Greenhouse Bulletin No. 120 Feb 1999

The greenhouse effect is a warming of the earth caused by an increased accumulation in the atmosphere of trace gases which are capable of absorption in that part of the infra red spectrum which is normally transparent. Although the most important of these gases is water vapour, its effect is usually regarded as being primarily reliant on the accumulation of carbon dioxide. Water vapour is treated as a "feedback" to carbon dioxide concentration, and the other greenhouse gases, which include methane, nitrous oxide, sulphur oxides, CFCs and ozone have their effects converted to "carbon dioxide equivalent".

It is thus of major importance that we have reliable measurements of atmospheric carbon dioxide concentration, not only for recent years, but for the whole period that humans have been emitting carbon dioxide through the combustion of fossil fuels.

Since 1958 accurate measurements of atmospheric carbon dioxide concentrations have been carried out by Charles D Keeling, first at the Scripps Institute of Oceanography, La Jolla, California, then from 1974 at the Mauna Loa volcano, Hawaii, and subsequently by other scientists at many other places. Most of these sites are in remote places, so the measurements represent the well-mixed background. There is still no proper record of the carbon dioxide concentrations over industrial regions, or over forests and other cultivated regions.

As I have pointed out frequently (Gray 1998) background carbon dioxide as measured at remote sites has been increasing in the atmosphere at an almost linear rate of about 1.4ppmv per year ever since 1972. The rate seems to be unaffected by the large increase in emissions form combustion of fossil fuels over the period (4.4Gt in 1972 to 6.4Gt in 1995, an increase of 45%).

The significance of this behaviour is difficult to judge without a knowledge of atmospheric carbon dioxide concentrations from before the industrial era to the beginnings of the atmospheric measurements.

Measurements from this period have been made on air trapped in ice cores, drilled mainly from the Antarctic and Arctic, which have extended back as far as 160,000 years with the "Vostok" ice core. ( 78° 28’S, 106° 48’E; Barnola et al. 1991). Assumed atmospheric carbon dioxide concentrations between 1734 and 1958 have depended heavily on measurements made by Neftel et al. (1985) on the Siple ice core from the Antarctic (75° 55’S. 83° 55’W). These measurements indicated a constant concentration of carbon dioxide in the atmosphere of about 280ppmv before 1750, and a steady increase in an approximately exponential fashion since then, to join the modern measurements.

These ice core measurements have attracted much criticism, notably from Jaworoski (1996,1997).

It is difficult to believe that a chemically active gas such as carbon dioxide can remain unaffected by burial in ice for as long as 160,000 years. There are questions whether the carbon dioxide can diffuse through the snow, react with dust particles, or form clathrate compounds under pressure The technique of drilling, removal and preservation of the ice core is very difficult, and there are many things that can go wrong. The ice core must be protected from drilling mud and from entrance of air from the present atmosphere through cracks.. Fresh snow does not trap air until it has been buried for many years. There are accusations that this "adjustment" of age, estimated from diffusion measurements, has been deliberately chosen so that it will fit into the modern record.

Most of these objections have now been overcome, with a recent study on the Law Dome ice cores by Etheridge et al (1996, 1998), which involved collaboration between several of the previous teams. The three ice cores from East Antarctica (66°S, 112°E), were from a region with an unusually heavy snow accumulation, and many improved techniques from experience of previous studies were applied. The necessary adjustment for entrapped air was determined experimentally. The dating of the layers used three different seasonal parameters , the oxygen isotope ratio, electroconductivity, and hydrogen peroxide concentration. They were checked from the known dates of several volcanic eruptions.

The results from the years 1006 to 1978 are shown in the figure below.

They differ in several respects from the Siple ice core results:

There is no "pre-industrial" equilibrium carbon dioxide concentration. There was variability in the order of 10ppmv between 1006 and 1800. It is therefore not possible to calculate the forcing due to presumed combustion of fossil fuels by subtracting a presumed past equilibrium value from the current value.

There was a marked fall of about 9ppmv in carbon dioxide concentration during the period of the "Little Ice Age" (about 1550 to 1850) with a period of very slow growth from 1800 to 1850. The authors are of the opinion that this fall in carbon dioxide concentration was caused by the fall in temperature, rather than the other way about. The carbon dioxide concentration in the period after 1850, extending into this century would be influenced by recovery from the Little Ice Age..

Between 1935 and 1945 the atmospheric carbon dioxide concentration was constant, or even declined slightly. The reason for this is unknown.

The measurements fit well with the modern results from the South Pole, but the whole record, particularly the recent modern one, does not follow an exponential curve, fossil fuel emissions, or comply with any of the current models, (Enting and Lassey 1993) which were used as a basis for future projections by the IPCC (Houghton et al. 1996)

The authors admit that some effects may have been regional, or at least mainly in the Southern Hemisphere.

Discussion

It is back to the drawing board for carbon cycle models. Atmospheric carbon dioxide concentration varies in a manner which has not been predicted successfully by existing models. There was significant variability before there could have been a human contribution. This variability appears to have followed temperature changes, rather than being responsible for them .Although there has been an increase during the period of industrial development, the increase has not been uniform. Thus, the period between 1935-45 showed no change. The period since 1972, when the increase has been linear despite an increase of over 45% in emissions, suggests that there are new carbon sinks being established in the ocean and in the terrestrial biosphere to absorb the increases. This behaviour plays havoc with previous predictions of global warming, but it is difficult to know how long the present apparently stable rate of increase will continue.

References

Barnola, J.-M, P.Pimienta, D. Raymond, and Y.S. Koretkovitch 1991. "CO2-- - climate relationship as deduced from the Vostok ice core: A re-examination based on new measurements and a re-evaluation of the air dating. Tellus 43B 83-90.

Enting, I G. and K.R. Lassey 1993, "Projections of future CO2, Technical Paper 27 Div of Atmos. Res. CSIRO, Australia.

Etheridges, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M Barnola, V.I. Morgan. 1996. "Natural and anthropogenic changes in atmospheric CO2 over the last 1000 years from air in Antarctic ice and firn" J. Geophys. Res. 101 (D2) 4115-4128

Etheridge, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, J.-M. Barnola and V.I. Morgan, 1998. "Historical CO2 recordsfrom the Law Dome DE08, DE08-2 and DSS ice cores.’ In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tenn, USA. http://www.cdmc.esd.ornl.gov/trends/co2/lawdome.html

Gray, V.R., 1998. "The IPCC future projections: are they plausible" Climate Research 10 155-162

Houghton, J.T., L.G. Meira Filho, B.A. Callander, N. Harris, A. Kattenberg and K. Maskell (Eds) Climate Change 1995 ,Cambridge University Press

Jaworowski, Z. 1996 "Reliability of Ice Core Records for Climatic Projections" in "The Global Warming Debate", (John Emsley, Ed.) European Science and Environment Forum , London, 95-105.

Jaworowski, Z., 1997. "Ice Core Data Show No Carbon Dioxide Increase" 21st Century Science and Technology 10 , (1) 42-52

Vincent R. Gray, M.A.,Ph.D., F.N.Z.I.C.
Climate Consultant
75 Silverstream Road
Crofton Downs
Wellington 6004,
New Zealand
Phone (FAX) (064) (04) 4795939
Email VINCEGRAY@xtra.co.nz

February 27th 1998

Richard Courtney               Comment on the above paper
Vincent Gray                      Responding to Richard Courtney

Subject: Re: paper on pre-industrial carbon dioxide
Date: Sun, 28 Feb 1999 13:50:49 GMT
From: Richard Courtney <richard@courtney01.cix.co.uk>
To: Vincent Gray <VINCEGRAY@xtra.co.nz>
CC: covey@rabbit.llnl.gov (Curtis Covey), daly@vision.net.au, nc@windstream.demon.co.uk, Jack Barrett <100436.3604@compuserve.com>, theodor.landscheidt@ns.sympatico.ca, Onar Aam <onar@con2.com>, 091335371@t-online.de

Dear Dr Gray:

Thank you for your fine paper published on John Daly's web site.

I have two points that you may consider pertinent. Firstly, you say:

"Since 1958 accurate measurements of atmospheric carbon dioxide concentrations have been carried out by Charles D Keeling, first at the Scripps Institute of Oceanography, La Jolla, California, then from 1974 at the Mauna Loa volcano, Hawaii, and subsequently by other scientists at many other places. Most of these sites are in remote places, so the measurements represent the well-mixed background."

I recently visited Hawaii and observed the Mauna Loa site, and this has convinced me that measurements of carbon dioxide from that site are not indicative of "the well mixed background." Mauna Loa emits carbon dioxide and is adjacent to Kileaua (the most active volcano on Earth). It seems very likely that Keeling's carbon dioxide measurements are significantly affected by variations in emissions of carbon dioxide from Mauna Loa and Kileaua together with wind direction relative to Kileaua. Indeed, Keeling adjusts his data for effects of Mauna Loa activity and deletes data from his time-series for the periods when Mauna Loa was especially active (of itself, an admission that his data are not direct measurements of "well mixed background"). But his reports do not mention any adjustments made for effects of Kilaeaua's activity.

The other point concerns your statement that;

"Fresh snow does not trap air until it has been buried for many years. There are accusations that this "adjustment" of age, estimated from diffusion measurements, has been deliberately chosen so that it will fit into the modern record."

In November 1998 I had correspondence with Dr Curtis Covey (an IPCC author) concerning my severe doubts at the ice-core data. Referring to my dispute that it was correct for the IPCC to have transposed the ice-core data by 83 years, he said;

"... such displacements might be considered a somewhat arbitrary calibration that diminishes the significance of the fit between ice-core and modern measurements. At last week's IPCC meeting I raised this general question with Haroon Khesghi of Exxon. Haroon referred me to Fortunat Joos of the University of Bern, who told me that this calibration is no longer used in recent work, and yet the remarkable agreement between ice-core and modern measurements continues."

I responded that I did not accept the 83 year transposition was acceptable. Diffusion occurs from regions of high to low concentration and, therefore, incomplete sealing of snow over an 83 year period would act like an 83 year running mean; it would not transpose all the carbon dioxide a similar amount in one direction. Also, if the IPCC has stopped using the transposition, what correction method is now used? And when will the IPCC publish this newly corrected data in place of the graph of historic atmospheric carbon dioxide concentration that it published in both its 1992 and 1994 reports ? I received no answer to these questions.

Again, congratulations on your paper.

All the best

Richard

Subject: Re: paper on pre-industrial carbon dioxide
Date: Mon, 01 Mar 1999 10:26:00 +1300
From: VINCENT GRAY <VINCEGRAY@xtra.co.nz>
To: RICHARD COURTNEY <richard@courtney01.cix.co.uk>
CC: Curtis Covey <covey@rabbit.llnl.gov>, daly@vision.net.au, nc@windstream.demon.co.uk, Jack Barrett <100436.3604@compuserve.com>, theodor.landscheidt@ns.sympatico.ca, Onar Aam <onar@con2.com>, 091335371@t-online.de References: 1

Thanks for your comments

According to Keeling et al (Geophysical Monograph 55 1989, "A Three Dimensional Model of Atmospheric CO2 Transport et. 1. Analysis of Observational data" American Geophysical Union Table A.4) measurements at Mauna Loa have been carried out "almost continuously" since March 1958, but there were problems of leakage from 1965 to 1969 and various other problems (which presumably included actual volcanic eruptions), leading to Table A.4 in that report which gives monthly CO2 figures from March 1958, but with gaps for June and Oct 1958, and Feb-April 1964. Some of the rest must have been estimated or interpolated.

The graph of Mauna Loa regularly published by the NOAA (http://www.cmdl.noaa.gov/ccg/figures) claims that figures from 1958 to May 1974 are from the Scripps Institute, and thereafter, from Mauna Loa readings made by NOAA (Pieter Tans) jointly with Keeling. NOAA also publish a graph of their results from Barrow, Mauna Loa, Samoa and South Pole, since 1975, which show the same linear trend, so I do not think that criticism of Mauna Loa results will alter the general agreement between many observers.

I do make the point, however, that all the stations are in remote sites, far from industrial or agricultural perturbation. Also the measurements are deliberately biased. The New Zealand results, for example, are only registered when the wind comes from the sea. The figure from the land is lower, but they do not want to know. There are a few measurements from industrial regions and from forests and pastures, but not over extended periods.

Etheridge et al try hard to justify their judgement of the delay in sealing the firn, including an eleborate piece of equipment to determine the point at which it became sealed; different for each core. It seems reasonable.

I am surprised that the implications of this work have yet to penetrate. After all it was published in 1996. The fact that there is no equilibrium "pre-industrial concentration" means that all the calculations of the supposed forcing from combustion of fossil fuels now have to be scrapped. The fact that the Little Ice Age caused a fall in carbon dioxide means that at least part of the subsequent rise in carbon dioxide must have been caused by the rise in temperature, as you have repeatedly pointed out by your reference to the paper by Kuo et al 1990. I am not sure that I can go along with the contention of Nigel Calder that the temperature increase is entirely responsible for the rise in carbon dioxide, but some of it must be, and people are going to have a hard time explaining the rest. I presume that Calder himself has had the Etheridge results pointed out to him, and I await eagerly his ultimate response.

Kindest Regards

Vincent Gray