Roman Period "megadrought" found in the USA southwest

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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So Bristlecones are acceptable now?

Latitude

“Dendrochronology is a precise science of using annual growth rings of trees to understand climate in the past”
“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.”
===================================================
…or about a 100 years long period of below normal temperatures
http://www.drroyspencer.com/library/pics/2000-years-of-global-temperature.jpg

MikeN

This is in line with Mann’s statements that global warming would lead to more droughts and hurricanes in the Southwest. The other implication is that warming from carbon dioxide will produce more LaNina’s, giving a negative feedback that lowers the overall global temperature. This is the reason that Mann says there was no Medieval Warm Period, that the tropics had LaNina like effects. When asked if this meant a negative feedback and models were vastly overstating warming, he said I agree with that… I think there’s a missing negative feedback.

Bruce Cobb

Sneaky buggers. Here I thought I was reading about some actual science being done, and then they had to spoil it right at the end with their manmade climate crapola.
Still, I suppose it was a requirement to pay the obligatory lip service to the CAGW meme for funding. Science in the service of ideology, how refreshing.

Mike McMillan

If they had narrower tree rings, doesn’t that mean instead that it was colder?
MBH 98 said so.
How did this get past Professor Hughes?

Jim Masterson

>>
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 climate science, you always have to add a hat-tip AGW.
Jim

2kevin

It’s only a virtual sample extracted from the code at Real Climate.

Mike Davis

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!

Katherine

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.
Based on what reasoning? Naturally Routson needed that CYA statement to get past CAGW censors. After all, his research was funded by the NSF.

Brian H

And none of it has diddly to do with CO2. Climate sh** happens. The Windmill Gods won’t help you.

loren anderson

that doctoral candidate should be advised that Rio means River, thus there is no Rio Grande River.

Gail Combs

No mention of the Anasazi collapse of 800 years ago????
I am disappointed.

Chuck Nolan

MikeN says:
November 4, 2011 at 4:50 pm
This is in line with Mann’s statements that global warming would lead to more droughts and hurricanes in the Southwest.
———————
Mike, isn’t this like a “one for one” in that for every hurricane you get don’t you lose one drought?
It sounds like Dr. Mann is covering his ……………..bases.

North of 43 and south of 44

Latitude says:
November 4, 2011 at 4:42 pm
“Dendrochronology is a precise science of using annual growth rings of trees to understand climate in the past”
“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.”
===================================================
…or about a 100 years long period of below normal temperatures
http://www.drroyspencer.com/library/pics/2000-years-of-global-temperature.jpg
___________________________________________________________________
Or 100 years of lack of fertilizer from animals.

Nick Shaw

There is so much to take from every pithy comment so far!!!
How come the researchers didn’t make any connection between the Roman and Medieval Warm Periods to their drought induced tree rings (if it wasn’t cold, that is, that immediately followed!)? Why does it somehow indicate it has something to do with AGW or CO2 in the future when neither of those things were mitigating factors in the past?
Statements such as this just make me want to throttle somebody and yell into their faces, “Get a clue, dumbass!!”

peterhodges

I have tracked down a ream of papers on the local paleoclimate, all of which confirm these findings of droughts for the Southwest during the warm periods…the Medieval Optimum, the Roman Optimum, and the entire first half of the Holocene.
Here in the Eastern Sierra, there have been three major climate regimes in the recent past…the last glacial, the first half of the Holocene, and the present climate.
Although in the last ten years winter, spring, and fall temperatures have fallen 10F, and precipitation has increased ~150%. Summers have cooled a few degrees. If this weather becomes the new norm, I suspect the climate may shift to that of the previous glacial.
Wonder how long that takes?

MikeN,
yes, extreme weather events happened in the past and will probably happen again. Mann’s bloviating shows that he simply wants to try and assign blame to his preferred cause if one does happen in the near future!! Unfortunately he has no mechanism and no studies to back up his mouth.

“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.”

For more information about the societal effects of these droughts, I found a couple links that are well worth reading.
http://www.thefurtrapper.com/anasazi.htm : The unraveling of the Chaco society began with a drought in 1130 A.D. Lack of rain depleted the storehouses and made the farmers question the power of the Chaco priests. The Chaco Phenomena was over.
http://www.thefurtrapper.com/mesa_verde.htm : After 1150 A.D., the Mesa Verde area of the San Juan Basin had the largest number of people in the Southwest. Increases in the number of people in cliff dwellings reduced the inhabitant’s ability to raise enough agriculture products to feed themselves. Around 1276, a long drought began that continued until the end of the century. Even without a drought, trying to raise enough food on the mesas and getting water out of the canyons played a big part in the abandonment of the Four Corners area

Latitude

“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.”
========================================================
Unfortunately, It looks like they used the official UofArizona 2000 year temp reconstruction, which show the Mann hockey stick. Looking at that, they didn’t see anything in the temp record, so looked for something else…..and called it a 50 year drought….within a 100 year period of slower growth….
http://www.atmo.arizona.edu/students/courselinks/spring06/atmo336/lectures/sec5/2000_Year_Temperature_Comparison.png
If they had looked at other 2000 year temp reconstructions, they would have seen that 50 year low spike in temps…..
http://notrickszone.com/wp-content/uploads/2010/08/spencer1.jpg
So was it drought? cold temps? combination of both?………….we’ll never really know.
Dendrochronology is a precise science……………….

Ulric Lyons

“And the climatic events behind these previous dry periods are really similar to what we’re experiencing today.”
Far from it. From glacial advance in Sierra Nevada, and the Alps and Norway from the early 2nd century, you can be sure this was a cold period: http://www.geo.arizona.edu/palynology/geos462/holobib.html
As for the 12th century, there were very cold periods in the 1120`s, 1140`s and 1170`s, as can be seen in these English records:
http://booty.org.uk/booty.weather/climate/1100_1199.htm
and accounts from Syria:
http://syrcom.cua.edu/Hugoye/Vol3No2/HV3N2Morony.html

Barbara Skolaut

“It seems they also confirmed a drought in the medieval warm period in the 12th century.”
Would that be the Medieval Warm Period that supposedly never existed?
Did any heads explode while researching this? Inquiring minds, etc. . . .

DesertYote

This is new??? I guess when the propagandists whant to respin old knowledge to swerver there anti-human ends, they have to claim that it is new knowledge.

rbateman

Mike Davis says:
November 4, 2011 at 5:09 pm
They wasted more money because Cook and others already did that study, and found the Southwest Megadrought that extended clear into Mexico.
Not only that, but when you compare instrumental readings with tree rings from the same area, the temperature does NOT correlate well (it’s very poor), but does a much better job when compared to precipitation.
Still at it wasting taxpayer money, which NSF gets from the Fed. Govt.
When are these climate gurus going to get it that climate has 4 states, not 2?

Kevin MacDonald

Anthony Watts says:
“one wonders how such a thing could happens when CO2 was at “safe” levels”

Only if “one” believes that CO­² is the driver for all climate change events, which nobody does. Pointless straw man comments like that do nothing to help the tone of the debate.

davidmhoffer

Wait…
They found a drought in North America during the Medieval Warm Period using Bristle Cone Pines? Would that be the same MWP that Mann et al insist was localized to Europe?
Then, having offended the self appointed demi-g_ds of dendrochronology, who will no doubt demand the resignation of the journal the paper was published in for having failed to consult with “modellers” first, they then spew out this gem:
Dendrochronology is a precise science of using annual growth rings of trees to understand climate in the past.
OK, took me a bit to stop laughing. How they untangle temperature, sunlight, CO2 levels, rainfall, soil nutrients, passing fertilizer deposition bio-life forms (goats going poop) from each other from the tree ring data, I’m not certain. That it isn’t precise… of that I am certain.

1DandyTroll

Why is it that the MWP or RWP or what ever warm period couldn’t be a sign of global warming or cooling according to the hysterical climate-loons, what with global results are affected by, and wholly compiled by, local effects.
So why is it a big deal for the climate drones that there has been earlier warming that effects the global results if they want current weather events to effect the same global results?

Gary Pearse

It would have been nice if they could have found some air bubbles in pine gum or some such to measure co2. Can we say from ice cores of these periods or other evidence that co2 was well below todays? The trolls are telling us mann was saying the same thing about warm periods and hurricanes and droughts thinking with such non sequitors we wouldn’t notice that man-made co2 had nothing to do with this. The author also mentioned present warming without mentioning agw warming. Intentional?

Kevin MacDonald says:
“Only if ‘one’ believes that CO ² is the driver for all climate change events, which nobody does.”
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.

John F. Hultquist

“. . . has revealed a previously unknown multi-decade drought period in the second century A.D.
If this is so, then great! Thanks! We have new information. Someone will search all the literature and soon inform us that, indeed this is new – or not.
They should have stopped after stating their findings.
Consider that they and others are still trying to figure out what Earth’s climates have done in the past. They repeatedly find that it changes. This, then, “proves” to them that in the future those climates will change even more (for the worse) because of CO2. Did some places not have better or nicer climates at the same time their place had a drought? That seems to be the case today. Drought in the USA Southwest while the PNW does fine. And, as an example of things not so bad – the current drought in their region is occurring at the same time tropical storm activity (ACE)
http://policlimate.com/tropical/index.html
is low.
Climate is complex. The World is complex. Get used to it.

“The tiny hole left in the tree’s trunk quickly heals as the tree continues to grow.”
That is false!
Tree’s NEVER heal.They wall off the injury.To prevent decay from spreading.That is what tree’s do when they are injured.

davidmhoffer

“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.”
So… whatever the cause is now, it is similar to the cause back then?
Whew. For a moment I thought it was CO2 from human activity. We’re off the hook. Good to know.

Kevin MacDonald

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.

Jay Davis

“Dendrochronology is a precise science of using annual growth rings of trees to understand climate in the past.”
Who do these so-called scientists think they are fooling when they write such drivel? When I read this, the author lost all credibility. Tree rings merely show good growth years and not-so-good growth years. The whys and wherefores causing the difference in growth from year to year, such as moisture, temperature and nutrient availability, has to be determined from other sources. All I can say is that PhD’s are now coming in cereal boxes!

David A. Evans

Is growth even consistent around the trunk? If not, growth patterns would depend on where you [took] the core.
DaveE.

“We did a lot of hiking and found a couple of sites of bristlecone pines, and one in particular that we honed in on,”

Whoops! Hasn’t someone made that mistake before?
In any case, I always thought the science was settled that tree rings were a proxy for temperature? Is this no longer true? Can we bury the (broken) Hockey Stick at last, then?

Kevin MacDonald says:
November 4, 2011 at 6:29 pm

Anthony Watts says:
“one wonders how such a thing could happens when CO2 was at “safe” levels”

Only if “one” believes that CO­² is the driver for all climate change events, which nobody does. Pointless straw man comments like that do nothing to help the tone of the debate.

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? Methinks you are building your own ‘straw man’ and knocking it down when you say:

Only if “one” believes that CO­² is the driver for all climate change events, which nobody does.

You’re right, nobody does. What you failed to notice is that nobody claimed that anybody believed that either.
Right back ‘atcha!

davidmhoffer

Jay Davis;
Who do these so-called scientists think they are fooling when they write such drivel?>>>
Most of the people…. most of the time…

rbateman

“The tiny hole left in the tree’s trunk quickly heals as the tree continues to grow.”
I feel sorry for the trees that made it over a thousand years, only to have holes drilled in them.
They should put the core back where they found it after photo and measurements, sealing it up.
Someday, they will lament over the loss of the bristlecone pines that were savaged by armies of grant-hungy climate golddiggers.

I found this an interesting drought study right here in our Sierra Nevada back yard.
Duration and severity of Medieval drought in the Lake Tahoe Basin
J.A. Kleppea, D.S. Brothersb, G.M. Kentc, F. Biondid, S. Jensene, N.W. Driscollf
Abstract
Droughts in the western U.S. in the past 200 years are small compared to several megadroughts that occurred during Medieval times. We reconstruct duration and magnitude of extreme droughts in the northern Sierra Nevada from hydroclimatic conditions in Fallen Leaf Lake, California. Stands of submerged trees rooted in situ below the lake surface were imaged with sidescan sonar and radiocarbon analysis yields an age estimate of ∼1250 AD. Tree-ring records and submerged paleoshoreline geomorphology suggest a Medieval low-stand of Fallen Leaf Lake lasted more than 220 years. Over eighty more trees were found lying on the lake floor at various elevations above the paleoshoreline. Water-balance calculations suggest annual precipitation was less than 60% normal from late 10th century to early 13th century AD. Hence, the lake’s shoreline dropped 40–60 m below its modern elevation. Stands of pre-Medieval trees in this lake and in Lake Tahoe suggest the region experienced severe drought at least every 650–1150 years during the mid- and late-Holocene. These observations quantify paleo-precipitation and recurrence of prolonged drought in the northern Sierra Nevada.
Steve McIntyre also has some interesting observations on these underwater tree rings at Climate Audit: http://climateaudit.org/2006/12/06/underwater-in-the-sierra-nevadas/

barry

This is the reason that Mann says there was no Medieval Warm Period

Are you able to provide words to corroborate this, whether direct quotes from Michael Mann or from the body of words in any of his studies?

barry

Gary Pearse says,

It would have been nice if they could have found some air bubbles in pine gum or some such to measure co2. Can we say from ice cores of these periods or other evidence that co2 was well below todays?

Assuming local climate = global climate is a first order mistake of high magnitude.
Records collated from various sources including ice cores indicate that global atmospheric CO2 levels were relatively steady for most of the holocene and started rising significantly towards the end of the 19th century.

Kevin MacDonald says:
“CO² is the primary driver of the current warming, it does not follow that CO² is the primary driver of all historical warming events.”
So now it’s all different?? Clearly you have no understanding of the null hypothesis.
• • •
barry says:
November 4, 2011 at 8:53 pm [ … ]
barry me boy, Mann’s very own debunked MBH98 hokey stick chart attempted to erase the MWP and the LIA.

barry

Smokey, would you humour me with a no-dodge, straight-up, unadorned answer to a question?
What would you say is the period for the Medieval Warm Period? Start and end dates, roughly?
(If you answer this question, you will be the first skeptic I’ve ever seen to do so)

Chad Jessup

I and the farmers will commend them for at least sensibly using tree ring thickness as a proxy for precipitation instead of using it as an indication for temperature. The archeological record has a long history of pointing to drought conditions in the West during the MWP.
Anthony – keep up the humor. Most of us get it.

Don K

“barry me boy, Mann’s very own debunked MBH98 hokey stick chart attempted to erase the MWP and the LIA.”
I believe that the disappearance of the MWP and LIA was an unexpected consequence of the data handling that was, quite unfortunately, overlooked in the peer review of the Mann et al paper. My impression is that they have been trying to get the known history back without losing the hockey stick ever since.
The hockey stick thing reminds one a bit of the Millerites who were pretty numerous, very loud, and — based on unequivocal biblical evidence — predicted the end of the world sometime in 1843 http://en.wikipedia.org/wiki/Millerism I mean, who are you and I to argue with the Book of Daniel as interpreted by Bible scientists?

Bill Jamison

This research ties in well to tree ring records in the Sierra Nevada mountains of California that show the same thing – decades or even century long “mega droughts”.
There’s a really cool story about how a scientist found full rooted pine trees in a lake near Lake Tahoe. The fact that the trees were deep in the water and full rooted indicated that they were growing when a flood occurred. Basically a extremely wet winter filled up the lake and killed the trees. Other evidence of trees in the Truckee River supported the research.
There is also evidence of massive flooding in Southern California from atmospheric river events that easily dwarf any seen by man in the last 200 years.

old44

Hardly suprising to anyone who has read Roman history.

barry

Mann tried to get rid of the MWP and LIA? That’s the biggest lie in the whole debate, and easily verified by going to the study behind the TAR ‘hockey stick’.
MBH99:

…Our reconstruction thus supports the notion of relatively warm hemispheric conditions earlier in the millennium, while cooling following the 14th century could be viewed as the initial onset of the Little Ice Age

MBH98:

The long-term trends in the reconstructed annual mean NH series (Fig. 5b) are quite similar to those of decadal Northern Hemisphere summer temperature reconstructions6, showing pronounced cold periods during the mid-seventeenth and nineteenth centuries…

(Smokey, MBH98 only goes back as far as 1400AD. It doesn’t cover the MWP. MBH99 does. You keep mixing up the name of the studies. The so-called ‘iconic’ graph that appeared in the TAR is from MBH99, not 98 – check the links above)

rbateman says:
November 4, 2011 at 8:25 pm
“The tiny hole left in the tree’s trunk quickly heals as the tree continues to grow.”
I feel sorry for the trees that made it over a thousand years, only to have holes drilled in them.
They should put the core back where they found it after photo and measurements, sealing it up.
Someday, they will lament over the loss of the bristlecone pines that were savaged by armies of grant-hungy climate golddiggers.
==========================
Extremely WELL SAID!
Chris
Norfolk, VA, USA