Over on Climate Audit, Steve McIntyre has been making a series of posts that have been putting the final nails in the coffin for Michael Mann’s MBH98 paper. This paper was responsible for the famous hockey stick graph which is based on tree ring data from Bristlecone Pine trees. Mann’s work implies them to be excellent proxy indicators of temperature, and due to their age, a profound record of temperature. Problem is, it looks like most of the results is Mann’s paper have been thoroughly discredited by the work of McKittrick and McIntyre in 2005, plus McIntyre’s more recent work.
At 4600-4800 years old for some of the oldest trees, Bristlecone Pines (BCP) certainly have seen most if not more than all of human recorded history, so it seems logical to look to them for answers about our temperature history.
One of the graphs Steve McIntyre recently produced was this one:
About this graph he notes:
Here’s the MBH98 PC1 (bristlecones) again marking 1934. Given that bristlecone ring width are allegedly responding positively to temperature, it is notable that the notoriously hot 1934 is a down spike.
Since 1934 is generally accepted now to be the hottest year on record in 20th century it is indeed curious that 1934 in Mann’s data shows up as a down spike.
But seeing what happened with 1934, one has to wonder what do these trees really record in their tree ring growths? Is it temperature as Mann speculates? Or is it any number of other things related to plant growth in various combinations?
I was curious about what others had to say about these ancient pines. One of the first articles I came across was by NOVA, the PBS science program. They had an in-depth article on the “Methuselah grove” where the most ancient trees reside in the White Mountains of California’s Inyo National Forest.
What caught my eye in the NOVA article were these passages:
It turns out that the bristlecone pine has evolved survival strategies that might make other, less hardy plants, well, green with envy. These strategies help it cope with one of the most flora-unfriendly environments on the planet.
But the really interesting one is this:
Bristlecone rings, which vary in width year to year, reveal that the trees have an innate ability to endure times of stress, such as a string of drought years. In such periods, the species can go almost dormant. “There is something a little fantastic,” wrote Edmund Schulman in the March 1958 National Geographic, “in the persistent ability of a 4,000-year-old tree to shut up shop almost everywhere throughout its stem in a very dry year, and faithfully to reawaken to add many new cells in a favorable year.”
No where in the NOVA article does it link temperature and tree ring growth for Bristlecone pines, but it seems clear that water is a major factor in BCP growth.
Another article I found on NASA’s Earth Observatory website initially talks briefly about temperature proxies, but then focuses on precipitation for the remainder of the article with a review of early work with BCP tree rings by Andrew Ellicott Douglass.
He wrote:
“Through long-past ages and with unbroken regularity, trees have jotted down a record at the close of each fading year—a memorandum as to how they passed the time; whether enriched by added rainfall or injured by lightning and fire…. So, in the rings of the talkative pines we find lean years and fat years recorded. The same succession of drought and plenty appears throughout the forest.”
The NASA article goes on to say:
In the 1950s one of Douglass’ former students and a respected tree researcher in his own right, Edmund Schulman, headed into the White Mountains to look at the trees rumored to be very old. He discovered Methuselah and the old bristlecone pines surrounding it. Around the trees, even older dead trees remained on the ground. Together, they gave a climate record of the Southwest United States that extends back 9,000 years, the longest record for a single tree species.
Douglas’ rings tell about rainfall in the southwestern United States, but trees also respond to changes in sunlight, temperature, and wind, as well as non-climate factors like the amount of nutrients in the soil and disease. By observing how these factors combine to affect tree rings in a region today, scientists can guess how they worked in the past. For example, rainfall in the southwestern United States is the factor that affects tree growth most, but in places where water is plentiful, like the Pacific Northwest, the key factor affecting tree ring growth may be temperature.
So in the case of the BCP in the USA desert southwest, it appears that since water is it’s scarcest resource, it has the most effect on it’s growth rather than temperature.
This situation fits well with Liebig’s Law, from Wikipedia:
Liebig’s Law of the Minimum, often simply called Liebig’s Law or the Law of the Minimum, is a principle developed in agricultural science by Carl Sprengel (1828) and later popularized by Justus von Liebig. It states that growth is controlled not by the total of resources available, but by the scarcest resource. This concept was originally applied to plant or crop growth, where it was found that increasing the amount of plentiful nutrients did not increase plant growth. Only by increasing the amount of the limiting nutrient (the one most scarce in relation to “need”) was the growth of a plant or crop improved.
Liebig used the image of a barrel—now called Liebig’s barrel—to explain his law. Just as the capacity of a barrel with staves of unequal length is limited by the shortest stave, so a plant’s growth is limited by the nutrient in shortest supply.
So when looking at trees that grow in a desert environment, you could naturally conclude that water, and not temperature is the shortest barrel stave.
No wonder 1934 is a negative on Man’s graph above, it was hot and dry that year. It’s been said that even grasshoppers were starving during that drought.
Above: USA Palmer drought index for 1934 see original source here
The White Mountains where Mann and other researchers took core samples from BCP’s is marked with the arrow above. Notice that the location is in the “extreme drought” area. Below is the map of all tree samples for the MBH98 paper:
It looks like, at least for 1934, BCP’s in the USA desert southwest are better at being rain gauges than “treemometers”. Given “Liebig’s barrel”, it makes one wonder whether BCP’s are a good proxy for temperature at all. Perhaps “Mann’s rain barrel” would be a better name for the MBH98 paper.
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No doubt the New York Times will run the story about the end of Mann made global warming. In my dreams anyway.
It’s not completely unconnected to ENSO, but, only weakly connected. Years with the best late season snow pack can be either ones with a very strong El Nino (rare, see below) or ones where moisture got delivered late, down from the north (typically but not always La Nina years). The secondary moisture control, summer monsoon, is so late in the season (typically after late July) that it’s almost too late. Plus. monsoon T-storms are hit or miss. Also, if the monsoon points west or, north, instead of NW, it may miss this area completely. Put is all together, and the Mannian notion of an indirect correlation, with greater precip driven growth being teleconnected to a general trend of more dominant El Nino ergo “global warm period / trend” sort of falls apart. If there is any teleconnection it would probably be with bad winters in the intermountain West and Northern High Plains. BTW – this year is such a year and snow pack is good in the White / Inyo Mountains.
Sorry, forgot to mention, storms coming from the W or SW (typical of El Nino) drop a lot of precip W of the Sierra, and on the W Slope of the Sierra. But east of the Sierra, their impact is limited. Only the strongest El Ninos will result in much moisture making it past the crest. The best “approach route” for snow bearing systems, in the White – Inyos is from the north. Which is typical of La Nina or neutral.
My exposure to tree rings was back in 76-77 when a visiting tree growth ring expert from the US gave a seminar on the water flows in the Colorado river. He thought that in the Colorado catchment tree growth rings going back 400 years were an excellent paleo rain gauge. Didn’t say anything about temperatures.
Just look at the picture of those trees. They are typical of the bristlecone pine trees we are talking about.
How can you possibly use a core sample to detect any kind of signal from that. Half the tree is dead at any one time and there is no bark on it on the other half of it.
The tree might be long-lived but any particular ring taken from a core drilled through any particular angle on the tree cannot tell you what the temperature was in 1716. Half the tree was dead in 1716, an maybe one little section was growing rapidly while nearby sections were trying to recover from insects in 1715.
Great tree, but the overlapping jumble of live and dead sections are not the “sweetspot’ for temperatures over the past 1,000 years. Mann picked them to use as his heaviest weighted data source because the jumbled mess of data produced can easily be manipulated.
Hey, I just came across this thread. I’ve been commenting over at Climate Audit on this very subject. Between my comments over there and finding this thread, I came across some information which everyone might find interesting. It’s a discussion on BCP ring widths by Harold C. Fritts. The paper can be found here: http://tree.ltrr.arizona.edu/~hal/tancient.pdf
Enjoy!
The excluded sites seem to be mostly in the very wet Pacific Northwest.
It would be interesting to see what would happen if they were included.
Even better, to see what would happen if they were the only data.
It is good to know the size of the cherry picking effect.
Sometimes very simple things have a vast impact on science. Therefore SteveMcIntyre deserves a Nobel Prize.
i pointed this out before to stmc. look at 1850. now google drought 1850
The PNW isn’t that wet. Seattle gets less annual rainfall than Dallas and New York City. It’s just that it tends to be an all-day, slow drizzle affair when it does happen. I’m sure there are some parts of the PNW that are very wet, but it’s not everywhere up here.
The excluded PNW sites are in various places. Some of them are west of the Cascades, and therefore, do not experience a very pronounced lack of summer moisture. Of course, believe it or not, east of the Cascades, in many years, the SW monsoon, while not reaching the area per se, injects enough moisture into N Nevada / the southern Columbia Plateau, that there is enough available for subsequent local convective events. So, even east of the Cascades, there is at least an even chance in any given year that summer moisture may be enough to prevent slowing of growth owing to drought stress.
One site I like is on Vancouver Island. Absolutely no moisture limitation. If there are treemometers anywhere, they are in the Marine West Coast climate zones.
Hi,
Sorry but this is a little OT. Seeing Tamino like the BCP for his PCA. I is best described like this.
Sorry, to differ, Steve. But I live very west of the Cascades, and my grass is always brown in the summer, green in the winter. The year after I moved out here (2002) we went 88 days without rain on Whidbey Island, and that wasn’t very out of the ordinary. It may be different closer to the Cascades where clouds coming in from the west and north pile up against the mountains and produce more precip, but along the I-5 corridor, we don’t get a lot of rain in the summer. Like I mentioned before, Dallas, NYC, just about any major city gets more ran than Seattle annually.
One gets the feeling that examining tree rings is about as scientifically valid as examining the entrails of goats.
One gets the feeling that examining tree rings is about as scientifically valid as examining the entrails of goats.
Only if those goats are grazing near Bristlecone Pines. 😉
According to Liebig’s Law, might it be prudent instead to use trees located in the cold climates where heat, not water would be the limiting factor?
BTW Does anybody of you know the percentage in the MBH98 graph which is taken The Bristlecone Pines Trees?
Per: It’s worse than you think. The 2005 paper, and on Mac’s site (ClimateAudit), it is claimed that the BCP samples are weighted 390 times as much as the others.