Old trees reveal Late Antique Little Ice Age around 1,500 years ago led to famine and social upheavals

From the Swiss Federal Research Institute WSL: Tree-ring measurements have revealed a period of extreme cold in Eurasia between 536 and around 660 CE. It coincides strikingly with the Justinian plague, migrations of peoples and political turmoil in both Europe and Asia, reports an interdisciplinary team, led by the Swiss Federal Research Institute WSL and the Oeschger-Zentrum of the University of Bern, in the journal Nature Geoscience.

New tree-ring width measurements from the Russian Altai mountains indicate a drastic cold period 1,500 years ago. Credit: Vladimir S. Myglan
New tree-ring width measurements from the Russian Altai mountains indicate a drastic cold period 1,500 years ago. Credit: Vladimir S. Myglan

WSL dendroclimatologist Ulf Büntgen and his fellow researchers were able for the first time to precisely reconstruct the summer temperatures in central Asia for the past 2,000 years. This was made possible by new tree-ring measurements from the Altai mountains in Russia. The results complement the climatological history of the European Alps, stretching back 2,500 years, that Büntgen and collaborators published in 2011 in the journal Science. “The course temperatures took in the Altai mountains corresponds remarkably well to what we found for the Alps,” says Büntgen. The combined findings allow for the first time to infer summer temperatures for large parts of Eurasia over the past two millennia.

Tree-ring widths in old trees reflect the summer climate in any given year in the past. Looking at these, the researchers were particularly struck by a cold phase in the 6th century. It exhibited even lower temperatures, longer duration and larger expanse than the temperature drops in the Little Ice Age (13th to 19th centuries CE). “This was the most dramatic cooling in the Northern Hemisphere in the past 2,000 years,” explains Büntgen.

The "Late Antique Little Ice Age" (LALIA) started 536 CE. The temperature drop stands out clearly in the reconstructed summer temperatures (blue shading left). (Graphic: Ulf Büntgen)
The “Late Antique Little Ice Age” (LALIA) started 536 CE. The temperature drop stands out clearly in the reconstructed summer temperatures (blue shading left). (Graphic: Ulf Büntgen)

Climate and culture

In light of this, the researchers refer to the period from 536 to around 660 CE for the first time as the “Late Antique Little Ice Age” (LALIA). This was triggered by three major volcanic eruptions in 536, 540 and 547 CE[1], whose climatic impact was prolonged further by the retardant effect of the oceans and a minimum in solar activity.

According to the team of naturalists, historians and linguists, this period bore witness to a whole series of social upheavals. After famine, the Justinian plague established itself between 541 and 543 CE, killing millions of people in the centuries that followed and possibly contributing to the decline of the Eastern Roman Empire.


Proto-Slavic-speaking people migrated, supposedly from the Carpathian region, into the eastern areas of modern-day Europe that had been abandoned by the Romans, thereby forming the Slavic language area. According to the researchers, this period of cool temperatures may also have fostered the expansion of the Arab Empire in the Middle East. The Arabian Peninsula received more rain, growing more vegetation, which may have sustained larger herds of camels used by the Arab armies for their campaigns.

In cooler areas, various peoples also migrated east towards China, maybe driven away by a lack of pastureland in central Asia. As a result, hostilities broke out in the steppe regions of northern China between nomadic groups and the local ruling powers. Subsequently, an alliance between these steppe populations and the Eastern Romans conquered the Sasanian Empire in Persia, leading to its collapse.

Major plague outbreaks, rising and falling empires, large-scale human migrations, and political turmoil (Horizontal bars, shadings and stars) coincide with the coldest decades of the last 2,000 years, the LALIA (blue lines).
Major plague outbreaks, rising and falling empires, large-scale human migrations, and political turmoil (Horizontal bars, shadings and stars) coincide with the coldest decades of the last 2,000 years, the LALIA (blue lines).

Strategies for modern-day climate change

While the researchers stress, however, that potential links between this period of cool temperatures and socio-political changes always need to be treated with great caution, they write that “the LALIA fits in well with the main transformative events that occurred in Eurasia during that time”.

Ulf Büntgen points out that their study serves as an example of how sudden climatological shifts can change existing political systems: “We can learn something from the speed and scale of the transformations that took place at that time,” he says. Knowledge about the effects of past climatic fluctuations could maybe contribute to developing strategies how to deal with modern climate change.

Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD

Ulf Büntgen,Vladimir S. Myglan,Fredrik Charpentier Ljungqvist,Michael McCormick,Nicola Di Cosmo,Michael Sigl,Johann Jungclaus,Sebastian Wagner,Paul J. Krusic,Jan Esper,Jed O. Kaplan,Michiel A. C. de Vaan,Jürg Luterbacher,Lukas Wacker,Willy Tegel& Alexander V. Kirdyanov

Climatic changes during the first half of the Common Era have been suggested to play a role in societal reorganizations in Europe1, 2 and Asia3, 4. In particular, the sixth century coincides with rising and falling civilizations1, 2, 3, 4, 5, 6, pandemics7, 8, human migration and political turmoil8, 9,10, 11, 12, 13. Our understanding of the magnitude and spatial extent as well as the possible causes and concurrences of climate change during this period is, however, still limited. Here we use tree-ring chronologies from the Russian Altai and European Alps to reconstruct summer temperatures over the past two millennia. We find an unprecedented, long-lasting and spatially synchronized cooling following a cluster of large volcanic eruptions in 536, 540 and 547 AD (ref. 14), which was probably sustained by ocean and sea-ice feedbacks15, 16, as well as a solar minimum17. We thus identify the interval from 536 to about 660AD as the Late Antique Little Ice Age. Spanning most of the Northern Hemisphere, we suggest that this cold phase be considered as an additional environmental factor contributing to the establishment of the Justinian plague7, 8, transformation of the eastern Roman Empire and collapse of the Sasanian Empire1, 2, 5, movements out of the Asian steppe and Arabian Peninsula8, 11, 12, spread of Slavic-speaking peoples9, 10 and political upheavals in China13.


h/t to Wim Rost

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Don B
February 16, 2016 4:53 am

A scientific void has been created by the irrational fear of carbon dioxide, and the funding of any study which is alarmist. Natural variability dominates. Congratulations to these authors.

February 16, 2016 4:59 am

Funny, but most of the tree growth I see in my backyard occurs in spring when conditions are relatively cool and moist. In the summer when it is hot and rainfall is at a minimum, the trees stop growing.
Could it be that what the trees are actually measuring is rainfall?

John Silver
Reply to  ferdberple
February 16, 2016 5:27 am

Neither, it’s sunshine, photons.


Reply to  John Silver
February 16, 2016 6:57 am

no it aint just photons, not by a long shot.

Reply to  John Silver
February 16, 2016 12:34 pm

Seen a tree grow in the desert or semi arid areas without water?

Reply to  John Silver
February 16, 2016 5:29 pm

Low temperature & higher CO2 (presumably in this case from volcanic eruptions) independently or together lead to less growth in C3 plants. Starch (not storage root “storage” starch) is normally made in chloroplasts (stroma) & held between thylakoids. It is meant to be used during the dark period for growth & “respiration”. Furthermore, if the days’ light is also limited (from volcanic ash) little starch is being made & that compounds the issue of little plant growth.
When temperature is low starch piles up inside leaves & high CO2 intself inclines the leaves to hod onto starch instead of allowing that starch to be utilized. Sugar (sycrose) is made in the C3 plant leaf cell’s cytosol & is meant to get shuttled into phloem for distribution in a matter of minutes. However, cool growing plant organs (buds & shoots) don’t act as the normal “sink” for sucrose; so that sucrose builds up in the leaf (“source”). If a leaf is thin then the impact of temperature on it is greater than a comparable thick C3 leaf.
Cold & elevated CO2 in the leaf increase carbohydrate levels in the leaf. Glucose molecules (of the sucrose) are the principal sugar that triggers regulation of levels of nuclear (& plastid) genes’ expression integral to the building of a leaf’s system of photosynthesis. A little sugar stimulates those genes (ex: increases Rubisco enzyme small subunit & up-regulates synthesis of the translocator of triose-phosphate), while over-abundance of sugar inhibits relevant genes. Hexokinase is the sugar sensor in this relationship & when sucrose is not shuffled out into phloem more of the leaf sucrose gets shunted to the vacuole where it is made into hexose.
Cold soil restricts phosphorus mobilization in the soil for root uptake & phosphorus (likewise nitrogen) deficiency provokes a dynamic that keeps sucrose being sent out to the phloem. If the leaf can not export triose-phosphate from the chloroplast this leads to more starch being held between thylakoids. Meanwhile a phosphorus (inorganic) deficiency does not allow photosynthesis to be sustained at it’s ideal rate &, even though low phosphorus is capable of facilitating the fixation of CO2, the leaf can not make enough starch to be used for growth.
Under low phosphorus conditions there is less ATP & then less of the precusor molecules that are intermediary stages for making starch are also fewer. It is the production of NADPH & ATP being made that is the regulator of actual assimilation of CO2 & not electrons (from light photons) being moved; depressed ATP leads to less regeneration of RUBP even though electrons still are moved along. Low phosphorus leads to less Rubisco enzyme action & thus integration of CO2 into plant goes down; leaf can have enough RUBP but if Rubisco enzyme levels low the CO2 inside that leaf can not be optimally processed.
Cold soil also restricts water movement & once CO2 incorporation slows with less that optimal water content in the plant electrons (from light photons) are still being shuttled (electron transport). But this keeps generating NADP+ which shifts the ratio of NADPH in chloroplasts to increase relative to the produced amount of ATP in chloroplasts. Downstream this aberation of NADPH:ATP ratio instigates senescence (age, lose cell division) in the leaf in reaction to adverse metabolites (ex: abscisic acid, proline) that are generated by that skewed ratio & then that leaf can’t contribute as much toward growth.
If plant has insufficient water the leaf stomata pores close under the influence of phyto-hormone abscisic acid & then less CO2 enters that leaf. I don’t know if the volcanic spike in CO2 was prolonged enough to cause the typical ice age change of reduced stomata density per area on a leaf, but that is another feature of elevated CO2. There is a typical seasonal variation of CO2 in the atmosphere but water is more of a growth rate limiter than carbon or light (good soil moisture, decent light & high humidity see little water going out of the plant & lots of CO2 coming in through open stomata creating a high photosynthesis rate).
When full on photosynthesis is occuring the amount of CO2 available becomes relevant & the number of stomata per leaf area factors into the amount of CO2 incorporated. Once light (photon) intensity rises all those electrons moved need to be matched with the complementary leaf enzyme systems in order to properly utilize the NADPH/ATP if the there are to be no side effects. Thus, insufficient nitrogen that leads to low numbers of Rubisco enzymes & also holds back that enzyme’s activity level can limit growth; the more adequate level of nitrogen in a leaf the more CO2 moves through the mesophyll toward the Rubisco enzyme.
Temperature impacts what are called dark & also day respiration; while temperature & internal pressure (partial pressure) of both CO2 & O2 both impact the process of photo-respiration. Most of in-the-dark leaf respiration (frees up CO2) is via mitochondria & once a leaf has loaded up with carbohydrates (ex: starch) each additional temperature rise for that leaf allows +/- 2 times more dark respiration; which in that cold period probably was uncommon on summer nights & another factor holding down growth.
Probably what let growth go forward in that cold was the fact that since rises in temperature cause less O2 solublity than CO2 solubility inside a leaf the ratio of O2 to CO2 was not going up (as it does in our warm summer growing season). On the other hand rising pH has no affect on O2 solubility but in contrast CO2 is more soluble inside the leaf as pH rises; thus any increase in pH augments the ratio of CO2 in relation to O2 inside the chloroplast stroma. Unlike the air, where these gasses mix, in between the cell spaces they move via diffussion. When a C3 leaf has high CO2 internal (partial) pressure (or at least low O2 partial pressure) then the wasting of CO2 plant managed to take in through the process called photo-respiration (common in our hot summer afternoons) does not go on. When photo-respiration is not going on then a C3 leaf doesn’t need ~ 20-25 photons to definatively assimilate one Mole of CO2 but only ~ 12-14 photons to get the same carbon mass – & I propose this is may also have been another factor contributing to plant growth despite what was a challenging frigid environment.

Tim Hammond
Reply to  John Silver
February 17, 2016 2:04 am

Photosynthesis requires water. The photons are used to split H2O to make sugars. No water, and photosynthesis cannot happen.

Reply to  John Silver
February 17, 2016 10:32 am

CO2+ H20+ photons = CH4 + O2
theres water involved in this whole thing called photosynthesis, you know…..

Reply to  ferdberple
February 16, 2016 7:42 am

ferdberple, the spring tree growth is mostly due to energy storage from the previous, entire warm season. So even if good spring growth occurs, if that summer experiences a drought, the next spring will have reduced growth.

Reply to  beng135
February 16, 2016 7:48 am

Posted too quick, ferdberple. So I’d agree w/you mostly — it is prb’ly mostly a measure of rain. But just to add, photosynthesis (and summer energy storage) does best w/optimal temps — colder than avg temps will reduce it (but then hotter than avg temps will too). So overall it’s darn hard to tell…..

Reply to  beng135
February 16, 2016 9:40 am

There is no one magic input.
Plants have an optimal growth rate. ANY shortage of ANY input slows growth from that point.
Sun, rain, nitrogen, phosphorus, heat, etc, etc, ANY ONE may be what is measured,
THE dominant nitrogen source in Pacific north west forests is salmon via bear feeding. Poor salmon season means less bear poo and less growth… as just one ignored example.
Then again, when rain and weather are good you do get more salmon… so bear poo as weather proxy might actually work…

Reply to  beng135
February 16, 2016 11:58 am

E.M. Smith,
Can you explain how more rain equals more salmon?
It would seem that high rainfalls would increase river flow which would make it harder for the salmon to swim upstream to spawn.

Gunga Din
Reply to  beng135
February 16, 2016 2:47 pm

There are lots of things involved with the growth of any plant. Nitrogen, phosphorus, water, light, CO2, temperature, etc. A shortage of any one will hinder it’s growth.
The width of a tree ring needs corroborating evidence, lots of it probably, to pin the cause down to one thing.
What is often ignored in past climate studies is the written historical records.
(What Mann and his hockey fans have chosen to ignore.)

Reply to  beng135
February 16, 2016 6:34 pm

@ beng 135, I agree with you but if the previous year was a poor “storage” year that would then show up the next summer with limited growth, so maybe the results should be moved to the next year?

February 16, 2016 5:02 am

That era is called ‘The DARK Age’.

February 16, 2016 5:03 am

I have read other articles over the years that said the sun did not cast a shadow for 18 months in Rome in 546-547. That was probably due to volcanic aerosols. That would also line up chronologically as a Bond event and was 1470 years ago.

February 16, 2016 5:04 am

That graph looks a bit wrong to me, where is MWP anyway, the LIA and current temps are out of proportion.
Having said that, my own distant ancestors around 600 AD started exodus from N.E Poland to the South of Europe to settle some 100 years later in the Roman Empire lands along warm Adriatic sea.
PS. There are some severe problems with LIGO paper, we do not need ‘ligogate’ and I hope that it turns out to be OK after all, but detailed explanations are required.

Reply to  vukcevic
February 16, 2016 5:18 am

Now you’ve done it ! lsvalgaard is going to come and attack everybody here…again !

Reply to  vukcevic
February 16, 2016 5:23 am

The graph also looks wrong to me. The obvious suspect is “calibration”. The mathematically incorrect procedure common to dendroclimatology, of selecting on the dependent variable.
Tree ring calibration has the effect of amplifying false positives, flattening the shape of the curve outside the calibration period, and falsely improving the calculated accuracy of the result. This leads to the classic hockey stick shape.
True calibration relies upon controlling all other variables during the calibration period. Something that is impossible for tree rings.

Reply to  vukcevic
February 16, 2016 5:33 am

We don’t need a Vukgate either. If you don’t take the trouble to read what they say, they owe you nothing.

Reply to  vukcevic
February 16, 2016 5:34 am

The MWP – if you can find it – is called the Medieval Climate Anomaly. See the current discussions at Climate Audit about flattened MWPs.
Clearly, calling it a Warm Period was against the researchers’ religion.
Find it difficult to work out what is so ‘anomalous’ about it, at least as they graph it here.

Reply to  vukcevic
February 16, 2016 6:38 am

DIdn’t Mikey resort to series concatenation as the rings diverged from temperature in the 1960s?

Reply to  skeohane
February 16, 2016 6:53 am

Tree rings are water/sun/INSECT INVASION guide. Not temperature.
One year not too long ago in NY we had a classic sudden insect invasion whereby the caterpillars ate all the leaves! I own a forest. It was decimated. The trees recovered but the rings on that year were very small, little growth. A super cold winter can be followed by a pleasant summer.
The trees have zero growth in winter but lots in summer. If the winter is cold and the summer is dry,the rings are also small.

Reply to  skeohane
February 16, 2016 8:49 am

I know the rings are not a proxy for temperature, I was just alluding to the ‘Hide the Decline’ situation Mikey found himself in when his proxy-rings showed cooling in the 60s.

Robert B
Reply to  skeohane
February 16, 2016 8:34 pm

I thought the same thing but that may yet happen. Notice that the Alp data shows significant cooling since 1940 and then only enough warming to be equal with the blip. After all the extra CO2 to boot.
Its a proxy of summer growing season so that the two areas line up for the period suggests widespread drought, volcanic activity or pest. Locust plagues were associated with disease and there was a major eruption in about 530-540. https://en.wikipedia.org/wiki/Extreme_weather_events_of_535%E2%80%93536
There only seems to be a short period of slow growth the corresponds to other eruptions, so bad timing of one or two those three could have happened. Locusts come out after drought and diseases like the bubonic plague (Justinian plague of the time) occur after locust plagues because of the abundant feed for rats.

Reply to  vukcevic
February 16, 2016 6:55 am

These are just proxy temps taken from a species of tree rings in the Altai Mountains of Mongolia. There’s a lot of questions this article didn’t address, such as the exact location of the ring samples, whether the dendros used PCAs to come up with their proxies, and how the tree rings were calibrated with locally derived thermometer temp reading, can these trees also be used as precipitation proxies, etc…
Not every locally derived temp proxy is going to match the global temp trends exactly. Local conditions can overwhelm any global signal.

Reply to  JP
February 16, 2016 1:14 pm

Plus several.
A concise explanation of potential (at least) problems with this article.
Whilst the Volkerwanderungs [Volkerwanderungen?] are [tolerably] well-known, the rings in question cannot be simply characterised as s o l e l y temperature-defined. See many posts above.
Was there temperature variation? Surely.
And the vulcanism may have been a major source [even t h e major source!].

February 16, 2016 5:17 am

” Knowledge about the effects of past climatic fluctuations could maybe contribute to developing strategies how to deal with modern climate change. ”
But, but…..I thought the climate has always been like yesterday !! LOL

Reply to  Marcus
February 16, 2016 5:43 am

1 million new climate refugees are headed for Germany this summer to help celebrate Groperfest 2016. German authorities are right on top of the problem, silencing news reports and arresting anyone seen protesting. Anything less would be culturally insensitive to the needs of the refugees to feel themselves a German.

Reply to  ferdberple
February 16, 2016 5:48 am

..I guess something got mixed up in the translations ? …. Or it could be that their culture just sucks compared to the civilized world !

Reply to  ferdberple
February 16, 2016 11:32 am

Satire, Marcus. Satire.

Gunga Din
Reply to  ferdberple
February 16, 2016 2:52 pm

Mike Jonas,
“Satyr”? Are talking about Al Gore or Bill Clinton? 😎

February 16, 2016 5:25 am

Interesting study, although the sourcing of the graphs could be better described, as other post 1950 tree rings suggest temperature declines iirc.
Note that the two graphs in the second table refer to Central Asia tree ring and Swiss tree ring records respectively.
The study makes much of volcanic forcings, something that other studies have raised doubt about.
Imho, the most provocative aspect of their graph is the very sharp drop around 160AD, which seems to be the deepest in the entire period. There are decent historical records from that era, so it would add credibility to the study if this excursion was in fact noted by its contemporaries.

Phil C
Reply to  etudiant
February 16, 2016 6:59 am

The Hatepe, or Taupe, eruption in New Zealand occurred in 180 AD(anywhere from 130 to 230 depending on whose radiocarbon dating is used. There are records(Fan Ye in China and Herodian in Rome)described strange weather and climate in 186AD. Given the variance in dates and uncertainties in tree ring dating along with a seeming lack of other contemporary descriptions it’s hard to pin down exact dates.
Suffice to say, any sharp downwards spikes in a temperature record are very likely to be due to volcanoes. There are many descriptions of widespread disruption of the climate from volcanoes.

Tom Halla
February 16, 2016 5:40 am

The Midieval Warm looks too cold in the charts, as the Norse were farming in
Greenland, something not currently possible, so that would imply that period was warmer than the recent history. The problem seems to be an inability to determine abolute temperature, rather than a decline relative to adjacent temperatures.

Tom Halla
Reply to  Tom Halla
February 16, 2016 5:43 am

“Medieval” i mean.

Reply to  Tom Halla
February 16, 2016 1:22 pm

Surely the Greenland farmers were post 950 AD – through to perhaps 1300-ish?
That period – for the Alps and Altai – does look cool – perhaps regional variation?
Perhaps differing variables – water, warmth, parasites, predation [is that the word for things eating plants (rather than animals)?] , etc.

February 16, 2016 5:43 am

Anyone who thinks dendroclimatology provides reliable indications of past temperatures is deluded.

Reply to  richardscourtney
February 16, 2016 5:50 am

+ 1,000

Reply to  richardscourtney
February 16, 2016 6:32 am

Either that or they are seeking a grant to prove that CO2 is bad and thus coal must be banned, which would go a long way towards solving the current glut in oil supply.
Once coal is outlawed, oil and gas will be the only remaining reliable energy source. Anyone that thinks CO2 is the world’s greatest danger hasn’t studied history. Get in bed with your enemies for oil, you will get screwed in the end.

Reply to  ferdberple
February 16, 2016 1:24 pm

Nuclear, where permitted, is also pretty reliable, if qualified, trained, experienced, well-motivated [etc.] staff are used.

Walt D.
Reply to  richardscourtney
February 16, 2016 6:59 am

It would appear that looking at trees from 1000 years ago, that there would be a strong survivor bias. What about all the other trees that were alive 1000 years ago but have since died?

Jay Hope
Reply to  richardscourtney
February 16, 2016 7:32 am


Reply to  Jay Hope
February 16, 2016 8:43 am

Jay Hope:
Yes, really.
Anyone who thinks dendroclimatology provides reliable indications of past temperatures is deluded.
Dendrochronology works because many variables affect tree ring growth. These include water supply, light supply, nutrient supply and etc..
Dendroclimatology assumes temperature during the growing season overwhelms all the other variables which affect tree ring growth. The assumption is known to be wrong because it is observed that dendrochronology works.

Bruce Cobb
February 16, 2016 5:54 am

I see the de rigueur attempted linking between natural climate change and today’s funding-inspired politically and sociologically forced idea of “climate change”. Too bad. In the bin it goes.

February 16, 2016 6:07 am

competition between trees has a huge effect on growth rates. you cannot compare today’s tree rings to tree rings from 1000 years ago and assume the temperatures are the same if the tree rings are the same.
A tree in a dense forest will grow slower than a tree in a clearing, given identical temperatures and soil conditions. Yet the tree rings will report different temperatures.
one might as well compare human skeletons from 1000 years ago with todays skeletons, and assume that if they are the same height they grew up in places with the same climate. The Tutsi and the Pygmy clearly cannot have both come from Africa. The Tutsi are tall because they are native to Africa. The Pygmy are short because they developed somewhere cold and later migrated to Africa to escape the cold. The original climate refugees.
On just such flimsy reasoning dendroclimatology was born.

February 16, 2016 6:11 am

“the researchers stress, however, that potential links between this period of cool temperatures and socio-political changes always need to be treated with great caution”
History shows that any sustained change in local climate is ALWAYS followed by socio-political changes & often migrations.
Famine will drive you further than gunpowder will throw you

Bruce Cobb
February 16, 2016 6:16 am

They started off with trees, and wound up with….a hockey stick.
Go figure.

R Shearer
February 16, 2016 6:43 am

Might a 0.8C higher average temperature and 15% or so increase in crop yields have been beneficial?

February 16, 2016 6:44 am

All this is hardly new, Y’all will enjoy David Keys book “Catastrophe ” an investigation into the origins of the modern world . Ballantine Books 1999

Sweet Old Bob
February 16, 2016 6:58 am

“Were able to precisely reconstruct summer temperatures “……!!! BS !!! I doubt they can PRECISELY measure ” summer temperatures ” there now !

Reply to  Sweet Old Bob
February 16, 2016 1:35 pm

+ lots

Gloateus Maximus
February 16, 2016 7:08 am

The Dark Ages Cold Period is well documented globally, not just from tree rings but ice and sediment cores and caves, among other paleoclimatic proxy data. AD 536 was especially cold.
Various causes have been hypothesized, but the strongest support is for depressed solar activity, same as for preceding and subsequent cool intervals, like the LIA.

Reply to  Gloateus Maximus
February 16, 2016 8:30 am

For eyewitness accounts of the obviously volcanic events of 535 see

Gloateus Maximus
Reply to  Dr Norman Page
February 16, 2016 8:50 am

Dr. P,
The Dark Ages Cold Period wasn’t triggered by an AD 535 eruption. Its effects were perhaps made worse by occurring during a preexisting cold period, as was the case with the eruption of Tambora during the Dalton Minimum in 1815.
The DACP is generally dated AD 450-950, although those aren’t hard and fast dates. Some date the onset of persistent cold to AD 250, such that the period has also been associated with the barbarian invasions of the Roman Empire and Folk Wanderings, extending into the pagan Norse descents on Europe.
IMO, by AD 900, the Medieval warming was already under way, which permitted the Norse to colonize Greenland from c. AD 1000.
The cold periods occurred between the named warm periods:
Holocene Climatic Optimum: ended c. 5000 years ago
Cold Period: c. 4500 years ago (various names)
Egyptian WP: centered c. 4000 years ago
CP: c. 3500 years ago (various names)
Minoan WP: c. 3000 years ago (not well named)
Greek Dark Ages CP: c. 2500 years ago
Roman WP: c. 2000 years ago
Dark Ages CP: c. 1500 years ago
Medieval WP: c. 1000 years ago
Little Ice Age CP: c. 500 years ago (depths during Maunder Minimum, 355-305 ya)
Modern WP: now.
Peak heat for each of the WPs since the Minoan has been cooler than for the preceding period.

Reply to  Gloateus Maximus
February 16, 2016 4:24 pm

The deepest drop on the JG/U tree ring study occurs around 530 AD. It looks like it lasts for around 20 years, afterwards….https://www.sciencedaily.com/releases/2012/07/120709092606.htm

Proud Skeptic
Reply to  Gloateus Maximus
February 16, 2016 6:55 pm

I have no problem with inferring from various proxy measurements that one period may have been warmer or colder than another. It’s when these folks start pretending that they can extrapolate these proxy data into an aerage global temperature measured to a half a degree that I start to roll my eyes.

Reply to  Gloateus Maximus
February 17, 2016 8:15 pm

I’m with Gloateus, its most likely the 1470 year climate cycle. Are we there yet?

FJ Shepherd
February 16, 2016 7:22 am

I am naturally skeptical of using tree rings as a way of determining past temperatures. Perhaps it is because of Michael Mann, his hockey stick graph, and the Yamal Peninsula:

Proud Skeptic
February 16, 2016 7:43 am

“WSL dendroclimatologist Ulf Büntgen and his fellow researchers were able for the first time to precisely reconstruct the summer temperatures in central Asia for the past 2,000 years.”
This is sloppy language. They were able to precisely measure the things that are believed to be an indicator of summer temperatures. Tree rings record growth. The growth is a result of several factors. Temperature is certainly one of them.
Let’s stop this crap about being able to reconstruct temperatures. We can get a sense of what happened with the temperatures and we may possibly have been successful in reconstructing them, but we will never be able to verify these against hard measurements and so it all remains a theory.

February 16, 2016 7:51 am

Other studies posted here also show a colder period starting in the 4th century:comment image?w=956

Reply to  ulriclyons
February 16, 2016 7:51 am

comment image

February 16, 2016 8:35 am

“…precisely reconstruct the summer temperatures …”
I do not think they understand the word precisely or they use it much different than I would.

Reply to  mkelly
February 16, 2016 8:56 am

Liberals have their own dictionary !

Reply to  Marcus
February 16, 2016 8:57 am

Up is down, left is right and good is evil ( CO2 ) …etc……

Stephen Wilde
February 16, 2016 10:02 am

That period is known as the Dark Ages for good reason.
It was a cold period between the Roman Warm Period and the Mediaeval Warm Period.
Part of the well known millennial climate cycling that AGW theory has tried to erase from the historical record.

Gloateus Maximus
Reply to  Stephen Wilde
February 16, 2016 10:12 am

And earth has been in a long-term cooling trend since the Minoan Warm Period, some 3000 years ago.
There are of course counter-trend reversals during both warm and cold periods, such as the Sui-Tang warm cycle late within the secular Dark Ages CP. This simulation reported last year found the Sui-Tang more regional than the Chinese equivalent of the early Medieval WP, the Song-Yuan WP.
A 2000 year simulation forced by the external forcings of the last two millennia is carried out with the Community Earth System Model. We compare climate changes over China between the peak Sui-Tang warm period (Sui-TangWP; 650–700 A.D.) and Song-Yuan warm period (Song-YuanWP; 950–1000 A.D.), which were two key culturally, economically, and educationally prosperous eras in Chinese history. The simulation indicates warm conditions in both periods, but the warmth is mainly seen in East China in the peak Sui-TangWP, and over the whole of China in the peak Song-YuanWP. The warming in the peak Sui-TangWP is attributed to the localized increase of atmospheric net energy with favorable heat transport, whereas the peak Song-YuanWP results from the increase of global solar radiation. The annual mean precipitation anomalies in the peak Sui-TangWP exhibit a meridional dipole pattern over East China, with enhanced precipitation in the region south of the Yangtze River and decreased precipitation to the north. In the peak Song-YuanWP, the precipitation enhances over most parts of China. The precipitation anomalies are largely attributed to the water vapor transport anomalies associated with monsoon circulation changes. The simulated climate changes are broadly consistent with reconstructions, but the magnitude is greatly underestimated. Based on the simulation and reconstructions, we suggest that the Sui-TangWP may have been a regional phenomenon in China, while the Song-YuanWP was a reflection of global/hemispheric-scale warm events that took place at the same time.

Reply to  Gloateus Maximus
February 16, 2016 2:42 pm

More like since the early Holocene. The peak warmth is probably about 8,000 years ago. There are Daansgard-Oesherger(sp?) events that punctuate the period, but mostly temps have been in a steady gentle decline since then.

Reply to  Stephen Wilde
February 16, 2016 2:40 pm

535 CE was so bad that that it is well documented as a year without a summer in the Mediterranean area. Writers mention the sun being no brighter or warmer than the moon. That same period saw the plague emerge from East Africa and spread over the Eastern Mediterranean, creating near wasteland in some areas. See Castrophe by David Keyes. He argues that events of 535 had historic repercussions that our current socioeconomic patterns are the direct result of. In effect the decidedly bad weather was the direct cause of the migration period.

February 16, 2016 10:09 am

This cooling period, cause and long term effects was covered in detail in the book “Catastrophe: A Quest for the Modern World” by David Keys published in 1999.

February 16, 2016 10:47 am

We’ve already determined that trees are no good for determining temperature.
Trees measure the quality of the growing season, and that alone.

James at 48
February 16, 2016 11:01 am

Cold periods wipe out the Eurasian Monsoon and dry out the Eurasian interior. Barbarians then fan out. Rinse, repeat. Except now there are WMD (but the barbarians also still like to use crummy dull knives to behead people as well).

February 16, 2016 12:06 pm

I have to wonder how much of the recent “warming” is simply due to increased growth due to CO2 fertilization. This would be particularly true at the tree line. Where air is thinnest, growth is limited by CO2 starvation (as for people it would be for O2 starvation). CO2 increase should push the treeline higher and also increase annual growth ring thickness.
I am very skeptical of attributing modern tree ring increases to temperature alone. I believe a good bit of it is due to CO2 fertilization.

February 16, 2016 12:55 pm

Back door way of saying that the debate on tree ring and temperature is valid. The recent debate on tree ring widths that show the relationship between temperature and growth is invalid. I think some academic careers could be over for posing such a ridiculous argument. First the verified tree accounts only go back to 900 ce. It gets a little fuzzy going further back. Second, the only confirmed way of relating information about temperature and tree rings is through isotopic measurements. Any “real” scientist would know this and the paper when it was written. And by the way, it matches warming and cooling trends… worldwide. Which is why i am still waiting for an explanation of how that happened in the absence of major increases and decreases in co2. Further, if they can explain it, are those factors the same or different today. …
This is a garbage study, intending to support current garbage work trying to prove CAGW. Calling it CAGW now is fading since none of the catastrophic predictions/projections have occurred in the appointed time frame. It’s just AGW now, and that may be in the dust bin of history as well.

February 16, 2016 1:39 pm

Much has been written about the extreme climactic events beginning in the 530’s; Justinian may have had a chance to restore Rome back to a semblance of itself if the lands had not been devastated by plague and many bad harvests. Also in historical circles, this era is sometimes referred to as the “Death of Nations”, since so many organized civilizations and peoples which had persisted for millennia simply disappeared, swallowed up, absorbed, or replaced by the invaders from the east – who were driven by starvation and warfare in their own lands.
It’s even thought that the Norse idea of a “Fimbulwinter”, which is entwined with the tales of Ragnarok, and essentially refers to a winter which lasts for years with no thaw, may be a distant memory of what transpired in the far north during the 6th century.

Joe Civis
February 16, 2016 1:40 pm

Hmmmm not sure what is wrong with my treemometer….. it doesn’t seem to be calibrated correctly I look out my window and it clearly shows 67.004 degrees F but my digital thermometer shows 72.5 degrees F…. can anyone help me calibrate my treemometers in my yard? Are the treemometers affected by wind chill?
/sarc off

February 16, 2016 2:37 pm

A relevant book I read 20 odd years ago “Catastrophe” by David Keys.
Writing about the explosion of Krakatoa in Indonesia that blew up in 535AD. He writes about all of the changes that occurred (mass migration, plagues, climate change, famine etc.) bringing on the ‘dark ages’ lasting some 150 years.
He makes the case that these events cleared out the past and led to the start of our modern civilization.

Hocus Locus
Reply to  Titus
February 16, 2016 5:05 pm

Thanks for that, will check out his book. Keys has found many historical references to the Krakatoa event, also see the fascinating PBS documentary Catastrophe! available on-line: Part 1, Part 2. From Cassiodorus [Italy, 536AD] “The sun … seems to have lost its wonted light, and appears of a bluish colour. We marvel to see no shadows of our bodies at noon, to feel the mighty vigour of the sun’s heat wasted into feebleness, and the phenomena which accompany an eclipse prolonged through almost a whole year.

February 16, 2016 5:04 pm

I’m a little disappointed that they don’t credit David Keys’ earlier thorough investigation of ice cores, tree rings, global historical records and other evidence, published in his book “Catastrophe”, in which essentially the same conclusions were reached.

Reply to  grdtobin
February 20, 2016 7:29 am

Exactly! Posted similar reference earlier, Keyes has been there and thoroughly done that.

Reply to  Lenore Smith
February 21, 2016 3:42 am

Admittedly, I haven’t been closely following progress on this topic, but my impression is that since David Keyes’ work, the main substantive progress has been the discovery that several massive volcanic eruptions occurred around the world in the same few years, including one in Central America.
Keyes thought on the basis of worldwide historic records and Indonesian legend that perhaps Krakatoa had erupted on a huge scale at this time. On site he filmed a deep layer of material due to such an eruption, but due to the absence of organic material within this mass, it was not possible to date this eruption to better than two or three thousand years, though he observed that 535 was in about the middle of this range.
So I guess the jury is still out concerning the date for that particular Krakatoa explosion.
Another question is why several widely distributed volcanoes were so violently active in the same interval. Is there a single geological or gravitational tidal phenomenon that can trigger that?

February 16, 2016 8:27 pm

From what I’ve seen and read as a layman about tree ring data, while inclement weather of any type can affect ring growth, the effects are different enough to where examination of the growth under microscope (and sometimes, chemically) can indicate if the stunted growth was from too hot, too cold, too wet or too dry conditions, and combinations thereof – especially if you have modern data for the same tree species to correlate with.

February 17, 2016 9:20 am

The takeaway should be simply that this adds to the very large body of work inferring significant variability in the past. Regardless of the details, just this knowledge increases the uncertainty in claims that somehow the current warming period is unprecedented. Chalk up a credit for the skeptics.

February 17, 2016 9:53 am

“’This was the most dramatic cooling in the Northern Hemisphere in the past 2,000 years,’ explains Büntgen.” Which is to say Yamal all over again: the LIA is bogus; the hockey stick is vindicated. –AGF

Jeff Alberts
February 17, 2016 9:22 pm

“Tree-ring measurements have revealed a period of extreme cold in Eurasia between 536 and around 660 CE.”
No, they haven’t. Next.

February 18, 2016 11:13 pm

Someone has to be asking this…………………….But where did they find 1400 year old trees………and did someone cut one down?

Reply to  Jeff
February 21, 2016 3:44 am

Fossilised, I guess.

Tom Billings
February 25, 2016 3:07 pm

There is little dispute that whatever happened in 535AD, it changed the human environment massively. It is notable that several texts already speak at length of these changes. One is “The Long Summer”, by Brian Fagan. It speaks of the movement of the “ecotone” between the Mediterranean air mass, and the Atlantic air mass, and the Continental air mass, each moving north and south. The effects that had on human politics were dramatic, because in agrarian societies all wealth was dependent on what crops could be grown, or not.
With wheat as the “imperial grain”, able to be stored and transported to feed armies with the least spoilage, the shift from the ecotone between the Mediterranean and Atlantic air masses was decisive for the Western Roman Empire. After 535, the ecotone moved long-term from what is now the English Channel to the coast of North Africa. The short, wet summers of the Atlantic Air Mass rarely allowed wheat the time to ripen and dry in the fields before harvest. As a result, the grain-fed cavalry armies of Justinian’s Constantinople-based Imperial Rome were not able to advance any farther North than grain from Egypt could be transported by ships. The Continental Air Mass that now predominated in the Eastern Mediterranean allowed sufficient time for one wheat crop a year, instead of the 2 of the Mediterranean Air Mass, and that allowed the Roman Empire of Constantinople to hold on, even after they lost their agriculturally most productive provinces after the Battle of the Yarmuk, with the Armies of the imperial Caliphate, the Arab copy of the Roman Empire of Constantinople.

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