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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A few years ago I led a program to recycle municipal sewage sludge as fertilizer. One of our projects, in partnership with with Scott Paper, was to accelerate the growth of cottonwood or black poplar for the purpose of producing white fibre for toilet paper manufacture. The application of bio-solids to sapling poplar plants induced tremendous growth with tree rings as wide as 1/2″ to 3/4″. We referred to the poplars as “nutrient pigs” and their growth out stripped that of unfertilized trees by two to three orders of magnitude. No change in weather, no change in temperature, just a change in nutrient dosage.
As a teenager I helped keep a market garden in the Fraser Canyon of British Columbia. The land, rich volcanic soil only required water in the very sunny climate to grow the most fantastic tomatoes I have ever tasted. Lots of them. I learned that summer that volcanic ash is rich in plant nutrients. So volcanoes may make it colder but they also sprinkle fertilizer just like flooding rivers and desert winds. I’m pretty skeptical of tree ring proxies.
Dave Duthie, Delta, British Columbia
Gene L. says:
February 6, 2012 at 11:09 am
It’s a reflection of the author. Only somebody who views himself as the veritable “king” of climatology would view trees in their most lofty position as representative of the entire world. It’s an ego thing.
The more applicable term to apply to Mann is simply: Epic Fail. He gives the science of geology a very bad name.
“who compared tree-ring temperature reconstructions with model simulations of past temperature changes.” ????
Sure – comparing one fairy tale to another produces “settled science”.
This has to be the most absurd claim ever – neither of the two is anything more than conjecture.
The whole concept is bizarre – the results of assumptions about tree ring proxies compared to assumptions run through a computer model based on assumptions ???
If an engineer came up with a theory about bending moment based on “science” like this would we let him build a skyscraper ??
I don’t think so.
Ruin the global economy and cede control of energy to the Chinese ? – Sure, why not if it reduces CO2 back to 350 ppm ?
“We know these tree rings capture most temperature changes quite well,”
No, we don’t! They record what the tree did in response to all external effects.
More fraud from the Old Master of Fraud.
In reporting on this latest from M Mann, the environmental report Energy and Environment closed with this subtle but pointed commentary:
Brian Luckman, a tree-ring expert and emeritus professor of geography at the University of Western Ontario, says Mann’s paper is interesting, but raises more questions than it answers.
“They make the comment that given these conditions, and based on their [tree] growth model, a certain number of sites should have missing rings,” Luckman said. “But they never actually go and look at chronologies to see whether they could identify those missing rings. That would be a reasonable thing to do.”
Let me get this straight….Luckman is suggesting that Mann and company didn’t actually look to see if tree rings went missing for a year or so…..and then they suggest that before writing an article saying that volcanos cause trees to not have tree rings for a year or so, perhaps Mann and company might look to see if the rings actually were missing…a “reasonable thing to do,” even?
Well, if you don’t validate models, why not go further, and not validate data???
On the other hand….if what this article portends is that Mann and Co will soon discover that when corrected, the treemometers actuallo DO find a Little Ice Age, this might be progress of sorts. The blame will go to volcanos and not to solar influences, but that may be of little matter. We appear to be currently at the beginning of a years-to-decades long “natural experiment” that will tell us a lot more about the effect of a changing sun on climate. If a cooling effect is large, then by implication the effect of the Maunder Minimum on cooling will also be large.
All you have to do to understand that the work of Mann is worthless is look to the temperature reconstruction of the last 10,500 years of the GISP2 Project ice core data by R. B. Alley.
All you have to do to understand the work of Mann is worthless is look at bristlecone pine data 75 miles from the Yamal Pennisula, or those in California, or anywhere else on Earth to see that there is no warming registered at all.
How does this guy get away with this crap?
[+emphasis]
So all of the trees at the boreal margin would thrive as long as the temperature was above
some key point. No water. no nutrients, no sunlight, NO PROBLEM? I don’t think so.
Given that X-Rays are used to estimate ring density, tree rings are the major storage site of heavy metals in trees, the ‘divergence’ in the Northern Hemisphere matches the removal of lead from petrol/gasoline, I am a bit surprised he is having a go a volcanoes now.
To a logical mind, the fact that the treemometers have a major flaw would prompt one to re-think the whole concept. To MM, it is simply evidence that it is worse than he thought and he needs to lower the shaft of the hockey stick quite a bit to compensate for the lost rings.
Methinks Prof Mann has been spending too much time playing The Sims on his Uni computer.
It’s amazing what ‘truths’ one can come up with when torturing data as to why it lied oh, so convincingly. Ah, but if Mann had only stopped to ponder that his tree ring hypothesis was based on a shifty proxy. Methinks he barked up the wrong tree. He’s doing it again.
I love reading these posts. Such an inquiring group of people here 🙂 WELL not all! Some are very stupid watermelons trying to disrupt the natural clean cycle of WUWT.
The issue of missing tree rings due to cold years is an inversely proportional problem of ice cores missing years of deposition due to warm years, no? If a year (or decade or a century) has less precip and/or more top-melting, an ice core might represent a much longer period, during some of which the glacier’s growth was negative. Without some very reliable chemical signatures of layers within a core that pins the layers to known dates or events, the certainty of an ice core’s period is much less reliable. And BOTH proxies might have missing (or reduced) signals during DRY years (and here dry=dry during the proxy’s growing season; summer for trees and winter for glaciers). Or am I missing something?
I’m not saying the cores can’t be useful and should be disregarded. I’m only saying there are more uncertainties and specific meanings can easily be overestimated.
The trouble with tree rings or never trust a skinny tree.
“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.”
No proxy, then.