Mann: Trees aren't behaving like I want them to – volcanoes to blame

From Penn State

Tree rings may underestimate climate response to volcanic eruptions

Some climate cooling caused by past volcanic eruptions may not be evident in tree-ring reconstructions of temperature change because large enough temperature drops lead to greatly shortened or even absent growing seasons, according to climate researchers, who compared tree-ring temperature reconstructions with model simulations of past temperature changes.

“We know these tree rings capture most temperature changes quite well,” said Michael Mann, professor of meteorology and geosciences and director of the Penn State Earth System Science Center. “But the problem appears to be in their response to the intense short-term cooling that occurs following a very large volcanic eruption. Explosive volcanic eruptions place particulates called aerosols into the stratosphere, reflecting back some fraction of incoming sunlight and cooling the planet for several years following the eruption.”

Tree rings are used as proxies for climate because trees create unique rings each year that often reflect the weather conditions that influenced the growing season that year. For reconstructing climate conditions, tree-ring researchers seek trees growing at the extremes of their growth range. Inferring temperature changes required going to locations either at the tree line caused by elevation or at the boreal tree line, the northern most place where the trees will grow.

For these trees, growth is almost entirely controlled by temperature, rather than precipitation, soil nutrients or sunlight, yielding a good proxy record of surface temperature changes.

“The problem is that these trees are so close to the threshold for growth, that if the temperature drops just a couple of degrees, there is little or no growth and a loss of sensitivity to any further cooling. In extreme cases, there may be no growth ring at all,” said Mann. “If no ring was formed in a given year, that creates a further complication, introducing an error in the chronology established by counting rings back in time.”

The researchers compared temperature reconstructions from actual tree-ring data with temperature estimates from climate models driven with past volcanic eruptions.

Comparing the model-simulated temperatures to the Northern Hemisphere temperatures reconstructed from tree-ring thickness, Mann, working with Jose D. Fuentes, professor of meteorology, Penn State, and Scott Rutherford, associate professor of environmental science, Roger Williams University, found the overall level of agreement to be quite good.

However, they report in the current issue of Nature Geoscience that “there is one glaring inconsistency; the response to the three largest tropical eruptions — AD 1258/1259, 1452/1453 and the 1809+1815 double pulse of eruptions — is sharply reduced in the reconstruction.”

Following the 1258 eruption, the climate model simulations predict a drop of 3.5 degrees Fahrenheit, but the tree ring-based reconstruction shows only about a 1 degree Fahrenheit dip and the dip occurs several years too late. The other large eruptions showed the same type of discrepancy.

Using a theoretical model of tree-growth driven by the simulated temperature changes, the team determined that the cooling response recorded by the trees after a volcanic eruption was limited by biological growth effects. Any temperature drop exceeding roughly 1 degree Fahrenheit would lead to minimal tree growth and an inability of trees to record any further cooling. When growth is minimal enough, it is likely that a ring will not be detectable for that year.

The potential absence of rings in the first one to three years following eruption further degrades the temperature reconstruction. Because tree-ring information is averaged across many locations to obtain a representative estimate of northern hemisphere temperature, tree-ring records with and without missing rings for a given year are merged, leading to a smearing and reduced and delayed apparent cooling.

The researchers also noted that aerosol particles forced into the air by volcanoes block some direct sunlight causing cooling and they produce more indirect, scattered light at the surface. Trees like indirect sunlight and grow better under those conditions. However, this effect is small compared to that of lower temperatures and shorter growing seasons.

By accounting for these various effects in the tree growth model, the researchers were able to reproduce the reduced and smeared cooling seen in the actual tree-ring temperature reconstruction, including the near absence — and delay — of cooling following the massive 1258 eruption.

“Scientists look at the past response of the climate to natural factors like volcanoes to better understand how sensitive Earth’s climate might be to the human impact of increasing greenhouse gas concentrations,” said Mann. “Our findings suggest that past studies using tree-ring data to infer this sensitivity have likely underestimated it.”


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So I’ll say the obvious. If trees respond so well to warmth then surely…………..

“Our findings suggest that past studies using tree-ring data to infer this sensitivity have likely underestimated it.”
A real euphemism to concede all tree-ring data is simply wrong from scratch.
Of course he would never admit it this way.


Love the confidence, we know that tree rings, capture ‘most’ climate changes ‘quite’ well.
Good job were not spending billions based on this work.
God help the bloke if he actually had to do some work based on financial systems, where things have to be 100% accurate.
Or engineering where the term ‘quite’ well kills people.

James Allison

Well waddaya know The Mann may have some competition. According to some academics down my way tree rings are also pretty clever at predicting Nini events. Shame about cutting down the Kauri forests.

Kurt in Switzerland

Does this mean that Prof. Mann will issue a new version of his hockey stick? Will the new one look like a downhill ski racer’s poles? Or perhaps an “accordion gate”?
Will it acknowledge the MWP & LIA? (and perhaps address that pesky bit of data post 1950, which showed a decline – requiring him to graft on temperature sensor data).
Not holding my breath…
Kurt in Switzerland

Next, he’ll discover rainfall affects tree growth. Wait for it!

Christopher Hanley

“We know these tree rings capture most temperature changes quite well,” said Michael Mann….
How can Mann and his colleagues know that?
The infamous ‘hidden decline’ repudiates that statement


“We know these tree rings capture most temperature changes quite well”
They do?

Markus Fitzhenry.

Volcanos don’t cool Earth, at least not whilst the energy evacuated, remains in Atmosphere. Eventual, if any, upper atmosphere disturbances would pass more Atmospheric mass to space, on a timescale unknown to me.
The enhancement of the potentiality of additional Atmospheric mass would warm in the near term, not cool. I don’t think volcano eruptions cause climate disturbances under a paradigm of greenhouse, I think the climatic result of volcano eruptions would be more like the Ned Nikolov & Karl Zeller, ATE principle.
The following is the thorey of DavidmHoffer when prehistoric Earth suffered a meteor shower and eventual loss of Atmospheric mass, with catastrophic results for biodiversity in a world with a dramatic loss of force of pressure (density).
The earth loses atmosphere to space as an on going process. The ultimate fate of the earth, millions of years from now, is to be a barren rock, just like the moon. What if we postulate, instead of a few large meteors, many small ones?
Many small meteors would leave no mark on earth surface because they would burn up before getting there. But throw enough of them at the atmosphere at once, over a period of years or even decades, and that is one hot upper and perturbed upper atmosphere with loss of atmospheric mass (I would think) to space heavily accelerated. Consider the chain of events that would follow:
o No more flying creatures. Not just Pterodactyls, but anything, even insects, that had evolved the ability to fly based on a denser atmosphere. All gone in short order.
o Predators dependent upon those species…gone.
o Plants dependent upon those species for pollination…gone.
o Plants dependent upon those species to control pests that would otherwise run rampant… gone.
But here is the doozy. We know that plants thrive in conditions of much higher CO2 than we have today, that’s why greenhouse operators pump it into their greenhouses raising levels to many times “normal”. The plants respond with better growth and need less water and humidity to remain healthy, suggesting they evolved at a time when CO2 levels were much higher than they are now. And, based on the faint sun hypothesis…when PRESSURE was also much higher than it is now. We haven’t tested plant growth at elevated pressures to my knowledge, but it makes sense that in reduced pressure, the ability of plants to capture CO2 from the atmosphere would also be reduced, and likely other effects would occur as well.
o The entire plant kingdom that had evolved to a given atmospheric pressure range, would have also died. Let’s keep going!
o A sudden drop in pressure would in turn result in a sudden drop in temperature. The temperate zones would have retreated, and retreated big time, from the poles toward the tropics, triggering… if not a full blown ice age, then something like the Little Ice Age. Mass extinctions world wide even in the tropics where temperatures would have held steady. And that would be followed by….
An earth steadily increasing in temperature commensurate with the steadily increasing insolation of the Sun for thousands of years.
Exactly as the geological record since the last ice age shows.
If one ties N&Z to Stephen Wilde to Faint Sun to Extinction Event….an awful lot of things start falling into place.

I think he’s just making it up as he goes along!


“We know these tree rings capture most temperature changes quite well,”
Erm, no they don’t.

I recently wrote an article whereby I looked in detail at the methods of temperature reconstruction used by Dr Mann and Hubert Lamb when carrying out my own reconstruction of CET back to 1538
It is very difficult to see how and why this myth surrounding the accuracy of tree rings has come about. As an approximate measure of precipitation they may be ok, but they are certainly no sort of reliable indicator of temperatures to fractions of a degree. It is disappointing that bona fide climate sciemtits do not point out the limited worth of tree rings and similar proxies.

Trees don’t grow in the winter. Look out the window and you can see how inactive they are.
This means they don’t record anything in the tree rings about the winter time.
What’s about the night time? I read that the trees are partially shut down (asleep)..
Q: What do tree rings really record and what not?

Poor Mr Mann, his specialty becomes ever more obsolete as more high quality satellite data streams in by the day. A third of a century of data now. Since I started my climate research 2 years ago, the length of time of this high quality unbiased data has grown by 6 percent. The climate sensitivity question will be answered not with tree rings, but by the work of the likes of Dr. Roy Spencer.

Phillip Bratby

I don’t seen any signs that an expert statistician has been involved in the paper. I wonder why not.

sunderland steve

“We know these tree rings capture most temperature changes quite well,” said Michael Mann,
Yeah, apart from those that occur outside the growing season and those that are masked/enhanced/suppressed by variation in precipitation.
Face it Michael, tree rings are useless for temperature reconstructions.


“quite well”.
Well thats me convinced. Where do I send my taxes?

Markus Fitzhenry.

Every tree is different, as we are.
They took a miniscule sample, averaged it and expected it to apply it to a universal theory.


So, what he’s saying is that tree rings are great for indicating when its bright and warm but they can’t show when its dull and cold. In-built warming bias, maybe…?

Doug UK

“We know these tree rings capture most temperature changes quite well,” said Michael Mann,
“They do – honestly! – believe me!! – I speak from a position of authority”
I suspect history will ponder the likes of Mann’s hubris for quite some while


Manns temperature model has gone COLD

Let me paraphrase this
… the big problem for trees is when there is too much cold.
Which is exactly the same for humans:-
1. 23,000 people die in the UK from cold … they don’t have records for heat because the hot weather prevents deaths.
2. In the 1690s some estimates suggestion a quarter of the Scottish population died from the cold.
3. Humans inhabit the planet from the equator to a point north/south … i.e. diminishing rapidly toward the poles. In other words, the amount of the world we humans populate is limited not by heat but by cold.
4. Many uplands in Britain are “fossilised” human landscapes of bronze age inhabitation from a time when it was warmer. There is zero evidence any part of Britain was too warm!!!
And Mann has the gall to call warming a problem!


“who compared tree-ring temperature reconstructions with model simulations of past temperature changes.”
roflmao !!

Christopher Hanley

“We know these tree rings capture most temperature changes quite well,” said Michael Mann….
“The infamous ‘hidden decline’ repudiates that statement..”….I should have added: or does it?

Dave Wendt

I’ve got a question that I don’t have time to run down myself at the moment,but I’m hoping someone here might have the answer for. Has anyone ever done an analysis of how well weather stations at the treeline in mountains and at the boreal forest margin correlate with GAT in the instrumental era?

Jimmy Haigh.

Charles Gerard Nelson says:
February 6, 2012 at 12:49 am
“I think he’s just making it up as he goes along!”
I agree – that’s exactly what I thought.

Dermot O'Logical

“For these trees, growth is almost entirely controlled by temperature, rather than precipitation, soil nutrients or sunlight”
I just can’t believe this can be true. Can a tree really grow at the same rate, regardless of the availability of water, nutrients and photosynthesis? That sounds, well, miraculous.


Agree with the comments regarding negative ability of tree rings as temperature proxies – but, and it is a big but – they are still useful as comparison sources for other palaeoclimate reconstructions. All temperature proxies are suspect, IMHO – but if you get a few that ‘agree’ and show some consistency, you at least can draw the conclusion that some ‘change’ happened. What really peaces me off is the way proxies are then compared to current measurements/trends and supposedly ‘realistic’ past temperatures are deduced (a la hockey stick). The day I see a proxy dataset being described correctly as ‘purely indicative only’ – instead of being touted as some form of real quantitative data, (especially by believers!) is the day I’ll start to take the palaeo-climate work more seriously!

Disko Troop

Mann. “Our findings suggest that past studies using tree-ring data to infer this sensitivity have likely underestimated it.”
Dare I say it…..”It’s worse than we thought!”
Surprise: Leaves Maintain Temperature, new findings may put dendroclimatology as metric of past temperature into question
A new study that shows their internal temperature remains constant at 21.4deg could challenge the way trees are used to determine historical climate data
The internal temperature of leaves, whether in the tropics or a cold-clime forest, tends toward a nearly constant 21.4 degrees Celsius, reports a study released today.
It had long been assumed that actively photosynthesising leaves – using energy from sunlight to convert carbon dioxide and water into sugar – are nearly as cold or hot as the air around them.
The new findings not only challenge long-held precepts in plant biology, but could upend climate models that use tree rings to infer or pre… .
Game over.


“I talk to the trees…. but they don’t listen to me.”
(From Paint Your Wagon)

“Nini”, huh? Generic for Ninas and Ninos. Nice! “Los Nini” with the article?

Gary Hladik

“Using a theoretical model of tree-growth driven by the simulated temperature changes, the team determined that the cooling response recorded by the trees after a volcanic eruption was limited by biological growth effects.”
Whoa! The simulated trees now agree with the simulated climate! Who’da thunk it? I think these guys should be rewarded with some simulated research grants!


Robinson says: February 6, 2012 at 12:45 am
“We know these tree rings capture most temperature changes quite well”
They do?
From the 1997 paper “Tree rings are really not that bad, actually OK at times on occasion, as temperature proxies”

paul in surrey

well you know what they say, its not the thing thats wrong, its our perception of what it should be doing thats wrong, there’s a name for that


Doesnt say anything yet about tree rings and warm temperatures. oh well, we’ll wait another 15 years. Then it will be:
“The problem is when solar activity and temperature increases beyond a certain point, this is not reflected in the tree rings, as they reach a maximum growth state determined by internal growth factors… etc etc”.
Yes Mr Mann, a hockey stick, that then declines. A 7 year old could understand it.


We know that new evidence, which shows our previous estimates to be even less reliable than we optimistically assumed, proves that our previous estimates are correct.
Yeah, whatever you say, Mike.


I am always amused when the word Skilful is used by Mann to describe his false machinations of proxy data. He has some front.

Old England

Did I miss any mention that CO2 levels have a very significant effect on rates of growth? Does Mann understand that – or is it ‘coveniently’ ignored? I wonder if tree ring data had any adjustments made to take account of the prevailing CO2 levels – let alone precipitation ?
Unless I misunderstand it plant growth is greater, even at lower temperatures, in higher concentrations of CO2. I’m not sure that there is research detailing the growth characteristics of appropriate tree species plotted against temperature and against CO2 levels. Without an accurate understanding of that then using tree ring data to try and calculate temperature is a non-starter as it can never be correct – it would simply be valueless guess-timation. Although having said that Mann seems to be unconcerned about the inescapable innacuracy.
I don’t have access to the data but if a 50% increase in CO2 levels creates a 10% increase in tree growth then, without adjusting for the CO2 level, might it suggest a 5% or 10 % (??) higher temperature? To make that CO2-related growth adjustment the species sensitivity to CO2 levels (at given temperatures) would need to be accurately known – but having reached that point the next variable (again an unknown) of precipitation levels which also affect growth comes into play ………
None of which seems to concern Mann – or am I mistaken ?

Allan MacRae

Please note my questions 3, 4 and 5 below, especially number 5.
Apparently this week’s answer is 5c) Volcanos !!!
“You could not make this stuff up.”
Oh wait! I just did! On Saturday morning!
Inside the mind of Mann… (queue music from Twilight Zone, Rod Serling speaks: “Hubris…”)
Of course – let the Mann speak! But do not expect a fair or open debate.
Some suggestions for question period:
1. Do you believe that the Uniformitarian Principle has been especially exempted for your particular brand of global warming science? Why?
2. Do you assume that Occam’s Razor can safely be ignored, just for advocates of dangerous humanmade global warming? Why?
3. Please explain the “Divergence Problem” and “Hide the Decline”.
4. Not one of your scary global warming predictions has materialized. You have demonstrated negative predictive skill. Do you see any problem with your predictive record?
5. What is this week’s explanation for the observed flat or cooling global temperatures in this century? Is it aerosols, dust, volcanoes. the appalling scarcity of buffalo farts, or other?
6. What journal editor are you trying to intimidate this week?
7. What climate realist are you trying to have fired from his university position this week?
8. Will you participate in a fair and open debate, this week, or any other?


So they were right to hide the decline.
Since the models do a bang up job predicting the future without volcanoes and China, they should do a bang up job estimating a portion of the anomaly. We can subtract this wonderful estimate and draw even more magical conclusions from the residue.
Is this not amazing that all these magical calculation always turn out one way.

wayne Job

I would believe that the last time the words needed to explain this character were uttered by Audrey Hepburn. Those words were an addlepated ninconpoop seems appropriate.

Why does this puff-piece bring to mind the great Polish historian of Marxism, Leszek Kolakowski, who, after defecting and abandoning Stalinist Eastern Marxism, said of the neo-Marxism of the 1960s West: ‘There are better arguments in favour of democracy and freedom than the fact that Marx is not quite so hostile to them as he first appears.’ ?
Perhaps it is that there have always been better ways to proxy past global temperatures than by tree-rings. The limitations of using tree rings to proxy temperature have always been known to outsider (to those that invented it!), and so to persist with dendrology when its failure becomes unavoidably apparent — to only use other measures to correct it — seems to exhibit a touch of the obsessiveness of those clinging desperately to a fag-end of a fading ideological dogmatism.

Markus Fitzhenry.

“”For these trees, growth is almost entirely controlled by temperature, rather than precipitation, soil nutrients or sunlight””
What barometer was available to assume the biological influx of Co2 and other nutrients. Was there an allowance for Atmospheric pressure levels at tree growth? What credence was given to air density in his paleontological proxies?
Climate Science, the art of seeing what is not there.


We all know that tree growth rates make an excellent thermometer.
And I would have gotten away with it too–if it wasn’t for those meddling volcanoes! (1)
1. peer-reviewed

Tony Mach

What, wait treemometers are not perfect thermometers? What a stunning revelation. So to recap, treemometers are perfect thermometers when it suits Mann, and then he disowns them when it is in the interest of “The Cause”™©. Gee, thanks Dr. Mann, for this valuable post-hoc rationalization!
And I wonder, if these treemometers fail to record a rapid drop in temperature, maybe they can equally fail a rapid drop in water supply (e.g. when a rapid increase in temperature occurs). Just a thought, Dr. Mann.

Claude Harvey

I’m confused. Is Mann talking about “regular trees” or “temperature trees”? We know from his previous work that not all trees are “temperature trees”. It takes a highly trained expert like Mann to tell us which trees are telling the truth about temperature and which of their neighbors are lying like rugs in the forest. It’s an ART!


“We know these tree rings capture most temperature changes quite well”
I wouldn’t buy a car that:- “Gets round most corners quite well”
I don’t buy this as a reason to buy into his theories either.


“Tree rings are used as proxies for climate because trees create unique rings each year that often reflect the weather…”
Erm, weather or climate?

richard verney

I cannot believe that this man is this stupid.
Trees are proxies for then prevailing growing conditions. Based upon our present understanding and problems with noise and resolution issues, it is not possible to separate out, on an individual basis, ring response to each individual factor that may influence the then prevailing growing conditions. Trees are a poor proxy for global temperatures not least because of their spatial distribution and the fact that oceans, arid desert and arctic/antarctic areas account for more than 80% of the area of the globe. Trees can at best provide an insight into conditions representing no more than 20% of the globe.
He claims that “We know these tree rings capture most temperature changes quite well,” and yet we know that that is not the case as is conclusively proved by:
(i) the infamous divergence problem (ie., the divergence in response post 1960 to temperature data); AND
(ii) the fact that they failed to capture the LIA (a well documented event that we know occurred); AND
(iii) the fact that they failed to capture the MWP (another well documented event that we know occurred).
In fact, it appears from the Climategate emails that tree ring response was tuned to data extracted from the instrument record for the period 1906 to about 1950. This begs the question, why were they not tuned to the entire instrument record. In particular why not include:
(i) the data 1850 to 1905? Presumably because the desired result was not obtained!; and/or
(ii) the data post 1950s through to the date of the study? Again, presumably because the desired result was not obtained!
In practice tree proxies should be scrapped until they can properly deal with and explain the divergence problem. At this stage, all efforts should be limited to collecting tree data for the period 1950 to 2011 and examining this in relation to the instrument record for the period. There are some volcano eruptions in this time frame and therefore the response to volcanoes will be seen.
Once tree rings can be tuned to the period 1950 to 2011 and from that tuning an accurate year on year (or at least semi decadal) plot back to 1850 can be reproduced there can be no confidence that tree rings are good for anything to do with temperature extraction. If when further extrapolated back in time they fail to show the LIA or the MWP something is still amiss and further study needs to be conducted or an acceptance that based upon present techniques and understanding tree rings are not a good proxy for temperature.
A life time of work needs to be consigned to the bin; it is back to the drawing board on this one, sorry mate but that is the only way forward.