Hide The Decline Fact Check
20 years ago, in April 1998, a paper appeared in the prestigious journal Nature that would go on to be one of the most contentious and influential climate science papers of all time.
Its lead author was Michael E. Mann, at the time a young researcher just starting his career. From the initials of Mann and his coauthors the paper came to be called MBH98, but to many people it’s best known for introducing the famous “hockey stick” graph.
Based on a statistical analysis of tree rings and other natural formations, it purported to show the average annual temperature of the Northern Hemisphere back to AD1400 as basically flatlining (the handle) for hundreds of years until it suddenly shot upward (the blade) in the 20th century.
A year later the same authors published an extended version going back to AD1000. Both versions presented the same stunning picture: the world’s climate had apparently followed a steady, gentle cooling trend for 900 years, then in the 20th century a violent warming trend began, unlike anything in the past millennium. The authors fingered rising CO2 emissions as the culprit.
Within two years the hockey stick rocketed to international fame, after becoming the centrepiece of the 2001 Report of the Intergovernmental Panel on Climate Change, where it appeared six times, always in full colour, and was heavily promoted at an international press conference by IPCC Chairman Sir John Houghton.
Governments around the world began using the hockey stick, with the full authority of the IPCC behind it, to promote the global warming alarm.
I’m John Robson, and this is a Climate Discussion Nexus backgrounder on Hiding the Decline.
There was always something dubious about this chart. And not just the way it erased the well-known Medieval Warm Period. It’s also that the Mann series switched from tree rings to temperature readings at the precise point the line changed direction dramatically. Which would normally get scientists excited about possible weaknesses in the methodology, particularly the discrepancy between the data sets, rather than pretending there was nothing to worry about. And finally it was very strange, at least from a scientific perspective, that this one paper got so much publicity because back in 1998 Mann and his colleagues were not the only ones studying ancient tree ring data and other researchers did not find what they did.
Just two months after MBH98 appeared, Nature published another climate reconstruction, this time by the late British scientist Keith Briffa and 4 coauthors.
Like Mann’s study, it used tree ring records from all over the Northern Hemisphere to estimate temperatures back to the year 1400. But unlike Mann’s paper, the result looked nothing like a hockey stick. It showed a lot of variability over time, and record warmth in the 1930s, but no special warming pattern since then.
In fact, it showed cooling up to 1993, with temperatures ending below the average of the past six centuries.
The climate science community was confronted with two studies at the same time, both using similar methods to study the same thing, and coming up with very different answers. Normally that kind of result means the science is not settled, the data may not be reliable, and the uncertainties need to be explained.
In this case, apparently, it meant instead that a body needed to be buried for political reasons. The story of the disappearance of the Briffa data is one of the darkest episodes in modern science.
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It’s long been known that the Earth’s climate is naturally variable. The study of ancient climate conditions is called paleoclimatology. In the first report of the Intergovernmental Panel on Climate Change, back in 1990, they summarized the conventional view among paleoclimate experts that at the end of the last ice age about 10,000 years ago, the climate warmed for about 4,000 years, reached a state much warmer than the present and stayed there for several millennia, then began cycling between cooling and warming.
The Roman era and the Medieval era were both relatively warm compared to the present, and the Little Ice Age, which ended in the early 1800s, was relatively cold. And now we are in another warm phase of the cycle, though according to the conventional view as of 1990, it’s nothing special compared to previous eras.
The 1990 IPCC diagram of the familiar cycle matches other records, such as this long term temperature reconstruction from ice cores taken out of the Greenland ice cap.
Similar evidence for past warming episodes comes from the Riviere Boniface region in the Ungava Peninsula of northern Quebec. In 1997, scientists from Laval University in Quebec published evidence of the remains of a black spruce forest preserved in peat in the arctic tundra. The trees grew over an interval spanning 1000 BC to almost 1600 AD.
How could there be a forest in the Arctic? Simple. It used to be warmer there than it is to this day. Periods of rapid forest growth there happened during the Roman and Medieval warm periods. But a major fire in the late 1500s wiped out the trees, and it’s been too cold for them to grow back ever since. In fact, it’s been considerably too cold. The authors point out that the forest remains they studied are 130 km north of the present tree line. For a forest to have grown so far north a thousand years ago means it had to have been much warmer there for a long time compared to what we’re now experiencing.
The problem for alarmists is that the existence of the Medieval Warm Period made it hard to claim that recent climate warming is anything unusual. So it had to go. Which made the Mann hockey stick very attractive to the IPCC.
MBH98’s headline conclusion was that today’s warming was unlike anything the Earth had seen in a thousand years. But, the critics would say, that’s based on studying tree rings. Maybe the warming happened, and the tree rings simply don’t show it. Which is where Briffa’s data was critical.
The 20th century is the one interval where we have both thermometer data and tree ring records, and we can see that the trees don’t show any warming. So, if they fail to respond to 20th century warming, how do we know that they don’t also miss it in earlier centuries?
A third paper published in 1998 emphasized these challenges. The lead author was UK scientist Phil Jones, and his list of coauthors included Keith Briffa and two others. They said that, of the various ancient climate records available, tree rings were probably the best, but they can be very unreliable.
Their own result fell between Mann’s and Briffa’s, with a clear Little Ice Age and a modern interval about as warm as the Medieval period. But since it was based on a very small data set they cautioned against reading too much into it.
Mann’s paper, by contrast, swept aside the uncertainties. He and his coauthors claimed “moderately high levels of confidence” that the 1990s were the warmest decade, and 1998 the warmest year, of the millennium – of the last 1,000 years. And that brought the IPCC calling.
In 1999 the IPCC was starting work on its Third Assessment Report. Out of all the people doing tree ring temperature analysis, they picked Michael Mann to write the summary.
Jones and Briffa were invited to serve as contributors, but under IPCC rules, it’s the Lead Authors who decide what goes in. By appointing Mann, the IPCC was signalling what message they were looking for. And soon they would be even more explicit about what they were after.
On September 1st 1999 the IPCC convened a meeting of the authors in Arusha, Tanzania, where they spent three days discussing what the first draft of the report should include. Ten years later a large library of emails among Jones, Briffa, Mann and other climate scientists would be leaked onto the internet, which is how we came to possess the inside details of what happened next.
On September 22nd 1999, three weeks after the Arusha meeting, IPCC Coordinating Lead Author Chris Folland sent around a note stating
A proxy diagram of temperature change is a clear favourite for the Policy Makers summary. But the current diagram with the tree ring only data [Briffa’s] somewhat contradicts the [Mann] multiproxy curve and dilutes the message rather significantly.
So he asked that Mann’s curve be given priority.
Now hold on a moment. It’s 1999, almost two years before the report was due to be released and before the expert review process had even started. Yet the IPCC leadership had already decided on the “message” they wanted in the Summary for Policymakers, and they didn’t want it “diluted” even though they knew the available data was contradictory and inconclusive?
Clearly the IPCC didn’t see their job as surveying the science and writing a summary that reflected the full range of data and of opinions. Instead they decided ahead of time on a compelling message, that man-made climate change was a pressing crisis, and then they looked for the science to support it.
Mann proposed doing what Folland wanted by circulating a diagram showing only his hockey stick and the Jones diagram, while leaving out Briffa’s altogether. Jones objected, and Briffa likewise was furious. He wrote to the author team:
I know Mike thinks his series is the 'best' and he might be right - but he may also be too dismissive of other data and possibly over confident in his… After all, the early (pre-instrumental) data are much less reliable as indicators of global temperature than is apparent in modern calibrations.”
But Briffa also understood the problem: The data didn’t support the story the IPCC wanted to tell.
I know there is pressure to present a nice tidy story as regards 'apparent unprecedented warming in a thousand years or more in the proxy data' but in reality the situation is not quite so simple. We don't have a lot of proxies that come right up to date and those that do (at least a significant number of tree proxies ) some unexpected changes in response that do not match the recent warming. I do not think it wise that this issue be ignored in the chapter.
He then acknowledged what was really at stake: They were being asked to override their scientific judgment in service of the IPCC’s political agenda.
I believe that the recent warmth was probably matched about 1000 years ago. I do not believe that global mean annual temperatures have simply cooled progressively over thousands of years as Mike appears to and I contend that that there is strong evidence for major changes in climate over the Holocene.
Mann then offered to put the Briffa data back in. But, he warned, they didn’t understand why the data sets differed, and climate skeptics might use this to cast doubt on their work and undermine the peoples’ faith:
So, if we show Keith's series in this plot, we have to comment that "something else" is responsible for the discrepancies in this case… We would need to put in a few words in this regard. Otherwise, the skeptics would have a field day casting doubt on our ability to understand the factors that influence these estimates and, thus, can undermine faith in the paleoestimates.
The real problem wasn’t that skeptics would cast doubt on their message, it was that the contradictions in the data would cast doubt on their message.
The black line is Mann’s curve, the pink one is Jones’, and the green one peeking from behind was Briffa’s modified data, attributed to a later paper published in 2000. The red line leading upwards at the end was from modern thermometer data. The diagram suggested, amazingly, that all the data were in perfect agreement.
Where did the discrepancy go?
For the next five years, nobody asked that question. Then in 2005, Stephen McIntyre of Toronto, a semi-retired mining consultant who had taken an interest in paleoclimate studies, got curious about it and looked up the Briffa paper. Right away, he noticed something odd.
The green curve was supposedly the one Briffa submitted to the IPCC. But it goes up to 1994 in the journal article, whereas the IPCC version stopped at 1960.
They had deleted the final 33 years of data—the declining portion.
McIntyre hunted through some online data archives and found the full Briffa series, then drew what the IPCC diagram would have looked like if they had used all the data.
What a difference. By deleting the last part of the blue line, they concealed the contradictions among the data sets, and the questions it raised about the validity of the methods.
The reason why Briffa’s data was a problem for them was that his temperature reconstruction from tree rings went sharply down in the last half of the 20th century when temperatures were going up. So the question for any rational observer was, if tree ring data went down while temperatures went up, what makes you think that these are a good measurement, or a good proxy, for temperatures? And if they went down when it was warm in the 20th century, how do we know they didn’t do that in the past? These are questions that every scientist would ask if they were presented with this data, and by concealing the data, they stopped people from asking that question.
McIntyre’s discovery didn’t attract much immediate attention, but when the Climategate emails came out, he began digging into the issue further. One of the most notorious emails was from Phil Jones dated just two months after the Arusha meeting, on November 16, 1999, when he was preparing a similar diagram that would go on the cover of a major report from the World Meteorological Organization. Writing to Mann and his MBH98 coauthors, Jones said:
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.
Jones was referring to this chart, which, like the IPCC diagram, made it look like all the data sets agreed and showed unprecedented recent warming. It achieved this effect by deleting the Briffa data after 1960, splicing in thermometer data to each series up to the year 2000, then smoothing over the splice, as Jones said, to hide the decline. That’s quite the trick.
To give you an idea of how big a story it was, the Climategate emails were released at approximately the same time as Tiger Woods’ implosion. And there were more, there were 22 million hits for Climategate and there were 21 million hits for Tiger Woods. It was a huge social media story, but it was barely covered in the national media.
In the aftermath of Climategate a number of inquiries were convened by the UK government into the conduct of Jones, Briffa and their British colleagues.
But, as would be expected in bureaucratic circles, the reports mostly served to whitewash the revelations, to protect the reputations of the universities involved, and of course to protect the notion that there was a proven man-made global warming crisis.
The main investigative team was headed by Muir Russell, and it conceded that a minor wrist slap was in order for this incident.
“In relation to “hide the decline” we find that, given its subsequent iconic significance (not least the use of a similar figure in the [IPCC Report], the figure supplied for the WMO Report was misleading in not describing that one of the series was truncated post 1960 for the figure, and in not being clear on the fact that proxy and instrumental data were spliced together.”
The operative word is there were “sort of” inquiries. None of the inquiries, however, squarely addressed or even addressed at all, the idea of senior IPCC scientists directing junior scientists to not, quote, “dilute the message”, or what the junior scientists had done to not, quote, “dilute the message.” The message they were trying to put out was that the change in climate was alarming, and so any data that they had that showed that it wasn’t alarming, they didn’t want to show. It would dilute the message.
The IPCC has never owned up to what happened, or issued a correction. In fact the fraudulent diagram is still on their website.
By hiding the decline, they misled world leaders and citizens on an issue that they themselves judged to be critically important. They falsified data to conceal their own uncertainty and the potential unreliability of the methods they were using. And that is not how science is done.
It’s been 20 years now since this body was buried. But it still stinks. So, next time you see an apparently tidy and compelling message from the IPCC, judge its credibility accordingly.
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For the Climate Discussion Nexus, I’m John Robson.