Tree Rings Vindicated. CO2 the Culprit

The tree ring debate faded from the news as has CO2 concentrations in the atmosphere while everyone analyses and over analyses the ClimateGate e-mails and who knew what when.  New CO2 evidence however suggests we might want to take a look at those tree rings again.

The tree ring kerfuffle, if you will, was over an e-mail string indicating that data had been manipulated. using a “trick”.  A good detailed explanation of the “trick” can be found at

In brief, there were TWO “tricks”.  The first was to simply omit some data from the tree rings.  The second was to fill in the missing data with actual temperature readings.  Here’s how the final temperature reconstruction from tree ring data looked:

But here is how the original graphs of the data looked:

The decline they had to "hide"

At the time of submission to the IPCC and published as a precursor to Copenhagen where the world was supposed to agree on major new carbon taxes to help stop global warming, this “trick” was never mentioned.  When it blew up due to the revelations in the ClimateGate e-mails, everyone asked the same question.  Why would anyone substitute tree ring data with temperature data but only for a small portion of the graph?  The point of the tree ring study was to show that it matched the temperature record and predictions of run away warming.  So why discard the data in the very part of the graph that was most important on that question?

The scientists involved came up with a pretty slippery answer.  There was a problem with tree ring data they said, it stopped responding to temperature.  The problem was noted from about 1950 on, with some areas showing a bigger problem than others.  Lots of theories as to why though no real answers, it’s still a mystery.  Funny they felt no need to explain that before they got caught doing a “trick”.  In any event, this has what to do with CO2 concentrations?

The “normal” amount of CO2 in the atmosphere has always been thought to be 280 ppm (parts per million).  This was based on studies of ice cores, and then supplemented by actual readings showing that CO2 started to rise fast in the 1900’s and temperature with it.  The result is a temperature versus CO2 graph that looks like this:

But recently, researchers have been questioning the 280 ppm flat line before 1900.  The first reason is that a paper was published explaining why CO2 levels from ice cores were too low.  In brief, they “max out” at about 280 ppm:

Then in addition, we have the revelation that there were scientists doing all sorts of research on atmospheric CO2 concentrations going back to the early 1800’s.  A full accounting of how their data was scrubbed to match the ice core data, and what the data should have looked like can be found here:

Some have been critical of the manner in which Beck reconstructed global atmospheric CO2 levels from this data, complaining that the measurements were taken from a lot of different places, using different instruments, and that the data series have been spliced together and may not be valid.  Odd, if that’s true then temperature readings from all over the world spliced together must also be invalid.  And splicing temperature data into tree ring data…

But let’s run with it for now.  Here is how Beck reconstructed CO2 concentrations, and graphed them compared to the IPCC temperature series as well as solar sun spot cycles.  The bottom graph shows temperature versus CO2 as the IPCC would have us view it:

Not such a good correlation to CO2 anymore.  But back to the tree rings.  What makes trees grow?  Well sunshine obviously, hence the theoretical linkage to temperature.  Moisture is an issue, if there isn’t enough (or too much) it will influence tree growth.  Soil nutrients.  Oh yeah, and CO2.  So here we have scientists all over the world trying to figure out why their tree rings stopped responding to temperature around 1950.  Some areas worse than others, but variations in moisture and sunshine explained the difference, but not the root cause.  There was no reason to suspect CO2 as the root cause because everyone knew CO2 concentrations had been stable.  Except maybe they weren’t.  Let’s take a look at that graph again and check out CO2 levels before 1950.  Uh oh.

If Beck is right, then we have an explanation for what has been called the Divergence Problem.  As temperatures went up from 1880 or so on, tree growth went along with it.  But more growth means you need more CO2, and when CO2 levels suddenly fell, the tree growth could no longer take advantage of the temperature increase.  Variation for other limiting factors would make this sporadic in different areas.  Wikipedia quotes 1950 as the date the issue appeared, but in the tree ring studies above, 1961 and 1981 were the years.  These were series from far northern climates, so temperature had to go up more before the growth it produced surpassed the ability of the CO2 levels to support it.

But wait… CO2 levels according to Beck were higher in the early 1800’s, and current CO2 levels are also higher than that patch from 1920 to 1950.  Shouldn’t we be seeing the Divergence Problem appear again?  Shouldn’t it have existed before?  The answer is yes to both.  These and other reports on “unprecedented” growth in cold climate bristle cone pines that is uncorrelated to temperature have recently been appearing:

For the past record, since no one was looking for the Divergence Problem as it was only discovered recently, it may have been overlooked.  However, a search does in fact turn up studies such as this one complaining of a divergence problem in…. the early 1800’s

Not to mention that the tree ring studies themselves show a large bump around 1800, which suggests that perhaps some of the growth should be attributed to CO2, not temperature.

Bump in 1800 time frame. Temperature or CO2?

Conclusion:  I have long held tree rings as a weak proxy for temperature.  The tree has no way of telling us what temperatures were like in the winter, their growth is heavily influenced by moisture and nutrients as well, which we cannot measure.  But it seems there is enough evidence from the tree ring record to suggest that the Divergence Problem is related primarily to CO2 concentrations, and that in turn, the criticism levelled by Zbigniew Jaworowski regarding ice core data, and by Beck on past CO2 levels is well justified.

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8 Responses to Tree Rings Vindicated. CO2 the Culprit

  1. Tonyb says:

    Hi David (I also left this below your comment on WUWT)

    I have a Thread running on this very subject over at TAv where Ernst Beck has put in an appearance. It would be very useful if you would read the linked article and comments and participate


  2. Charlie says:

    very nicely summed up – I was thinking of writing one of these myself, but you’ve saved me the trouble 🙂 I really think people are so deep into defending their position on either anti or pro AGW that they forget to come back to first principles from time to time. Its pretty clear that some if not all of the basics just arent up to scratch to be drawing these higher level abstracted conclusions of the IPCC.

    A case of not seeing the forest for the trees, perhaps?

  3. Tonyb says:

    Hi David

    Thanks for your great contributions at the Historic CO2 thread over at Air Vent.

    After doing my research and reading all the comments, my belief in the accuracy of many of the historic measurements has increaed from 55% to 65%. I was impressed by Becks depth of knowledge, although his idiosyncratic phrasing had us all dumbfounded at first regarding moon gravity 🙂

    I wondered if you felt less or more confident about your tree ring theory than before the 150 comments?

    Also, this 12 year synchronous cycle of warm temperatures in NH and SH during the 1930’s is intriguing. Have you got any data on that as I would like to follow it up? If true, and the considerable outgassing that must have occured stacks up numerically, it seems to vindicate history, Beck AND your tree ring theory.

    Leading directly on from that, no one seems to have answered my very basic question so I have repeated it below and hope you can do so-preferably by reference to a clear cut graph!

    ” There has been cited above the theoretical CO2 movements for each 1 degree change in SST. These seem to be well established.

    All things being equal, what is the temperature tipping point whereby an ocean that is outgasing becomes one that is drawing in CO2? Presumably there must also be a neutral state in between?

    In the UK our sea surface temperatures in the coldest part of the winter (about now) are around 8C and in a warm summer will reach 18C by October. Presumably we must be responsible both for outgasing and for drawing in CO2, but which is the dominant state?’


  4. davidmhoffer says:

    For some reason I can’t get wordpress to let me upload an excel file. Basicaly I took the NASA/GISS dataset from 1880 on and prepared two graphs, one of the global average and one of the two arctic zones and put them in a graphic. As you can see global temps don’t very much in comparison to the arctic zones. I tried graphing all the latitude bands but it was just spaghetti.

    In any event, you can see the period I am talking about easily in the 2nd graphic. The arctic temps move up, but the antarctic is crazy volatile, with 2 degree swings in a single year.

  5. Tonyb says:

    Sorry, what is the left hand scale of the graph respresenting?


    • davidmhoffer says:

      Sorry Tony, I should have labelled the axis. GISS records temp anomalies in 100’ths of degrees. So you should read “200” as plus 2.00 degrees C over average for the entire time period. Also there were no temp readings for the antarctic for the first few years, hence the flat line at zero.

  6. Tonyb says:

    Hi David

    I think that particular axis label is the last one I would have guessed at-thanks for the clarification 🙂

    I would refer back to your post 115 where you gave the figures and your link above.

    I note the SH readings commenced some 25 years later than the NH. Should they therefore both share the same ‘0’ axis?

    The warm NH is clearly observable around 1920 to 1950. There is synchronicity with the SH around 1932 to 1942, but as you say there is remarkable oscillation here. from warm to cold and back again throughout the extended period. This must have led to considerable outgassing and presumably absorption again-right before the Mauna Loa readings started, but captured by the last of the old style readings.

    This leads me back to my query in my post on March 13th. At what temperature is there outgassing and at what temperature absorption by the oceans? Without knowing when that happens it is difficult to do any sort of calculation to see if the high co2 readings can possibly be correct.

    Jonathan Drake sent me this link which basically looks at Schneiders work .

    He also sent me a graphic privately where he has time shifted the temperatures shown above over the CO2 readings from Beck and we end up with something not dissimilar to your linked graphic.

    If you would like to see it please send me an email as it is not on the net but exists only as a graphic. He has given me permission to forward it.


    • davidmhoffer says:

      I note the SH readings commenced some 25 years later than the NH. Should they therefore both share the same ‘0′ axis>>

      The database just has a “zero” anomaly for those years prior measurements being taken in the SH so there’s no “time shift” or anything like that. The data points are all for the year they were taken in.

      As for calculating the amount of outgassing that would happen due to a given temperature change, I wouldn’t know how to do that. I would expect though that it would be large. Its not only 2 degree swings in one year, its several swings and from the lowest to the highest its 4 degrees in a very short time. If the ocean was at maximum CO2 absorbed (and I don’t know how you would know that) when the temp went up, the CO2 has to come out. But when temps fall, it only goes back in as fast as it is exposed to the ocean surface for absorption.

      sorry, but that’s about as far as my “expertise” can take you 🙂

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