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.
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.
http://www.stuff.co.nz/national/6370049/Forest-giants-forecast-trouble-ahead
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!
“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 http://www.climate-skeptic.com/wp-content/uploads/2009/11/briffa_recon.gif.
“We know these tree rings capture most temperature changes quite well”
They do?
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
http://judithcurry.com/2011/12/01/the-long-slow-thaw/
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.
tonyb
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.
I don’t seen any signs that an expert statistician has been involved in the paper. I wonder why not.
“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?
Every tree is different, as we are.
They took a miniscule sample, averaged it and expected it to apply it to a universal theory.
Deluded.
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…?
“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 !!
“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?
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?