A Review of Temperature Reconstructions

By Andy May

This is an update to a 2016 post; the original post is here.

We often hear that the planet is warming faster than ever before, or at the fastest rate since the beginning of the industrial era! Is it true? We haven’t had thermometers for very long. How do thermometer readings compare to temperature proxies like ice cores and tree rings? Greenland is a good place to start, we see the high-resolution Greenland ice core temperatures all the time. How accurate are they? How do Greenland temperatures compare to temperatures elsewhere?

In previous posts (here and here), I’ve compared historical events to the Alley and Kobashi GISP2 Central Greenland Temperature reconstructions for the past 4,000 years. Unfortunately, these two reconstructions are very different. Steve McIntyre suggested I consider a third reconstruction by Bo Vinther. Vinther’s data can be found here. Unfortunately, Vinther is significantly different from the other two. Nothing agrees very well.

The Alley data has been smoothed, but the details of the smoothing algorithm are unknown. I smoothed the other datasets, so they visually have the same resolution as the Alley dataset. Both datasets (Kobashi and Vinther) were first smoothed with a 100-year moving average filter. Then 20-year averages of the smoothed data were taken from the one-year Kobashi dataset to match the Vinther 20-year samples. The Alley data is irregularly sampled, but I manually averaged 20-year samples where the data existed. If a gap greater than 20 years was found that sample was skipped (given a null value).

All three reconstructions are shown in Figure 1. There is no reason to prefer one of the three reconstructions over the other two, so I simply averaged them. The average is the blue line. I’m not presenting this average as a new or better reconstruction; it is merely a vehicle for comparing the three reconstructions to one another and to other temperature reconstructions. I’m trying to show the variability in common temperature reconstructions for the past 2,000 to 4,000 years. This post is less about the actual temperatures, than the temperature reconstructions and how they compare.

Figure 1

There are some notable outliers apparent in the comparison. In particular, we see the odd 700AD 2.5 degree C Kobashi spike and the scatter in the interval from 700BC to 100BC. The Minoan Warm Period (1600BC to 1300BC) is completely missing in the Vinther reconstruction. The estimates agree better from 900 AD to the present than they do prior to 900 AD. Perhaps as the ice gets older, accuracy and repeatability are lost? Figure 2 shows the same average and the maximum and minimum value for each 20-year sample.

Figure 2

The average temperature for the 4,000-year period is -30.8°C. The average minimum and maximum suggest this value is plus or minus 0.3°C. Perhaps we are simply seeing the error in these methods and nothing more. For those who want to see the messy details of the average temperature calculation, the spreadsheet can be downloaded here. As noted in my previous post, the error in the time axis is probably at least ±50 years. Loehle has suggested a time error of ±100 years based on 14C laboratory errors. These values give us some perspective in interpreting the reconstructions. Below is a comparison of the average to the same historical events we have used before.

Figure 3, click on the image or here to download a PDF

This average temperature reconstruction shows a steady decline in temperature since the Minoan Warm Period, interrupted by ±120-year cycles of warm and cold. Don’t take the apparent 120-year cyclicity too seriously all the data was smoothed with a 100-year moving average filter. After the end of the Little Ice Age, the Modern Warm Period begins, and temperatures rise to those seen in the Roman Warm Period. The Modern Warm Period is equivalent to the Medieval Warm Period within the margin of error. We need to be careful because we are comparing actual measurements to averaged proxies.

When proxies are averaged, all high and low temperatures are dampened. In particular, the Medieval Warm Period is somewhat smeared and dampened due to the Vinther record. The Vinther Medieval Warm Period peak is earlier than the Kobashi and Alley peaks. Major volcanic eruptions fit this timeline reasonably well. Rabaul is dated to 540AD. Thera-Santorini occurred in 1600BC and Tambora in 1815. The HadCRUT 4.4 point shown with a red star is an average of several HADCRUT4 surface temperature grid points in the Greenland area thought to be comparable to the Greenland average temperature.

Comparisons to broader temperature reconstructions
Dr. Craig Loehle published a global composite temperature reconstruction in 2007 and a corrected version in 2008. This reconstruction has been widely reviewed and appears to have stood the test of time. Subsequent work seems to support the reconstruction. In Figure 4 we show his global reconstruction compared to the Greenland average and the recent temperature reconstruction of the extratropical (90° to 30°N) Northern Hemisphere by Christiansen and Ljungqvist. The graph in Figure 4 shows temperatures as anomalies from 1600 to 1800 since each line represents a different area.

Figure 4

All the reconstructions show a trend of decreasing temperature from 900AD to the Little Ice Age, roughly from 1400 to 1880 AD. They also show a temperature peak around 1000 AD. The Northern Hemisphere peak is much higher than the Greenland or global peaks. The most striking thing about Figure 4 is that the temperature swings seen in the extra tropical Northern Hemisphere are larger than in the other reconstructions. There are likely three reasons for this, the first is the global reconstruction averages more proxies. The proxies have different resolutions, anything from one-year to several hundred years and the dating uncertainty is high in each proxy sample. These issues dampen any extremes. The second issue is the Southern Hemisphere and the Northern Hemisphere warm and cool at different times. Since the hemispheres are out of phase, global extremes are further dampened. Finally, the Northern Hemisphere is always anomalous, it has more extreme warming and cooling than the other large regions of the earth. The reason for this is unclear, but it could be because most of the land is in the Northern Hemisphere, between 30N and 60N. The Arctic is mostly ocean, so it escapes some of the extremes seen in the Northern Hemisphere between 30N and 60N.

Temperature changes are amplified in the Arctic and Antarctic, independently of where the land masses are, over geological time, as Chris Scotese explains in his climate history. This is also suggested by Flannery, et al. So, a combination of polar amplification and extra land causes the Northern Hemisphere to be anomalous. Finally, Figure 5 shows the Greenland average compared to two Arctic reconstructions. One is the ice core component of the Arctic reconstruction by Kaufman, 2009 (data here) and the other is the Sunqvist, 2014 “PAGES2K” Arctic reconstruction (data can be found here). In Figure 5, the Arctic and PAGES2K temperature anomalies have been shifted to the average central Greenland temperature for the period for comparison purposes.

Figure 5

These two multi-proxy Arctic reconstructions agree fairly well with the Greenland average if we assume a ±0.3°C temperature error and ±50-year time error. It is interesting that the peak about 400AD is seen in the Arctic and Greenland reconstructions but not in the Loehle global reconstruction in Figure 4. The Sunqvist, 2014 reconstruction was used as presented in his paper, it seemed to be carefully constructed. Sunqvist,et al. did include some tree ring data (fewer than 1% of the proxies), but they used it carefully and tree ring data did not dominate his reconstruction.

Kaufman’s Arctic reconstruction used a lot of tree ring data (4 of 23 proxy records) as can be seen in his Figure 3 and in his dataset. Tree ring data does provide an accurate chronology, but it provides a poor temperature proxy due primarily to what has been called the “divergence” problem. Tree rings may correlate well to temperatures in a “training” period but show little correlation to temperature longer term. There are several possible reasons for this. First, as Keith Briffa explained, the twentieth century tree ring data diverges strongly from historical tree ring data. This could be a result of increasing CO2 in the atmosphere causing the assumed temperature to tree ring correlation to change.

A second likely factor is that forests adapt to long-term climatic changes by adjusting tree density and tree size, this diminishes their usefulness in measuring long-term changes. Tree ring width and density tend to reflect summer temperatures, precipitation, and many other factors, but extracting the average annual air temperature from them is problematic. Loehle discusses this problem and other problems with tree ring data here and here. For this reason, only the ice core records (seven proxy records of 23) from Kaufman’s reconstruction were used to plot the “Arctic” line in Figure 5.

Figure 6 compares Kaufman’s “All proxies” reconstruction to his ice core, sediment (including lake varves), and tree ring proxies. The ice core, sediment, and tree ring proxies only agree reasonably well for the last 500 years, before that the tree ring proxies diverge dramatically downwards. The lake and marine sediment proxies (12 of the 23) are also lower than the ice core proxies, but not so dramatically. We all know of another paleoclimatologist who took advantage of this divergence.

Figure 6

When all the proxies are used the earlier temperatures are much lower and the modern warm period has a higher peak. The recent peak in Figure 6 is the twenty-year average around 1945. The proxy reconstruction then drops, the last point is centered on 1985. I didn’t bother to “hide the decline.” Except for the sharp drop from 1945 to 1985 Kaufman’s ice core proxies fit the rest of the reconstructions shown above reasonably well.

There are many Greenland area temperature reconstructions, they use ice core data, lake and marine sediment core data and other proxies, mainly tree rings. They are not perfect and contain errors in the temperature estimates and dating errors. The exact error is unknown, but by comparing reconstructions we can see that they generally, except for the tree ring proxies, agree to within 0.3°C and in time, to within 50 years or so. Why is this important? Natural climate cycles are poorly understood. Some, like the very irregular, but short-term (~3-7 years) ENSO cycle (La Nina and El Nino) we can identify, but because they are irregular, and the cause is unknown, we cannot model them. The same is true of the ~60 to 80-year Atlantic Multidecadal Oscillation (AMO) and the ~50-70-year Pacific Decadal Oscillation (PDO). These events affect the weather and climate all over the world, but they are not accurately included in the GCM’s (General Circulation Models) used by the IPCC, and other organizations, to compute man’s influence on climate. Thus, some portion of the Modern Warm Period attributed to humans may, in fact, be attributable to these or other natural climate cycles.

During the 1980’s and 1990’s the PDO was mostly positive (warming). From the mid 1990’s to today the AMO has been mostly positive and undoubtedly contributing to warming. There have been numerous attempts to see a pattern in these multidecadal natural climate cycles. Most notably, Wyatt and Curry identified a low-frequency natural climate signal that they call a “stadium wave.” This model is based on a statistical analysis of observed events (especially the AMO) and not on the physical origins of these long-term climate cycles. But it does allow predictions to be made and the veracity and accuracy of the stadium wave hypothesis can and will be tested in the future.

Another recent paper by Craig Loehle discusses how the AMO signal can be removed from recent warming, leaving a residual warming trend that may be related to carbon dioxide. He notes that when the AMO pattern is removed from the Hadley Center HADCRUT4 surface temperature data the oscillations are dampened and a more linear increase in temperature is seen. This trend compares better to the increase in carbon dioxide in the atmosphere and allows the computation of the effect of carbon dioxide on temperature. The calculation, for the post-1970 period, results in a temperature trend of 0.83°C per century. This is roughly half of the observed trend of 1.63°C. Loehle suggests that the AMO may be the best indicator of natural trends. If this is true, then half of recent warming is natural and half is man-made. It also suggests that the equilibrium climate sensitivity to carbon dioxide is about 1.5°C per doubling of CO2, half the IPCC preferred value. This value also compares well to other recent research.

The use of temperature proxies to determine surface air temperatures prior to the instrument era is very important. It is the only way to determine natural long-term natural climate cycles. Currently, in the instrument record, we can see shorter cycles like the PDO, AMO, and ENSO. When these are incorporated into models, we see that half or more of recent warming is likely natural, belying the IPCC idea that “most” of recent warming is man-made. Yet, these shorter cycles are clearly not the only cycles. When we look at longer temperature reconstructions, we see 40,000, 80,000 or 120,000-year glacial periods interrupted by brief 10,000 to 18,000-year interglacial periods. These longer periods will probably only be fully understood with more accurate reconstructions. Intermediate ~1,500-year cycles, called “Bond events,” the 2,450-year Bray, and the 1,000-year Eddy cycles have also been identified and need to be better understood.

Tree ring proxies older than 500 years and younger than 100 years are anomalous. This anomaly is large enough to cast doubt on any temperature reconstruction that uses tree rings. Between lake and marine sediment proxies and ice core proxies it is hard to tell which is more likely to be closer to the truth. They agree well enough to be within expected error. All proxies diverge from the mean with age, none are accurate (or more precisely in good agreement) prior to 1100 AD. It does appear that all proxies except for tree ring proxies, could be used for analytical work back to 1100 AD. Unfortunately, the uncertainty in dating the samples, the poor temporal resolution, and the lack of temperature accuracy preclude comparing these proxy records to modern temperatures. Statements like “warming today is the fastest in the last 1,000 years [or more]” have no credibility. Computing the speed of warming requires accurate dating and an accurate temperature measurement.

The Northern and Southern Hemispheres are out of phase with one another and cool or warm separately. This makes global temperature averages problematic. This is probably due to Earth’s orbital eccentricity and regular changes in the Earth’s orientation, relative to its orbital plane. For these reasons, the Sun affects Earth’s climate differently by latitude. CO2 may be a global effect, but solar forcing is not, it is hemisphere specific. This must be considered when calculating natural warming, it discourages focusing on a global average temperature as a climate change metric. The unique climate of the Northern Hemisphere, which is more extreme than the other regions of the world, must also be considered.

The other very important use for temperature reconstructions is to study the impact of climate changes on humans and the Earth at large. Historical events are often known to the day and hour, only when we have reconstructions with more accurate time scales can we properly match them to major events in history. In addition, this post makes it clear that combining multiple proxies causes severe dampening of the temperature response because proxy sample dating errors cause peaks and valleys in the record to be mismatched, reducing apparent variability and accuracy. Multiple proxy reconstructions show less temperature variation than occurred. The National Academy of Sciences/National Research Council and Wegman Committee investigations into the “Hockey Stick” documented this problem well. They also showed that dating accuracy will probably never be better than 50-100 years with current dating tools. Tree ring dates are more accurate than this, but tree rings are a poor and inconsistent indicator of temperature. A proper comparison of warming or cooling rates between the twentieth and twenty-first centuries and any period prior to 1900 will probably never be possible, short of dramatic improvements in proxies or proxy technology.

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May 2, 2021 2:14 pm

Andy ==> Thanks for this — just in case close readers aren’t paying attention, Greenland/NH temperatures begin to rise circa 1700 or so. Not at the oft claimed “beginning of the modern industrial age.” 150 years before CO2 built up enough to affect surface air temperatures.

Abolition Man
Reply to  Kip Hansen
May 2, 2021 3:49 pm

Wasn’t that around the beginning of the Atlantic Slave Trade?
I think we have found the other source of gorebull warming; any use of data, facts or reason to argue against this thesis is neo-colonialist, neo-imperialist and raaaaacist!

Last edited 11 days ago by Abolition Man
Reply to  Abolition Man
May 2, 2021 4:04 pm

AbMan ==> That would a media-only logical leap . . .

Abolition Man
Reply to  Kip Hansen
May 2, 2021 6:40 pm

So no facts, just their feelings? By the way, be careful of using media and logical in the same sentence or paragraph!

Ron vdS
Reply to  Kip Hansen
May 2, 2021 4:24 pm

If error bars were also included in the graphs the peaks in the error bars would show warming at or above the rate we see today or they could be used to further smooth the data. It does depend if you want to be a realist or a warmist.

May 2, 2021 2:25 pm

HADCRUT4 is adjusted data with the adjustments highly correlated with CO2. I’m not sure how to test for a CO2 impact in such data.

Reply to  Nelson
May 3, 2021 3:20 am

It appears there is no way to test for anything that may have an impact on HADCRUT dats.
#DataGate! First ever audit of global temperature data finds freezing tropical islands, boiling towns, boats on land
HadCrut4 Global Temperature, 1850 – 2018.

Absurdity everywhere in Hadley Met Centre data

What were they thinking?
The fate of the planet is at stake, but the key temperature data set used by climate models contains more than 70 different sorts of problems. Trillions of dollars have been spent because of predictions based on this data – yet even the most baby-basic quality control checks have not been done.
Thanks to Dr John McLean, we see how The IPCC demands for cash rest on freak data, empty fields, Fahrenheit temps recorded as Celsius, mistakes in longitude and latitude, brutal adjustments and even spelling errors.
Why. Why. Why wasn’t this done years ago?
So much for that facade. How can people who care about the climate be so sloppy and amateur with the data…?

Also, here.
DATA-Climate Bombshell: Global Warming Scare Is Based on ‘Careless and Amateur’ Data, Finds Audit

…The Hadley Centre and Met Office will find it difficult to dismiss McLean as a crank. In March 2016, he advised them of certain errors which they promptly corrected. So he’s an authority they take seriously.
Dr McLean audited the HadCrut4 global data from 1850 onwards for his PhD thesis, and then continued it on afterwards til it was complete:
“I was aghast to find that nothing was done to remove absurd values… the whole approach to the dataset’s creation is careless and amateur, about the standard of a first-year university student.”
– John McLean
His supervisor was Peter Ridd, famously sacked for saying that “the science was not being checked, tested or replicated” and for suggesting we might not be able to trust our institutions
Data is incredibly, brazenly, sparse
The Hadley Met Centre team have not even analyzed this data with a tool as serious as a spell checker.
For two years the entire Southern Hemisphere temperature was estimated from one sole land-based site in Indonesia and some ship data. We didn’t get 50% global coverage until 1906. We didn’t consistently get 50% Southern Hemisphere coverage until about 1950.
McLean’s findings show there is almost no quality control on this crucial data. The Hadley Met Centre team have not even analyzed this data with a tool as serious as a spell checker. Countries include “Venezuala”,” Hawaai”, and the “Republic of K” (also known as South Korea). One country is “Unknown” while other countries are not even countries – like “Alaska”.
The real fault of the modern day institutes is not so much the lack of historic data, but for the way they “sell” the trends and records as if they are highly certain and meaningful…

Richard Page
May 2, 2021 2:31 pm

Ok. This is something I’ve never understood – given that, even with warm and cool spikes, the trend is a fairly even descent towards the next ice age, what causes the modern warm period to buck that trend and increase temps to where they were just after the Roman Warm Period? Looking at the graphs, if we’d followed the trend, warming should have stopped at a cooler level. Either each of those warm periods have far higher spikes that we’re just not seeing on a smoothed average or our warming really is anomalous.
Btw – I’m hoping for the second because otherwise, when that spike goes down the other side it’s going to get a damned sight colder than we were expecting.

May 2, 2021 2:37 pm

The average temp went down from approximately 1940 to 1980 while CO2 went up 15%. Unless the people who claim CO2 warms the atmosphere can explain the cooling, then there is no need to pay any attention to CO2 warming claims. Waiting……..

Rud Istvan
May 2, 2021 2:43 pm

Andy, great post. I dug into some of this for the Climate chapter (reviewed by Lindzen) in Arts of Truth, and then essay Cause and Effect (Shakun 2012) and A High Stick Foul (Marcott 2013). Steve Mcintyre has separately debunked tree rings as dicey.

What I found is that the paleoproxies behind these reconstructions are unreliable and inconsistent, even when properly used (upside down Tiljander and strip bark bristle cone pines and Marcott’s coretop redatings are improper). They are inconsistent with each other. This was driven home by Shakun 2012, once his statistics were deconvoluted in the essay, where his supposed effect PRECEDED his supposed cause.

I concluded, as you have, that ‘precise’ reconstructions are very difficult and do not agree with each other very well. But qualitative temperature differences are easy, and show significant natural variation. Two examples. 1. There are root penetrated Viking graves on Greenland that are now fully encased in permafrost, so it WAS warmer when these burials occurred. 2. The last Thames ice fair was (if I recall correctly) 1818, so it WAS colder in the LIA.

Reply to  Rud Istvan
May 2, 2021 6:02 pm

Further, modern temperatures include UHI which has nothing to do with CO2 but has an influence from population growth.

Pamela Matlack-Klein
Reply to  cementafriend
May 3, 2021 3:02 am

I would like to see what happens to these graphs if UHI is removed. My actual observations tell me that UHI is significant. If Viking graves that were dug during the MWP are currently still locked in permafrost then surely this tells us the Modern Warm is cooler than the MWP.

Reply to  Rud Istvan
May 3, 2021 5:14 am

That’s interesting about the Viking graves…would you have a reference to that or do you know of any images?

May 2, 2021 2:54 pm


How does the data recently published by Happer fit into all this?

Reply to  Andy May
May 2, 2021 9:11 pm

Yes. In it, they show that almost all of the atmospheric CO2 is saturated and can’t be responsible for any global warming. You say
half of recent warming is natural and half is man-made.
Seems like your conclusion is in direct conflict with their results.

Chris Hanley
May 2, 2021 2:57 pm

Affirming a disjunct ‘making the false assumption that when presented with an either/or possibility, that if one of the options is true that the other one must be false’ is a logical fallacy.
Global temperature may be affected by ‘natural fluctuations’ and CO2 including human emissions.

Chris Hanley
Reply to  Chris Hanley
May 2, 2021 3:11 pm

That comment is made in anticipation of future comments, not on the article.

Reply to  Chris Hanley
May 3, 2021 3:36 am

“How does one begin to detect, isolate & quantitatively measure only CO2 re-emitted IR in the 15 μ band? Physicist Dr. Happer – the chances of CO2 re-emitting IR & not releasing the IR in molecular collisions ~ a billion to one. If AGW cannot be measured, does it exist?”
Dr. William Happer

Robert of Texas
Reply to  Chris Hanley
May 2, 2021 8:28 pm

I don’t think most serious people who study climate reject that CO2 cannot cause additional warming – it is how much that is debatable. If it is half of what they (IPCC and friends) claim, then the entire premise of catastrophic global warming is patently wrong. Over time there will be a conversion from fossil fuels to other forms of energy – my bet is most electricity will be generated from nuclear sources. There is plenty of time for this conversion to occur naturally – there is no excuse for a desperate and disruptive push to Green intermittent energies.

Alan the Brit
Reply to  Robert of Texas
May 2, 2021 11:08 pm

“there is no excuse for a desperate and disruptive push to Green unreliable energies.”……….there, corrected that for you!!! 😉

Reply to  Alan the Brit
May 3, 2021 7:01 am

” ….. there is no reason for etc. …..”
There, re-corrected etc.

Reply to  Robert of Texas
May 3, 2021 7:01 am

Robert says:”I don’t think most serious people who study climate reject that CO2 cannot cause additional warming – it is how much that is debatable.”

Robert sets parameter for discussion by saying people who disagree with him are probably not serious.

Well I say CO2 does not cause warming. And I am serious about that.

So was Hoyt Hottel.

Pamela Matlack-Klein
Reply to  mkelly
May 3, 2021 7:27 am

If CO2 caused any warming I believe it would be obvious. Isn’t an 800-year lag time sufficient to demonstrate there is zero warming from CO2?

Reply to  mkelly
May 3, 2021 8:48 am

The IPCC has framed the debate by assuming that the world is a univariate system and that the only significant variable is CO2, so the political debate is limited to whether CO2 causes warming or not. I believe very strongly that the world is a multi-variate system where CO2 is but a trace gas that cannot have much of an influence on the multi-variate system because there isn’t enough of it in the system to have much of an effect on the system.

So, whether CO2 has a warming effect or not is dependent in two things which are not allowed as part of the political debate: (a) a small effect due to its lack of abundance and (b) even if it has a warming effect other variables may have their own cooling or warming effect so that the state of the system cannot be determined by CO2 alone.

Unfortunately, in politics those who frame the debate usually end up winning it precisely because they are allowed to frame it. Real science should not be constrained by artificial limits that are politically motivated.

Clyde Spencer
May 2, 2021 3:04 pm

… it discourages focusing on a global average temperature as a climate change metric.

Indeed, not only should the NH be treated separately from the SH, but the daily highs and lows should not be averaged; they should be shown paired on a graph.

What I’d really like to see is a comparison of daily high and low temperatures for each of the Köppen climate groups, perhaps also separated out by hemisphere.

Rud Istvan
Reply to  Clyde Spencer
May 2, 2021 3:46 pm

CS, I did a bit of research on this a few years ago. I am not nearly as certain as you that SH and NH should be climate decoupled.

In favor of that view are, for example, the obvious ITCZ and the vast differences between the Arctic (ocean surrounded by land) and Antarctic (land surrounded by ocean).

BUT disfavoring that view are paleoproxies that show the MWP ~simultaneous in both hemispheres (even the Antarctic Peninsula), the importance of ocean heat transport by currents that cross hemispheres (not just the deep thermohaline circulation), and the Peter Lewis (Judith’s husband) paper that albedo is surprisingly about the same in both hemispheres over decades.

Rud Istvan
Reply to  Andy May
May 2, 2021 6:28 pm

Yup. My bad (old memory).

Michael S. Kelly
Reply to  Rud Istvan
May 3, 2021 11:34 am

Maybe Lewis was his maiden name…

Reply to  Rud Istvan
May 3, 2021 4:04 am

Would it not be important to remember the sun, as well, Rud, which does shine over both hemispheres?

Curious George
May 2, 2021 3:12 pm

Why don’t any data extend beyond year 2000?

May 2, 2021 3:21 pm

l think its almost a certainly that the larger swings in temps in the NH is due to the fact of the the far larger landmass. As blocking highs over land can form “heat domes” during the summer. But over extended snowfields in winter they can be the cause of intense cold.

May 2, 2021 3:23 pm

“The Modern Warm Period is equivalent to the Medieval Warm Period within the margin of error, We need to be careful because we are comparing actual measurements to averaged proxies.”

The modern period is not covered by your proxies. Data for the Alley recon ends in 1855. Vinthner is more recent, but as you say, differs from the others.

The comparison to measurements is worthless, not only because of the kind of data, but because it is measuring something totally different. Any specific location will be far more variable than the global average. As you noted, the NH and SH are out of phase, and that alone damps change in the combined. This cancelling operates at many levels in a global figure.

Last edited 11 days ago by Nick Stokes
Robert of Texas
Reply to  Nick Stokes
May 2, 2021 8:29 pm

Well stated.

Reply to  Nick Stokes
May 2, 2021 11:49 pm

With regards to reconstructions, we should heed Hubert Lamb’s maxim that ‘We can understand the (temperature) tendency but not the precision’ so whilst accuracy to tenths of a degree is impossible, determining the general shape and direction of temperature travel is reasonable. Certainty in determining great historical temperature precision lies only in models


May 2, 2021 3:54 pm

As well as looking for temperatures changes l think it would be useful to look for signs of a dryer or wetter climate as well. As this could give a clearer picture of what was going on with the weather/climate over the area at the time.

Abolition Man
May 2, 2021 4:03 pm

Thanks for this informative post!
It’s quite the mouthful to chew on for a while, but lots of flavor makes it worth the effort!
So half the warming we are experiencing may be completely natural, and the ECS may be only about half of what the IPCC claims. This will be a great disappointment to those in northern Canada and Siberia who were hoping to wear their mukluks year round!
A modest warming cycle continuing would be about the best news humanity could ask for. It’s sad that our leaders are too stupid or corrupt to acknowledge that!

May 2, 2021 4:40 pm

Some nice snap-shots can be found by reliable proxies. For instance oxygen isotope ratios in bivalve shells at a fjord beach in Svalbard show that about 9800-9900 years ago, max and min water temperatures were about 15 and 3 C respectively. Today the corresponding max and min are 6 and 0 C. A fall of 6 C in both average temperature and temperature range.

As Wardaddy would have said, that “wasn’t nothing”.


Last edited 11 days ago by Hatter Eggburn
Geoff Sherrington
May 2, 2021 4:44 pm

Our author Andy May is essentially discussing analytical chemistry methodology, for a substance not often analysed in materials seldom analysed. Mainly, substance carbon dioxide (and isotopes) in natural ice material.
The very simplified systematic way that analytical chemists might approach this is:
1.      There is a proposed method. (a) Is it specific, (b) is it able to detect the concentrations we expect, (c) if other substances also give a reaction, can we correct for them, (d) is the cost acceptable (e) do we have access to the equipment required?
2.      Can we make measurements to allow estimation of precision (the spread of measurements about the best value?
3.      Can we make measurements for estimation of accuracy (how far from the best value are our results?).
For these ice cores, assume that point 1. is cleared to proceed and let’s look at precision and accuracy.
Precision estimation usually involves analysis of a number of samples that should be similar to each other. In the lab, we can split most materials into many parts and analyse each fraction many times. We can take samples located very close to each other at the sampling site, that should be much the same, and analyse these. (Example, putting down several short, test drill holes quite close to each other for replicate comparison).
Accuracy estimation usually involves  a. comparison of measurements done by several labs, (b) ultimate standard materials, often from international projects to get a best value, (c) calibration materials, either made from an inert base with known, added amounts of the analyte of interest or from material from the site with known, added increments of analyte.
There is a great deal of reading to be done by an interested person like me, wanting to assess what the actual precision and accuracy ranges are for the Greenland studies. At this stage I do not know if all of the above steps have been done and done well.
This blog content seeks comments from people who have looked. However, I seldom see references to replicate sampling (e.g. several adjacent drill holes) apart from at the last stages of analysis, where typically figures might be given in this case for the performance of the mass spectrometer or other device used to measure isotopes and their ratios. Too much emphasis on the last stage process is almost guaranteed to hide large errors back early in the process.
Simply, how well have the customary systematic requirements been filled?  Would they pass the strict demands that miners face in reporting a new mine-to-be to the Stock Exchange? From the discord of those bumps on Andy’s time series graphs, one would be prudent to be sceptical. Geoff S

Rud Istvan
Reply to  Geoff Sherrington
May 2, 2021 5:00 pm

GS, I absolutely cannot disagree with your critique. See my comment above on the absurdity of Shakun’s synthesized paleoproxies (2012).

Yet, we skeptics mostly have to work with what we are given by Warmunists. A methodological critique is appropriate, but will fall on mostly deaf (cause ignorance) ears. Hence my comments on two irrefutable qualitative natural variation above. Because once you introduce that degree of past qualitative natural variation, the whole modern ‘climate science’ edifice fails.

May 2, 2021 5:14 pm

We must face reality….Fahrenheit invented the thermometer in 1714. For the first hundred years they were imprecise until glass that didn’t dissolve was developed. By 1850 they were considered a reasonably repeatable scientific instrument accurate to 1/4 of a degree C.
Before that time, proxies have no standard of comparison and are verified against each other. Proxies are about +/- 2 C accurate compared to thermometers in recent times, so worse prior to 1800 so are really much less accurate than claimed by believers.

Robert of Texas
Reply to  DMacKenzie
May 2, 2021 8:35 pm

The thermometers may have been able to to measure to 1/4 of a degree (I doubt all those used in collecting temperature data were of that quality), but the process of reading them in the field was no better than +/- 1 degrees at best, and most likely it was +/- 2 degrees due to humans eye-balling a mounted thermometer “around” the appointed time-of-day.

Jim Gorman
Reply to  Robert of Texas
May 3, 2021 7:16 am

Exactly. And, if you read some of the NWS requirements, they used +/- 2 deg well into the 20th century.

May 2, 2021 5:17 pm

I always cringe when I see “reconstruction” and “model” mentioned in the same writing. I have to wonder which one is being adjusted to match the other.

Rud Istvan
Reply to  ScienceABC123
May 2, 2021 5:38 pm

You may be right logically, but that does no good attacking Warmunist positions. Think of irrefutable simple counters, then pound them home. As I did above using the qualitative v quantitative distinction, which alone suffices to prove the big concept of natural variation.

Robert of Texas
May 2, 2021 8:45 pm

This is hands-down one of the best posts I have ever read! Clear and easy to follow. Tipping my hat to Andy May.

It is clear from numerous sources that the reconstructions are failing to record true peaks and dips. Archaeology is just one field that can be used to refute many of the proxy reconstructions – where there is evidence of human occupation or available plant residues/pollen.

It had never occurred to me that the North and South hemispheres could be canceling each other out in the record – seems obvious now that I have read it.

There simply is no useful reason to be trying to calculate a “Global Temperature”. Climates are more local then that.

The other elephant in the room is the Urban Heat Island Effect. It seems like this could be easily demonstrated in various areas so there would be a deeper understanding of it, but instead they assume to understand it and “smudge” the modern data to make it less obvious.

If man-induced land surface heating by CO2 is occurring at even half the rate they claim, I frankly would be surprised. I suspect it will be closer to 1/4 to 1/3 of the claimed forcing, the rest being UHI introduced error and natural warming.

Pat Frank
May 2, 2021 9:28 pm

No proxy reconstructed temperature is a physical temperature. Not even one of them.

Not one proxy conversion is based in a physical theory establishing a causal relation between temperature and proxy.

They all just use statistical lofting of some time-series data into the (very poor) air temperature measurement record.

Statistics is not a substitute for physics. Not even in the fairyland of consensus climate so-called science.

Geoff Sherrington
Reply to  Pat Frank
May 2, 2021 9:43 pm

Spot on. Just now I had started to write about the assumptions made to link isotope measurements to past proxy temperatures. This would be about my 10th essay about that topic,so easy. Yet, there is little if any scientific validation of the idea that evaporation of water favours the lighter isotopes departing. That might be qualitatively correct, but to make an untested, quantitative relation out of it beggars belief.
Andy, your error quote “The average minimum and maximum suggest this value is plus or minus 0.3°C” is hard to support for numbers that have been through that conversion.
Does anyone have a reference to the definitive study for this proxy temperature conversion? Geoff S

Pat Frank
Reply to  Geoff Sherrington
May 3, 2021 10:25 am

Oxygen isotope fractionation of water is well established physically Geoff. Exactly that was used to prepare 18-O2 and 17-O2 from heavy water at the Isotope Fractionation plant at the Weizmann Institute when I was post-docing there.

The plant was essentially a bazillion-plate still. 🙂

dO18 use as a paleo-thermometer runs into problems with monsoon rain out. No one knows the paleo-monsoon tracks, so that no one knows where the heavy water rained out. At any given locale, the monsoon conditions will have varied seasonally. The deterministic scatter put into dO18 data disallows valid usage of physics to derive a true temperature from the 16-O/18-O ratios.

I discussed dO18 in my WUWT post about proxy temperatures linked in my comment above.

Pace Andy, but nothing in Alley’s paper ameliorates the presently fatal problems of proxy temperature reconstruction.

Judgments about warmer/wetter – colder/dryer is about all that’s available.

May 3, 2021 12:03 am

Great post Andy.

Does anyone know what the justification is for averaging local temperatures on an annual basis and arriving at a single global average?

Whenever I look at temperatures for a specific UK location over a couple of hundred years they look flat or falling. I know the UK isn’t the globe but we have the longest continuous temperature record in the world.

For me, the concept of a global average temperature seems far-fetched especially as looking at the global average in degrees celsius shows negligible warming.

It seems the only true test of warming would be an average local temperature on a monthly basis.

Reply to  Andy May
May 3, 2021 5:32 am


But if that were the case then the Arctic wouldn’t have warmed at roughly twice the rate of the rest of the globe according to extrapolated and adjusted temperature records.

Jim Gorman
Reply to  Redge
May 3, 2021 7:43 am

Let me add that if mitigation is being considered, regional variations are extremely important Do I need a dam for flood control or for water storage for example.

Biomes don’ develop over a 30 year span of weather. That was chosen as the MINIMUM period to supposedly detect a temperature trend. Why are we not using the whole satellite period as the common base? Why not the whole 20th century for a baseline? What is the best length of time to determine whether a change is natural or manmade?

If you are going to compare current “anomalies” to those calculated for 1900, then you must have confidence in the temperature measurements from 1900. To not use them to determine a century baseline because “they aren’t accurate” just doesn’t compute.

When you build something you start with the basic ingredients and build up to the full structure. In other words, the sum of the parts equal the whole. The same should apply to a Global Average Temperature. The process should be able to be broken down into regional pieces, each of which contribute to the whole. If this can’t be done or it shows a faulty whole, then why believe in a GAT.

Pat Frank
Reply to  Redge
May 3, 2021 10:27 am

Redge, good question.

See Essex, C., R. McKitrick, and B. Andresen, Does a Global Temperature Exist? J. Non-Equilib. Thermo., 2007: p. 1–27


Global average surface air temperature is a physically meaningless metric.

Reply to  Pat Frank
May 3, 2021 10:54 am

That’s really useful. Pat. I wasn’t aware of this paper.

Thank you.

Pat Frank
Reply to  Redge
May 3, 2021 12:05 pm

Redge, you might also enjoy Essex and McKitrick Taken by Storm.

They discuss air temperature there, as well. And lots of other stuff about the problems of modeling climate.

Reply to  Pat Frank
May 3, 2021 12:24 pm

Cheers Pat

Bill Toland
May 3, 2021 12:10 am

I regard proxy reconstructions of Earth’s temperature as worthless and pointless. The physical evidence that today’s temperature is colder than it has been for most of the last 10000 years is utterly overwhelming. Sea level was higher during the Medieval Warm Period and the Holocene Climate Optimum. Trees grew at higher latitudes and altitudes during both these periods. The current level of Arctic sea ice is greater than it has been for most of the last 10000 years. What the vikings did in Greenland during the Medieval Warm Period is simply not possible today.

May 3, 2021 12:30 am


Could plse explain again on what basis the 50 % unnatural warming is estimated? I dont gey that.

Reply to  Andy May
May 3, 2021 8:35 am

CO2 (g)+ 2H2O (l) + cold = HCO3- + H3O+ (arctic/antarctic)
The area where the CO2 must dissolve in the ocean is getting smaller on account of it getting warmer in the arctic. Hence the zigzag in Hawaii.
However, the reaction is a in equilibrium. Meaning more hydronium ion from the waste of 7 billion people, +++ animals ++++ factories makes the oceans less alkaline, hence the reaction goes to the left, bringing more CO2 in the air.
2 variables: the declining areas where CO2 dissolves + the waste of all of the world
that nobody has ever even mentioned anywhere. I think you will find that that will explain the rise in CO2, mostly.
Not that I think that CO2 causes any warming. That is just a red herring.

Reply to  HenryP
May 3, 2021 8:38 am

I am active on a Dutch blog. I am very interested in using (some of ) your text and pictorials here, after translation, of course. I will mention your name. Is that OK?

Reply to  Andy May
May 4, 2021 7:31 am

Andy, many thanks!

Reply to  HenryP
May 3, 2021 8:34 am

Sorry. See my reply to Andy below.

Last edited 10 days ago by HenryP
Eric Vieira
May 3, 2021 1:55 am

What does “equilibrium climate sensitivity to carbon dioxide is about 1.5°C per doubling of CO2” really mean ? I suppose this covers the period where CO2 was half of what it is now to our current time, during which the concentration range was where the relation was somewhat linear. Wijngaarden & Happer have shown that the CO2 and Water IR-bands (the main GHGs) are almost completely saturated, so that a doubling of CO2 from the current value will have only a very small effect. The effect is non-linear. To even use the ECS value means one admits a linearity between temperature and CO2 concentration, although this isn’t true anymore. This is the paradigm that fuels the climate alarmism against CO2 and other GHGs, and unfortunately is at the roots of all the failed climate models (see Pat Frank). This could also be one of the strongest arguments against alarmist propaganda. CO2 and other GHGs belong out of the discussion. There is no climate emergency, period, or in other words: changing CO2 output will not change anything.

Reply to  Eric Vieira
May 3, 2021 9:04 am

Eric what is the temperature increase to half mole of CO2 with 1000 J energy input? Now what is the temperature increase of a mole of CO2 with the same 1000 J energy input. How about if the energy input has no IR?

CO2 cannot do warming.

Eric Vieira
Reply to  Eric Vieira
May 5, 2021 7:24 am

Sorry people: a fixed increase “per doubling of” means a logarithmic progression. The fact that the absorption bands of the two main GHGs are close to saturation, means that additional CO2 will not lead to notable increases in warming. To mkelly: GHGs absorb mainly in the IR and LW bands. The energy input is mainly from the sum or the reemitted thermal radiation from the Earth’s surface. Saturation means that the totality of this radiation is already absorbed by the existing GHG molecules. If you increase the number of absorbing molecules, it doesn’t change anything anymore. This energy is just distributed between more molecules, but it doesn’t increase.

Ben Vorlich
May 3, 2021 3:18 am

Funny you should say “Statements like “warming today is the fastest in the last 1,000 years [or more]” have no credibility.”

I had the misfortune to see BBC TV News yesterday where their man Shukman showed a Hockey Stick reconstruction when doing an item on coal, CO2 and Cop XXVI. I shouted something similar but in stronger at the TV and turned him off

May 3, 2021 5:15 am

Trouble with tree rings is that..


Bruce Cobb
May 3, 2021 8:55 am

When in doubt, you should always cool the past and warm more recent temperatures. Safer that way, and besides, that’s how “the science” is done. Amiright?

May 3, 2021 10:39 am

Andy, I really appreciate the seriousness with which you try to understand what we are really seeing!
I would like to add one big question which I rarely see discussed. Beside the Proxies we do have also written, historical documents which are even less accurate (subjective?) however if I think about the historical documents from Greenland at the time it was settled until it was abounded and compare them to current conditions, it appears as if it must have been warmer in southern Greenland 1000 years ago?
Isn‘t that an oddity when looking at the different proxies and what they tell about the comparison between today and 1000 years ago?

Bill Rocks
May 3, 2021 11:09 am

Very helpful review. Again, thanks for your hard work and this informative communication.

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