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kassy

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Paleoclimatology papers
« on: July 09, 2020, 02:23:31 PM »
This is collection thread for paleoclimatology papers.

Many have been posted before but lots are harder to find over time. So lets collects links to them here.
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kassy

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Re: Paleoclimatology papers
« Reply #1 on: July 09, 2020, 02:28:07 PM »
CO2 in Earth's atmosphere nearing levels of 15m years ago

Last time CO2 was at similar level temperatures were 3C to 4C hotter and sea levels were 20 metres higher

...

a team of researchers from the University of Southampton constructed a new high-resolution record of atmospheric CO2 during the Pliocene using data derived from the boron levels in tiny fossils about the size of a pin head collected from deep ocean sediments of the Caribbean Sea.

This confirmed trends previously observed in ice cores, but also allowed a more precise estimate of the CO2 range in that geological epoch, when levels of solar radiation were the same as today.

“A striking result we’ve found is that the warmest part of the Pliocene had between 380 and 420 parts per million CO2 in the atmosphere,” one of the co-authors Thomas Chalk, said. “This is similar to today’s value of around 415 parts per million, showing that we are already at levels that in the past were associated with temperature and sea-level significantly higher than today.”

...

https://www.theguardian.com/environment/2020/jul/09/co2-in-earths-atmosphere-nearing-levels-of-15m-years-ago

Open access:
Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation

Abstract
The Piacenzian stage of the Pliocene (2.6 to 3.6 Ma) is the most recent past interval of sustained global warmth with mean global temperatures markedly higher (by ~2–3 °C) than today. Quantifying CO2 levels during the mid-Piacenzian Warm Period (mPWP) provides a means, therefore, to deepen our understanding of Earth System behaviour in a warm climate state. Here we present a new high-resolution record of atmospheric CO2 using the δ11B-pH proxy from 3.35 to 3.15 million years ago (Ma) at a temporal resolution of 1 sample per 3–6 thousand years (kyrs). Our study interval covers both the coolest marine isotope stage of the mPWP, M2 (~3.3 Ma) and the transition into its warmest phase including interglacial KM5c (centered on ~3.205 Ma) which has a similar orbital configuration to present. We find that CO2 ranged from 389+38−8ppm to 331+13−11,ppm, with CO2 during the KM5c interglacial being 371+32−29ppm (at 95% confidence). Our findings corroborate the idea that changes in atmospheric CO2 levels played a distinct role in climate variability during the mPWP. They also facilitate ongoing data-model comparisons and suggest that, at present rates of human emissions, there will be more CO2 in Earth’s atmosphere by 2025 than at any time in at least the last 3.3 million years.

https://www.nature.com/articles/s41598-020-67154-8
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kassy

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Re: Paleoclimatology papers
« Reply #2 on: July 09, 2020, 02:40:22 PM »
Major New Paleoclimatology Study Shows Global Warming Has Upended 6,500 Years of Cooling
https://phys.org/news/2020-06-major-paleoclimatology-global-upended-years.html



Over the past 150 years, global warming has more than undone the global cooling that occurred over the past six millennia, according to a major study published June 30 in Nature Research's Scientific Data, "Holocene global mean surface temperature, a multi-method reconstruction approach."

The findings show that the millennial-scale global cooling began approximately 6,500 years ago when the long-term average global temperature topped out at around 0.7°C warmer than the mid-19th century. Since then, accelerating greenhouse gas emissions have contributed to global average temperatures that are now surpassing 1°C above the mid-19th century.

The research team worked in collaboration with scientists from research institutions all over the world to reconstruct the global average temperature over the Holocene Epoch—the period following the Ice Age and beginning about 12,000 years ago.

"Previous work has shown convincingly that the world naturally and slowly cooled for at least 1,000 years prior to the middle of the 19th century, when the global average temperature reversed course along with the build-up of greenhouse gases. This study, based on a major new compilation of previously published paleoclimate data, combined with new statistical analyses, shows more confidently than ever that the millennial-scale global cooling began approximately 6,500 years ago."

... Since the mid-19th century, global warming has climbed to about 1°C, suggesting that the global average temperature of the last decade (2010-2019) was warmer than anytime during the present post-glacial period.

Holocene global mean surface temperature, a multi-method reconstruction approach, Scientific Data, 2020
https://www.nature.com/articles/s41597-020-0530-7
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kassy

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Re: Paleoclimatology papers
« Reply #3 on: July 09, 2020, 04:24:42 PM »
Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century


Significance
The SADA is an annually-resolved hydroclimate atlas in South America that spans the continent south of 12°S from 1400 to 2000 CE. Based on 286 tree ring records and instrumentally-based estimates of soil moisture, the SADA complements six drought atlases worldwide filling a geographical gap in the Southern Hemisphere. Independently validated with historical records, SADA shows that the frequency of widespread severe droughts and extreme pluvials since the 1960s is unprecedented. Major hydroclimate events expressed in the SADA are associated with strong El Niño Southern Oscillation (ENSO) and Southern Annular Mode (SAM) anomalies. Coupled ENSO-SAM anomalies together with subtropical low-level jet intensification due to increasing greenhouse gas emissions may cause more extreme droughts and pluvials in South America during the 21st century.

https://www.pnas.org/content/early/2020/07/02/2002411117

Open access
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vox_mundi

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Re: Paleoclimatology papers
« Reply #4 on: July 10, 2020, 03:46:19 PM »
We Are Already Committed to a 3°C World
https://phys.org/news/2020-07-carbon-dioxide-earth-atmosphere-higher.html

By 2025, carbon dioxide levels in Earth's atmosphere will be higher than at any time in the last 3.3 million years

Dr. Thomas Chalk, a co-author of the study, added: "Focussing on a past warm interval when the incoming insolation from the Sun was the same as today gives us a way to study how Earth responds to CO2 forcing. A striking result we've found is that the warmest part of the Pliocene had between 380 and 420 parts per million CO2 in the atmosphere. This is similar to today's value of around 415 parts per million, showing that we are already at levels that in the past were associated with temperature and sea-level significantly higher than today. Currently, our CO2 levels are rising at about 2.5 ppm per year, meaning that by 2025 we will have exceeded anything seen in the last 3.3 million years."

During the Pliocene epoch, around 3 million years ago our planet was more than 3°C warmer than today with smaller polar ice caps and higher global sea-levels.

Professor Gavin Foster, who was also involved in the study, continued: "The reason we don't see Pliocene-like temperatures and sea-levels yet today is because it takes a while for Earth's climate to fully equilibrate (catch up) to higher CO2 levels and, because of human emissions, CO2 levels are still climbing. Our results give us an idea of what is likely in store once the system has reached equilibrium."

Concluded Dr. de la Vega, "Having surpassed Pliocene levels of CO2 by 2025, future levels of CO2 are not likely to have been experienced on Earth at any time for the last 15 millions years, since the Middle Miocene Climatic Optimum, a time of even greater warmth than the Pliocene."

Elwyn de la Vega et al. Atmospheric CO2 during the Mid-Piacenzian Warm Period and the M2 glaciation, Scientific Reports (2020)
https://www.nature.com/articles/s41598-020-67154-8

... Our upper quartile range (389+38−8ppm) suggests that CO2 during the mPWP is very likely to have been ≤ 427 ppm (using the distinctions of the IPCC). Atmospheric CO2 rose by 2.5 ppm from 2017 to 2018, if this rate is sustained, our new data indicate that CO2 will surpass even the highest mPWP values within the next 4 to 5 years (i.e. by 2024–2025).
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Tom_Mazanec

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Re: Paleoclimatology papers
« Reply #5 on: July 10, 2020, 09:58:19 PM »
And of course, CO2e is even higher than CO2.

kassy

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Re: Paleoclimatology papers
« Reply #6 on: July 10, 2020, 10:03:13 PM »
Also water is wet.

None of that is paleoclimatology and hence of topic.
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KiwiGriff

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Re: Paleoclimatology papers
« Reply #7 on: July 10, 2020, 10:20:04 PM »
We often discus equilibrium climate sensitivity and ignore earth system sensitivity as the time scales are to large for our ape brains to cope with.


Earth system sensitivity inferred from Pliocene
modelling and data
Daniel J. Lunt1,2*, Alan M. Haywood3
, Gavin A. Schmidt4
, Ulrich Salzmann2,5, Paul J. Valdes1
and Harry J. Dowsett6
Quote
Quantifying the equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is one of the cornerstones of climate research. Components of the Earth’s climate system that vary over long timescales, such as ice sheets and vegetation, could have an important effect on this temperature sensitivity, but have often been neglected.Here we use a coupled atmosphere–ocean general circulation model to simulate the climate of the mid-Pliocene warm period (about three million years ago), and analyse the forcings and feedbacks that contributed to the relatively warm temperatures.Furthermore, we compare our simulation with proxy records of mid-Pliocene sea surface temperature. Taking these lines of evidence together, we estimate that the response of the Earth system to elevated atmospheric carbon dioxide concentrations is 30–50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity. We conclude that targets for the long-term stabilization of atmospheric greenhouse-gas
concentrations aimed at preventing a dangerous human interference with the climate system should take into account this higher sensitivity of the Earth system.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.177.6584&rep=rep1&type=pdf
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Tom_Mazanec

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Re: Paleoclimatology papers
« Reply #8 on: July 10, 2020, 11:28:56 PM »
The paleoclimate papers are saying that the earth was so much warmer and the seas so much higher when CO2 was at the level it is now. But this is an underestimate of what we are facing, because the CO2e is higher still.

kassy

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Re: Paleoclimatology papers
« Reply #9 on: July 10, 2020, 11:35:15 PM »
Paleoclimatology is not about what we are facing now (although it can help establish bounds).
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kassy

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Re: Paleoclimatology papers
« Reply #10 on: July 19, 2020, 10:38:29 PM »
ShortBrutishNasty was thoughtful enough to send a link to me about James Hansen's latest article about paleo, and model, evidence about slowing of the MOC during periods of high GMSTA, see below:

Title: "Every Rock Has a Story & The Rock Whisperer" by James Hansen July 17, 2020

http://www.columbia.edu/~jeh1/mailings/2020/20200717_RockStories.pdf

Extract: "Curiously, at almost exactly the same moment that I received an e-mail from Ethan Baxter, I received one from the Rock Whisperer, my friend Paul Hearty, with a copy of his current paper on rocks in South Africa. He and co-authors show that in the Mid-Pliocene (about 3 million years ago), when atmospheric CO2 was about the same as today, it was a few degrees warmer and sea level was 15-30 meters higher (50-100 feet). One of Paul’s co-authors is Maureen Raymo, the new Director of Columbia’s Lamont-Doherty Earth Observatory, who dubbed Paul the Rock Whisperer for his remarkable ability to read the story in the rocks.

In 2006, when I was concerned that the IPCC projections of sea level rise were unrealistically conservative, I suspected that something was wrong with the ocean models that IPCC relied on. For one thing, the models did not properly include the cooling effect of ice melt on the North Atlantic and Southern Oceans. So, we ran climate simulations with our coarse-resolution global model, and were startled by the result: we found that the world was on the verge of shutting down both the Southern Ocean and North Atlantic overturning circulations, with enormous potential consequences for future sea level, because of amplifying feedbacks for Antarctic ice.

This would be a hard story to sell, given the coarse resolution of our model, and the fact that our result seemed to differ from all the other models. And why did Earth’s history not reveal such rapid feedback-driven change in the past? That’s when I discovered the papers of Paul Hearty for the last interglacial period, the Eemian, about 120,000 years ago, when global temperature reached levels perhaps as much as 1-2°C warmer than the preindustrial (1880-1920) level.

Hearty’s reading of the rocks painted a picture of the Eemian that was consistent with what we were finding in our climate modeling. We needed to develop that story, so we started to work with Paul Hearty, but first we needed an explanation for what was wrong with the ocean models.

The most crucial information about the ocean models was provided by observations of heat uptake by the oceans. Here the expert, the ocean heat whisperer if there is such a thing, was a young post-doc, Karina von Schuckmann, with whom we began to collaborate in about 2010."

Hearty, P. J., Rovere, A., Sandstrom, M. R., O'Leary, M. J., Roberts, D., & Raymo, M. E. (2020). Pliocene‐Pleistocene stratigraphy and sea‐level estimates, Republic of South Africa with implications for a 400 ppmv CO2 world. Paleoceanography and Paleoclimatology, 35, e2019PA003835. https://doi.org/10.1029/2019PA003835

https://www.essoar.org/doi/10.1002/essoar.10503699.1

Abstract: "The Mid-Pliocene Warm Period (MPWP, 2.9 to 3.3 Ma), along with older Pliocene (3.2 to 5.3 Ma) records, offers potential past analogues for our 400-ppmv world. The coastal geology of western and southern coasts of the Republic of South Africa expose an abundance of marine deposits of Pliocene and Pleistocene age. In this study, we report differential GPS elevations, detailed stratigraphic descriptions, standardized interpretations, and dating of relative sea-level indicators measured across ~700 km from the western and southern coasts of the Cape Provinces. Wave abrasion surfaces on bedrock, intertidal sedimentary structures, and in situ marine invertebrates including oysters and barnacles provide precise indicators of past sea levels. Multiple sea-level highstands imprinted at different elevations along South African coastlines were identified. Zone I sites average +32 ± 5 m (6 sites). A lower topographic Zone II of sea stands were measured at several sites around +17 ± 5 m. Middle and late Pleistocene sites are included in Zone III. Shoreline chronologies using 87Sr/86Sr ages on shells from these zones yield ages from Zone I at 4.6 and 3.0 Ma, and Zone II at 1.04 Ma. Our results show that polar ice sheets during the Plio-Pleistocene were dynamic and subject to significant melting under modestly warmer global temperatures. These processes occurred during a period when CO2 concentrations were comparable to our current and rapidly rising values above 400 ppmv."

Hat tip SBN.
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pikaia

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Re: Paleoclimatology papers
« Reply #11 on: September 04, 2020, 12:00:00 PM »
https://advances.sciencemag.org/content/6/36/eaaz9588

"We find that CE 2018 sea ice conditions were the lowest of the last 5500 years, and results suggest that sea ice loss may lag changes in CO2 concentrations by several decades."

kassy

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Re: Paleoclimatology papers
« Reply #12 on: September 28, 2020, 12:58:27 PM »
Ancient volcanoes once boosted ocean carbon, but humans are now far outpacing them
The closest analog to modern times is no longer very close, study finds

A new study of an ancient period that is considered the closest natural analog to the era of modern human carbon emissions has found that massive volcanism sent great waves of carbon into the oceans over thousands of years -- but that nature did not come close to matching what humans are doing today. The study estimates that humans are now introducing the element three to eight times faster, or possibly even more. The consequences for life both in the water and on land are potentially catastrophic. The findings appear this week in the journal Proceedings of the National Academy of Sciences.

Researchers at Columbia University's Lamont-Doherty Earth Observatory examined ocean conditions 55.6 million years ago, a time known as the Paleocene-Eocene Thermal Maximum (PETM). Before this, the planet was already considerably warmer than it is today, and the soaring CO2 levels of the PETM drove temperatures up another 5 to 8 degrees C (9 to 14 degrees F). The oceans absorbed large amounts of carbon, spurring chemical reactions that caused waters to become highly acidic, and killing or impairing many marine species.

...

Up to now, marine studies of the PETM have relied on scant chemical data from the oceans, and assumptions based on a certain degree of guesswork that researchers fed into computer models.

The authors of the new study got at the questions more directly. They did this by culturing tiny shelled marine organisms called foraminifera in seawater that they formulated to resemble the highly acidic conditions of the PETM. They recorded how the organisms took up the element boron into their shells during growth. They then compared these data with analyses of boron from fossilized foraminifera in Pacific and Atlantic ocean-floor cores that span the PETM. This allowed them to identify carbon-isotope signatures associated with specific carbon sources. This indicated that volcanoes were the main source -- probably from massive eruptions centered around what is now Iceland, as the North Atlantic ocean opened up, and northern North America and Greenland separated from northern Europe.

The researchers say the carbon pulses, which others estimate lasted for at least 4,000 to 5,000 years, added as much as 14.9 quadrillion metric tons of carbon to the oceans -- a two-thirds increase over their previous content. The carbon would have come from CO2 emitted directly by the eruptions, the combustion of surrounding sedimentary rocks, and some methane welling up from the depths. As the oceans absorbed carbon from the air, waters became highly acidic, and remained that way for tens of thousands of years. There is evidence that this killed off much deep-sea life, and probably other marine creatures as well.

Today, human emissions are causing carbon dioxide in the atmosphere to skyrocket, and the oceans are again absorbing much of it. The difference is that we are introducing it much faster than the volcanoes did -- within decades instead of millennia. Atmospheric levels have shot up from about 280 parts per million in the 1700s to about 415 today, and they are on a path to keep rising rapidly. Atmospheric levels would already be much higher if the oceans were not absorbing so much. As they do, rapid acidification is starting to stress marine life.

"If you add carbon slowly, living things can adapt. If you do it very fast, that's a really big problem," said the study's coauthor Bärbel Hönisch, a geochemist at Lamont-Doherty. She pointed out that even at the much slower pace of the PETM, marine life saw major die-offs. "The past saw some really dire consequences, and that does not bode well for the future," she said. "We're outpacing the past, and the consequences are probably going to be very serious."

https://www.sciencedaily.com/releases/2020/09/200914172931.htm

The seawater carbon inventory at the Paleocene–Eocene Thermal Maximum
https://www.pnas.org/content/early/2020/09/08/2003197117


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vox_mundi

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Re: Paleoclimatology papers
« Reply #13 on: September 29, 2020, 06:30:23 PM »
New Evidence Suggests It Was Matter Ejected From the Chicxulub Crater That Led to Impact Winter
https://phys.org/news/2020-09-evidence-ejected-chicxulub-crater-impact.html

A team of researchers from the U.S., Australia and the U.K. has found evidence that suggests material thrown into the atmosphere by the asteroid that struck the Earth approximately 66 million years ago, and not massive wildfires, led to a mass extinction event. In their paper published in Proceedings of the National Academy of Sciences, the group describes their study of sediment from the Chicxulub crater and other ocean areas and what it showed them.

In this new effort, the researchers suggest that while some of the material in K–Pg boundary records is likely burnt material from massive wildfires, most of it came from material ejected from the crater at the impact site.

The work involved analyzing sediment samples from within the Chicxulub crater and from other ocean sites near the crater. In their analysis, the researchers focused on polycyclic aromatic hydrocarbons (PAHs), which can provide evidence of a source of black carbon. In so doing, they found that the samples came from a fossil source, not from burned material from wildfires. They also found that the characteristics of the PAHs showed they came about due to rapid heating, which, the researchers note, was consistent with rocky material ejected from an impact crater. The researchers also found small amounts of charcoal in the samples, indicating that some small amount of burned biomass had also made its way into the atmosphere. They conclude that the material in the K–Pg boundary records came mainly from material ejected from the crater and not from wildfires.



Shelby L. Lyons et al. Organic matter from the Chicxulub crater exacerbated the K–Pg impact winter, Proceedings of the National Academy of Sciences (2020)
https://www.pnas.org/content/early/2020/09/22/2004596117

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Tor Bejnar

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Re: Paleoclimatology papers
« Reply #14 on: September 29, 2020, 10:33:45 PM »
Maybe this is old news for everybody reading Vox_Mundi's post, but what was known as the "K/T" boundary [for Cretaceous-Tertiary] got renamed the "K/Pg" boundary [Cretaceous-Paleogene], the Tertiary Period being split/replaced by the Paleogene and Neogene in 2008 [as a first approximation, any way].  "K/Pg" is sometimes still referred to as "K/T", as on "Vox's" first chart.
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vox_mundi

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Re: Paleoclimatology papers
« Reply #15 on: September 29, 2020, 10:56:57 PM »
Thanks for the insight, Tor. I did not know the history behind the name change.
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

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kassy

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Re: Paleoclimatology papers
« Reply #16 on: January 06, 2021, 10:50:45 AM »
The next research is not really paleoclimatology but complimentary to it.

The most interesting tidbit is that stuck weather shows up in warm to cold transitions too.

Quote
Drought Of The Century In The Middle Ages: Parallels To Climate Change Today?

The transition from the Medieval Warm Period to the Little Ice Age was apparently accompanied by severe droughts between 1302 and 1307 in Europe; this preceded the wet and cold phase of the 1310s and the resulting great famine of 1315-21.

In the journal Climate of the Past, researchers from the Leibniz Institutes for the History and Culture of Eastern Europe (GWZO) and Tropospheric Research (TROPOS) write that the 1302-07 weather patterns display similarities to the 2018 weather anomaly, in which continental Europe experienced exceptional heat and drought.

Both the medieval and recent weather patterns resemble the stable weather patterns that have occurred more frequently since the 1980s due to the increased warming of the Arctic.

According to the Leibniz researchers’ hypothesis based on their comparison of the 1302-07 and 2018 droughts, transitional phases in the climate are always characterized by periods of low variability, in which weather patterns remain stable for a long time.

...

“We want to show that historical climate change can be reconstructed much better if written historical sources are incorporated alongside climate archives like tree rings or sediment cores. The inclusion of humanities research clearly contributes to a better understanding of the social consequences of climate change in the past and to drawing conclusions for the future,” explains Dr Martin Bauch from the GWZO, who heads the junior research group.

The study now published evaluates a large number of historical sources: chronicles from present-day France, Italy, Germany, Poland, and the Czech Republic. Regional and municipal chronicles provided information on historical city fires, which were an important indicator of droughts. Administrative records from Siena (Italy), the County of Savoy (France) and the associated region of Bresse shed light on economic developments there.

Using the data, it was possible, for example, to estimate wheat and wine production in the French region of Bresse and compare it with wheat production in England. Since these yields depend strongly on climatic factors such as temperature and precipitation, it is thus possible to draw conclusions about the climate in the respective production years.

While the summer of 1302 was still very rainy in central Europe, several hot, very dry summers followed from 1304 onwards. From the perspective of climate history, this was the most severe drought of the 13th and 14th centuries.

“Sources from the Middle East also report severe droughts. Water levels in the Nile, for example, were exceptionally low. We therefore think that the 1304-06 drought was not only a regional phenomenon, but probably had transcontinental dimensions,” reports Dr. Thomas Labbé from the GWZO.

Based on the recorded effects, the team reconstructed the historical weather conditions between the summer of 1302 and 1307. Through evaluations of the 2018 drought and similar extreme events, it is now known that, in such cases, a so-called “precipitation seesaw” usually prevails. This is the meteorological term for a sharp contrast between extremely high precipitation in one part of Europe and extremely low precipitation in another.

“This is usually caused by stable high and low pressure areas that remain in one region for an unusually long time. In 2018, for example, very stable lows lay over the North Atlantic and southern Europe for a long time, which led to heavy precipitation there and an extreme drought in between in central Europe,” explains meteorologist Dr Patric Seifert from TROPOS, who was responsible for reconstructing the large-scale weather situations for the study.

https://www.eurasiareview.com/06012021-drought-of-the-century-in-the-middle-ages-parallels-to-climate-change-today/

A prequel to the Dantean Anomaly: the precipitation seesaw and
droughts of 1302 to 1307 in Europe

https://cp.copernicus.org/articles/16/2343/2020/cp-16-2343-2020.pdf
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KiwiGriff

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Re: Paleoclimatology papers
« Reply #17 on: January 29, 2021, 08:32:33 PM »
Palaeoclimate puzzle explained by seasonal variation
Quote
Scientists have long been baffled by the mismatch of climate simulations of the past 12,000 years with temperature reconstructions from geological records. It now emerges that seasonal biases in the records explain the disparity.
Understanding past climate change is crucial for putting modern global warming in context. Reconstructions of climate during the Holocene — the current interglacial epoch, which began 11,700 years ago — based on geological evidence suggest that a peak in global mean annual temperatures between 10,000 and 6,000 years ago was followed by a cooling trend, which then reversed in the post-industrial era1,2. However, computational simulations of Holocene climate reveal only a long-term warming trend3. Writing in Nature, Bova et al.4 report an analysis that effectively brings Holocene climate reconstructions in line with computational simulations. This result has important implications for our understanding of the drivers of climate change during the Holocene and for the context of post-industrial warming.
https://www.nature.com/articles/d41586-021-00115-x

Paper Abstract
Seasonal origin of the thermal maxima at the Holocene and the last interglacial
Samantha Bova, Yair Rosenthal, Zhengyu Liu, Shital P. Godad & Mi Yan
Nature volume 589, pages548–553(2021)
Quote
Proxy reconstructions from marine sediment cores indicate peak temperatures in the first half of the last and current interglacial periods (the thermal maxima of the Holocene epoch, 10,000 to 6,000 years ago, and the last interglacial period, 128,000 to 123,000 years ago) that arguably exceed modern warmth1,2,3. By contrast, climate models simulate monotonic warming throughout both periods4,5,6,7. This substantial model–data discrepancy undermines confidence in both proxy reconstructions and climate models, and inhibits a mechanistic understanding of recent climate change. Here we show that previous global reconstructions of temperature in the Holocene1,2,3 and the last interglacial period8 reflect the evolution of seasonal, rather than annual, temperatures and we develop a method of transforming them to mean annual temperatures. We further demonstrate that global mean annual sea surface temperatures have been steadily increasing since the start of the Holocene (about 12,000 years ago), first in response to retreating ice sheets (12 to 6.5 thousand years ago), and then as a result of rising greenhouse gas concentrations (0.25 ± 0.21 degrees Celsius over the past 6,500 years or so). However, mean annual temperatures during the last interglacial period were stable and warmer than estimates of temperatures during the Holocene, and we attribute this to the near-constant greenhouse gas levels and the reduced extent of ice sheets. We therefore argue that the climate of the Holocene differed from that of the last interglacial period in two ways: first, larger remnant glacial ice sheets acted to cool the early Holocene, and second, rising greenhouse gas levels in the late Holocene warmed the planet. Furthermore, our reconstructions demonstrate that the modern global temperature has exceeded annual levels over the past 12,000 years and probably approaches the warmth of the last interglacial period (128,000 to 115,000 years ago).


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El Cid

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Re: Paleoclimatology papers
« Reply #18 on: January 29, 2021, 10:00:34 PM »
Palaeoclimate puzzle explained by seasonal variation
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Scientists have long been baffled by the mismatch of climate simulations of the past 12,000 years with temperature reconstructions from geological records.

I have seen this one and I call it bullshit. They find that reality and models don't match so they try to tweak reality to fit the models (instead of the other way around!).
Never mind that models don't replicate the Green Sahara or Holocene Optimum European and American temperature and precipitation matters. Never mind that treelines were higher in the mountains and more to the North by hundreds of kms than now during the Holocene Optimum. Hundreds of papers show that H.Optimum vegetation signals (often significantly) warmer temperatures than now (eg.trees instead of shrubs/tundra, broadleaf forest instead of conifers,etc.). Instead of drawing the glaringly obvious conclusion that our models are very poor, they realign reality. Amazing.

KiwiGriff

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Re: Paleoclimatology papers
« Reply #19 on: January 30, 2021, 05:53:45 AM »
As always El Cid one paper is not going to change the present consensus  of a clear holocene climate optimum followed by long term cooling trend .
However.
The result is interesting and it will spark more research to find if the conclusion holds up .
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kassy

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Re: Paleoclimatology papers
« Reply #20 on: January 30, 2021, 01:14:33 PM »
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Instead of drawing the glaringly obvious conclusion that our models are very poor, they realign reality. Amazing.

That is not really the issue. They reexamined the record. The old one suffered from several selection biases. This does not mean the for example HCO heat was not there just that it is problematic to translate those record to global surface temps.

After converting the seasonally biased SST records into mean annual SST records, Bova and colleagues infer that the climate has been warming since the early Holocene — that is, there is no evidence for a Holocene thermal maximum in mean annual temperatures (Fig. 1). They suggest instead that the Holocene thermal maximum is a seasonal feature driven by a peak in summer insolation in the Northern Hemisphere that occurred during the early Holocene.

This is not a shocking discovery because we have known for a long time that the actual changes were from milankovich forcing.

It is also rather similar to this research although they both have different angles:

Mid-Holocene Northern Hemisphere warming driven by Arctic amplification

Abstract

The Holocene thermal maximum was characterized by strong summer solar heating that substantially increased the summertime temperature relative to preindustrial climate. However, the summer warming was compensated by weaker winter insolation, and the annual mean temperature of the Holocene thermal maximum remains ambiguous. Using multimodel mid-Holocene simulations, we show that the annual mean Northern Hemisphere temperature is strongly correlated with the degree of Arctic amplification and sea ice loss. Additional model experiments show that the summer Arctic sea ice loss persists into winter and increases the mid- and high-latitude temperatures. These results are evaluated against four proxy datasets to verify that the annual mean northern high-latitude temperature during the mid-Holocene was warmer than the preindustrial climate, because of the seasonally rectified temperature increase driven by the Arctic amplification. This study offers a resolution to the “Holocene temperature conundrum”, a well-known discrepancy between paleo-proxies and climate model simulations of Holocene thermal maximum.

https://advances.sciencemag.org/content/5/12/eaax8203
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El Cid

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Re: Paleoclimatology papers
« Reply #21 on: January 30, 2021, 01:38:24 PM »
.... the annual mean northern high-latitude temperature during the mid-Holocene was warmer than the preindustrial climate, because of the seasonally rectified temperature increase driven by the Arctic amplification. This study offers a resolution to the “Holocene temperature conundrum”, a well-known discrepancy between paleo-proxies and climate model simulations of Holocene thermal maximum.

https://advances.sciencemag.org/content/5/12/eaax8203

kassy, your article actually supports what I said!

They find that while most models say that NH mid-to high latitude temperatures SHOULD HAVE BEEN lower according to most models but were in fact WARMER ("Holocene Optimum conundrum") according to paleoproxies. This is exactly what I said. Furthermore, they say that when they deliberately choose only those models that have a very strong Arctic Amplification then those models do reproduce the proxies.

Conclusion: Most models underestimate Arctic Amplification. Don't use those models! Use reality and try to find models that fit that reality! This is what the guys in your article did. And the authors quoted by Kiwi did the exact opposite.

kassy

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Re: Paleoclimatology papers
« Reply #22 on: January 31, 2021, 02:57:31 PM »
El Cid we are not disagreeing on main lines just on nuances.

First off they did not realign reality, they just solved a puzzle related to the global temperature as resolved from the paleo record vs the model output. This is fine. This means that we don´t need to try to get models to reach those global temps (but i don´t think anyone was doing that).

Global models give global temps but they do not generate detail very much.

problem in a nutshell:

Evaluation of CMIP5 palaeo-simulations to improve climate projections

Abstract
Structural differences among models account for much of the uncertainty in projected climate changes, at least until the mid-twenty-first century. Recent observations encompass too limited a range of climate variability to provide a robust test of the ability to simulate climate changes. Past climate changes provide a unique opportunity for out-of-sample evaluation of model performance. Palaeo-evaluation has shown that the large-scale changes seen in twenty-first-century projections, including enhanced land–sea temperature contrast, latitudinal amplification, changes in temperature seasonality and scaling of precipitation with temperature, are likely to be realistic. Although models generally simulate changes in large-scale circulation sufficiently well to shift regional climates in the right direction, they often do not predict the correct magnitude of these changes. Differences in performance are only weakly related to modern-day biases or climate sensitivity, and more sophisticated models are not better at simulating climate changes. Although models correctly capture the broad patterns of climate change, improvements are required to produce reliable regional projections.

paywalled but the essence is in the bolded quotes.
https://www.nature.com/articles/nclimate2649

So the big problem is actually that the models don´t have the resolution needed for our current problem. We have four choices which do not really meaningfully diversify until much later this century.

If anything we need much better more detailed models and we should have invested in a CERN like climate change research program a couple of decades ago.

So the nuances are that i actually like the paper and i think we need better models since we cannot do without them. But we agree that current models are not sufficient.  ;)

PS:
https://pmip3.lsce.ipsl.fr/

https://wiki.lsce.ipsl.fr/pmip3/doku.php/pmip3:wg:p2f:papers
https://wiki.lsce.ipsl.fr/pmip3/doku.php/pmip3:wg:p2f:paperseval

Some papers and other stuff from the Paleoclimate Modelling Intercomparison Project for people interested to check out what kind of research they are doing.
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El Cid

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Re: Paleoclimatology papers
« Reply #23 on: January 31, 2021, 05:06:06 PM »
Although models correctly capture the broad patterns of climate change, improvements are required to produce reliable regional projections.[/b]

Exactly. Broad trends are usually OK, but localized effects and changes in atmospheric circulation are poor

kassy

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Re: Paleoclimatology papers
« Reply #24 on: February 24, 2021, 01:55:41 PM »
The Ruddiman Hypothesis: A Debated Theory Progresses Along Interdisciplinary Lines

In the 1990s marine geologist and current University of Virginia emeritus professor William Ruddiman participated in the summer gatherings of the Cooperative Holocene Mapping Project (COHMAP), which focused on Earth’s conditions beginning around 20,000 years ago during the last glacial period and continuing on into the present interglacial Holocene that began around 12,000 years ago.  In COHMAP, Ruddiman interfaced with pollen experts, climate scientists, and others who specialized on the Holocene. 

Around the time COHMAP wrapped up, a substantial Antarctic ice record detailing past atmosphere composition came out, showing high methane concentrations ten thousand years ago and decreasing steadily for a few thousand years. The record indicated that around 6000 years ago, atmospheric methane and carbon dioxide rebounded and rose in concentration, instead of expectedly declining, given the Earth’s orientation in the solar system – its “orbital” configuration – that shapes the Earth’s temperature and carbon and methane geochemistry.

Shortly thereafter, Antarctic ice core data from earlier interglacials started coming in, and Ruddiman noted that in previous interglacials methane and carbon dioxide trends kept going down. “It seemed obvious to me that this interglacial was anomalous. And the only thing I could think of was that it might be humans.”

Expanding his focus, Ruddiman began developing his hypothesis that it was primarily humans’ forest clearing for agriculture that released carbon dioxide and methane-emitting rice cultivation that accounted for the upward spike in greenhouse gases emissions before modern times.

Some climate scientists, especially geochemists like the well-known Wally Broecker -- objected to Ruddiman’s explanation and claimed that geochemical ocean dynamics caused the unexplained rise in the carbon release. Importantly, Broecker and others claimed that the Stage 11 Interglacial was the best analogue to the Holocene and its comparison did not support Ruddiman’s claim. The objectors also held that before the 19th century, the less numerous humans could not have massively cleared   forests with the carbon impacts  Ruddiman suggested (see here; and for background on debate in media and science, see Richard Blaustein’s 2015 article). 

But in recent years that is what ecologists, botanists, and archaeologists have been establishing – massive and early preindustrial deforestation.  Moreover, archaeobotanists, prominently Dorian Fuller of University College London, have documented the large expansion of rice patty agriculture thousands of years ago, explicating the methane rise. And offering strong support for the Ruddiman hypothesis, a consortium of over 250 archaeologists published a well-noted August 2019 Science article, “Archaeology assessment reveals Earth’s early transformation through land use,” that posited “a planet largely transformed by hunter-gatherers, farmers and pastoralists by 3000 years ago.”  (Stephens et al., 2019)

...

Scientists earlier held that the Marine Isotope Stage 11 (MIS11) interglacial that occurred from 424,000 and 374,000 years ago as the best Holocene analogue.   Ruddiman disagreed as early as 2005, saying it mismatched with the Holocene’s complete orbital configuration – which is made up of “eccentricity” (the Earth’s rotation around the sun), its “obliquity” (the Earth’s tilt axis); and “precession” (the Earth’s wobble on the axis). In particular, the Stage 11 obliquity does not match up to the Holocene pattern by thousands of years.

Over time, more ice data and glacial-interglacial time refinements came out, and making use of this more precise data, Steve Vavrus and colleagues (2018) underscore a current appreciation  of that Stage 19 is a better analogue than Stage 11. In addition to Vavrus, Ruddiman points to the work of University College London palaeogeographer Polychronis Tzedakis, who, along with Ruddiman was a co-author on Vavrus’s Scientific Reports paper, as particularly important for clarifying the interglacial past and MIS19.

Comparing the MIS19 conditions that would match with 1850 in the Holocene, Vavrus’s 2018 Scientific Reports s paper states: “The mean-annual global temperature falls by 1.27 K while the 5-6 K cooling in the high Arctic is the most pronounced anywhere.” While the Earth would not have had another ice age, in the Holocene absent an early greenhouse gas upturn, a year-round “glacial inception” would have set in parts of Canada and Russia that today are snowed over seasonally.

Ruddiman and Vavrus highlight different but complementary aspects of the Vavrus-led study. “We now have six or seven previous interglaciations to look at the carbon dioxide trends and all of those must have been natural – humans were not an active force on the land,” Ruddiman says. “And none of those previous interglaciations show any kind of rising trend like what is happening in past 7000 years. In my mind, the record from the natural previous interglaciations rules out any natural explanation for the rise in carbon dioxide in this interglaciation.”

Vavrus highlights that the simulation’s outcomes have the same ultimate portent to which his earlier research points. “The argument that a few numbers of humans had a huge impact on the environment – if that is true, and our evidence suggests that it is – is all the more reason to be concerned about the much bigger impact we are having on the present-day environment with so many more people in the world and the amount of carbon emissions much higher in the present,” Vavrus says.

...

The study found that Europe forest cover peaked 8,000-6,000 years ago, and that forests then covered around three quarters of Europe. Shortly after 6,000 years ago, significant deforestation began. The northern Europe needle-leaf forests persisted further in time, while deciduous forests in mid-latitude western Europe were felled in earnest for agriculture early, beginning around 6000 years ago. By 3,000 years ago, quite extensive European deforestation had taken place.  Today, fragmented forests cover less than half of Europe. Woodbridge and colleagues offer that most forest losses occurred before the industrial revolution.

Ruddiman adds that while “Europe’s Lost Forests” covers Europe and is not a global estimate, it is complemented by much research in China with 50,000 archaeological communal sites that point to enormous population increases 8,000 to 4,000 years ago, indicating deforestation. “Since these people are farmers, and we are talking about areas of natural forests, they had to clear those forests to get the sunlight to the land so they could grow crops.” Ruddiman gives a rough estimate that Europe and China combined account for roughly a preindustrial removal of 45% of natural forest.

https://www.globalpolicyjournal.com/blog/24/02/2021/ruddiman-hypothesis-debated-theory-progresses-along-interdisciplinary-lines

Great overview of science supporting Ruddimans Early Anthropocene theory.
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El Cid

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Re: Paleoclimatology papers
« Reply #25 on: February 24, 2021, 03:57:38 PM »
I was sold on Ruddiman's hypotheses long ago.

And the corollary is - as surpsising as it is - that our ancestors' forest fellings saved us from falling into the next ice age. Basically, humans saved themselves from the ice age by killing the forests.

Tor Bejnar

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Re: Paleoclimatology papers
« Reply #26 on: February 24, 2021, 05:56:45 PM »
... and for 40 years it's been "too much of a good thing" (especially after those 'evil Republicans' created the EPA whose first task was to decrease global cooling pollution).  :'(   [Actually, :) for reducing smog and atmospheric lead and all that, but it sure helped tip the balance we had unintendedly created.]
Arctic ice is healthy for children and other living things.

kassy

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Re: Paleoclimatology papers
« Reply #27 on: February 24, 2021, 06:30:22 PM »
I was sold on Ruddiman's hypotheses long ago.

And the corollary is - as surpsising as it is - that our ancestors' forest fellings saved us from falling into the next ice age. Basically, humans saved themselves from the ice age by killing the forests.

That is the simplified version. From the MIS19 research:
While the Earth would not have had another ice age, in the Holocene absent an early greenhouse gas upturn, a year-round “glacial inception” would have set in parts of Canada and Russia that today are snowed over seasonally.

Glacial Inception in Marine Isotope Stage 19: An Orbital Analog for a Natural Holocene Climate
https://www.nature.com/articles/s41598-018-28419-5

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kassy

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Re: Paleoclimatology papers
« Reply #28 on: February 24, 2021, 06:49:45 PM »
'Missing ice problem' finally solved
https://www.sciencedaily.com/releases/2021/02/210223110705.htm

paper:

A new global ice sheet reconstruction for the past 80 000 years

Abstract
The evolution of past global ice sheets is highly uncertain. One example is the missing ice problem during the Last Glacial Maximum (LGM, 26 000-19 000 years before present) – an apparent 8-28 m discrepancy between far-field sea level indicators and modelled sea level from ice sheet reconstructions. In the absence of ice sheet reconstructions, researchers often use marine δ18O proxy records to infer ice volume prior to the LGM. We present a global ice sheet reconstruction for the past 80 000 years, called PaleoMIST 1.0, constructed independently of far-field sea level and δ18O proxy records. Our reconstruction is compatible with LGM far-field sea-level records without requiring extra ice volume, thus solving the missing ice problem. However, for Marine Isotope Stage 3 (57 000-29 000 years before present) - a pre-LGM period - our reconstruction does not match proxy-based sea level reconstructions, indicating the relationship between marine δ18O and sea level may be more complex than assumed.

...

Recent work in the Hudson Bay region in North America5,6,7 shows that during part of MIS 3, ice-free conditions may have existed. Under this interpretation, the climatic conditions in this area were favorable to allow the growth of forests, with a climate that was potentially analogous to present8. This would indicate that not only was the Laurentide Ice Sheet reduced in size but it also had to be far enough removed from southern Hudson Bay to not strongly affect the climate there. Pico et al.9, through GIA modeling, provided additional support for a reduced extent Laurentide Ice Sheet to explain high relative MIS 3 sea-level indicators along the eastern coast of the United States. The dating methods used for inferring reduced ice sheet extent are near the limit of their reliability during mid-MIS 310. If regarded as minimum ages, then these deposits could be from an earlier ice-free period, such as the last interglacial.

Our reconstruction, called PaleoMIST 1.0 (Paleo Margins, Ice Sheets, and Topography), is created independently of indirect proxy records and far-field sea-level records. This allows us to investigate two of the most contentious problems when assessing past ice sheet configuration and sea level. First, our reconstruction can achieve the sea-level lowstand observed in many far-field locations at the LGM. Since our model adheres to ice physics, geological observations, and local relative sea-level change, we consider it to be a plausible depiction of the ice sheet configuration at the LGM. Therefore, the origin of the long-debated missing ice problem was likely from the starting assumptions on where ice was distributed and the Earth rheology model, while achieving the far-field sea-level lowstand is a nonunique problem. Second, the ice volume in our reconstruction is unable to match the pre-LGM δ18O values based on empirical relationships between ice volume (and therefore sea level) and δ18O but is consistent with some of the sea-level indicators and prior GIA studies6,9,11,12. From our results, we propose that these relationships of δ18O proxy records to sea level and ice volume are not valid.


https://www.nature.com/articles/s41467-021-21469-w
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