The CO2 Hockey Stick

Willis Eshenbach’s graph of Mauna Loa and Ice Core CO2 data.

The above graph is certainly convincing evidence of a remarkably rapid increase of atmospheric CO2 since 1800. Note how there is a very good match between the most recent ice core data and the actual measurements made at Mount Mauna Loa in Hawaii. Note also that Mauna Loa measurements have been confirmed at other observatories around the world, such as Cape Grim in Tasmania. There can certainly be little doubt about the accuracy of the data after about 1950.

About ten years ago I saw the Law Dome data, now included in the above graph, which all but convinced me that something very serious and unprecedented was happening to CO2 concentrations in the atmosphere so I started looking further afield to find other data and other arguments which would either support or cast doubt on this view.

The data prior to about 1700 looks almost too good to be true because it is so very flat and smooth. Perhaps something else is going on. It has been pointed out (notably by Murray Salby, the guy who was fired by Macquarie University) that, maybe, over time, the CO2 trapped in bubbles in ice cores can diffuse between different layers, so smoothing any ups and down of its variation over time.

Then I found out about stomata at  (

Recent stomata studies show that CO2 was variable and the average CO2 concentrations have been significantly higher during the Holocene Interglacial Period than are indicated by the ice core record.

Stomata are the tiny “mouths” in leaves through which a plant absorbs its “food”, CO2. When concentrations of CO2 are high the plant needs fewer stomata to obtain the required amount of CO2 and when low the opposite is the case. Hence fossil leaves provide an alternative proxy to ice cores for ancient CO2 concentrations. As we can see in the diagram, the two do not match. The stomata densities indicate that CO2 levels were both higher and more variable during the last 1000 years than indicated in the upper diagram. There are two conflicting stories. It’s a “he said, she said” situation.

A further piece of information is the Bomb Test Curve:

The Bomb Test Curve shows the injection and subsequent decay of radioactive CO2 in the atmosphere caused by the atomic bomb tests of the1960s (image: Hakanomono).

There is a mathematical description in TFC, Chapter 13. Suffice to say here that we can conclude that residence time of CO2 in the atmosphere is only 10 years and that less than 20 percent of recent increases in atmospheric CO2 are anthropogenic in origin, the rest comes out of the deep ocean in regions of upwelling. It follows that the ice core graph indicates that either there has been a dramatic recent change in deep ocean circulation or there is something wrong with the ice core proxy CO2 methodology and the stomata data is correct.


Reid, J. (2019) The Fluid Catastrophe, Cambridge Scholars Publishing, Newcastle upon Tyne.

18 Replies to “The CO2 Hockey Stick”

  1. I’m sorry, John, but you are comparing apples and oranges. Beck and stomata are measuring surface CO2 levels, which vary greatly from place to place.

    What we are interested in, however, is the background level of CO2. This is measured at Mauna Loa, at the South Pole, and a few other places. It is generally lower and far more stable than the background levels.

    Beck himself posted a comment on one of my threads saying that his data should NOT be compared to background data as you are doing, viz:

    “Ernst Beck June 5, 2010 at 2:44 am
    Dear Willis,
    I agree, the near ground data listed in my first paper do not reflect background data.”

    Best regards,


  2. Willis

    I have no quibble with the validity of Mauna Loa data as measuring background level as you discuss in your WUWT post. When I was a working scientist, I used to visit the Cape Grim Observatory and I well understand how the samples are screened for wind direction and so on, to eliminate local influences. I had not heard of Beck until now.

    My beef is with proxy data. To me, as someone experienced in looking at time series, the flat part of the ice core CO2 curve looks just too good to be true. If it is true it provides a powerful argument that we do indeed need to worry about recent CO2 increases.

    There are two arguments that it is not true. One is the stomata proxy data which show both higher concentrations and much greater variability. At issue is whether the ice-core proxy data are right or the stomata data are right. Why should you assume that stomata proxy is a less valid measure of background concentrations than are ice-core data? Presumably, both effectively average data over time rather than respond to short term peaks. The dip in stomata-derived CO2 during the Younger Dryas looks very convincing.

    The other is the Bomb Test Curve which indicates a rapid interchange between atmospheric CO2 and the deep ocean reservoir. A simple first order diffusion model indicates that most of the observed increases in CO2 are not anthropogenic as described in pages 120-126 of TFC. I can send you a pdf of this section if you give me your email address but I cannot post it here for contractual reason.

  3. as a former professional gas analyst, I’ve always had big doubts about the ice core records. Too much probability of diffusion and adsorption losses into the background surfaces.

  4. I don’t see the rapid increase in CO2 concentration in the atmosphere as presaging the end of days. It may be the highest it has been for 11 million years or whatever, but I don’t see that it matters if 7 billion humans are responsible or not.

    There are other gasses that that really are unprecedented and that we are certainly responsible for. It is a straw man argument that is easy for the catastrophists to prosecute against a few industrialised economies. There are many other absurdities, e.g. “Adani will destroy the reef”, that don’t need esoteric argument, but are quite simple. Even the punters in Queensland worked that one out.

    1. The temperature hockey stick turned out to be a mistake and, in my view, this one is too. It is harder to disprove because, this time, no-one has rigged the data. Let’s get the science right then discuss the implications.

  5. It would appear the ice data veracity is dependent on the properties of the ice/gas diffusion properties under in-situ conditions. To me, the very steady CO2 levels seem likely to be too smooth to be true. Surely the temperature swings responsible for the ice ages should have expressed some CO2 variation.


    One common assumption in interpreting ice-core CO2 records is that diffusion in the ice does not affect the concentration profile. However, this assumption remains untested because the extremely small CO2 diffusion coefficient in ice has not been accurately determined in the laboratory. In this study we take advantage of high levels of CO2associated with refrozen layers in an ice core from Siple Dome, Antarctica, to study CO2 diffusion rates. We use noble gases (Xe/Ar and Kr/Ar), electrical conductivity and Ca2+ ion concentrations to show that substantial CO2 diffusion may occur in ice on timescales of thousands of years. We estimate the permeation coefficient for CO2 in ice is ∼4 × 10−21 mol m−1 s−1 Pa−1 at −23°C in the top 287 m (corresponding to 2.74 kyr). Smoothing of the CO2 record by diffusion at this depth/age is one or two orders of magnitude smaller than the smoothing in the firn. However, simulations for depths of ∼930–950 m (∼60–70 kyr) indicate that smoothing of the CO2 record by diffusion in deep ice is comparable to smoothing in the firn. Other types of diffusion (e.g. via liquid in ice grain boundaries or veins) may also be important but their influence has not been quantified.
    It would be pretty important to get this right.

    1. Wonderful reference, RobK!
      For decades people like myself and Murray Salby have suspected something like this was going on. It is nice to have some experimental evidence at last. I see the paper is 2008. The glaciologists have certainly kept very quiet about it.

  7. I’ve always been concerned about the density of CO2 at Mauna Loa’s elevation of 11145.01 ft. vs. the density at ocean level in Antarctica and Alaska. Same for the remote locations in Antarctic and Alaska far from industrial sources vs. Mauna Loa being downwind from a busy jet corridor and a large city.

    Yet the readings are almost identical and the remote locations show the same rise as Mauna Loa.

    Please explain how all three are nearly identical.

    1. Frank
      1. Technicians at the smapling lab are careful to only sample under the right meteorological conditions, e.g. when the wind is from a range of directions. At the Cape Grim Baseline Monitoring station near the NW tip of Tasmania, they only sample when the wind direction is between South and West so avoiding pollution from, say, Melbourne, which is North West.
      2. The lower atmosphere is very turbulent and so is well mixed both horizontally and vertically. Just look at a weather map.

  8. A little late in the discussion, but this is a a subject I have discussed many times before…

    Ice cores reflect ancient CO2 (and other gases) levels quite accurate, with one huge drawback: it is always a mixture of several years, depending of the local snow accumulation rate: the higher the local snow precipitation, the faster the firn pores are closing and don’t allow further exchange with the atmosphere.
    The fastest snow accumulation is at the summit of coastal Law Dome with yearly precipitation of 1.2 meter of ice equivalent where two cores were drilled, totaling some 150 years of layers when rock bottom was reached. The gas mixtures found in these cores were the average from only about a decade and interestingly, there is an overlap of about 20 years (1960-1980) with direct measurements in the atmosphere at the South Pole. The data in these 20 years overlap each other within the repeatability of the ice core CO2 measurements (1.2 ppmv, 1 sigma):
    A third core was drilled at Law Dome, more down slope, which has less resolution (~20 years), but goes back over 1,000 years.
    That one shows a drop of about 8 ppmv around 1600, which may be the result of the temperature drop in the LIA:

    If we may assume that the MWP was at least as warm as the current period, the opposite warming since the LIA would give about 8 ppmv extra, or about 285 ppmv…

    The diffusion in the Siple Dome ice core as estimated from CO2 increases near melt layers, as mentioned by RobK, is very modest: in the top layer at 2.74 kyr back in time brings the resolution of that ice core from 20 to 22 years and at full depth (60-70 kyr) from 20 to 40 year. No big deal at all.
    Moreover, that is for a relative “warm” coastal core (-23°C), for the inland ice cores at -40°C the diffusion, even over 800,000 years is orders of magnitude smaller and negligible in the resolution of 600 years (Vostok) and 560 years (Dome C).
    Even in the latter ice core, the current 115 ppmv increase over 170 years would show up as a detectable “peak” of about 35 ppmv…

    At last, not only CO2 shows a (real) HS, the 13/12C ratio shows the same, but reverse HS and methane shows a HS too:

    The reverse HS for the 13C/12C ratio is independently confirmed by a similar reverse HS in the carbonate of coralline sponges, which has the same ratio as in the surface waters where they did grow:
    Both drops of the 13C/12C ratio in the ocean surface and the atmosphere have one common cause: the use of fossil fuels. The drop is enormous, near one per mil, compared to a few tenths of a per mil over the past 800,000 years over glacial and interglacial periods…

  9. John.

    About the stomata (index) data: the differences between the stomata (index) data and ice core data are that the stomata data are based on the local/regional CO2 levels of the previous growing season, while the ice core data are direct measurements in air mixtures from the bubbles with the same equipment as direct measurements in the atmosphere.

    Local CO2 on land in the first few hundred meters has a variable bias, compared to “background” CO2 levels in 95% of the atmosphere depending of local decomposition of organic material, wind speed (for mixing with the bulk atmosphere) and wind direction (changes in land use over time…).

    In the discussions I had with the late Ernst Beck about his historical CO2 compilation, I did found a modern CO2 monitoring station at a few km from the historical one in Giessen (Germany) which is the cause of his historical CO2 “peak” around 1942. That shows some 40 ppmv monthly averaged bias compared to “background”:
    Still with huge month by month variability (extreme with no wind under inversion!).
    That bias can be compensated for by calibrating the stomata data against… ice cores, firn and direct measurements over the past century, but that doesn’t help if e.g. the main wind direction changed over certain periods like from the MWP to the LIA, from the seaside to more from the land side and all the difference in bias that gives.

    Anyway, in my opinion, stomata data are interesting to detect fast (regional) changes like during the Younger Dryas, but the absolute level should be taken with a grain of salt…

    1. Ferdinand
      Thank you for an interesting and well-informed discussion. I believe you are largely right about stomata. However the variation in stomata density during the Younger Dryas looks very real to me and there is no corresponding variation in ice core proxy CO2 concentrations; strong evidence that there is something seriously wrong with the latter.

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