A Closer Look At Those Climate Change Graphs

One of the most controversial of all the “Climategate” emails is this message from November 1999, written by Phil Jones of the University of East Anglia’s Climatic Research Unit:

Dear Ray, Mike and Malcolm,

Once Tim’s got a diagram here we’ll send that either later today or
first thing tomorrow.

I’ve just completed Mike’s Nature trick of adding in the real temps
to each series for the last 20 years (ie from 1981 onwards) amd from
1961 for Keith’s to hide the decline. Mike’s series got the annual
land and marine values while the other two got April-Sept for NH land
N of 20N. The latter two are real for 1999, while the estimate for 1999
for NH combined is +0.44C wrt 61-90. The Global estimate for 1999 with
data through Oct is +0.35C cf. 0.57 for 1998.

Thanks for the comments, Ray.


Naturally most of us would assume that it is impossible for good science to be predicated on “tricks” or attempts to “hide the decline” in a data set. What was Jones talking about, and what exactly was his team trying to accomplish?

Defenders of the CRU’s research have complained that the Climategate emails, particularly this one, have been “taken out of context.” However, thanks to the efforts of the indefatigable Steve McIntyre, the circumstantial context of these emails is slowly coming together, and the fascinating story of the corrupting nexus between climate science, politics, and public funding is beginning to emerge.

Starting with their First Assessment Report, issued in 1990, the UN’s Intergovernmental Panel on Climate Change (IPCC) has insisted that man-made carbon dioxide emissions have significantly contributed to an enhanced greenhouse effect, and have caused the Earth’s climate to warm significantly. For their efforts, they shared the 2007 Nobel Peace Prize with Al Gore.

Phil Jones’ “hide the decline” email was written while Jones, Michael Mann, and others at the East Anglia CRU were hard at work drafting the IPCC’s Third Assessment Report, which was scheduled to be released in 2001. The heart of the report was going to be a CRU-prepared temperature diagram that would convincingly illustrate their assumption that the Earth’s climate had warmed significantly during the twentieth century, and that the Earth was warmer in the year 2000 than at any time during the past one thousand years. All the CRU team needed to do was to figure out which data sets should be included in the chart, and how those numbers needed to be crunched in order to support that assumption.

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Climate science is a relatively new scientific discipline, one that merges elements of geophysics, meteorology, biology, and archeology into an attempt to understand what controls the climate of our planet. Part of the research carried out by climatologists involves measurements of the current climate; other research involves trying to piece together a picture of the climate in past eras, and determine how the Earth’s climate has changed over time.

It is this attempt to recover past climate data that poses the greatest problem. Because there were no thermometers before the eighteenth century, climate scientists must rely on approximate temperature measurements gleaned from historical and physical sources like almanacs, ice cores, and tree rings. Because this data is approximated, rather than measured, it is denoted as “proxy data.”

Anyone who performs environmental measurements will tell you that observed values largely depend on the testing methods and mediums that are used. Some methods and equipment do a much better job of detecting certain phenomena than others. Likewise, data derived from ice cores and tree rings isn’t always consistent, because (as would be expected) water and trees react to temperature differences in different ways.

The chart that Jones, Mann, et. al. were working to produce for the 2001 IPCC report spanned from 1000 AD to the year 2000, thereby including roughly 700 years of proxy data, 250 years of sporadic actual temperature measurements, and 40 years of relatively trustworthy modern climate studies. They eventually decided that the best numbers for the 700 years of proxy data would be derived from the tree ring analysis of Dr. Keith Briffa.

Briffa knew exactly why they wanted it, writing in an email on September 22: ‘I know there is pressure to present a nice tidy story as regards “apparent unprecedented warming in a thousand years or more”.’ But his conscience was troubled. ‘In reality the situation is not quite so simple – I believe that the recent warmth was probably matched about 1,000 years ago.’

Another British scientist – Chris Folland of the Met Office’s Hadley Centre – wrote the same day that using Briffa’s data might be awkward, because it suggested the past was too warm. This, he lamented, ‘dilutes the message rather significantly’.

Over the next few days, Briffa, Jones, Folland and Mann emailed each other furiously. Mann was fearful that if Briffa’s trees made the IPCC diagram, ‘the sceptics [would] have a field day casting doubt on our ability to understand the factors that influence these estimates and, thus, can undermine faith [in them] – I don’t think that doubt is scientifically justified, and I’d hate to be the one to have to give it fodder!’

Finally, Briffa changed the way he computed his data and submitted a revised version. This brought his work into line for earlier centuries, and ‘cooled’ them significantly. But alas, it created another, potentially even more serious, problem.

According to his tree rings, the period since 1960 had not seen a steep rise in temperature, as actual temperature readings showed – but a large and steady decline, so calling into question the accuracy of the earlier data derived from tree rings.

This is the context in which, seven weeks later, Jones presented his ‘trick’ – as simple as it was deceptive.

All he had to do was cut off Briffa’s inconvenient data at the point where the decline started, in 1961, and replace it with actual temperature readings, which showed an increase.

And this is exactly what Jones and Mann did. As part of a 1999 “first order draft” of the forthcoming Third Climate Assessment Report, they submitted an early version of their now-infamous “hockey stick” chart that simply truncated the data line derived from Briffa’s tree ring studies as it became entangled with other data lines after 1950. The chart that was included in the final 2001 version of the report contained an altered tree ring data line created by eliminating the tree ring data collected after 1960 and replacing it with actual measured temperature data.


(The published “hockey-stick”chart)


(blow-up from The Daily Mail)

Needless to say, such a mixture of estimated proxy data and measured data does not produce a reliable result. Even if standard, well-known statistical methods are used (and they were), the now-questionable origin of the data sets ought to spur interest in a closer examination of Jones and Mann’s work, and an effort to produce new versions of their diagrams based on data sets that have not been aggressively massaged. Unfortunately, at this time the CRU is either unwilling or unable to make much raw data available for review.

It seems clear from the emails between the CRU scientists, and their generally testy attitude toward those who would question their work, that deep down they are uncertain whether their work would stand up against rigorous scientific scrutiny. Yet there is no doubt that this group of scientists still believes they are on the right track — they are convinced that greenhouse-induced global warming is real, and that if mankind does not immediately begin altering the way he interacts with the planet, permanent damage will be done. They further believe that attempts question their work are actually harming the planet, since such questions inevitably lead to delays in governing bodies implementing climate change policies.

To this end, they had no problem starting with a conclusion (which is the antithesis of good scientific research, even if you believe that you are right) and selectively using the “right” data in order to support their conclusion. It seems they were also interested in guiding the UN and other international policy-making organizations toward making the “right” policy decisions. In their own eyes they were blameless — after all, they were the last best hope to save the world.

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