, 1975,
Freyer, 1978c: open squares). All 13C measurements have not been corrected
for N2O contamination (Craig and Keeling, 1963), which is at the most in the area of + 0.6‰
The search for background places.
Keeling then sought for places on earth not (or not much) influenced by local production/uptake, thus far from forests, agriculture and/or urbanization. He had the opportunity to launch two continuous measurements: at Mauna Loa and at the South Pole. Later, other “baseline” stations were added, all together 10 from near the North Pole (Alert, NWT, Canada) to the South Pole, all of them working continuous nowadays under supervision of NOAA (previously under Scripps Institute), some 60 other places working under other organizations and many more working with regular flask sampling.
We are interested in CO2 levels in a certain year all over the globe and the trends of the CO2 levels over the years. So, here we are at the definition of the “background” level:
Yearly average data taken from places minimal influenced by vegetation and other natural and human sources are deemed “background”.
For convenience, the yearly average data from Mauna Loa are used as reference. One could use any baseline station as reference or the average of the stations, but as all base stations (and a lot of other stations, even Schauinsland, at 1,000 m altitude, midst the Black Forest, Germany) are within 5 ppmv of Mauna Loa, with near identical trends, and that station has the longest near-continuous CO2 record, Mauna Loa is used as “the” reference.
As the oceans represent about 70% of the earth’s surface, and all oceanic stations show near the same yearly averages and trends, already 70% of the atmosphere shows background behavior. This can be extended to near the total earth for the part above the inversion layer.
Measurements above the inversion layer.
Above land, diurnal variations are only seen up to 150 m (according to http://www.icsu-scope.org/downloadpubs/scope13/chapter03.html ).
Seasonal changes reduce with altitude. This is based on years of flights (1963-1979) in Scandinavia (see the previous reference) and between Scandinavia and California (http://dge.stanford.edu/SCOPE/SCOPE_16/SCOPE_16_1.4.1_Bishoff_113-116.pdf ), further confirmed by old and modern https://wiki.ucar.edu/display/acme/ACME flights in the USA and Australia (Tasmania). In the SH, the seasonal variation is much smaller and there is a high-altitude to lower altitude gradient, where the high altitude is 1 ppmv richer in CO2 than the lower altitude. This may be caused by the supply of extra CO2 from the NH via the southern branch of the Hadley cell to the upper troposphere in the SH.
From the previous references:
Figure 3. Amplitude and phase shift of seasonal variations in atmospheric CO2
at different altitudes, calculated from direct observations by harmonic analysis
(Bolin and Bischof, 1970)
From https://wiki.ucar.edu/display/acme/ACME :
As one can see, again the values above the inversion layer are near straight and agree within a few ppmv with the Mauna Loa data of the same date. Below the inversion layer, the morning values are 15-35 ppmv higher. In the afternoon, these may sink to background again.
If we take the 1000 m as the average upper level for the influence of local disturbances, that represents about 10% of the atmospheric mass. Thus the “background” level can be found at 70% of the earth’s air mass (oceans) + 90% of the remaining land surface (27%). That is in 97% of the global air mass. Only 3% of the global air mass contains not-well mixed amounts of CO2, which is only over land. These measured values show variations caused by seasonal changes (mainly in the NH) and a NH-SH lag. Yearly averages are within 5 ppmv:
Figure 5. Yearly average CO2 levels at different baseline stations plus a non-baseline station (Schauinsland, Germany, only values taken when above the inversion layer and with sufficient wind speed).
Background CO2 levels can be found everywhere over the oceans and over land at 1000 m and higher altitudes (in high mountain ranges, this may be higher).
2. The historical data
2.1. The compilation by Ernst Beck.
Note: this comment was written weeks before we heard of the untimely death of Ernst Beck. While I feel very uncomfortable that this is published now, as he can’t react anymore on this comment, I think that one need to know the different viewpoints about the historical data, which is a matter of difference in opinion, and has nothing to do with what one may think about Ernst Beck as person.
What about the historical data? While I only can admire the tremendous amount of work that Ernst Beck has done, I don’t agree with his interpretation of the results. Not in light of the above findings of what one can see as “background” CO2 levels.
The historical measurements show huge differences from place to place, sometimes within one year, and extreme differences within a day or day to day or over the seasons for the same place. That there are huge differences between different places shows that one or more or all of these places are not measuring background CO2, but local CO2 levels, influenced by local and/or regional sources and sinks. This is clear, if one looks at the range of the results, often many hundreds of ppmv’s between the lowest and highest values. Modern measurements, sometimes interestingly done at the same places as the historical one’s, either don’t show such a wide range, and then can be deemed background for the modern ones and therefore the historical one’s must be inaccurate as method or there were problems with the handling or with the sampling. Others show huge variations also today, which means that neither the modern, nor the historical data are background.
But let us have a look at the compilation of historical CO2 measurements by Ernst Beck:
Figure 6. Compilation of historical data by Ernst Beck.
Beck only gives the yearly and smoothed averages and the instrument error. That doesn’t say anything about the quality of the places where was measured, thus which of these measurements were “background” and which were not. One may be pretty sure that measuring midst of London, even in 1935, would give much higher (and fluctuating) CO2 levels than near the coast with seaside wind. Moreover, a peak of some 80 ppmv around 1942 is hardly possible, but removing such a peak in less than 10 years is physically impossible. The total amount of CO2 involved is comparable to burning down one third of all living vegetation on land and growing back in a few years time. The oceans are capable of having a burst of CO2 with a sudden decrease of pH, but simply can’t absorb that amount back in such a short time span, even if the pH would go up again (and what should cause such a massive change in pH?). Therefore I decided to look into more detail at the peak period in question, the years 1930-1950.
2.2. The minima, maxima and averages
Here is a plot of all available data for the period 1930-1950, as used by Ernst Beck (plus a few extra I did find in the literature). These can be found at his page of historical literature:
Figure 7. Minima, maxima and averages of historical measurements in the period 1930-1950
Not all measurements were published in detail. Several authors did provide only an average, without any indication of number of samples, range or standard deviation. But for those where the range was given, the results are widely varying. What is obvious, is that where the range is small, in most cases the average of the measurements is around the ice core values (Law Dome in this case, the values of three cores, two of them with a resolution of 8 years and an accuracy of 1.2 ppmv, 1 sigma). That is especially the case for the period 1930-1935 where several measurements were performed during trips over the oceans. And even most of the worst performers show minima below the ice core values.
And as one can see, the “peak” around 1940-1942 is completely based on measurements at places which were heavily influenced by local/regional sources and sinks. That doesn’t say anything about the real background CO2 level of that period. Moreover, the fact that the average of measurements at one part of the world is 600 ppmv and at the other side of the globe it is 300 ppmv within the same year, shows that at least one of them must be at the wrong place.
2.3. The accuracy of some apparatus
Some of the measurements were done at interesting places: Point Barrow and Antarctica, where currently baseline stations are established. Unfortunately, for these measurements, the portable apparatus was as inaccurate as could be:
Barrow (1948) used the micro-Schollander apparatus, which was intended for measuring CO2 in exhaled air (some 20,000 ppmv!). Accuracy +/- 150 ppmv, accurate enough for exhaled air, but not really accurate to measure values of around 300 ppmv.
The same problem for Antarctica (1940-1941): Accuracy +/- 300 ppmv, moreover oxygen levels which were too low at high CO2 (1700 ppmv), which points to huge local contamination.
2.4. What caused the 1941 peak?
The 1941 peak is heavily influenced by two data series: Poona (India) and Giessen (Germany). With a few exceptions, the results of Poona should be discarded, as these were mostly performed within and below growing vegetation, which may be of interest for those who want to know the influence of CO2 on growth figures, heavily influenced by CO2 production from soil bacteria, but not really suitable to know the background CO2 levels of that time.
Giessen is a more interesting place, as the measurements were over a very long period (1.5 years), three samples a day over 4 heights were taken. And we have a modern CO2 measuring station now, only a few km from the original place, taking samples every 30 minutes. Thus let us see what the historical and modern CO2 levels at Giessen are, compared to baseline places:
Figure 8. Historical data of Giessen, during a few days of extra sampling to measure diurnal changes.
Figure 9. A few days in the modern summer life of CO2 at Linden-Giessen compared to the raw data from a few baseline stations for the same days.
Data for Linden-Giessen are from http://www.hlug.de
Baseline stations hourly average CO2 levels, derived from 10-second raw voltage samples, are from ftp://ftp.cmdl.noaa.gov/ccg/co2/in-situ/
These are all raw data, including all local outliers at Barrow, Mauna Loa, the South Pole and Giessen. It seems to me that it is rather problematic to figure out anything background-like from the data of Giessen, modern and historical alike. And I have the impression that Keeling made not such a bad choice by starting measurements at the South Pole and Mauna Loa, even if the latter is on an active volcano.
2.5. Estimation of the historical background CO2 levels.
Francis Massen and Ernst Beck used a method to estimate the background CO2 levels from noisy data, based on the fact that at high wind speeds, a better mixing of ground level CO2 with higher air masses is obtained (see http://www.biokurs.de/treibhaus/CO2_versus_windspeed-review-1-FM.pdf ). This works quite well, if you have a lot of data points with wind speeds above 4 m/s and a relative narrow range at high wind speeds. Here the “fingerlike” data range at high wind speed measured at Diekirch (small town in a shielded valley of Luxemburg):
Figure 10. CO2 levels vs. wind speed at Diekirch, Luxemburg.
Compare that to a similar plot of the historical data from Giessen:
Figure 11. Historical CO2 levels at Giessen vs. wind speed.
There are only 22 data points above 4 m/s, still a wide range (300 ppmv!) and no “finger” in the data at high wind speeds.
Further, the historical three samples of Giessen, taken in the morning, afternoon and evening already give a bias of some 40 ppmv (even the continuous modern sampling at Giessen shows a huge bias in averages). The afternoon measurements have a higher average than the morning and evening samples, which is contrary to almost all other measurements made in that period (and today): during daylight hours, photosynthesis lowers the CO2 levels, while at night under an inversion level, CO2 from soil respiration builds up to very high levels. And at the other end of the world (Iowa, USA) in 1940, CO2 levels of 265 ppmv were found over a maize field. Unfortunately, there are no measurements performed at “background” places in that period, except at Antarctica, which were far too inaccurate.
My impression is that the data of Giessen show too much variation and are too irregular, either by the (modified Pettenkofer) method, the sampling or the handling of the samples.
2.6. Comparing the historical peak around 1941 with other methods:
The ice core data of Law Dome show a small deviation around 1940, within the error estimate of the measurements. Any peak of 80 ppmv during years should be visible in the fastest accumulation cores (8 years averaging) as a peak of at least 10 ppmv around 1940, which is not the case (see Figure 7.).
Stomata data don’t show anything abnormal around 1940 (that is around 305 ppmv):
And there is nothing special to see in the d13C levels of coralline sponges around 1940. Coralline sponges follow the 13C/12C ratios of CO2 in the upper ocean waters. Any burst and fall of CO2 in the atmosphere would show up in the d13 levels of the ocean mixed layer: either with a big drop if the extra CO2 was from vegetation, or with a small increase, if the extra CO2 was from the deep oceans. But that is not the case:
Figure 13. d13C levels of coralline sponges growing in the upper ocean layer.
Besides the quality of the measurements themselves, the biggest problem is that most of the data which show a peak around 1941 are taken at places which were completely unsuitable for background measurements. In that way these data are worthless for historical (and current) global background estimates. This is confirmed by other methods which indicate no peak values around 1941. As the minima may approach the real background CO2 level of that time, the fact that the ice core CO2 levels are above the minima is an indication that the ice core data are not far off reality.
3. About stomata data.
Stomata index (SI) is the ratio between the number of stomata openings to the total number of cells on leaves. This is a function of CO2 levels during the previous growing season (Tom van Hoof, personal communication). Thus that gives an impression of CO2 levels over time. As that is an indirect proxy of CO2 levels, one need calibration, which is done by comparing the SI of certain species over the past century with ice core and atmospheric CO2 measurements. So far, so good.
The main problem of the SI is the same as for many historical measurements: the vegetation of interest grows by definition on land, where average CO2 levels may vary within certain limits for one period of time, but there is no guarantee that these limits didn’t change over time: the MWP-LIA change might have been caused in part by changes in the Gulf Stream away from NW Europe, this bringing less warm wet air over land, even changing the main wind direction from SW to E. That may have introduced profound changes in type of vegetation, soil erosion, etc., including changes in average CO2 levels near ground over land.
Further, land use changes around several of the main places of sampling might have been enormous: from wetlands and water to polders and agriculture, deforestation and reforestation, all in the main wind direction, as all happened in The Netherlands over a full millennium.
Stomata index data may be useful as a first approximation, but one shouldn’t take the historical levels as very reliable, because of a lack of knowledge of several basic circumstances which may have influenced the local/regional historical CO2 levels and thus the SI data.