Mann's not so Explosive Findings on Volcanos’ Climate Influence in Tree Rings

Guest essay by Patrick J. Michaels and Paul C. Knappenberger –

A new paper overturns old suppositions regarding volcanoes, tree-rings, and climate sensitivity.

According to a 2012 press release accompanying a paper published in the journal Nature Geoscience, a research team led by Penn State’s Dr. Michael Mann concluded that the cooling influence of historical volcanic eruptions was underrepresented by tree-ring reconstructions of the earth’s temperature.

This, the press release went on to tell us, had potential implications when trying to determine the earth’s equilibrium climate sensitivity (ECS)—i.e., how much the global average surface temperature will rise as a result of a doubling of the atmosphere’s pre-industrial concentration of carbon dioxide. While most recent studies place the ECS noticeably less than earlier studies (including those most heavily relied upon by the U.N.’s Intergovernmental Panel on Climate Change (IPCC) and thus the U.S. Obama Administration), the 2012 Mann study was an exception. It implied that many existing determinations of the ESC were underestimates.

From the press release:

“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.”

Fast forward to today.

Appearing on-line in the journal Geophysical Research Letters (and sans press release) is a paper led by Penn State’s Martin Tingley that examined how the temperature response from volcanic inferred from tree-rings compared with that of observations. Tinsley’s team concluded that tree-ring based temperature proxies overestimated the temperature response caused by large volcanic eruptions. Instead of responding only to the cooler temperatures, the tree rings also included signals from reduced light availability (from the shading effect of volcanic aerosols) and the two effects together produced a signal greater than what would have been produced by cooler temperatures alone. This is basically the opposite of what Mann and colleagues concluded.

In an article posted to the website RealClimate back in 2012 touting his team’s findings, Mann took time to point out the “wider implication” of his findings:

Finally it is worth discussing the potential wider implication of these findings. Climate scientists use 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, e.g. to estimate the equilibrium sensitivity of the climate to CO2 doubling i.e. the warming expected for an increase in radiative forcing equivalent to doubling of CO2 concentrations. Hegerl et al (2006) for example used comparisons during the pre-industrial of EBM simulations and proxy temperature reconstructions based entirely or partially on tree-ring data to estimate the equilibrium 2xCO2 climate sensitivity, arguing for a substantially lower 5%-95% range of 1.5–6.2C than found in several previous studies. The primary radiative forcing during the pre-industrial period, however, is that provided by volcanic forcing. Our findings therefore suggest that such studies, because of the underestimate of the response to volcanic forcing in the underlying data, may well have underestimated the true climate sensitivity.

It will be interesting to see if accounting for the potential biases identified in this study leads to an upward revision in the estimated sensitivity range. Our study, in this regard, once again only puts forward a hypothesis. It will be up to other researchers, in further work, to assess the validity and potential implications of this hypothesis.

Based on the new results of Team Tingley, it seems that Mann’s hypothesis is wrong. Using tree ring temperature proxies overestimate the climate sensitivity.

“It will be interesting to see” if this is recognized over at RealClimate.

But regardless, there is no escaping the fact that the Tingley study provides additional evidence that the earth’s climate sensitivity to human greenhouse gas emissions is likely less than advertised by the UN IPCC and the Obama Administration. The direct result being that headlong pursuit of carbon dioxide emissions limits should be reconsidered in light of this and other scientific literature.


Mann, M. E., Fuentes, J.D., and S. Rutherford, 2012. Underestimation of volcanic cooling

in tree-ring-based reconstructions of hemispheric temperatures, Nature Geoscience,

5, 202-205.

Tingley, M. P., Stine, A.R., and P. Huybers, 2014. Temperature reconstrictions from tree-ring densities overestimate volcanic cooling. Geophysical Research Letters, doi:10.1002/2014GL061268.

Global Science Report is a weekly feature from the Center for the Study of Science, where we highlight one or two important new items in the scientific literature or the popular media. For broader and more technical perspectives, consult our monthly “Current Wisdom.”

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October 10, 2014 4:20 am

Is there anything about climate science when compared to reality that MM and the rest have got right?

Reply to  NeilC
October 10, 2014 7:58 am

Yes. The earth does in fact have a climate. After that it seems the answer is no.

Reply to  NeilC
October 10, 2014 11:16 am

Hello NeilC
“Is there anything about climate science when compared to reality that MM and the rest have got right?”
The short answer to your above question by some one like me it will be:
When compared to reality, what you call a climate science of MM and the rest does not really exist in the terms of what could be a real climate science.
The so called Climate science of MM and the rest is a very biased one by the point of scientific evaluation when reality considered…..a “science” treading far beyond the accepted Scientific method to a point that MM itself becomes just a mediocre fraudster. When it comes to the “MM and the rest have got something right with their science [warming “science” about climate] when compared to reality”, my take is that while the rest have got something right the MM as far as I can tell has got nothing at all right and he not able to see the “rest” playing [using] him as a kicking ball in the AGW issue for some more extra noise.
Really sorry if that hurts someones feelings, but is my plain explanaition of my view point in the case of MM,….. CAN’T PUT IT ANY OTHERWAY, the guy has left no much room there with his actions and behavior.
Now in a longer manner of answering, I do have to explain the above view point of mine and probably having a better answer to your question, but only if you still interested in getting further with my answer to your question.

Reply to  whiten
October 10, 2014 11:55 pm

Mann’s wallet and life is based on him supporting the UNFCCC. There is nothing more to say.

October 10, 2014 4:36 am

Reply to  Admad
October 10, 2014 4:37 am

Mods, many apologies, wring link!

October 10, 2014 4:47 am

Anthony, should you put a link to Steyn in humor and satire or political climate. Sorry if there is one there and I missed it. It would be appropriate for any one interested in tree rings, circuses etc

Stephen Richards
October 10, 2014 5:08 am

Oh you mean that treemometers are not treemometers. Well, well, who’d a thunk it.

Reply to  Stephen Richards
October 10, 2014 8:29 am
October 10, 2014 5:11 am

Fix the template it has been screwed up for months!!

October 10, 2014 5:16 am

Looks like Tingley is running rings around Mann.

October 10, 2014 5:17 am

To quote some climate scientist or the other, “We can’t find Mikey Mann’s intelligence and it is a travesty that we can not.”

parochial old windbag
October 10, 2014 5:57 am

The science is so settled.

Owen in GA
October 10, 2014 6:00 am

I don’t usually go in for text corrections, but there are two instances I have to ask about:

… a paper led by Penn State’s Martin Tingley that examined how the temperature response from volcanic inferred from tree-rings compared with that of observations. Tinsley’s team concluded …

One scientist named Tingley, right?

Tingley, M. P., Stine, A.R., and P. Huybers, 2014. Temperature reconstrictions from tree-ring densities overestimate volcanic cooling. Geophysical Research Letters, doi:10.1002/2014GL061268.

Did the article really misspell reconstructions as reconstrictions in the title? (I have misspelled a title before on a poster presentation, but that was in high school on a hand-lettered poster – embarrassing as could be.)

Reply to  Owen in GA
October 10, 2014 8:40 am

Nothing is more irritating than people who brag about how good spellers they are, as if it some major accomplishment, and not a trivial use of memory.

Reply to  Tom Trevor
October 10, 2014 9:26 am

Baad spelarz uv tha werld, younyte!

Will Nelson
Reply to  Tom Trevor
October 10, 2014 10:58 am

It is a man with no great imagination who can think of only one way to spell a word.

Otter (ClimateOtter on Twitter)
Reply to  Tom Trevor
October 10, 2014 2:45 pm

Shakespear spelled his name 13 different ways.

James the Elder
Reply to  Tom Trevor
October 10, 2014 9:45 pm

Nothing is more irritating than people who use bad grammar to criticize good spellers.

October 10, 2014 6:08 am

Hilarious … see my many posts on volcanoes, and in particular on Mann’s overestimation of volcanic effects.

Scott Scarborough
October 10, 2014 6:30 am

Mann’s contention makes no sense. How could tree rings know a cooling is from Volcanos or just a plain cooling of the planet? Is he contending that increased aerosols in the air cause trees to grow faster? If tree rings don’t respond correctly to a cooling how can you be sure they respond correctly to a warming?

October 10, 2014 6:30 am

” … worth discussing the potential wider implication of these findings …”
If you believe as I do, that science is subject occasionally to fashionable but extremely stupid ideas, then you have to realise that like a system that’s been perturbed, it somehow returns to its own equilibrium point, or it wouldn’t survive. This is science temporarily returning to sanity by junking junk science without appearing to actually do so.

Pamela Gray
October 10, 2014 6:31 am

I also think tree ring data is fairly poor as a temperature proxy. Except in extreme cases. Super stratospheric events that prevent oceanic solar recharging via veiling and set up additional loss of heat via triggered El Nino conditions over months and years, especially around the tropical band, could lead to severe cases. Not only is oceanic heat lost, but no heat is gained. The oceanic currents would then distribute this condition globally, leading to evidence of severe cold, which IS seen in tree rings as killing freezes. And it takes a LOT of cold to cause extensive freeze damage in tree rings.

Reply to  Pamela Gray
October 11, 2014 12:19 am

“I also think tree ring data is fairly poor as a temperature proxy.”
That’s why the supporters of UNFCCC policy based science love it? If you search long enough you will eventually find a tree that supports your political agenda.

October 10, 2014 6:53 am

Owen in Ga: Typos are mine. Thanks for catching them.

October 10, 2014 7:07 am

Past volcanic eruptions cannot be quantified but only guessed at, in terms of their influence on insolation.
All climate sensitivity estimates are via a series of assumptions, all unverified. Thus all CS figures (and these range from I K to over 8K, according to the lights of the individual who derived the figure) are elaborate guesses.
Now here comes two scientists from Penn State, one saying “tree rings underestimate” and the other says “Nay, but they overestimate”. And now we are to send the CS guessers back to their workstations to scratch their heads over tree rings and guess again. This is what is meant by the expression “Pseudo-Science”.

October 10, 2014 7:15 am

So is Mann concluding tree ring data is useless? Does this conflict with his previous “findings”?

David Chappell
October 10, 2014 7:43 am

Oh to be a fly on the wall in Penn State Senior Common Room (if they have such a thing). Incipient civil war?

Joseph Bastardi
Reply to  David Chappell
October 10, 2014 8:58 am

good point!

Chuck L
Reply to  David Chappell
October 10, 2014 9:06 am

I can’t imagine that many of Mann’s colleagues are pleased with his antics but it seems the $’s he brings in to Penn State rule supreme there.

Reply to  Chuck L
October 10, 2014 12:31 pm

It reigns supreme at Old Main and among the Board of Trustees, but among the rank and file faculty, there’s some integrity left.

Ian Magness
October 10, 2014 8:19 am

I don’t pretend to be an expert on tree rings. All I know is that, over the past 20 years of having a plot of land in the south-east of England, I have had to cut back or fell a great many trees and I can tell you that the principal determinant of tree ring width here is rainfall, not temperature. Trees grow very well – as in recent years – in wet years and can stop growing altogether in dry years. Temperature is much less important to tree growth and, at least where I live, high and low temperature in any year only has a tenuous link with low and high rainfall. Both the coldest winters and the hottest summers can have almost no rainfall and either extreme can halt tree growth.
In conclusion, what is all this nonsence about? There is no way here that you can use tree ring growth as a proxy for temperature.
Real science please.

Louis Hooffstetter
Reply to  Ian Magness
October 10, 2014 1:02 pm

Tree rings are proving to be almost as good a proxy for paleotemperatures as goat entrails.

Reply to  Louis Hooffstetter
October 10, 2014 4:35 pm

Does that make Mann a “Silly Billy”?

October 10, 2014 8:26 am

The first and foremost policy priority will be to eliminate the EPA’s “endangerment finding” on CO2 emissions.
1. Congres amending the Clean Air Act to specifically define pollutants (blocking CO2) would be the best option.
2. If unable to do 1. then Congress should use its appropriation authority to block any federal funds in regulating CO2.

Chuck L
Reply to  joelobryan
October 10, 2014 9:23 am

Regarding number 2, Congress, specifically the House, lacks the courage to do so, preferring to flap their gums and criticize the EPA rather than actually doing something about it. They are contemptible cowards.

Reply to  Chuck L
October 10, 2014 2:34 pm

They can’t do that. They can pass a budget, or pass continuing resolution without funding for a given area, Obama vetoes it, and then media go about the House is shutting down government over a temper tantrum, eating babies, pushing old ladies off a cliff, and generally make it appear that they are the ultimate evil.

David Ball
October 10, 2014 8:29 am
Ian Magness
Reply to  David Ball
October 10, 2014 9:59 am

That’s an excellent and informative article.
Thank you!

October 10, 2014 9:36 am

Does this mean D’Arrigo was right about missing rings not being missing? Will Mann tweet an apology?

Oscar Bajner
October 10, 2014 9:59 am

When Rob Wilson called Mickey Mann’s Volcanic drivel “A crock of sh…” a lot of climate (TM) folk
reached for their pitched fawkes, (paging an then thars fysics) but the more experienced mannites
just turned his paper upside down, et Voila.

Gary Pearse
October 10, 2014 10:37 am

I’m unhappily surprised with the cost of all this fun stuff, that it wouldn’t have been obvious at the outset for those looking at volcanic dusts cooling off the planet and affecting tree rings, that they would not automatically think that it would reduce insolation and further reduce tree ring growth. Indeed, I would have thought the reduction in insolation would be the biggest factor (the cooling is what? 0.5C or so?). Any forester/botanists out there? This shows that the narrow, linear “thought” process of these proxymorons. How did Mann rationalize that temp is under-represented!!! Sheesh. Peer review, agh! I’m bowled over that scientists wouldn’t give a thought to the trees full reaction and not just to temperature. And the foresters! Surely they have a literature on this?…probably not.

Reply to  Gary Pearse
October 10, 2014 10:06 pm

Kudos for “proxymorons”.

October 10, 2014 11:00 am

Mann study was an exception as is the person himself but not in any good way what so ever .
So is it a real surprise that why someone who knows they are doing checks Mann’s work it turns out to poor at best ?

October 10, 2014 11:30 am

Pierrehumbert gave a talk admitting if the oceans caused past cycles of cooling then the earth is probably less sensitive to CO2, but if aerosols were the forcing agent, then the planet has high sensitivity. He admitted knowledge of ocean oscillations was limited so he chose aerosols and then went on to claim all hell will break out as soon as those aerosol are washed from the atmosphere.
Furthermore sulfates are the models fudge factor of choice, so there seemed to be a big push to prove volcanic aerosols were big forcing agents, even though the paleoclimate data often found no correlations.

Reply to  jim Steele
October 10, 2014 11:44 am

Volcanism is just one of the “natural forcings” now desperately being sought to let the Team wriggle off the hook upon which they’ve impaled themselves.
Consider all the advances in real climatology which have occurred over the past 30 years without producing any changes in the models, despite their having failed so miserably and utterly. Just among ocean oscillations, in the ’90s the PDO & AMO were discovered, for instance. Then, in just the past decade, SORCE showed the previously unsuspected great variation in the UV component of TSI.

Reply to  sturgishooper
October 10, 2014 12:40 pm

Ben Santer’s desperado stand: he has now taken to citing fabricated volcano aerosols as the source of the 18 year so called ” pause”.

Brian R
October 10, 2014 11:46 am

Mann seems to think that the only thing at influences tree growth is temperature. Never seems to consider the other things necessary for growth.

October 10, 2014 12:48 pm

Great photo and an interesting pileus on the ash cloud. Looks like the cloud plowed right through it.

Arno Arrak
October 10, 2014 3:25 pm

With normal volcanoes there is no such thing as volcanic cooling and no one knows what supervolcanos like Yellowstone will do. .What happens in an eruption is that hot volcanic gases ascend first into the stratosphere which they warm. This is followed by cooling a couple of tears later but it never reaches the ground level whose temperature remains unaffected. Most so-called “volcanic cooling” periods are nothing more than misidentified La Nina periods. That is because the ENSO oscillation that consists of alternating El Nino peaks and La Nina valleys is either poorly represented in global temperature charts or even wiped out by computer processing. The oscillation is not synchronous with the occurrence of volcanoes. As a result a volcanic eruption may coincide with an El Nino peak, a La Nina valley, or something in between. If it coincides with an El Nino peak it will be followed by a La Nina valley which is immediately appropriated for its volcanic cooling. This is the origin of the fake “volcanic cooling” that follows Pinatubo eruption. But if the eruption coincides with a La Nina valley it is followed immediately by an El Nino peak and the volcanologists are left scratching their head about the mysterious disappearance of that volcanic cooling they expect. That is what happened to El Chichon. But they are so insistent that cooling must be there that they have even written it into climate models. That is now the only place where El Chichon cooling exists today. If you look at some well-known eruptions like Krakatoa you find ninimal coolimng because it erupted just when an El Nino was almost over. And that despite the celestial displays reported the wprld over. Or take Katmai/Novarupta, the greatest eruption of the twentieth century, which left no trace of cooling because it coincided with the early beginning of an El Nino peak. All of which leads me to the conclusion that volcanic eruptions cannot possibly leave any trace of themselves in tree ring records. For more info read my book, pp. 17 – 21.

Gary Pearse
Reply to  Arno Arrak
October 10, 2014 5:20 pm

What about reduced solar insolation with big volcanic eruptions causing reduced chlorophyll activity in trees? I was amazed that this hadn’t been considered by dendrochronologists in looking for a fingerprint of vulcanism.

October 10, 2014 8:55 pm

A possible article for someone with an academic background in botany (especially dendrology) to run with; I seriously question the qualifications of most of the climatologists doing tree-ring analyses. How many of them have degrees in botany with specialization in dendrology? What qualifies them to assert that tree-ring widths are influenced EXCLUSIVELY by temperatures. As other comments have pointed out, major volcanic eruptions can influence precipitation and atmospheric transparency. Reduced/changed precipitation patterns can influence tree-ring width. Reduced atmospheric transparency cuts down photosynthesis, which cuts down tree-ring growth.
The real showstopper, however, is that plant growth (and therefore tree-ring width) responds directly to CO2 not neccesarily to its side-effects. Let’s do a thought experiment (gedankene experiment) with two observers. A tree is grown in a greenhouse for several years, with the CO2 levels being monitored. They are adjusted up and down during the experiment. The temperature is not monitored. After several years, the tree is cut down, and the tree-rings are analyzed and compared with the CO2 corresponding levels. Tree rings are wider when CO2 is higher. We submit this data to 2 analysts…
a) Michael Mann will look at the data, and infer that increased CO2 caused higher temperatures, which caused the wider tree-rings.
b) An independant botanist/dendrologist will look at the data, and infer that the increased CO2 meant more plant food which caused more growth. No inference about higher temperatures.
To summarize, I question the qualifications of most climatologists doing dendroclimatology to claim that wider tree-rings are due to higher temperatures and only to higher temperatures. Even more so, when much of their funding depends on global warming hype.

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