November 2001
Vol. 31, No. 11, pp 62–64.
In Box

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Letters from our readers

Karl Zeitsch

It is with great sadness that I inform you that Karl Zeitsch, your “furfural expert” (Chemical Innovation 2000, 30 [3], 34–38; 30 [4], 29–32; 2001, 31 [1], 41–44), died on September 12. He left us as he had lived his life: After spending 10 days walking through the Italian Alps, he returned to spirited discussions with our company on the implementation of the “gaseous acid catalyst” furfural production process and then played a tennis match. He died on the court of a heart attack.

Karl was my mentor and friend for a quarter of a century. We met as commissioning engineers at the Cukorova furfural plant in Turkey. Our technical friendship flourished; and, when he retired from Krupp in 1990, he joined me for 8 years in South Africa as a technical consultant.

He was a technology junkie, the most learned and skilled chemical engineer I have ever encountered. The publication of his recent papers and book has challenged conventional technical thinking on furfural. His other talents were playing tennis and writing poetry. I believe he always wrote in English and expected to publish an anthology of his poetry soon.

His three articles in your magazine were just the tip of the iceberg. It is no exaggeration to say that virtually everything worthwhile published on furfural in the past 20 years—patents, books, and papers—was written by Karl. He and I have had a prolific correspondence over the years, much of it in advance of anything published, and I will ensure that this information is not lost.

You will see from our letterhead that we have formed a company to market Karl’s furfural innovations and patents: the wide-ranging technology that Karl called SupraYield. The latest patent and the jewel in our crown is s-SupraYield, the gaseous acid catalysis process proposed in Chemical Innovation this year. It will revolutionize the manufacture of furfural and will be a fitting memorial to a remarkable man.

Jon Buzzard
International Furan Technology (Pty) Ltd.
Durban, South Africa

Global warming

I accept Robert Essenhigh’s logical point about the relationship between carbon dioxide and temperature (Viewpoint, May 2001, pp 44–46): Which is cause and which effect? The Vostok ice-core data show a correlation, and it may even be supposed that temperature and CO2 act both as cause and effect (1). I must, however, disagree with his main argument.

First, Essenhigh’s focus on the absorption of water and CO2 in the spectral region of the water bands, to support his claim that “water accounts, on average, for >95% of the radiative absorption [of outgoing radiation]”, misses the point. The point is that CO2 absorbs in other spectral regions; closing these spectral “windows” (through greater optical depths of CO2) will lead to more absorption. There is no need to invoke the “Schuster–Schwartzschild Integral Equation of Transfer”. The “. . . total net absorption [of infrared radiation] over the whole globe is about 75 × 1015 W, an average of 150 W/m2, roughly one-third by CO2 and two-thirds by water vapor” (2). CO2 may be a “minor” atmospheric gas, in the sense that it is present at lower concentrations than water vapor, but its contribution to warming is not necessarily negligible.

Second, current knowledge about the role of the oceans in the global carbon cycle needs to be emphasized. The oceans are a net sink, not a source, for CO2. Battle and co-authors recently reported that “world oceans annually sequestered . . . 2.0 ± 0.6 Gt of carbon . . . between mid-1991 and mid-1997” (3). This is known from a variety of experiments, including measurements of

  • atmospheric oxygen, which decreases with fossil fuel burning (the changes in O2 can be inferred from measured O2/N2 ratios);
  • isotopically labeled CO2 (e.g., the 14C produced in nuclear explosions);
  • CO2 partial pressures in the oceans compared with those above them (if the partial pressure is higher in the atmosphere, the flux has to be into the oceans, driven by the pressure difference); and
  • the ratio of carbonates to other sea-bound matter.

Collectively, these add up to a convincing picture of the oceans as net sinks.

The net CO2 flux into the oceans, at ~2 Gt carbon/year, is a large fraction of the anthropogenic CO2 (6–7 Gt carbon/year). It is not true, as Essenhigh implies, that anthropogenic CO2 is “lost in the noise”. In fact, anthropogenic contributions can be calculated to quite high accuracy (±~20%), because we know how much fossil fuel we are burning each year. We can therefore calculate the amount of extra CO2 that should end up in the atmosphere.

Furthermore, Essenhigh’s insistence on the oceans as source rather than sink leads him to a very strange position vis-à-vis the seasonal CO2 variation. The Mauna Loa data show a CO2 increase in fall–winter and a decline in spring–summer. The fall–winter increase is explained mainly by contributions from the terrestrial biosphere (e.g., plant decay) and the spring–summer decrease by plant growth (4). Essenhigh denies the existence of seasonal terrestrial (biomass) CO2 sources, although they are indicated in the literature. (Ciais and co-authors [5] reported evidence for one such large Northern Hemisphere source.) If the warming of the oceans were the source of CO2, then the seasonal CO2 variation would surely rise in spring–summer and fall in the autumn and winter—the opposite of what is observed (4)!

In conclusion, I do not consider that there is any basis in current scientific thinking for the statements by Essenhigh that CO2 contributions to trapping of infrared radiation are negligible and that the oceans act as source for rising atmospheric CO2 levels.

Peter S. Doidge
Member, New Zealand Institute of Chemistry
Glen Waverley, Victoria, Australia


  1. Kandel, R. Physics Today 1993, 46 (12), 66–68.
  2. Mason, B. J. Contemporary Physics 1995, 36, 299–319.
  3. Battle, M.; Bender, M. L.; Tans, P. P.; White, J.W.C.; Ellis, J. T.; Conway, T.; Francey, R. J. Science 1999, 287, 2467–2470.
  4. Heimann, M.; Keeling, C.; Fung, I. Y. In The Changing Carbon Cycle: A Global Analysis; Trabalka J. R., Reichle, D. E., Eds.; Springer-Verlag: New York, 1983; Chapter 2.
  5. Ciais, P.; Tans, P. P.; Trolier, M.; White, J.W.C.; Francey, R. J. Science 1995, 269, 1098–1102.

Robert Essenhigh replies:

Response pro or con to an article is always appreciated because it says that there is someone out there listening. However, I believe Peter Doidge has misunderstood my positions, and he raises some arguable points of his own. He has two general points, the first concerning the water/CO2 ratio and the second regarding the ocean as a CO2 source or sink.

Taking his second point first: Doidge is, of course, totally correct that the best current data do show the ocean as, ultimately, a net sink and I do not see anything to argue about there. But this is a dynamic in–out process, not a static one, so it also has to be taken in the right time frames. All the processes that can be identified, such as absorption in the surface ocean, transport to the intermediate or deep sea, and “final” carbonate (sediment) formation, have very different time constants, ranging from 1 to 500 years or more. For the Mauna Loa oscillatory behavior, we only have to consider the annual fluctuation of the surface temperature of the sea (or possibly annual plant growth). Whether this sea-temperature oscillation is then actually driving the Mauna Loa oscillations is, I believe, still an open question, but the numbers as I summarized them in my article do support it.

The “standard” explanation (seasonal variations due to plant growth) is, from what I have seen of the numbers, much less supportable. There is no space here to go into the details of all the problems involved with the plant-growth explanation. However, the graph given by Bolin (1) from 1958 to 1984 clearly shows the peak in the spring with the minimum in the fall, the exact opposite of Doidge’s statement. I think his position on this needs review.

The more significant point may be the matter of the relative importance of water and CO2 in absorption. First, Doidge seems to be confused over the spectral range covered by the engineering gray-body approximation. His statement that gray-body coverage is limited only to the water bands is not correct; by definition, the complete wavelength range is covered.

The question of the influence of the different bands is a very pertinent point. To get this in proper perspective the necessary numbers are needed, and I have set these out in Table 1 (below). These are reductions from the standard Hottel and Egbert graphs (2) for the variation of absorptivity (α) with temperature on a pL basis (concentration p times path length L), with the data taken for the standard temperature of 15 °C. These reductions are believed to be original here. They are based on the standard expression for the bands (2) that, in sum, is

α = Σαi0(1 – eki pL)

where ki is the band absorption coefficient. The reductions in Table 1 are for the three gases: water, CO2, and methane, at 15 °C. The water and CO2 reduce to four bands and the methane to three. Three of the water and CO2 bands substantially overlap. The effect of band overlap is known (3) and has to be included in due course but can be omitted at this time; indeed, omission of the integral equation of transfer outcomes has more impact.


Table 1. Radiation absorption and absorption coefficient values at 15 °C
Band, µm
α0, %
k, (m•atm)–1
Lsat, m
Water p = 1% p = 0.04%
0.8 20
8 200
55 1,350
665 16,500
Carbon dioxide
p = 0.04%
p = 0.0002%
Table 1 includes the maximum absorption per band (αi0 value), the ki values for each band, and the saturation distance (Lsat) at which the absorption has reached 99% of the maximum for that band. For CO2 and methane, Lsat is calculated at concentrations of 0.04% and 0.0002%, respectively. For water, Lsat is calculated both at 1% and at 0.04%. The first level corresponds to about 60% relative humidity at 15 °C, giving a H2O/CO2 mol ratio of 25:1. The second value takes into account possible water reduction by rain-out and, at 0.04%, is set the same as for CO2, a commonly assumed ratio. The values of ki and Lsat, band by band, show the much stronger absorption by water (shorter Lsat) than by CO2.

This puts the focus on the relative concentrations of the two gases, where the full comparison does require solution of the equation of transfer—contrary to Doidge’s position. But a good working evaluation is possible using the Lsat values, noting that these are calculated for surface level concentrations and do not include the effect of pressure reduction due to altitude. This can be included, but again, I am not addressing pressure reduction here for lack of space.

A good yardstick for comparing the Lsat values is the height of the tropopause at 10 km. On this basis, the most obvious point is that the atmosphere is essentially transparent to methane, so that absorption by it can be disregarded. For water and CO2, the two short wave bands and, at the higher concentration, the 5–8 mm water band all saturate essentially at “ground level” (<100 m), which again implies outcomes that require separate discussion; but the small values of αi0 for these bands should be noted. The fourth high-concentration water band and the third CO2 band are question marks, but they can be contributors at the higher altitudes when the effect of reduced density with altitude is taken into account. This leaves only the third and fourth water bands at the lower concentration (which takes account of water reduction by rain-out) and the third and fourth CO2 bands as, possibly, the primary absorbers.

A full evaluation of the relative importance of these longer wavelength bands requires solution of the radiation of equation of transfer, for which there is no space here. However, the relative importance of these bands can be evaluated by the αi0 values. For the longest wavelength bands, these are 39% for water and 6.5% for CO2, a ratio of 6:1. This alone would set water at about 85% of the absorption, and set CO2 as being, at best, second order. With the inclusion of the 5–8 µm water band, 19% is added to the water absorption, for a total H2O/CO2 ratio of nearly 9:1, setting the water at ~90% absorption, as stated in the original article.

In summary, I agree with Doidge that there is indeed a lack of scientific thinking on this matter but, in evaluating where the balance of error lies, I would prefer to leave that to the reader. Many more points could be addressed, for example, the idea that atmospheric oxygen decreases measurably from fossil fuel combustion, but these are of essentially minor importance and can be left for another time.

Overall, I see no support for Doidge’s positions, and the numbers I have seen still support the conclusion that water is dominant and that CO2 is trivial. Once again, if there is good reason to disagree with this, can we please have the numbers?


  1. Bolin, B. In The Greenhouse Effect, Climate Change, and Ecosystems; Bolin, B., Doos, B. R., Jagger, J., Warrick, R. A., Eds.; John Wiley: New York, 1986; Chapter 3, Fig. 3.2.
  2. Hottel, H. C.; Egbert. R. B. Trans. Am. Soc. Mech. Engrs. 1941, 63, 297.
  3. Hottel, H. C.; Sarofim, A. Radiative Transfer; McGraw-Hill: New York, 1967.

Yohimbe and alcohol

I enjoyed reading your article on the Web and just had one comment (Schwartz, D. A. Have I got an herb for you! Chemical Innovation 2001, 31 [9], 29–33). I have known a number of people who have taken yohimbe by itself with no ill effects; however, I have also heard from a reliable source that it is quite deadly if taken with a significant amount of alcohol. Adverse effects can include severe liver and kidney damage. Since it is not implausible that people taking herbal aphrodisiacs would also be consuming alcohol, perhaps a strong word of caution is due. I have seen no reports in either the professional or popular medical literature on this potential problem with yohimbe, but it might be worth checking out.

Dennis Stillings
Director, Archaeus Project
Waimea, HI

Debra A. Schwartz replies:

Your point is well taken that a word of caution would have served readers well, and I regret that one did not appear. [CI also takes responsibility for this omission.—Ed.]

I did further research to address your concern about mixing significant amounts of alcohol with yohimbe. Jim Duke, whom I interviewed for the Chemical Innovation article, has gathered perhaps the most extensive herbal database in the United States. He looked through his files and found no published work showing contraindications for combining yohimbe (the bark) or yohimbine (the pharmaceutical) with alcohol. However, Duke, a retired economic botanist formerly with the U.S. Department of Agriculture and currently senior science adviser to Nature’s Herbs (a division of Twin Laboratories Inc., Ronkonkoma, NY), cautioned against combining any alkaloid, such as yohimbe and its derivatives, with alcohol because of the potential synergistic effects. Depending on the dose, yohimbe and yohimbine may cause side effects including anxiety, elevated heart rate, hallucinations, and headache. Taking yohimbe or yohimbine with a glass of grapefruit juice doubles the effect, Duke said. St. John’s wort has the opposite effect—it decreases the potency of yohimbe.

As your letter shows, further research into yohimbe’s effects would provide important information on its safety and effectiveness. Thank you for asking.

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