At a glance - Clearing up misconceptions regarding 'hide the decline'

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added "At a glance" section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a "bump" for our ask. This week features "Clearing up misconceptions regarding 'hide the decline'". More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.

At a glance

It's been many years since 'climategate' - when in 2009, the email server at the Climate Research Unit, University of East Anglia, was hacked. The unidentified hacker helped themselves to thousands of emails. These were sifted through and a selection was in due course made available for public download on a Russian server.

What followed was typical of the tactics used in the campaign to deny the existence of human-caused climate change and is illustrative for that reason. A lot of this manufactured controversy centred on one email, written by Dr Phil Jones, in which the following sentence was picked out and trumpeted all over the media:

"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) and from 1961 for Keith's to hide the decline."

"Gotcha!", the deniers proclaimed.

Climategate was marketed to the public by encouraging them to take such sentences at face value - without any idea of what they actually meant. The notion being planted was that climate scientists were busy covering up declining temperatures.

It meant nothing of the sort. The people in that email were not talking about temperatures. They were talking about tree-rings.

"Mike's Nature trick" referred to a technique described in a 1998 Nature paper. The paper presented a 600 year-long global temperature reconstruction by Michael Mann and colleagues. Michael has long used tree-ring growth patterns in ancient wood to reconstruct conditions at the time those rings formed. The basic idea is that in cold, dry years, trees grow more slowly so their rings are relatively narrow and densely-spaced. In warm wet years, it's the opposite.

The "trick" is the technique of plotting recent instrumental data - in other words direct temperature measurements - alongside the reconstructed tree-ring data for the time they overlap. Why? Because it's one way of checking if the reconstructed tree-ring data are a good proxy for temperatures of the past. It therefore makes entire sense to run such checks. Now to the 'decline'. What declined?

Beyond a certain point on the timeline, around 1960, the temperature reconstructions based on some tree-ring data fell away and downwards from observed thermometer records. They declined from reality. This only happened with certain tree-ring datasets from specific places. Known as the 'divergence problem', it had been discussed in the scientific literature since the mid 1990s - 15 years before 'climategate'. However, not a lot of people realised that. How lucky for the deniers. "Hide the decline!", they chanted feverishly, to anybody who would listen.

Everything that occurs in the physical world has a cause. The divergence of temperature reconstructions, based on tree-ring growth, from the observational temperature record is a case in point. The loss of tree-ring sensitivity to temperatures kicked in around 1960. It only affected certain tree-species at certain locations. However, in those cases the post-1960 tree-ring datasets do not reflect the actual conditions. In other words, the data are useless. That's the decline for you. Much ado about nothing.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

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Click for Further details

In case you'd like to explore more of our recently updated rebuttals, here are the links to all of them:

Myths with link to rebuttal	Short URLs
Ice age predicted in the 1970s	sks.to/1970s
It hasn't warmed since 1998	sks.to/1998
Antarctica is gaining ice	sks.to/antarctica
CRU emails suggest conspiracy	sks.to/climategate
What evidence is there for the hockey stick	sks.to/hockey
CO2 lags temperature	sks.to/lag
Climate's changed before	sks.to/past
It's the sun	sks.to/sun
Temperature records are unreliable	sks.to/temp
The greenhouse effect and the 2nd law of thermodynamics	sks.to/thermo
We're heading into an ice age	sks.to/iceage
Positives and negatives of global warming	sks.to/impacts
The 97% consensus on global warming	sks.to/consensus
Global cooling - Is global warming still happening?	sks.to/cooling
How reliable are climate models?	sks.to/model
Can animals and plants adapt to global warming?	sks.to/species
What's the link between cosmic rays and climate change?	sks.to/cosmic
Is Al Gore's An Inconvenient Truth accurate?	sks.to/gore
Are glaciers growing or retreating?	sks.to/glacier
Ocean acidification: global warming's evil twin	sks.to/acid
The human fingerprint in global warming	sks.to/agw
Empirical evidence that humans are causing global warming	sks.to/evidence
How do we know more CO2 is causing warming?	sks.to/greenhouse
Explaining how the water vapor greenhouse effect works	sks.to/vapor
The tricks employed by the flawed OISM Petition Project to cast doubt on the scientific consensus on climate change	sks.to/OISM
Is extreme weather caused by global warming?	sks.to/extreme
How substances in trace amounts can cause large effects	sks.to/trace
How much is sea level rising?	sks.to/sealevel
Is CO2 a pollutant?	sks.to/pollutant
Does cold weather disprove global warming?	sks.to/cold
Do volcanoes emit more CO2 than humans?	sks.to/volcano
How do human CO2 emissions compare to natural CO2 emissions?	sks.to/co2
Climate scientists could make more money in other careers	sks.to/money
How reliable are CO2 measurements?	sks.to/co2data
Do high levels of CO2 in the past contradict the warming effect of CO2?	sks.to/pastco2
What is the net feedback of clouds?	sks.to/cloud
Global warming vs climate change	sks.to/name
Is Mars warming?	sks.to/mars
How the IPCC is more likely to underestimate the climate response	sks.to/underestimat
How sensitive is our climate?	sks.to/sensitivity
Evidence for global warming	sks.to/warming
Has the greenhouse effect been falsified?	sks.to/falsify
Does breathing contribute to CO2 buildup in the atmosphere?	sks.to/breath
What is causing the increase in atmospheric CO2?	sks.to/CO2increase
What is methane's contribution to global warming?	sks.to/methane
Plants cannot live on CO2 alone	sks.to/plant
Is the CO2 effect saturated?	sks.to/saturate
Greenhouse warming 100 times greater than waste heat	sks.to/waste
How will global warming affect polar bears?	sks.to/bear
The runaway greenhouse effect on Venus	sks.to/venus
What climate change is happening to other planets in the solar system?	sks.to/planets
Has Arctic sea ice returned to normal?	sks.to/arctic
Was Greenland really green in the past?	sks.to/green
Is Greenland gaining or losing ice?	sks.to/greenland
Human activity is driving retreat of Arctic sea ice	sks.to/arcticcycle
The albedo effect and global warming	sks.to/albedo
Does CO2 always correlate with temperature?	sks.to/correlate
Human fingerprints on climate change rule out natural cycles	sks.to/cycle
Global warming and the El Niño Southern Oscillation	sks.to/elnino
The Pacific Decadal Oscillation (PDO) is not causing global warming	sks.to/pdo
Is the science settled?	sks.to/settled
The difference between weather and climate	sks.to/weather
Clearing up misconceptions regarding 'hide the decline'	sks.to/decline

 

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