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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One other comment about narrow growth rings: we also know that severe defoliating insect outbreaks that last for a period of years also correlate very well with reduced growth. In the case of bristlecone pines in the SW, I would lean more toward the drought thesis, but in other areas of the globe, we frequently see very tight growth rings for periods of 10 years or more that coincide with known defoliating insect outbreaks. In some years, trees may appear to have produced almost no radial growth, and thus one growth ring may actually represent 2 years in time.
As stands grow up and before natural thinning occurs, overstocked stands also show very much reduced radial growth for a number of years.
“Increasing climate temperatures = increasing civilization
Decreasing climate temperatures = decreasing civilization”
You need to consider rainfall too. Cold and drought are the main problems but a problem too is that a warm wet environment is not conducive to civilisation either because food and water are abundant so the people don’t need to work too hard whilst at the same time natural predators, parasites and diseases are rife to keep the death rate high.
The best inducement to civilisation is a regularly varying mix of not too extreme weather types such as in the mid latitudes where changing seasons force people to be adaptable.
“… there is reason to believe that human-driven climate change will increase the frequency of extreme droughts in the future, said Routson”
Why don’t they just put a WUWT style ad:
“Donations accepted: fling funds”
At least it is above board and straight forward.
I was speaking from a historical context. History requires no justification. I was not referring to localized climate, but global instead. Globally a warmer, wetter, world is better for civilization (especially if it is CO2 enhanced). Carbon usage also varies as civilization ebbs and waxes. We don’t have to understand it – to make the observation historically. GK
That there were droughts in the past is beyond dispute, but it is not an excuse for us to be cavalier now. The natural conditions which contributed to droughts in the past, are now exacerbated by man-made forcing and it is likely that these unfortunate events will be more frequent and of a greater duration. Although I’m sure you will dispute the relationship between CO2 in the atmosphere and weather events, even climate change, those of us who do accept this connection are deeply concerned about our collective capacity to cope with challenging climate changes and extreme weather events. (Texas -drought, widfires -everywhere; massive flooding – everywhere; uncharacteristic weather events -NE states and everywhere; heat waves – europe and southern states etc)
The US Department of Energy has recently released data which shows that global warming gases released into the atmosphere “made an unprecedented jump” in 2010, with a 500 million metric ton increase in a single year. This represents a 6% rise between 2009 and 2010. This is not good news.
Hugh Pepper says:
“The natural conditions which contributed to droughts in the past, are now exacerbated by man-made forcing and it is likely that these unfortunate events will be more frequent and of a greater duration.”
“Likely”? Based on what? Hugh, you may believe that, but like astrology and Scientology, there is zero evidence to support your belief. OTOH, there is ample evidence that the added CO2 is beneficial to the biosphere. Think of it as harmless airborne fertilizer, you’ll sleep better.
Hugh Pepper – Droughts, floods, hurricanes, tornadoes, earthquakes, volcanic eruptions, and other natural phenomena have occured in the past, are occuring now, and will occur in the future. Man has absolutely no control over them. Man can only try to mitigate the damage caused by them through intelligent siting of buildings and cities, better engineered structures and so on. Therefore if you tell me we should not build along coastlines that are frequently hit by hurricanes, I’ll agree with you. If you tell me we shouldn’t build in flood plains, I’ll agree with you. But don’t tell me we have to lower our standard of living, or deny others the chance to improve theirs, because of a definitely unproven (and as far as I’m concerned false) hypothesis that an odorless, colorless trace gas required by all green plants to produce the oxygen and food that sustains life on this earth will cause the planet to overheat!
Hmmm, this happened while a “green president” was in power. This happened while thousands of wind farms and solar farms came into service. This happened when everyone replaced their incandescent(s) to flourescent(s). This happened while recycling is at maximum and bio-fuel production is exploding. This happened despite all the climate conferences and despite A.Gore.
You do understand the repercussions, of performing the same actions, over and over, expecting a different result. The question arises – Do YOU finally accept the result?? GK
Just thought of something – if those trees were recently cored, then we now have tree rings NEWER than the old Greybill proxies (which IIRC, was back in 1993).
This means that we can now see if RECENT rings accurately follow the last 17 years of temperature rise.
Kinda like a two-for-one data source. They extended the past, AND updates the proxies.
So it’s probable that their work not only showed previous droughts not caused by CO2, but could show that the trees aren’t following current instrumental temperature records.
Who’s our resident Dendrochronologist?
Hugh Pepper says:
November 5, 2011 at 12:03 pm
Assertion is easy. Verification, however, requires proof. You assert that “this is not good news”. Is it bad news? If so, why?
John A @ur momisugly <a href=http://wattsupwiththat.com/2011/11/04/roman-period-megadrought-found-in-the-usa-southwest/#comment-788489
That is the journalist’s copy, not the words of Michael Mann. Remember I asked you,
Even so, I will deal with what you have cited. I hope you return the courtesy.
Parsing the journo’s take, we find
…
So the MWP and LIA exist after all?
It’s not that Mann denies anomalous warmth and coldness in the MWP and LIA, he just doesn’t agree with the character of those periods and touted by skeptics (ie, MWP global and warmer than recent)
Your quote is from 2005. Mann has consistently said (from 1999 to present) that there was anomalous warmth in the medieval period and qualified that it was mainly restricted to the Northern Hemisphere and unlikely to have been as warm as the last few decades. He has also consistently referenced the LIA in his work, and discussed the spatial and temporal parameters of that period, too (as well as potential drivers for both) The lie about this is given out by skeptics who are intemperate, and can’t or won’t speak to the truth of the matter.
I’ve already cited Mann directly from his two most controversial papers, MBH98 and 99 identifying and qualifying the MWP and LIA.
Will you acknowledge that?
From a more recent study, Mann et al 2008.
And so on.
The abstract of a 2009 paper, “Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly” goes;
Michael Mann, his colleagues and the paleoclimate community acknowledge that the medieval period was warm, and that there was a cold period, popularly known as the Little Ice Age. Mann has not tried to ‘get rid’ of these phenomena. On the contrary, he discusses their breadth and magnitude, to say the least.
Die-hard skeptics, it seems, have decided that MWP = warmer than today, and any conclusion that differs from this is someone trying to ‘get rid of’ the MWP. But that’s not skepticism, that’s just jingoism.
John, will you acknowledge that Mann describes a medieval warm period and a cool period known as the Little Ice Age in his work?
Barry,
you disqualify yourself with being a stout defender of Mann and his hockey stick……
with all his nonsense….
Please, there is a lot of new work, which show, that (1) the LIA was deeper in temps as the little bit, which Mann concedes, as well as (2) temps in the MWP were much higher that Mann concedes (which means the “stick” is not straight as he insist ….only “a tiny bit curved”)
(3) In still temporary absence of studies in the Southern Hemisphaere (which will come up in time), he just invents that the deeper LIA and higher MWP occured on the North. Hem.,
(4) please see the latest graph of global land temps of BEST from 1800-2000 (and as you
know, the 1800-1850 temps are on land higher than in a. the South.Hem. and b. over the ocean, total of the three still depper still….. how do you integrate these BEST values 1800-50 into the hockey stick……?
Please put Mann et al to their rest, they have disqualified themselves in climate science…..
Check and critize my book, please find mistakes….. that would be of service to science, forget Mann and his crowd, they will be taken out of science anyway in a couple of years….
@Caleb says:
November 5, 2011 at 4:34 am
“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.”
But then as those cold winters are evident on all continents across the hemisphere, it does tend to imply external forcing.
Ian W says:
“Kevin – your reasoning is lacking. The entire alarmist case is based on two provisos:
1. The current climate is ‘unprecedented’”
No one is arguing that the current climate is unprecedented, making this a straw man rather than a provisio.
Ian W says:
“2. The current level of CO2 is ‘unprecedented’”
No one is arguing that the current level of CO² is unprecedented, making this a strawman.
Ian W says:
“Therefore the reasoning is that the CO2 level caused the climatic effect. ‘as there is nothing else that could have caused it’.”
No one is arguing that correlation equals causation, warming is ascribed to CO² because we know it’s physical properties, so this is yet another straw man.
Ian W says:
“What this study has done is show that proviso 1 is false.”
Even if people were arguing for your first provisio (which, per my earlier link, they’re not; its a straw man), this study is regional and, in itself, tells us nothing of the global picture. Consequently, despite creating two staw man provisios, you have still failed to make your case.
@ur momisugly Kevin MacDonald: No one is arguing that correlation equals causation, warming is ascribed to CO² because we know it’s physical properties, so this is yet another straw man.
Your implied straw man is that we skeptics don’t know the physical properties of C02, i.e. that it is a greenhouse gas. We know why warming is ascribed to C02, and it has little to do with science or reality. Your argument is a big FAIL.
Barry:
No Barry I will not.
Mann made clear that he regards the previously well-accepted paradigm of global medieval warmth as false because his fabulous statistical exercise told him so. The quote was not something that David Appell simply made up and put in Mann’s mouth – it was clearly something that Mann was communicating through his works from 1999 onwards.
I find your arguments to be “sophisticated” because they are sophistry, designed to make Mann look as though he was arguing for a Medieval Warm Period and Little Ice Age as global phenomena when he clearly wasn’t.
In fact Mann spent a great deal of time and effort claiming that the Modern Warming was unprecendented in the last 600, 1000 and even 2000 years. He even described those events as being localised to the North Atlantic basin.
He only changed his tune relatively recently because a) his reconstructions of past temperatures were found to be riddled with errors and veridically false statements and b) despite his and the Hockey Team’s best efforts to block, the evidence for Medieval Warmth and Little Ice Age cold continued to be described in all parts of the globe.
Are you going to continue to claim Mann was arguing for the global reach of these phenomena when he clearly wasn’t or will you do the decent thing and apologise?
Bruce Cobb says:
“Your implied straw man is that we skeptics don’t know the physical properties of C02, i.e. that it is a greenhouse gas. We know why warming is ascribed to C02, and it has little to do with science or reality. Your argument is a big FAIL.”
I was addressing a specific poster and my comments, my comments were directed only at him and implied nothing about the state of knowledge amongst the wider “skeptic” community. Ian W’s incorrect assertion that the entire case for AGW theory hinges solely on the correlation between temperatures and CO² requires, by definition, that there is no physical mechanism that backs the theory up. Given those circumstances, it is fair to infer that Ian W is unaware of the physical properties of CO².
Kevin MacDonald says:
“No one is arguing that the current climate is unprecedented…”
…which means the null hypothesis remains unfalsified. Therefore, the alternate CO2=CAGW conjecture is on the rocks and sinking fast.
RE: Main Article
“Dendrochronology is a precise science of using annual growth rings of trees to understand climate in the past.”
Of course, “Dendrochronology” is a precise science for measuring relative *time* by tree-ring correlation. It might be better to say something like ‘Dendro-climatology’ is an imprecise science using the unique properties of annual tree growth-rings to estimate possible climatic conditions in the past.
I cannot ‘continue’ to claim Mann was arguing the MWP was global, because I never did in the first place. As I said, Mann argues that it is a regional phenomenon. The result is warmer global temperatures, but not as warm as today.
Mann did not try to ‘get rid’ of the MWP. It is there in his reconstructions along with the LIA. He just doesn’t think the MWP was globally as warm as today. Neither you nor anyone else commenting here is qualified to judge the truth of the matter, and he is entitled to his opinion. It is not a controversial opinion in the halls of paleoclimate, where different groups using different methods and data find similarly. OTOH, a small number of papers suggest the MWP was global in extent/warmer than today.
It’s worth getting familiar with the literature on this. these links are a good pace to start.
http://agwobserver.wordpress.com/2009/09/08/papers-on-the-mwp-as-global-event/
http://agwobserver.wordpress.com/2009/11/17/papers-on-reconstructions-of-modern-temperatures/
http://agwobserver.wordpress.com/2010/02/24/papers-on-temperature-reconstructions-from-boreholes/
http://agwobserver.wordpress.com/2010/02/28/underground-temperatures-as-indicators-of-surface-temperatures-part-1/
http://agwobserver.wordpress.com/2010/03/03/underground-temperatures-as-indicators-of-surface-temperatures-part-2/
Having read many (not all) of these papers I know that Mann’s conclusions are common across paleoclimate studies. Because his work is not out of step with the wider body of the science, I conclude that the relentless attack on him is politically motivated.
A couple of suggestions came to me upthread to quit defending Mann. And if I did? If we threw out all of Mann’s work on paleoclimate? The preponderance of scientific opinion would remain that there was an MWP and an LIA and recent temps are very likely warmer than a thousand years ago. I don’t need Mann, but the skeptics certainly do. It helps the cause to have a bogeyman.
But all I wanted to do was point out that there is an MWP and an LIA in Mann’s work. He hasn’t tried to get rid of them, he just describes them differently to skeptics, who – as an article of faith, not reason – believe that the MWP was definitely warmer than today. In order to hold that opinion, they must dismiss 90% of papers on global or hemispheric paleoclimate, and instead focus on highly selected papers, usually about a small region or locale or, more often, non peer-reviewed ‘blog’ science.
barry,
Give up on the silly claim that the MWP was regional. Here’s an interactive chart clearly showing the MWP’s global reach in both hemispheres. And the MWP was exceeded by several even warmer periods – when CO2 remained very low.
Mann is just backing and filling, trying to obfuscate his earlier claims that tried to erase the MWP and the LIA. Michael Mann is a climate charlatan who collects plenty of taxpayer loot for his alarmism. But what do you get out of being his apologist?
If you check out the chart with care, Smokey, you will discover that the MWP happens at different times in different places, by up to 700 years apart. This accords with Mann’s take of a temporally/spatially incoherent MWP, so it’s not a good chart to use as a rebuttal. Also, some of the indicators on that chart are to do with rainfalland other climate indicators, not temperature.
I have to credit you with substantiating my claim that skeptics don’t refer to the peer-reviewed literature, but instead rely on blog science. Thanks, me hearty.
To substantiate my comments above, simply roll over all the graphs and note where the MWP lies. For instance, at Lake Teletksoye, the peak of the MWP is around 1400, while temps are quite low around 1200. OTOH, sea surface temperatures in Iceland peak at 750AD, while the temperature in 1400 is lower than recent. And in Southern Alaska MWP peaks at 1000 – 1100, while 750 and 1400 are cool periods. These 3 reconstructions contradict each other.
There’s plenty more like that from your chart corroborating the view that the MWP was not spatially or temporally coherent. I’ve pointed this out to you on a previous occasion when you brought this chart up, but it seems to have made no impression. At the very least, you are consistent. 🙂
Smokey says:
“…which means the null hypothesis remains unfalsified. Therefore, the alternate CO2=CAGW conjecture is on the rocks and sinking fast.”
The null hypothesis contains no physical mechanism that can explain recent warming, it is on far shakier ground than AGW theory.
Klewless. The null does not require a “mechanism”. It simply states that other unknown mechanisms are likely responsible for the warming. This has not only not been rejected, it is far and away more likely to be true than the AGW WAG.
“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.
So now they are rain gauges. Seems like only yesterday they were thermometers.
Barry:
Oh please Barry you protest too much. Mann clearly has a right to his own opinion but he has not right to his facts. You make references to attacks on Mann as politically motivated because you deny the clear demonstration of evidence from multiple sources that those “facts” were confabulated.
There is clear evidence that Medieval Times had a sustained period of longer summers and milder, shorter winters than today, evidence such as tree lines being more poleward and higher altitudinally than they are today. It would be surprising given the differing nature of paleoclimatic proxies that we can say exactly when this period began and when it ended.
I cannot say for certain that the Medieval Period was universally warmer than it is today, but I can point to evidence from all over the world that the current warm period is far from unprecedented.
Mann’s “opinion” was offered as the “smoking gun of AGW” and the clear highlight of the IPCC TAR. It turned out that that “opinion” was confabulated and that Mann knew well before Steve McIntyre got involved that one proxy dominated his reconstruction to such an extent that without it, the distinctive shape disappeared, and his public statements to the effect that his results were robust to the removal of dendroclimatic indicators, as well as his claim to not have calculated the R2 metric on his results were knowingly false when he made them.
These statements made by me are not politically inspired. They are based on facts which are beyond dispute.