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.
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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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You left out some important parts of what they had to say, but we’ll return to that issue later.
For now, tell us which of the regions you do acknowledge as equaling and/or exceeding HTM temperatures of the Present?
No response yet? Perhaps you need a little help. Looking at regions which were warmer than Present in the Holocene, we find a few regions. Let’s see…how about North America, South America, Greenland, the Arctic, Europe, Asia, North Africa, South Africa, Australia, New Zealand, South America, and the Antarctic? What else…the West Pacific, the Mediterranean, the Norwegian Sea?
To answer the question about the regions which had HTM temperatures, you needed to look no farther than the same report you quoted. Like a naked person avoiding an ivy patch, you keep dodging the more inconvenient things the same report has to say. For one example:
The implications from other examples of what this same report had to say are rather problematic for your assertions and the report’s own comments. Why, do you suppose, your quotation and others in the report create conflicts with the report’s own sources?
This is all irrelevant, nothing more than rhetorical posturing, we are discussing global temperatures, not regional ones, you are defending Smokey’s assertion that current global temperatures fall within the parameters of the Holocene, show me where this is true or concede the point.
Kevin MacDonald suffers from incurable cognitive dissonance – what George Orwell called “doublethink”. Temperatures during the Holocene have been much higher than present. And much lower, too. Currently we are near the middle of the range; not even close to the parameters. But MacDonald incredibly believes that we are now outside Holocene parameters.
No credible scientist disputes the fact that we are well within Holocene parameters. But Kevin MacDonald does. At WUWT we get to read what real climate scientists like Richard Lindzen and John Christy say. We also get to see what the nutcases say. Intelligent readers can sift the wheat from the chaff, and decide who is credible and who isn’t.
The one thing we can agree upon is that you are indeed attempting to use “irrelevant, nothing more than rhetorical posturing,” in the face of overwhelming evidence of HTM temperature in the early and mid-Holocene across every continent on the face of this planet. If you think not, then feel free to point to one or more continents where the temperatures did not remain 0.5C to 2C or more greater than the Present. The question of whether or not these regional HTM temperatures were or were not truly HTM in a global average earlier in the Holocene depends upon the reliability of the regional datasets. Yet you are trying desperately to avoid a discussion of their reliability by the self-serving declaration that it is all “irrelevant” and “rhetorical” in their significance. Nothing could be further from the truth, of course, because any putative global average is composed of a number of lesser regional and local temperatures. You are in effect saying the data is irrelevant in the face of interpretive and subjective rhetoric in the AR4 report, which is totally backwards from reality.
Now, please be kind enough to state exactly which of the regional and/or local temperature dataasets used to compile the supposed global average temperature which were NOT HTM temperatures during the Holocene, and cite each source of that dataset. We need to see whether or not we can agree upon the quantitative values of the temperatures and the means by which they were determined.
Yet [you’re] are unable to point to a period during the Holocene globally warmer than the current era.
Yeah, but you’re still citing regional variations despite the fact we’re discussing global ones, its like you’re addicted to straw man fallacies.
At the moment, we are discussing the source you cited as alleged support for your argument and what it had to say about the regional components it used to compile an overall global average. Nearly every regional component your source used to compile the global average temperature was a HTM temperature. They represented every continent on the planet. Since you are relying upon a statement claiming the overall global average is not HTM, we need to see which of the regional components used to compute the average we can agree upon as being less than HTM. Since you refuse to identify this evidence, it appears that you must not understand the evidence of your own source citation and/or fear it cannot withstand any scrutiny.
The following charts are not intended for Kevin MacDonald. Kevin has cognitive dissonance and he will never agree with any facts that contradict his belief system. But for those who might still wonder if the MWP was global, these charts tell the story.
First, there is plenty of evidence from both the Northern Hemisphere and the Southern Hemisphere showing that the planet warmed and cooled concurrently and therefore globally:
click1
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click3
Both hemispheres show simultaneous major warming and cooling events, indicating that the events were truly global in extent.
Various locations showing temperature parameters:
click1
click2
click3
click4
click5
click6
click7
click8
click9
click10
click11
click12
click13
The belief that today is warmer than the MWP is based on tree ring proxies. However, tree rings are not very good at determining past temperatures [not to mention the shenanigans that Mann and Briffa engaged in by cherry-picking a small subset of available tree ring proxies; when the entire set is used along with the proper statistical methodology, the hockey stick shape entirely disappears]. Tree ring growth is correlated much more closely to CO2 than to temperature.
Finally, it must be repeated that the planet is emerging from the Little Ice Age along the same trend line. There has been no acceleration of the very *mild* upward trend, despite a 40% increase in [harmless, beneficial] CO2.
Conclusion: CO2 has little if any effect on temperature, and the demonization of “carbon” is simply a nefarious ploy to extract more taxes from the populace based on a thoroughly debunked belief system.
These particular IPCC reports are based upon certain papers, and those papers rely upon assumptions and conclusions based upon imaginary data substituted for absent observations of proxy temperatures. It is another example of circular citations vouching for each other using reconstruction modeling lacking key empirical observations. You can be confident to a sigma 5 level that Kevin MacDonald can neither undeerstand or acknowledge the fallacies in his claimed sources of authority.
Again, you are evading the question. We are debating the question of whether or not your own examples are just such evidence. Your own sources indicate that every continent of the planet experienced HTM temperatures during the Holocene. It is now up to you to explain how it is possible for every continent to experience HTM temperatures in your source/s without them adding up to an average global temperature which is also HTM. Obviously, you can make a number of arguments about timing and other issues which have a potential for supporting your assertions, but we need to see you actually make those arguments and support them with the observational evidence. Otherwise, any claims about the global average temperature not being HTM is a claim lacking observational evidence. Fair warning: the sources you may choose to rely upon may be false and unreliable.
Smokey and D. Patterson say:
“Yet more irrelevant straw man fallacies about globally asychronous regional temperature variations”
I’m paraphrasing, but you get the gist. None of Smokey’s links show a time where the Holocene showed globally sychronous temperatures as warm as current temperatures, unless you can provide this evidence you can’t argue that current global temperatures fall within the parameters of the Holocene.
Kevin MacDonald is a textbook example of cognitive dissonance. I have literally thousands of charts, graphs and peer reviewed citations showing the various warming episodes during the Holocene. Temperatures have been gradually declining since the beginning of the Holocene. The charts and citations I’ve posted throughout this thread and others show that all regions of the planet experienced a MWP that was at least as warm as current temperatures, and most probably warmer.
Prior global warming episodes were certainly even warmer than the MWP. No credible scientist disputes that fact. During those warmer events, CO2 remained quite low, negating the belief that CO2 causes global warming. It may cause minuscule added warmth, but the amount is insignificant and can be completely disregarded for all practical purposes.
But someone afflicted with cognitive dissonance cannot agree with even one of the many charts and graphs I’ve posted, as Kevin MacDonald’s comment above demonstrates. If he agreed with even one chart, his carefully constructed belief system would come crashing down, causing him extreme discomfort and disharmony. That must be avoided at all cost, therefore, Kevin has no choice in the matter. He simply must reject out of hand any and all facts which contradict his catastrophic global warming belief system.
Fortunately, scientific skeptics are largely immune from cognitive dissonance because we are just saying, “Prove it.” Provide solid empirical evidence that CO2 will cause runaway global warming and climate disruption. But there is no such evidence. None at all. There are only always-inaccurate computer models, which the real world is falsifying.
We do “get the gist” of the false arguments you copied from the Grist. We also see how your own source citations from AR3 confirmed the Early and Mid-Holocene generally had HTM global temperatures and as synchronous as any set of average global temperatures ever can be. When you then tried to use the interpretative statements in AR4 to deny a synchronous global average temperature in direct contradiction to the evidence in its own data sources, we offered you every opportunity to defend those false interpreations. Since you refuse to be responsive to the questions regarding the apparent invalidity of the AR4 interpretive statements regarding the Holocene temperatures, we can only conclude you must be avoiding the need to acknowledge that you are incapable of defending the false statements made in AR4 and by you. Nonetheless, you can take this one last chance to defend those false statements, before we perforce must conclude you are only trolling and propagandizing this blog with no genuine intent to engage in a genuine sientific debate.
Your own data sources indicate HTM temperatures in their datasets for each of the continents. Each of these datasets has a certain amount of temporal overlap within the Holocene time period, which varies according to your cited authorities versus other authorities. Depending on the source/s used and their reported time periods for the datasets, most or all of the validated datasets indicate periods in the Holocene when the HTM were likely to be globally synchronous. In other words, your own cited sources, despite interpretive comments to the contrary, tend to indicate in each of the data sources that the Early Holocene to Mid-Holocene generally experienced HTM temperatures, and those HTM temperatures were often nearly globally synchronous or fully globall synchronous for periods of hundreds to thousands of years.
You are free to attempt to show the readers which coring datasets provided by your sources demonstrate a failure to reach HTM temperatures in its region and in the resulting synchronous global average. You won’t, of course, because you cannot. What you do not want the readers to learn is the failure of your sources to actually make an observation of the temperatures for some of critical the regions they used in compiling the fabricated global average you are referencing in AR4. Before you attempt to deny or simply ignore this information, show us what your sources have to say about the Early Holocene and Mid-Holocene SST for Marsden Square 317. Otherwise, you’ll be dismissed as just another drive by troller looking to disrupt a blog, rather than engage in an honest scientific debate.
Naturally, if you cannot or will not supply the Early to Mid-Holocene SST reported by your sources for Marsden Square 317, you would have absolutely no means of knowing the SST was low enough to make the global average temperature not HTM temperatures.
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