From the University of Arizona, one wonders how such a thing could happen when CO2 was at “safe” levels. They are using bristlecone pines again, which may very well be a better proxy for rainfall than for temperature. At least there was no competition bias from sheep ranching then. It seems they also confirmed a drought in the medieval warm period in the 12th century.
UA scientists find evidence of Roman period megadrought
A new study at the University of Arizona’s Laboratory of Tree-Ring Research has revealed a previously unknown multi-decade drought period in the second century A.D.
IMAGE: Dendrochronologists extract a small, pencil-shaped sample of wood from a tree with a tool called an increment borer. The tiny hole left in the tree’s trunk quickly heals as the…Click here for more information.
Almost nine hundred years ago, in the mid-12th century, the southwestern U.S. was in the middle of a multi-decade megadrought. It was the most recent extended period of severe drought known for this region. But it was not the first.
The second century A.D. saw an extended dry period of more than 100 years characterized by a multi-decade drought lasting nearly 50 years, says a new study from scientists at the University of Arizona.
UA geoscientists Cody Routson, Connie Woodhouse and Jonathan Overpeck conducted a study of the southern San Juan Mountains in south-central Colorado. The region serves as a primary drainage site for the Rio Grande and San Juan rivers.
“These mountains are very important for both the San Juan River and the Rio Grande River,” said Routson, a doctoral candidate in the environmental studies laboratory of the UA’s department of geosciences and the primary author of the study, which is upcoming in Geophysical Research Letters.
The San Juan River is a tributary for the Colorado River, meaning any climate changes that affect the San Juan drainage also likely would affect the Colorado River and its watershed. Said Routson: “We wanted to develop as long a record as possible for that region.”
Dendrochronology is a precise science of using annual growth rings of trees to understand climate in the past. Because trees add a normally clearly defined growth ring around their trunk each year, counting the rings backwards from a tree’s bark allows scientists to determine not only the age of the tree, but which years were good for growth and which years were more difficult.
IMAGE: A cross section of wood shows the annual growth rings trees add with each growing season. Dark bands of latewood form the boundary between each ring and the next. Counting…Click here for more information.
“If it’s a wet year, they grow a wide ring, and if it’s a dry year, they grow a narrow ring,” said Routson. “If you average that pattern across trees in a region you can develop a chronology that shows what years were drier or wetter for that particular region.”
Darker wood, referred to as latewood because it develops in the latter part of the year at the end of the growing season, forms a usually distinct boundary between one ring and the next. The latewood is darker because growth at the end of the growing season has slowed and the cells are more compact.
To develop their chronology, the researchers looked for indications of climate in the past in the growth rings of the oldest trees in the southern San Juan region. “We drove around and looked for old trees,” said Routson.
Literally nothing is older than a bristlecone pine tree: The oldest and longest-living species on the planet, these pine trees normally are found clinging to bare rocky landscapes of alpine or near-alpine mountain slopes. The trees, the oldest of which are more than 4,000 years old, are capable of withstanding extreme drought conditions.
“We did a lot of hiking and found a couple of sites of bristlecone pines, and one in particular that we honed in on,” said Routson.
To sample the trees without damaging them, the dendrochronologists used a tool like a metal screw that bores a tiny hole in the trunk of the tree and allows them to extract a sample, called a core. “We take a piece of wood about the size and shape of a pencil from the tree,” explained Routson.
“We also sampled dead wood that was lying about the land. We took our samples back to the lab where we used a visual, graphic technique to match where the annual growth patterns of the living trees overlap with the patterns in the dead wood. Once we have the pattern matched we measure the rings and average these values to generate a site chronology.”
“In our chronology for the south San Juan mountains we created a record that extends back 2,200 years,” said Routson. “It was pretty profound that we were able to get back that far.”
IMAGE: Doctoral candidate Cody Routson of the environmental studies laboratory at the University of Arizona’s department of geosciences scrambles up a mountain slope to sample a bristlecone pine tree. Click here for more information.
The chronology extends many years earlier than the medieval period, during which two major drought events in that region already were known from previous chronologies.
“The medieval period extends roughly from 800 to 1300 A.D.,” said Routson. “During that period there was a lot of evidence from previous studies for increased aridity, in particular two major droughts: one in the middle of the 12th century, and one at the end of the 13th century.”
“Very few records are long enough to assess the global conditions associated with these two periods of Southwestern aridity,” said Routson. “And the available records have uncertainties.”
But the chronology from the San Juan bristlecone pines showed something completely new:
“There was another period of increased aridity even earlier,” said Routson. “This new record shows that in addition to known droughts from the medieval period, there is also evidence for an earlier megadrought during the second century A.D.”
“What we can see from our record is that it was a period of basically 50 consecutive years of below-average growth,” said Routson. “And that’s within a much broader period that extends from around 124 A.D. to 210 A.D. – about a 100-year-long period of dry conditions.”
“We’re showing that there are multiple extreme drought events that happened during our past in this region,” said Routson. “These megadroughts lasted for decades, which is much longer than our current drought. And the climatic events behind these previous dry periods are really similar to what we’re experiencing today.”
The prolonged drought in the 12th century and the newly discovered event in the second century A.D. may both have been influenced by warmer-than-average Northern Hemisphere temperatures, Routson said: “The limited records indicate there may have been similar La Nina-like background conditions in the tropical Pacific Ocean, which are known to influence modern drought, during the two periods.”
Although natural climate variation has led to extended dry periods in the southwestern U.S. in the past, there is reason to believe that human-driven climate change will increase the frequency of extreme droughts in the future, said Routson. In other words, we should expect similar multi-decade droughts in a future predicted to be even warmer than the past.
###
Routson’s research is funded by fellowships from the National Science Foundation and the Science Foundation Arizona. His advisors, Woodhouse of the School of Geography and Development and Overpeck of the department of geosciences and co-director of the UA’s Institute of the Environment, are co-authors of the study.
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OMG, my previous post was damn near unintelligible. That is the last time I try to do a quick post, reaching around two monitors to get to the keyboard while keeping an eye on test data 🙁
Latitude says:
November 4, 2011 at 6:00 pm
…
So was it drought? cold temps? combination of both?………….we’ll never really know.
Dendrochronology is a precise science……………….
The droughts are the optimal interpretation. Colder temperatures would have resulted in shortened growing seasons but not other known effects. There are dendro samples from eastern Sierra Nevada collected from now-drowned pines that sprouted in ravine bottoms that are presently too wet for pines sprout or survive. Since at least some of the trees lived for two centuries or more, that means that the catchments for these ravines were subjected to very low precipitation. Lake Tahoe also ceased to feed the Truckee River for extended periods.
California’s state government funded several studies in the mid-’70s in response to concerns over the drought taking place at the time. These droughts also appear to correlate with incursions of salt tolerant vegetation into the Sacramento-San Joaquin Delta. This indicates that river flows in the San Joaquin and Sacramento catchments were at times very low compared to modern flows.
Yet another classic post on W.U.W.T.. Dont knock the Bristlecone Pines. They tell a valuable story relating to their patch over a long time.
Most important story. Over 2,000 years the climate changed, was it hot, was it cold or arid. Matters not it CHANGED.
Now plot the ring anomalies and start looking for comparisons. Dont forget drought can be cold. Driest place on earth, Antarctica.
The Link to the sunken trees was terrific. Can they use their Dollars to put it all together and build a good climate record for the region.
“What we can see from our record is that it was a period of basically 50 consecutive years of below-average growth,” said Routson. “And that’s within a much broader period that extends from around 124 A.D. to 210 A.D. – about a 100-year-long period of dry conditions.”
According to Loehle’s non-tree-ring temperature reconstruction graph, the above period had sudden drop in temperatures. http://www.vukcevic.talktalk.net/LL.htm
I enjoyed reading this up until the comment “there is reason to believe that human-driven climate change will increase the frequency of extreme droughts in the future”.
It is sad that this kind of obviously stupid and unnecessary statement has become essential if you want to continue to receive grant funding.
Mann cannot be too happy about this kind of article, as it is yet another example shredding the supposed logic of his infamous ‘hockey stick’ – in this case, previous warm periods and bristle cone pines reacting positively to extra moisture.
barry says:
“Mann tried to get rid of the MWP and LIA? That’s the biggest lie in the whole debate…”
A lie?? Come on, barry, Mann and his acolytes are still trying to call the MWP the “MWA” [Medieval Warming Anomaly] or some such Orwellian term. Mann would like nothing better than to get rid of the MWP. Not that he’s getting any traction. When honest data is used, Mann’s chart becomes ho-hum.
And IMHO tree rings aren’t very good proxies for past temperatures. They work better for past precipitation or drought conditions, and CO2 levels. Not that tree rings are anything like a proxy gold standard; they’re not. Tree growth is affected by many variables, and temperature by itself has only a very small effect.
But the “Team” loves their tree rings. Briffa used one tree, YAD061, to make his hokey stick. Deleting that one tree erases the entire hockey stick shape. That is just pseudo-science.
There is a direct connection between tree rings and grant money. It would be as if references to astrology generated grants; everyone would be putting natal charts into their peer reviewed papers. Tree rings may have their place, but the government should not be handing out our tax money based on them.
Finally, to answer your question, the MWP ended somewhere between 1250 – 1300 AD. There is no universally accepted ending year, which is apparently what you want. Further, the MWP had cold episodes just like the LIA had warm years.
In general, the peak of the MWP was as warm or warmer than the MWP [Modern Warming Period]. Therefore, what we’re seeing now can be completely explained by natural variability, with no necessity to add an extraneous variable like a minor trace gas to the explanation. William of Ockham would understand.
Mike Davis says:
November 4, 2011 at 5:09 pm
They wasted money to find something that was already known. The times they are talking about are known transition periods from warm to cold. Maybe they should have studied historical climate records first!
I rather like this example from John Daly’s paper on Tasmanian sea levels. Academics without common sense:
On this issue, Hamon regrets to inform us – “We cannot apply a correction for atmospheric pressure in this case, as no Hobart data for for 1888 are available.” That lack of atmospheric pressure and wind data means that the Shortt observation would need a wide error bar after all…
Although Hamon did not have those atmospheric pressure or wind figures, they were on public record. Once I concluded from the email discussion that pressure and wind uncertainty was the primary reason for the long 1888 error bar used by Pugh et al., it took me about half an hour at the public library to find the relevant data on pressure and wind in 1888.
On 24th February 1888, the atmospheric pressure at Hobart was 29.96 inches, which converts to 1014.7 millibars. The wind was light south-easterly[10]. This information was contained in the `Shipping News’ of one of the local papers of the time, the Daily Telegraph.
‘Nuff said.
“. . . has revealed a previously unknown multi-decade drought period in the second century A.D.”
Having read the comments here, they haven’t done their homework. The drought was “previously unknown” to them. Talk about mental virginity.
I was once (pre-internet) given a 3000-word essay on a subject about which only two textbooks (one rather short, the other only partially relevant) had ever been published. It took a while to find that out before I could start thinking about writing.
There is one good thing about Mann’s hockeystick. When the historians are looking back, it can be used as documentation for the Teams bad science.
Flat, and then rising? But where is the LIA and the MWP? Who made this up?
They cannot dissappear the hockeystick.
Very good, hey?
how come a drought could bein southern US if US didn’t exist…
it is high school geopgraphy stupid….
Jer0me says:
“Is it really a ‘straw man’ to say that alarmists are claiming there is a ‘safe’ level of CO2 above which were are heading for disaster?”
No, but it is a straw man to argue that was the point I was making. Watts is implying that for AGW theory to be true carbon dioxide must be instrumental in in previous warming events (otherwise why mention it when linking to an article regarding a historical event?); this is simply not true.
Tree rings on my farm do seem to record the droughts that have occurred in my lifetime. They don’t record the worst winters, for they were not growing during those winters. Individual trees also record ups and downs of their individual lives. However the extended New England drought of the mid 1960’s appears in all the older trees. I conclude tree rings do better at recording rain than temperature.
RE: Ulric Lyons says: November 4, 2011 at 6:08 pm
That link to records from Syria is very interesting. It gives one a clear idea of how devastating drought and cold waves can be to small villages of farmers. Also how a change in weather patterns can help one part of the world while ruining another. Usually people over-simplify, regarding the Middle East, and blame everything on overgrazing. The booms that resulted from irrigation were interesting to read about.
One interesting article I read back around 1986, in a small newspaper in Gallup, New Mexico, described an archeologist looking up from some pottery shard he was whisk-brooming, and seeing a reporter actually be interested in his obscure work (at that time.) He explained to the reporter he was bothered by facts not fitting his theory, and how he was having his arm twisted by the facts, and being forced to come up with a new theory.
As I recall the site he was investigating had not been abandoned during the period of extended drought, but just after the rains returned. It made no sense that the ancient ones had survived the hard times, but bailed when the good times returned.
What the archeologist was surmising was that the irrigation systems had actually worked well, and been improved upon, during the extended drought, but that, when the rains returned, they were not gentle winter rains, but rather summer “gully washers.” The carefully-built irrigation systems were not merely knocked down, but also left high and dry, for the streambeds were eroded and lowered to a degree where water no longer flowing into the inlets, and the canals were rendered useless.
The irony of the theory was not lost on me: After years of praying for rain, it was rain and not drought that ruined things.
I’d like to find that old article. It would be nice to read something where neither the scientist nor the reporter felt any need to link their discussion to Global Warming. Those were the days!
Barry:
But of course. I’m glad you asked.
This is from Mann’s embarrassingly hagiographic interview conducted by the wretched David Appell for Scientific American in 2005:
I covered this article at the time. You can find it if you Google “site:climateaudit.org hagiography”
Oh, and you’re welcome.
(what are the chances that Barry will acknowledge his error? I’m not holding my breath)
Further down into Mexico and Yucatan, the first Mayan civilization collapsed entirely, due due long term drought in the 1./2/ Cty., Little is left of it…. this is what long decadal droughts produce….. Colorado is located at the periphery of this antique civilization…..
…… What was the CO2-output at this time? Anybody knows? At which CO2-level will we collaps again?…..
JS
Kevin MacDonald says:
November 4, 2011 at 7:29 pm
Smokey says:
“WHAT??
CO2 as the primary cause of runaway global warming, climate catastrophe and climate disruption is the central claim of the red faced, spittle-flecked alarmist crowd. Without “carbon” to demonize, what would they have? DDT? Methane? Ozone? Pf-f-f-ft.”
CO² is the primary driver of the current warming, it does not follow that CO² is the primary driver of all historical warming events.
Kevin – your reasoning is lacking. The entire alarmist case is based on two provisos:
1. The current climate is ‘unprecedented’
2. The current level of CO2 is ‘unprecedented’
Therefore the reasoning is that the CO2 level caused the climatic effect. ‘as there is nothing else that could have caused it’.
What this study has done is show that proviso 1 is false. The current climate is not unprecedented.
If the climate conditions now have happened before when the ‘unprecedented’ levels of CO2 were not present – then the argument ‘as there is nothing else that could have caused it’. fails as obviously something else caused the previous similar climate conditions when CO2 was not at its current ‘unprecedented’ levels.
This paper has just disproved the AGW hypothesis
All that happens is that the permanent climate zones change in intensity and latitudinal position cyclically over time as a result of an interaction between variations in the oceans and the sun.
There is no climate change for the globe as a whole in terms of any significant change in the global equilibrium temperature (or energy content ). The so called faint sun paradox is the evidence for that.
Those changes in the permanent climate zones are the global thermostat in action because such changes reflect adjustments in the rate of energy flow through the system. Such adjustments always serve to negate any factors that seek to alter the energy content of the entire system.
The coming and going of south west US drought conditions is just one regional manifestation of such changes as is the coming and going of drought conditions in the Sahel.
If we can get the timing and location of past regional climate changes defined with adequate precision (apparently not yet) I am sure we will find that regional changes in the climate zones occur around the world in each hemisphere approximately in unison as the global energy budget is adjusted to maintain system stability.
All that the surface record ever tells us is the regional response (where the sensors are – mostly in populated mid latitudes in the northern hemisphere) to a mix of shifting climate zones overhead and UHI effects.
Only the satellite record has any value in global terms and that will always be much more stable than surface temperature records because satellites measure variations in the energy budget for the globe as a whole and so are unaffected by the larger regional swings which occur as the climate zones shift about or UHI effects develop around surface sensors.
Forget about global climate change. Everything we observe boils down to shifting climate zones which adjust the rate of energy flow through the system.
Offers of research funds welcome 🙂
And here was me, believing than Dendrochronolgy, was a method of dating wood & wooden artifacts by examining their ring width sequencies.
Just finished reading “Cahokia Mounds: America’s First City” by William Iseminger. From p. 150:
“There is evidence of climate change occurring at different times in the Midwest that may have affected the growth and development of Cahokia and also contributed to its demise. A period of more favorable climate began about the time that Cahokia developed as a major community and continued to about AD 1135. Around that time, a period of drought occurred that lasted for about 35 years or more, adding an element of stress to an already fragile economy and political system.”
The medieval drought may have stretched as far as the midwest. I can’t imagine what a 35 year drought would do to the corn belt today.
Did anyone notice that both of these droughts came at the end of a warming period, just before it went cold?
Smokey,
Good. A first! Now, you realize that MBH98 starts in 1400. It has nothing to do with the medieval warm period. The graph you are always linking to is from MBH99, which does cover the MWP time frame.
Now answer my rebuttal Barry…
Oh and the exact link was http://climateaudit.org/2005/02/22/mann-and-the-hockey-stick/
Well, now “barry”, you’ve asked a good number of questions and been politely answered, so please answer one or two of the questions posed to you.
“Darker wood, referred to as latewood because it develops in the latter part of the year at the end of the growing season, forms a usually distinct boundary between one ring and the next. The latewood is darker because growth at the end of the growing season has slowed and the cells are more compact.”
Not exactly. Hopefully I won’t come across as the “pedantic” forester on this list, but latewood is darker mostly because the cell walls are much thicker than in so-called earlywood. Cell wall thickness is very closely correlated to specific gravity, so latewood is much denser and stronger than is earlywood.
In Douglas-fir growing in areas of mild climate and intermittent late summer rains, latewood proportions can be significant, producing fairly wide bands.
Increasing climate temperatures = increasing civilization
Decreasing climate temperatures = decreasing civilization
Is there anything else, we REALLY need to know? GK