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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Tears of Joy rolled down my face as I read the comments on Mann. I do not need to say a thing. Bravo/Brava, commenters!!!!
Unfortunately, I cannot resist saying something. Mann has been forced to recognize that there is a real world, that trees live in the real world, and that investigation of the facts on the ground are necessary for claims that some set of trees can be used as proxies for temperature. It must have hurt him deeply to accept those facts. He does his best to spin them.
Mann’s recognition of the importance of these facts should have come before he was granted a Phd. The recognition should have come before publication of any version of his Hockey Stick. Responsible people failed in their duties.
Now that Mann has been forced to take account of the facts on the ground, his work on temperature proxies must surely fall apart. That “falling apart” will be evident in his own work as it is evident in each paragraph quoted above.
If you get a chance, make sure that your Congressional representative knows that Mann’s work on temperature proxies is about to disappear like a puff of smoke.
“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.”
So what! Anthropogenic CO2 emissions are small compared to natural emissions and yet they dominate the global heat budget, throwing the entire global climate into chaos whereas before man’s interference with the carbon cycle there was perfect balance and stability, global paradise. /sarc
Seriously though, that may very well explain the “lag” they see in response. The temperature decrease is initially offset by the efficiency increase. But, of course, that would mean temperature isn’t the dominant factor in tree ring growth and we all know that just can’t be true. [Oops, how did that sarcasm tag come back? I better turn it off again.] /sarc
“The lack of a larger cooling in proxy records of climate change following large volcanic eruptions such as those of Tambora in 1815 and Krakatau in 1883 has long been a puzzle for climatologists. These records, however, may have been biased by enhanced tree growth for several years following each eruption induced by additional diffuse radiation caused by the stratospheric volcanic aerosol clouds from the eruptions.
http://climate.envsci.rutgers.edu/pdf/TreeRingCorrection3.pdf
The trees are part of the fossil fuel conspiracy. Only possible explanation, …..
Tree rings are a good proxy for:
1. Temperature.
2. Rainfall,
3. Tree density,
4. Forest fires,
5. Volcanoes,
6. Forest fires – fertiliser effect,
7. Lightning – fertiliser effect and partial tree destruction,
8. Wild animal and bird populations – fertiliser effect,
9. Carbon dioxide concentration – fertiliser effect,
10. Exposure to wind, and
11. Mannian maths to distort.
Assume you are a budding climatologist, and you are confronted with a situation in which measured data conflicts with a model output. Do you think-
a-the model is wrong
b-you have misinterpreted the measured data
c-the natural process which produced the measured data has somehow malfunctioned
If you chose c, congrats! You are a climate scientist.
“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”
And the research proving this can be found where exactly?
Mike.
Juergen says:
February 6, 2012 at 1:07 am
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?
Trees do not grow in the winter as you point out, so they record nothing about winter conditions. At night, the trees respire, they use O2 and give off CO2 to stay alive just like we do. I have never tried to wake one up, so I don’t know whether they sleep or not. ;^)
What do tree rings record?
1. they record temperature during the growing season, but too hot can be the same as too cold in terms of growth.
2. they record the amount of available water, so rainfall may be inferred.
3. they record the amount of available nutrients like Nitrogen
Basically, they record whether the tree was growing normally (enough warmth, wet, and food) or whether it was stressed (too cold, too hot, too wet, too dry, or starving for nutrients)
What they do not record directly is temperature, that has to inferred and would require a knowledge of the other parameters as well.
It’s no accident this appears at the same time as this:
http://wattsupwiththat.com/2012/01/30/new-paper-speculates-on-volcanoes-during-the-little-ice-age/
Hey Mikey, when you can explain why the temperature vs. ring width stopped correlating in the 1960s, and get an empirical grasp of what you write about, I might read something you write again. You may also want to brush up on history so you have some comprehension of perspective on actual climate we have dealt with and recorded as humans. With these in your ruck sack you might wander in from far left field.
“…most temperature changes”…? “MOST”…?? “MOST“???
What happens to the rest, Michael?
Epic Fail, folks!
“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.”
If there’s a missing ring, how do you know there’s a missing ring? Oh, because it doesn’t match the climate model! So we make a tree ring model, and tweak it to match the climate model..and bingo..it all agrees!
Mikesixes says:
February 6, 2012 at 8:26 am
Bwaaaaahahaha…!!!! Made my day.
Steve M. from TN says:
February 6, 2012 at 9:12 am
Receives honorable mention on same funniness scale. Is there a marker where the tree ring is missing?
Old England says:
February 6, 2012 at 2:32 am
Did I miss any mention that CO2 levels have a very significant effect on rates of growth? Does Mann understand that – or is it ‘conveniently’ 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 inaccuracy.
I can – to a little degree – agree with Mann that CO2 levels should not have been a factor in his dendro-assumed temperature records. But ONLY across the early years of tree growth, the years prior to the 1950’s and 1960’s, when we know mannkind at last began emitting significant levels of CO2 into the atmosphere. Prior to that point in the 1960’s, we are told CO2 levels were steady. Note that actual CO2 measurements varied all over the place!
(Note, strategically) that Mann’s variations from the paleo temperature proxies and the tree-growth thicknesses also began to deviate as soon as his assumptions about CO2 levels and steady-state tree ring growth began to deviate!)
Therefore, after reading everybody’s comments above, we have – at a minmum! – the following tree-growth-to-worldwide-climate-to-temperature-reconstruction-due-to-volcanoes errors and omissions:
1) Any volcanoes erupting between fall through winter through early spring (with respect to the “winter” of the limited sites he chose to investigate!) will NOT be reflected in tree ring changes.
2) Volcanoes erupting will – at most! – only affect 1 to 2 years of ring growth. From the weather-is-not-climate part of climate reconstructions?
3) CO2 levels greatly increase today’s growth rate by 12 to 27 percent (based on Idso’s measurements of worldwide plant responses) particularly for resource-restrained plants in marginal areas. Which is what Mann prefers to study.
4) Tree rings may not appear when growth is restrained by extreme cold.
5) Only valid data that fits the pre-assumed model data of climate is acceptable to Mann.
Any that I’ve missed?
Now, who pal-reviewed this “paper” and how much did his/her universtiy receive in Man-made gifts (er, grants) from the taxpayers?
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.
No, tree growth is not almost entirely controlled by temperature. Precipitation, Soil, Sun are more important.
With the trees underestimating temp effects, I can see where we are going to get another paper with the re-taped hockey stick that can now magnanimously show the MWP and the LIA but these dwarfed by the “underestimated” temp rise of the last half century. Watch for it and remember this prediction. It should be out in about 6 months to a year (they are already working on it and, of course, they don’t have to wait long for peer review.
I would like to know the source of Dr. Mann’s temp-controlled trees so I can purchase a few. The drought out here seems set to continue for at least another year and the temperature has been warmer than the (recently-reset) 30 year average. Trees that are not precipitation-dependent and that thrive with higher heat would be exactly what I need!
Oh, they cut down the last ones to use in tree-ring measurements? Darn.
“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.”
Whatever your views on using tree rings as temperature proxies just reading the paragraph above it seems that the virtual world has more validity than data from the real world.
“We know these tree rings capture most temperature changes quite well,” said Michael Mann,…”
Does anyone know who the “we” is in the above statement. Does it refer to the other members of the “team”. Or does it just refer to M. Mann and his mistress. Many would like to know. GK
Am I following this correctly?
A) The *new* suggestion is that tree ring analysis isn’t set in stone after all, that there are things that it doesn’t do well? … AND …
B) They compared the actual data collected against the results of models, indicating (again) that the models are the best evidence they have?
You have got to be kidding me…
Actually, I have another question:
How is it that dendrochronology, using trees at the limits of their growth range (either boreal zones or at the upper edge of altitude) can be used to reflect GLOBAL conditions?
Using FDA standards of efficacy for new drugs, these tree ring experts aka published paper mill workers for hire would be laughed at and not invited in the building.
Tree ring studies correlated with CO2 vs temp.
Throughout the 20th century there were many (about 65!) volcanic eruptions – averaging at least one eruption of VEI 4 or greater – about one every two years.
On the other hand, those with a VEI of 6 or more (i.e. those large enough to leave a measurable ‘mark’ on the temperatures – such as Tambora in 1815 or Pinatubo in 1991) number a scant 100 in the past 100,000 years.
If the Mann-ly models don’t account for this, they are defective.
Smokey
Have you also got a graph showing the WORST 30 published proxies? Now that would be instructive.
tonyb
I don’t understand the part about ‘ Tree rings respond to temperature quite well’. I thought that given that a ‘Hockey stick’ shape is a characteristic signature of fitting a temperature to uncorrelated random brownian noise, that it is proof that tree rings are uncorrelated to temperature and their use should be discarded.
Take a large number of brownian (red) noise runs , call it ‘tree rings’ and fit the last 1/4 or so of the runs to an upwards slope (simulating temp) and weight the runs (as Mann did) so that those having the best fit have a higher weight and you will always get a ‘hockey stick’. It is a characteristic signature. Garbage in, garbage out