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kassy

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Re: Paleoclimatology papers
« Reply #50 on: March 21, 2022, 11:29:50 AM »


Ancient greenhouse warming informs potential future climate change scenarios

56 million years ago a period of abrupt global warming known as the Paleocene-Eocene Thermal Maximum (PETM), was caused by a massive release of greenhouse gases, likely triggered by volcanic activity. A new study now confirms that just prior to the PETM there was an additional shorter rise in atmospheric CO2, with total carbon emissions similar to modern-day levels.  This drove a brief, smaller episode of warming and ocean acidification. Together these two events provide unique insights into how Earth’s current climate could respond if the rate of carbon emissions continue to climb.

Evidence of environmental change at the PETM is recorded in marine sediments that contain the ancient remains of foraminifera, a group of microscopic organisms that are preserved as fossils. Scientists can measure the chemical composition of foraminifera shells to reveal the temperature and pH of the oceans millions of years in the past.

“The PETM is an important geologic climate event because it is one of best comparisons to current climate change and can help inform us how the Earth System will respond to current and future warming,” said Dr Tali Babila, Postdoctoral Research Associate currently at the University of Southampton, who is lead author on the study.

Despite decades of research, the sequence of environmental changes leading up to the PETM has been an enigma because in nearly every marine record the beginning of the event was nearly erased by the ocean acidification that occurred, until now.

A collective team of international geoscientists, led by the University of Southampton and University of California Santa Cruz including Utah State University, KU Leuven, Penn State and U.S. Geological Survey overcame the lack of fossils from the time, by drilling sediment cores along the eastern United States now part of the Atlantic Coastal Plain. At the time of the PETM, this region was a shallow continental shelf, which offered higher sedimentation rates due to its proximity to land and a measure of protection from ocean acidification that preserved some of the missing sediment record.

The team then used a revolutionary laser sampling technique they developed on fossilised plankton shells in the sediment samples. They used a laser beam the width of a human hair to sample the microscopic plankton and send the vaporized particles to a mass spectrometer. The scientists could then analyse the boron chemistry of the shell to estimate the acidity, and hence carbon content, of the oceans at the time.

The results, published in the journal Science Advances, found evidence for a substantial increase in carbon emissions, on the order of what we see released by human activities today, just before the PETM began. “This had previously been suggested as a possible trigger for the large scale global warming that followed but scientists lacked a direct measure of carbon dioxide until this study,” explained Dr Babila.

“Usually, this type of analysis would require thousands of fossils which would not have been possible because of the scarcity of samples. Our novel application of the laser sampling technique is a major geoscience advancement bringing new and incredible detail never before seen in Earth’s past,” she added.

What is revealed allows the scientists to draw closer parallels with anthropogenic climate change.  The short-lived precursor event appears more similar to what might occur if the current rate of carbon emissions were to be rapidly curbed, while the larger carbon release of the PETM more closely  parallels the likely environmental consequences of a continued pathway of rising atmospheric carbon dioxide emissions.

Dr Babila concluded, “Whilst natural geological processes such as rock weathering and carbon burial eventually meant Earth eventually recovered from the PETM, it took hundreds of thousands of years. So this is further proof that urgent action is needed today to rapidly cut the amount of carbon being release into the atmosphere to avoid long-lasting effects.”

https://www.eurekalert.org/news-releases/946294

OA paper:
https://www.science.org/doi/10.1126/sciadv.abg1025

Quote
DISCUSSION
Regional environmental trends in the Salisbury Embayment
Several key observations are ubiquitous among Paleocene-Eocene boundary shelf sections within the Salisbury Embayment in the Mid-Atlantic Coastal Plain. Surface ocean warming of 3° to 5°C (derived by Mg/Ca) at the CIE onset is recorded at the SDB (Fig. 2) and Bass River core sites (25). Planktonic foraminiferal B/Ca records at SDB are of similar absolute values, magnitude, and trends seen in nearby shelf and pelagic sites, in support of previous findings of near-uniform global surface ocean acidification signal

The discussion is much longer but it´s technical.

Long ago (noughties?) a paper came out which showed we were beating the PETM by matching the carbon output but with a faster pace. Great science. That should really help as an argument to do something about AGW because emulating the biggest extinction event ever is clearly not a good idea. Everybody knows you should brake before the cliff...
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jai mitchell

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Re: Paleoclimatology papers
« Reply #51 on: March 21, 2022, 08:33:04 PM »
This was an astounding lecture on the linkage between the Paleocene-Eocene Thermal Maximum, The "dinosaur killer" Chixulub Crater impact and the Deccan Traps eruptions (leading to a large increase in CO2).

Enjoy!

« Last Edit: March 21, 2022, 08:45:46 PM by jai mitchell »
Haiku of Futures Passed
My "burning embers"
are not tri-color bar graphs
+3C today

kassy

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Re: Paleoclimatology papers
« Reply #52 on: May 03, 2022, 01:52:21 PM »
Carbon, climate change and ocean anoxia in an ancient icehouse world

A new study describes a period of rapid global climate change in an ice-capped world much like the present -- but 304 million years ago. Within about 300,000 years, atmospheric carbon dioxide levels doubled, oceans became anoxic, and biodiversity dropped on land and at sea.

"It was one of the fastest warming events in Earth's history," said Isabel Montañez, distinguished professor in the Department of Earth and Planetary Sciences at the University of California, Davis.

Although several other 'hyperthermal' or rapid warming events are known in Earth's history, this is the first identified in an icehouse Earth, when the planet had ice caps and glaciers, comparable to the present day. It shows that an icehouse climate may be more sensitive to changes in atmospheric carbon dioxide than warmer conditions, when CO2levels are already higher. The work is published this week (May 2) in Proceedings of the National Academy of Sciences.

Montañez' lab has studied the period from 300 million to 260 million years ago, when Earth's climate went from a glacial icehouse to a hot, ice-free greenhouse. In 2007, they showed that the climate swung back and forth several times during this period.

More recently, Montañez' team and others have been able to home in on a transition 304 million years ago, the Kasimovian-Gzhelian boundary or KGB. They used multiple proxies, including carbon isotopes and trace elements from rocks and plant fossils, and modeling to estimate atmospheric CO2 at the time.

The researchers estimate that about 9000 Gigatons of carbon were released into the atmosphere just before the K-G boundary.

"We don't have a rate, but it was one of the fastest in Earth's history," Montañez said. That doubled atmospheric CO2from approximately 350 parts per million, comparable to modern pre-industrial levels, to about 700 ppm.

Deep ocean dead zones

One of the consequences of global warming is marine anoxia, or a drop in dissolved oxygen in the ocean. Melting ice caps release fresh water onto the ocean surface, creating a barrier to deep water circulation and cutting off the supply of oxygen. Without oxygen, marine life dies.

Lack of oxygen leaves its mark in uranium isotopes incorporated into rocks forming at the bottom of the ocean. By measuring uranium isotopes in carbonate rocks in present-day China, the researchers could get a proxy for the amount of oxygen -- or lack of it -- in the ocean when those rocks were laid down.

About 23 percent of the seafloor worldwide became anoxic dead zones, they estimate. That lines up with other studies showing big losses in biodiversity on land and at sea at the same time.

The effect of carbon release on ocean anoxia was significantly greater than that seen in other studies of rapid warming during 'greenhouse' conditions. That may be because the baseline level of atmospheric CO2 was already much higher.

"If you raised CO2 by the same amount in a greenhouse world, there isn't much affect, but icehouses seem to be much more sensitive to change and marine anoxia," Montañez said.

The massive carbon release may have been triggered by volcanic eruptions that tore through carboniferous coal beds, Montañez said. The eruptions would also have started fires, and warming may have melted permafrost, leading to the release of more organic carbon.

...

https://www.sciencedaily.com/releases/2022/05/220502170851.htm

paper:

Marine anoxia linked to abrupt global warming during Earth’s penultimate icehouse

...

Mechanism of Marine Anoxia.

To interrogate the potential mechanisms that may have been responsible for significant ocean anoxia during the KGB warming, we carried out climate model simulations using the fully coupled Community Earth System Model (CESM), version 1.2 (58), with a KGB event paleogeography. Our simulations suggest that ocean deoxygenation was tied, at least in part, to enhanced thermocline stratification and weakened deep meridional overturning circulation in the Northern Hemisphere. In a glacial state (low CO2 [LowCO2] simulation, 280 ppm), deep-water formation occurs in both hemispheres of the Panthalassic Ocean (Fig. 5 A and B). Ocean warming in an interglacial state (high CO2 [HighCO2] simulation, 560 ppm) decreases surface seawater density and induces a poleward migration of isopycnal outcrops, as compared with the glacial state, indicating enhanced seawater stratification during warming within the late Paleozoic icehouse (Fig. 5 C–E). Critically, increased surface stratification reduces mixed-layer depths (Fig. 5 A and B and SI Appendix, Fig. S10), which will decrease ocean-interior oxygen concentrations (Fig. 5F) (59). Warming-induced surface stratification in the northern high latitudes also causes a shutdown of deep convection that, in turn, leads to a 61% reduction in maximum overturning in the Northern Panthalassic Ocean (SI Appendix, Fig. S10). These results suggest that a restructuring of circulation regimes may have played a role in inducing anoxia, although additional work is necessary to quantify the effects on the global marine redox landscape.

Additionally, the greater extent of anoxia observed at the KGB per degree of warming, relative to other C-perturbation events that occurred under greenhouse climates, can be attributed to multiple reasons. First, the logarithmic relation between temperature change and atmospheric pCO2 predicts that the same rate of C injection may cause a greater temperature increase when the baseline, prewarming pCO2 is low in icehouse conditions than when prewarming pCO2 is high in greenhouse conditions. Furthermore, the climate sensitivity can also be amplified (by a factor of 2 or more) in icehouse conditions, due to ice-sheet changes that constitute a positive feedback (with stronger impact of sea ice than land ice), relative to greenhouse conditions (60). The greater warming response to pCO2 change under icehouse conditions would lead to more widespread anoxia through reduced O2 solubility and/or weakened ocean ventilation (Fig. 5) (1). Second, abrupt warming during icehouse conditions could have led to a pulse of phosphorus input to the ocean released during weathering of previously glaciated catchments (61, 62), promoting increased primary productivity that would have ultimately elevated oxygen consumption from the water column, enhancing ocean anoxia (via expansion of OMZs). Last, the late Paleozoic continental configuration, and thus the circulation patterns in the Paleo-Tethys Ocean, might have created a large-scale nutrient trap that promoted widespread euxinia in the region (e.g., South China) (63).
Collectively, our findings from the late Paleozoic icehouse provide a unique insight into global warming–induced ocean deoxygenation in a glacial state. More broadly, this work highlights that the extent of deoxygenation, relative to temperature change, can be highly variable for different C-injection events, particularly between those that occurred under different climate states (Fig. 4). Although the drivers of this difference in redox stability in response to warming under different climate states are not well constrained, our study provides a clear motivation for further study of this issue.

https://www.pnas.org/doi/full/10.1073/pnas.2115231119
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kassy

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Re: Paleoclimatology papers
« Reply #53 on: May 06, 2022, 01:34:46 PM »
WHAT ANCIENT POLLEN TELLS US ABOUT FUTURE CLIMATE CHANGE

Around 56 million years ago, Earth’s climate underwent a major climatic transition. A huge release of carbon into the ocean and atmosphere raised atmospheric carbon dioxide (CO₂) concentrations – which meant temperatures going up by 5 to 8°C and rising sea levels.

Sound familiar?

This event, called the Paleocene–Eocene Thermal Maximum (PETM), happened over the course of a few tens of thousands of years, but the causes and consequences of this transition are still widely debated.

...

Evidence for the PETM comes mostly from ancient marine sediments, but if we are to learn from this period what might happen as a result of our current climate change crisis, we need to understand what happened on the land as well.

To date, little information has been available concerning how the PETM climate changed life on land, so our research team used globally distributed fossil pollen preserved in ancient rocks to reconstruct how terrestrial vegetation and climate changed across this period.

Our new research, led by myself (Dr Vera Korasidis, University of Melbourne) and Dr Scott Wing at the Department of Paleobiology at the Smithsonian’s National Museum of Natural History and published in the journal Paleoceanography and Paleoclimatology, demonstrates that an increase in the concentration of atmospheric CO₂ played a major role in shifting Earth’s climate and plant life.

We could see a similar increase in the coming centuries as a result of anthropogenic (that is caused by humans) increases in CO₂.

To understand how terrestrial vegetation changed and moved during this period, we used a recently developed approach based on fossil pollen preserved in ancient rock deposits. It uses the distinct, species-specific appearance of pollen grains observed using a microscope.

...

Pollen preserved in rocks for tens of millions of years allows us to reconstruct both ancient floral communities, and past climates.

For the first time, we have applied this approach worldwide, to fossil samples from 38 PETM sites from every continent except Antarctica. This new pollen analysis shows that the PETM plant communities are distinct from pre-PETM plant communities at the same sites.

These shifts in floral composition, due to massive plant migrations, indicate that changes in vegetation as a result of climate change were global, although the types of plants involved varied by region.

When we say plant migration we mean plant movement, as the seeds that are spread grow better in one place and climate than in another – in this case at higher, cooler latitudes over lower, warmer ones.

Plants can migrate over 500 metres each year, so over thousands of years, they can move huge distances.

For example, in the Northern Hemisphere, the bald-cypress swamps of Wyoming in the US were suddenly replaced with palm-dominated seasonally dry subtropical forests. Likewise, in the Southern Hemisphere, wet-temperate podocarp forests were replaced by forests of subtropical palms.

We assigned each species a category based on climate, called a Köppen climate type. Examples of this include tropical rainforest, arid desert, temperate hot summer and polar tundra.

This tells us that the PETM brought warmer and wetter climates towards the poles in both hemispheres, but warmer and more seasonally dry climates to the mid-latitudes.

...

https://pursuit.unimelb.edu.au/articles/what-ancient-pollen-tells-us-about-future-climate-change

See link for full discussion.

Or directly to the paper:
Global Changes in Terrestrial Vegetation and Continental Climate During the Paleocene-Eocene Thermal Maximum

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021PA004325
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kassy

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Re: Paleoclimatology papers
« Reply #54 on: May 08, 2022, 03:29:05 PM »
Here's a Glimpse at a Future Hothouse Earth if Greenhouse Gasses Aren't Curbed

Throughout our planet's history, Earth has fluctuated between a hothouse and an icehouse.

Today, our home is supposed to be in a period of global cooling, but human emissions of greenhouse gasses are reversing that natural trend at a rapid and unprecedented rate.

One of the last times Earth went from an icehouse to a hothouse this quickly and dramatically, about 304 million years ago, our planet experienced major upheaval.

During the Kasimovian–Gzhelian boundary (KGB), atmospheric carbon levels doubled in roughly 300,000 years, from around 350 parts per million to 700 ppm. Now, new research suggests about 23 percent of the seafloor during this time were deprived of oxygen.

The findings are based on a fresh analysis of trace elements in a slab of ancient black shale in South China. The isotopes of carbon and uranium within this rock suggest that on top of global warming, rising sea levels, and melting glaciers, we also need to worry about ocean anoxia.

Anoxia is defined as a lack of oxygen. It can occur with climate change because when ice caps melt and add fresh water to the ocean surface, it obstructs atmospheric oxygen from dissolving and circulating in the sea.

Under extreme anoxic conditions, life in the ocean struggles to survive. Even areas with low oxygen, called hypoxia, are known as 'dead zones'.

The new results are supported by previous research on ancient bedrock in South China, which found major losses to biodiversity in the sea during the KGB boundary.

When modeling these ancient climate changes, the authors of the current study realized the importance of timing.

"If you raised CO2 by the same amount in a greenhouse world, there isn't much effect, but icehouses seem to be much more sensitive to change and marine anoxia," explains sedimentary geochemist Isabel Montañez from the University of California, Davis.


In other words, if human emissions had rapidly increased during a natural period of global warming, instead of global cooling, ocean anoxia wouldn't be nearly as big a threat.

Perhaps the reason has to do with the fact that greenhouse gasses in a hothouse world are already high, so emissions don't have as strong a melting effect on ice sheets and permafrost.

But during a period of global cooling, there are more ice sheets and glaciers trapping fresh water, ready to infiltrate the surface of the ocean and obstruct oxygen dissolving.

Researchers suspect the massive release of carbon that caused climate change between 290 and 340 million years ago was probably stimulated by volcanic eruptions.

Extensive wildfires would then have added even more carbon to the atmosphere, as would permafrost melt.

https://www.sciencealert.com/here-s-a-glimpse-at-a-future-hothouse-earth-if-greenhouse-gasses-aren-t-curbed

The paper:

Marine anoxia linked to abrupt global warming during Earth’s penultimate icehouse
https://www.pnas.org/doi/full/10.1073/pnas.2115231119

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kassy

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Re: Paleoclimatology papers
« Reply #55 on: May 16, 2022, 06:57:37 PM »
Algae reveal clues about climate changes over millions of years

Scientists identify and investigate algae which register sea water temperatures of the warmest months

Organisms adjust their cell walls according to environmental conditions such as temperature. Some adaptations involve changes in lipids which may still be preserved long after the rest of the organisms has been degraded. Researchers at the University of Göttingen studied a specific group of lipids called long chain diols which are found in sea sediments all over the world, and which can be preserved for millions of years. The researchers discovered that these lipids are produced by an, until now, unknown group of marine eustigmatophyte algae which evolved before the currently known species originated.

This finding changes our understanding of the composition and evolution of these algae, as previously they were considered to consist of a relatively small group of mainly soil and freshwater species. In addition, the researchers show that a ratio of these distinctive lipids, known as the Long chain Diol Index, can be used to reconstruct summer sea surface temperatures from the past. The research was published in the Proceedings of the National Academy of Sciences (PNAS).

For this study, combining expertise from the University of Göttingen's Geoscience Centre (Geobiology) and the Experimental Phycology and Culture Collection of Algae, the researchers took samples of seawater from the Mediterranean each month between April to October 2019 and analyzed them for lipid and DNA content. The DNA data revealed the occurrence of an early evolving group of marine eustigmatophyte algae which had not been identified before. Similarities in patterns of the eustigmatophyte DNA and the specific lipid concentrations, combined with in-depth analyses of previously published DNA and lipid datasets, show that these marine algae are the main producers of the long chain diols. "These lipids have been found in sediments from all over the world, dating from millions of years ago right up to now. But until now, no-one matched the unique lipid signature to these particular algae," says first author Dr Sebastiaan Rampen, who carried out this research at Göttingen University.

"A wide variety of techniques can be used to deduce ancient climates across Earth's history," Rampen explains. "What is exciting about our discovery is that we have demonstrated that the ratio of these unique lipids reveals temperatures in the warmest months. This explains why readings obtained by this method sometimes differ from other temperature reconstructions that give average temperatures across the year. Combining different methods now provides complementary information to help us better understand the Earth's climate going back millions of years."

This project was made possible thanks to funding from the German Research Foundation (DFG)

https://www.sciencedaily.com/releases/2022/05/220513103449.htm
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morganism

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Re: Paleoclimatology papers
« Reply #56 on: May 26, 2022, 05:01:06 AM »
Global record of “ghost” nannofossils reveals plankton resilience to high CO2 and warming

(...)
Despite their microscopic size, coccolithophores can be hugely abundant in the present ocean, being visible from space as cloud-like blooms. After death, their calcareous exoskeletons sink to the seafloor, accumulating in vast numbers, forming rocks such as chalk.

"The preservation of these ghost nannofossils is truly remarkable," says Professor Paul Bown (UCL). "The ghost fossils are extremely small ‒ their length is approximately five thousandths of a millimetre, 15 times narrower than the width of a human hair! ‒ but the detail of the original plates is still perfectly visible, pressed into the surfaces of ancient organic matter, even though the plates themselves have dissolved away".

The ghost fossils formed while the sediments at the seafloor were being buried and turned into rock. As more mud was gradually deposited on top, the resulting pressure squashed the coccolith plates and other organic remains together, and the hard coccoliths were pressed into the surfaces of pollen, spores and other soft organic matter. Later, acidic waters within spaces in the rock dissolved away the coccoliths, leaving behind just their impressions - the ghosts.

"Normally, palaeontologists only search for the fossil coccoliths themselves, and if they don't find any then they often assume that these ancient plankton communities collapsed," explains Professor Vivi Vajda (Swedish Museum of Natural History). "These ghost fossils show us that sometimes the fossil record plays tricks on us and there are other ways that these calcareous nannoplankton may be preserved, which need to be taken into account when trying to understand responses to past climate change"

Ghost nannofossils are likely common in the fossil record, but they have been overlooked due to their tiny size and cryptic mode of preservation. We think that this peculiar type of fossilization will be useful in the future, particularly when studying geological intervals where the original coccoliths are missing from the fossil record".

The study focused on the Toarcian Oceanic Anoxic Event (T-OAE), an interval of rapid global warming in the Early Jurassic (183 million years ago), caused by an increase in CO2-levels in the atmosphere from massive volcanism in the Southern Hemisphere. The researchers found ghost nannofossils associated with the T-OAE from the UK, Germany, Japan and New Zealand, but also from two similar global warming events in the Cretaceous: Oceanic Anoxic Event 1a (120 million years ago) from Sweden, and Oceanic Anoxic Event 2 (94 million years ago) from Italy.

"The ghost fossils show that nannoplankton were abundant, diverse and thriving during past warming events in the Jurassic and Cretaceous, where previous records have assumed that plankton collapsed due to ocean acidification," explains Professor Richard Twitchett (Natural History Museum, London). "These fossils are rewriting our understanding of how the calcareous nannoplankton respond to warming events."

Finally, Dr. Sam Slater explains: "Our study shows that algal plankton were abundant during these past warming events and contributed to the expansion of marine dead zones, where seafloor oxygen-levels were too low for most species to survive. These conditions, with plankton blooms and dead zones, may become more widespread across our globally warming oceans."

http://astrobiology.com/2022/05/discovery-of-ghost-fossils-reveals-plankton-resilience-to-past-global-warming-events.html

Global record of “ghost” nannofossils reveals plankton resilience to high CO2 and warming

https://www.science.org/doi/10.1126/science.abm7330

kassy

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Re: Paleoclimatology papers
« Reply #57 on: May 27, 2022, 07:48:34 PM »
Not proper paleo but useful background work:

Scientists shine new light on role of Earth’s orbit in the fate of ancient ice sheets


Scientists have finally put to bed a long-standing question over the role of Earth’s orbit in driving global ice age cycles.

In a new study published today in the journal Science, the team from Cardiff University has been able to pinpoint exactly how the tilting and wobbling of the Earth as it orbits around the Sun has influenced the melting of ice sheets in the Northern Hemisphere over the past 2 million years or so.

Scientists have long been aware that the waxing and waning of massive Northern Hemisphere ice sheets results from changes in the geometry of Earth’s orbit around the Sun.

There are two aspects of the Earth’s geometry that can influence the melting of ice sheets: obliquity and precession. 

Obliquity is the angle of the Earth’s tilt as it travels around the Sun and is the reason why we have different seasons.

Precession is how the Earth wobbles as it rotates, much like a slightly off-centre spinning top. The angle of this wobble means that sometimes the Northern Hemisphere is closest to the Sun and other times the Southern Hemisphere is closest, meaning that roughly every 10,000 years one hemisphere will have warmer summers compared to the other, before it switches.

Scientists have determined that over the past million years or so, the combined effects of obliquity and precession on the waxing and waning of Northern Hemisphere ice sheets has resulted, through complicated interactions within the climate system, in ice age cycles lasting approximately 100 thousand years.

However, before 1 million years ago, in a period known as the early Pleistocene, the duration of ice age cycles was controlled only by obliquity and these ice age cycles were almost exactly 41,000 years long.


For decades, scientists have been puzzled as to why precession did not play a more important part in driving ice age cycles during this period.

In their new study, the Cardiff University team reveal new evidence suggesting that precession did actually play a role during the early Pleistocene.

Their results show that more intense summers, driven by precession, have always caused Northern Hemisphere ice sheets to melt, but before 1 million years ago, these events were less devastating and did not lead to the complete collapse of ice sheets.

Lead author of the study Professor Stephen Barker, from Cardiff University’s School of Earth and Environmental Sciences, said: “Early Pleistocene ice sheets in the northern hemisphere were smaller than their more recent counterparts, and limited to higher latitudes where the effects of obliquity dominate over precession. This probably explains why it has taken so long for us to find evidence of precession forcing during early Pleistocene.

“These findings are the culmination of a major effort, involving more than 12 years of painstaking work in the laboratory to process nearly 10,000 samples and the development of a range of new analytical approaches. Thanks to this we can finally put to rest a long-standing problem in paleoclimatology and ultimately contribute to a better understanding of Earth’s climate system.

“Improving our understanding of Earth’s climate dynamics, even in the remote past, is crucial if we hope to predict changes over the next century and beyond. Ongoing changes may be manmade, but there’s only one climate system and we need to understand it.”

https://www.eurekalert.org/news-releases/954013

Imprisoned science:

Persistent influence of precession on northern ice sheet variability since the early Pleistocene

Abstract
Prior to ~1 million years ago (Ma), variations in global ice volume were dominated by changes in obliquity; however, the role of precession remains unresolved. Using a record of North Atlantic ice rafting spanning the past 1.7 million years, we find that the onset of ice rafting within a given glacial cycle (reflecting ice sheet expansion) consistently occurred during times of decreasing obliquity whereas mass ice wasting (ablation) events were consistently tied to minima in precession. Furthermore, our results suggest that the ubiquitous association between precession-driven mass wasting events and glacial termination is a distinct feature of the mid to late Pleistocene. Before then (increasing), obliquity alone was sufficient to end a glacial cycle, before losing its dominant grip on deglaciation with the southward extension of Northern Hemisphere ice sheets since ~1 Ma.

https://www.science.org/doi/10.1126/science.abm4033

Mass wastage in ice...interesting idea.
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kassy

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Re: Paleoclimatology papers
« Reply #58 on: June 01, 2022, 01:45:15 PM »
Palms at the poles: Fossil plants reveal lush southern hemisphere forests in ancient hothouse climate


Plant fossils dating back 55 to 40 million years ago, during the Eocene epoch reveal details about the warmer and wetter climate. These conditions meant there were palms at the North and South Pole and predominantly arid landmasses like Australia were lush and green. By focusing on the morphology and taxonomic features of 12 different floras, the researchers developed a more detailed view of what the climate and productivity was like in the ancient hothouse world of the Eocene epoch.

...

The fossils date back 55 to 40 million years ago, during the Eocene epoch. At that time, the world was much warmer and wetter, and these hothouse conditions meant there were palms at the North and South Pole and predominantly arid landmasses like Australia were lush and green. Reichgelt and co-authors looked for evidence of differences in precipitation and plant productivity between then and now.

Since different plants thrive under specific conditions, plant fossils can indicate what kinds of environments those plants lived in.

By focusing on the morphology and taxonomic features of 12 different floras, the researchers developed a more detailed view of what the climate and productivity was like in the ancient hothouse world of the Eocene epoch.

Reichgelt explains the morphological method relies on the fact that the leaves of angiosperms -- flowering plants -- in general have a strategy for responding to climate.

"For example, if a plant has large leaves and it is left out in the sun and doesn't get enough water, it starts to shrivel up and die because of excess evaporation," Reichgelt says. "Plants with large leaves also lose heat to its surroundings. Finding a large fossil leaf therefore means that most likely this plant was not growing in an environment that was too dry or too cold for excess evaporation or sensible heat loss to happen. These and other morphological features can be linked to the environment that we can quantify. We can compare fossils to modern floras around the world and find the closest analogy."

The second approach was taxonomic. "If you travel up a mountain, the taxonomic composition of the flora changes. Low on the mountain, there may be a deciduous forest that is dominated by maples and beeches and as you go further up the mountain, you see more spruce and fir forest," says Reichgelt. "Finding fossils of beech and maple therefore likely means a warmer climate then if we find fossils of spruce and fir." Such climatic preferences of plant groups can be used to quantitatively reconstruct the ancient climate in which a group of plants in a fossil assemblage was growing.

The results show that the Eocene climate would have been very different to Australia's modern climate. To sustain a lush green landscape, the continent required a steady supply of precipitation. Warmth means more evaporation, and more rainfall was available to move into Australia's continental interior. Higher levels of carbon dioxide in the atmosphere at the time, 1500 to 2000 parts per million, also contributed to the lushness via a process called carbon fertilization. Reichgelt explains that with the sheer abundance of CO2, plants were basically stuffing their faces.

"Southern Australia seems to have been largely forested, with primary productivity similar to seasonal forests, not unlike those here in New England today," Reichgelt says. "In the Northern Hemisphere summer today, there is a big change in the carbon cycle, because lots of carbon dioxide gets drawn down due to primary productivity in the enormous expanse of forests that exists in a large belt around 40 to 60 degrees north. In the Southern Hemisphere, no such landmass exists at those same latitudes today. But Australia during the Eocene occupied 40 degrees to 60 degrees south. And as a result, there would be a highly productive large landmass during the Southern Hemisphere summer, drawing down carbon, more so than what Australia is doing today since it is largely arid."

Hutchinson says the geological evidence suggests the climate is highly sensitive to CO2 and that this effect may be larger than what our climate models predict, "The data also suggests that polar amplification of warming was very strong, and our climate models also tend to under-represent this effect. So, if we can improve our models of the high-CO2 Eocene world, we might improve our predictions of the future."

Future projects will expand the data set beyond Australia to ask what global productivity does during a hothouse climate on a global scale.

"We have large datasets of plant fossils that have been collected around the world, so we can apply the same methods that we use here to ask what happens to global biosphere productivity," says Reichgelt.

https://www.sciencedaily.com/releases/2022/05/220531111823.htm

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Tor Bejnar

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Re: Paleoclimatology papers
« Reply #59 on: June 01, 2022, 07:55:45 PM »
Quote
"Southern Australia seems to have been largely forested, with primary productivity similar to seasonal forests, not unlike those here in New England today,"
This was an odd statement (to my thinking).  "New England" happens to not only be an area in northeastern USA (including Connecticut, the source of the article), but is a region within New South Wales, Australia.  The Australian New England may have some climatic similarities to the American one, but I'm guessing the author of that sentence isn't aware of them [https://en.wikipedia.org/wiki/New_England_(New_South_Wales)].
Arctic ice is healthy for children and other living things because "we cannot negotiate with the melting point of ice"

kassy

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Re: Paleoclimatology papers
« Reply #60 on: June 24, 2022, 03:05:29 PM »
Not paleontology per se but the trigger for the PETM spike if they are correct.

Stretching of the continents drove ancient global warming event, say scientists


Scientists at the University of Southampton have discovered that stretching of the continents is likely to have caused one of the most extreme and abrupt episodes of global warming in Earth history.

The researchers, working with colleagues at the University of Edinburgh, the University of Leeds, the University of Oldenburg, the University of Florence and the Chinese Academy of Sciences, studied the effects of global tectonic forces and volcanic eruptions during a period of extreme environmental change 56 million years ago.

During this time, some sequence of events caused the planet to warm by 5-8˚C, culminating in the ‘Palaeocene-Eocene Thermal Maximum’ or PETM, which lasted about 170,000 years. This caused the extinction of many deep-sea organisms, reshaping the course of evolution of life on Earth.

The team propose that the extensive stretching of the continental plates in the northern hemisphere – rather like the pulling of a toffee bar that thins and eventually separates – massively reduced the pressures in the Earth’s deep interior. This then drove intense, but short-lived melting in the mantle – a layer of sticky, molten rock just below the planet’s crust. The team show that the resulting volcanic activity coincided with, and likely caused, a massive burst of carbon release into the atmosphere linked to PETM warming.

The researchers’ findings are due to be published in the journal Nature Geoscience.

more on:
https://www.eurekalert.org/news-releases/956737
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kassy

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Re: Paleoclimatology papers
« Reply #61 on: June 30, 2022, 02:54:52 PM »
More PETM. end-Permian mass extinction (252 million years ago)The fires:

Wildfires May Have Sparked Ecosystem Collapse During Earth's Worst Mass Extinction
https://phys.org/news/2022-06-wildfires-ecosystem-collapse-earth-worst.html

Researchers at University College Cork (UCC) and the Swedish Museum of Natural History examined the end-Permian mass extinction (252 million years ago) that eliminated almost every species on Earth, with entire ecosystems collapsing. The researchers discovered a sharp spike in wildfire activity from this most devastating of mass extinctions. Promoted by rapid greenhouse gas emissions from volcanoes, extreme warming and drying led to wildfires across vast regions that were previously permanently wet. Instead of capturing carbon from the atmosphere, these wetlands became major sources of atmospheric carbon, enhancing the sharp warming trend. The research is published in PALAIOS today.

"Sifting through the fossil plant records of eastern Australia and Antarctica, we found high abundances of burnt, or charcoalified, plants throughout the late Permian Period. From this high baseline, charcoal abundances reached a prominent peak right at the top of the last Permian coal beds, indicating a major but short-lived increase in wildfires. This was followed by low charcoal for the next three million years of the Early Triassic Period. It was an end-Permian burnout, followed by an Early Triassic depression" comments Dr. Chris Mays, Lecturer in Paleontology at University College Cork (UCC) and lead author of the study.

The researchers highlight that in today's world, wildfires have caused shocking mass animal die-offs in several regions around the world (e.g. California 2018, 2020, Australia 2019-20). Over the same time, our warming global climate has led to prolonged droughts and increased wildfires in typically wet habitats, such as the peat forests of Indonesia and the vast Pantanal wetlands of South America. These major 'carbon sinks'―regions of natural capture of carbon from the atmosphere―are crucial in our fight against climate change. As the fossil record reveals, without these regions of carbon capture, the world can stay intolerably warm for hundreds of millennia.

"The potential for wildfires as a direct extinction driver during hyperthermal events, rather than a symptom of climatic changes deserves further examination. Unlike the species that suffered the mass extinctions of the past, we have the opportunity to prevent the burning of the world's carbon sinks and help avoid the worst effects of modern warming" comments Dr. Mays.

Chris Mays et al, End-Permian Burnout: The Role Of Permian–Triassic Wildfires In Extinction, Carbon Cycling, And Environmental Change In Eastern Gondwana, PALAIOS (2022).
https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/37/6/292/614825/END-PERMIAN-BURNOUT-THE-ROLE-OF-PERMIAN-TRIASSIC?redirectedFrom=fulltext
« Last Edit: August 04, 2022, 05:08:52 PM by kassy »
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kassy

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Re: Paleoclimatology papers
« Reply #62 on: June 30, 2022, 02:55:03 PM »
And recovery:

Shrimps and worms ‘were among first to recover after largest mass extinction’

The end-Permian mass extinction – around 252 million years ago – killed more than 90% of species on Earth.

...

It took millions of years for biodiversity life on Earth to return to pre-extinction levels.

But by examining trails and burrows on the South China seabed, researchers from China, the US and the UK pieced together sea life’s revival by pinpointing what animal activity happened when.

Alison Cribb, a collaborator in the study from the University of Southern California, added: “The first animals to recover were deposit feeders such as worms and shrimps.

“The recovery of suspension feeders such as brachiopods, bryozoans and many bivalves took much longer.
...

“We were able to look at trace fossils from 26 sections through the entire series of events, representing seven million crucial years of time, and showing details at 400 sampling points, we finally reconstructed the recovery stages of all animals including benthos, nekton, as well as these soft-bodied burrowing animals in the ocean.”

Researchers say the findings matter because the end-Permian crisis was caused by global warming and ocean acidification, and the data reveals the resilience of the soft-bodied animals to high CO2 and warming.

https://www.independent.co.uk/news/science/earth-shrimps-co2-school-earth-sciences-b2112344.html

another article:

Professor Zhong-Qiang Chen, director of the study, said: "The trace fossils show us when and where soft-bodied, burrowing animals flourished in this Early Triassic greenhouse world.

"For example, elevated temperatures and extended anoxia coincided with low values of behavioral and ecologic diversities across the Permian-Triassic boundary, and it took about 3 million years for ecological recovery of soft-bodied animals to match the pre-extinction levels."

https://phys.org/news/2022-06-shrimps-worms-animals-recover-largest.html


The paper:

Resilience of infaunal ecosystems during the Early Triassic greenhouse Earth

https://www.science.org/doi/10.1126/sciadv.abo0597
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trm1958

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Re: Paleoclimatology papers
« Reply #63 on: June 30, 2022, 05:18:43 PM »
And the sun is about two and a half percent brighter than it was at the Great Dying so we have even less margin now.

dnem

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Re: Paleoclimatology papers
« Reply #64 on: June 30, 2022, 10:56:57 PM »
I live in the green, damp and humid US mid-Atlantic region - in Maryland. Being in arid, brown and fire prone landscapes makes me anxious. I'd take our hot and humid summers over drought and fire prone regions every time.

kassy

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Re: Paleoclimatology papers
« Reply #65 on: September 01, 2022, 12:44:07 PM »
Enhanced ocean oxygenation during Cenozoic warm periods

Earth's past warm periods witnessed the shrinkage of the open ocean's oxygen-deficient zones

When oxygen becomes scarce, life has a hard time. This is just as true for mountain regions above 7000 meters but also for bodies of water. For example, in tropical ocean regions off of West America and West Africa and in the northern Indian Ocean, only specialized microbes and organisms with a slow metabolism such as jellyfish can survive.

In the last 50 years, oxygen-deficient zones in the open ocean have increased. This poses major problems not only for marine ecosystems, but also for coastal inhabitants and countries that rely on fisheries as a source of food and income. Scientists have attributed this development to rising global temperatures: Less oxygen dissolves in warmer water, and the tropical ocean's layers can become more stratified. But how will this development continue, and what happened in past warm periods?

A team led by Alexandra Auderset and Alfredo Martínez-García at the Max Planck Institute for Chemistry in Mainz has shown in a recent study that, in the open ocean, oxygen-deficient zones shrank during warm periods of the past.

The past oxygen content of the oceans can be read in sediments

The researchers read this finding from marine sediment archives. Drill cores can be used to determine past environmental conditions in a similar way to tree rings. Among other things, the sediment layers provide information about the oxygen content of the sea in the past. This is due to microorganisms such as foraminifera, which once lived on the sea surface and whose skeletons sank to the sea floor where they became part of the sediment. During their lifetime, these zooplankton absorbed chemical elements such as nitrogen, whose isotope ratio in turn depended on environmental conditions. Under oxygen-deficient conditions, bacterial denitrification occurs. In this process, the nutrient nitrate is chemically reduced to molecular nitrogen (N2) by bacteria. As they prefer to absorb light isotopes from the water instead of heavy ones, the ratio of light 14N shifts to heavy 15N in periods when the bacteria were active in the oceans. This changing isotopic signal, in turn, can be used to determine the extent of earlier oxygen-deficient zones.

The tropical Pacific Ocean was well oxygenated during past warm periods

Using nitrogen isotopes from foraminifera, the scientists from Mainz and Princeton University showed that denitrification of the water column in the eastern tropical North Pacific was greatly reduced during two warm phases of the Earth's modern era, the Cenozoic, about 16 and 50 million years ago.

"We had not expected this clear effect. From the correlation between high global temperatures and low denitrification rates, we conclude that the tropical Pacific's oxygen-deficient zones shrank," says Auderset about the results, which were recently published in the journal Nature.

"It's been a decades-long campaign to develop the methods that allowed for these findings," says Daniel Sigman, Dusenbury Professor of Geological and Geophysical Sciences, whose group collaborated in the study. "And it turns out that even these first results are altering our view of the relationship between climate and the ocean's oxygen conditions."

It cannot, however, yet be precisely estimated what this means for the current expansion of the oxygen-deficient open ocean zones: "Unfortunately, it remains unclear whether our finding of shrinking marine oxygen-deficient zones is applicable to the coming decades or only to the much longer term," adds the paleoclimatologist Auderset. "This is because we don't yet know whether short- or long-term processes were responsible for the change."

Searching for the cause

One leading possibility for the decline in oxygen-deficient zones under warming involves a reduction in the upwelling-fueled biological productivity of tropical surface waters. A decline in productivity could have occurred because winds weakened in the equatorial Pacific under warmer climate.

In the current study, the authors also found that during the two warm periods of the Cenozoic -- the mid-Miocene climate optimum about 16 million years ago and the early Eocene climate optimum about 50 million years ago -- the temperature difference between high and low latitudes was much smaller than at present. Both, the global warming and the weakening of high-to-low latitude temperature difference, should have worked to weaken tropical winds, reducing the upwelling of nutrient-rich deep seawater. This, in turn, would have resulted in lower biological productivity at the surface and less sinking of dead algal organic matter into the deep ocean, providing less fuel for the oxygen consumption that produces oxygen-deficient conditions. This chain of events can occur relatively quickly. Thus, if a similar change applies to human-driven global warming as well, then there could be a decline in the extent of open ocean oxygen deficiency in the coming decades.

Alternatively, the cause may lie in the Southern Ocean, thousands of kilometers away. During past prolonged warm periods, the exchange water between Southern Ocean surface waters and the deep ocean ("deep ocean overturning") may have accelerated, leading to higher oxygen in the ocean interior as a whole and thus shrinking the low-oxygen zones. If stronger Southern Ocean-driven deep ocean overturning was the main cause of the shrunken tropical oxygen-deficient zones, then this effect would take more than a hundred years at earliest to come into play.

"Both mechanisms probably play a role," says Alfredo Martínez-García, "The race is now on to figure out which mechanism is most important."

https://www.sciencedaily.com/releases/2022/08/220831113639.htm
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FishOutofWater

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Re: Paleoclimatology papers
« Reply #66 on: September 05, 2022, 10:40:37 PM »
Here's something from the Rutgers web site that helps explain the apparent discrepancies.

Our study also underscores the importance of seasonal changes, specifically Northern Hemisphere summers, in driving many climate systems


Summer temperatures were higher in the early Holocene and that warmth melted the ice. However, remnant ice made fall and winter colder so the annual average temperature in the early Holocene was cooler.
« Last Edit: September 05, 2022, 11:51:42 PM by FishOutofWater »

kassy

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Re: Paleoclimatology papers
« Reply #67 on: September 11, 2022, 08:38:36 PM »
Ice age ‘weather balloon’ probes ancient temperatures high in the atmosphere

Rare isotopes trapped in ice give scientists a new window on Earth’s past climate

Reconstructing ancient climates is murky business. Cores of sediment or ice contain records of temperatures that date back hundreds of thousands or even millions of years, but typically only near Earth’s surface or in the ocean. Now, by measuring rare oxygen isotopes, a team of geochemists has developed a way to deduce long-ago global temperatures 10 kilometers up in the atmosphere, creating, in effect, a paleo–weather balloon. The technique will help scientists study past climates, not only to better understand what conditions were like as life evolved, but also to ground-truth computer models’ predictions about global warming.

“There are not a lot of geological archives that store information about past temperature at high elevations,” says James Russell, a paleoclimatologist at Brown University who wasn’t involved in the work. “This new method gives us a way to see what the Earth’s upper atmosphere was doing.”

To create the new probe, Laurence Yeung, a geochemist at Rice University, and his colleagues relied on so-called “clumped isotopes,” where two or more atoms in a molecule are replaced by isotopic cousins of different weights. They targeted oxygen molecules (O2) in which rare oxygen-18 isotopes replaced both of the more common atoms of oxygen-16. In today’s atmosphere, the molecule exists at levels of just 4 parts per million, forming naturally at an altitude of about 10 or 11 kilometers. The colder it gets, the more these rare molecules are created, which means tiny variations in their abundance can be used as a thermometer. Once formed, winds mix the molecules throughout the atmosphere, and some get trapped in air bubbles within compacted ice. Yeung was keen to apply the method to the Last Glacial Maximum (LGM), a cold period 20,000 years ago, which plays a critical role in many climate models.

The challenge was measuring small variations of an exceedingly rare gas, which Yeung says was akin to weighing a Boeing 737 jet to within the weight of a grain of sand. To achieve such precision, Rice graduate student and co-author Asmita Banerjee worked in a freezer room, cutting 100-gram chunks of ice taken from ice cores from Greenland and Antarctica that dated to the LGM. She carefully melted the ice and collected the gasses in the air bubbles. After filtering out nitrogen, argon, and other trace gases, she ran the remaining oxygen through a souped-up mass spectrometer customized to tally all the oxygen atoms present by weight. “We kind of hot-rodded it,” Yeung says.

Banerjee put in a “heroic effort,” he says. She spent weeks performing the analysis for 102 samples, with each laboratory run taking about 9 hours. “I do try to make sure I’m not sleeping here,” Banerjee says. “That’s a personal boundary for me.”

Based on the proportional abundance of O2 made of oxygen-18 in the samples, the team concluded that the upper troposphere—a region of the atmosphere corresponding to an altitude of 10 to 11 kilometers—was between 6℃ and 9℃ colder in the LGM than today, they report in the 17 August issue of AGU Advances. Those temperatures are not as cold as previous high-altitude estimates that were based on records from mountain lake sediments. “This illustrates the power of having this tracer that integrates the global signal rather than looking at a specific location,” Yeung says.

The number also allowed the team to calculate the “lapse rate,” or the rate at which air temperatures fall with height, an important damper on climate change. When Earth’s surface warms, it puts more water vapor and heat into the upper troposphere. But in the upper troposphere—above the planet’s clouds and heat-trapping gases—heat can efficiently radiate into space, offsetting some of the heating below. The reverse is also true, the new study suggests. During the frigid LGM, the upper troposphere dried and cooled, reducing some of the leakage to space and keeping the planet a bit warmer. The lapse rate is “always buffering against changes in the surface temperatures,” Russell says.

The study’s estimate of the strength of this buffering effect fits with climate model predictions better than those based on the mountain lake records, says Brian Soden, a climate scientist at the University of Miami. “They came up with results that are more consistent with how we think the climate works,” he says. “That’s reassuring, from my perspective.”

https://www.science.org/content/article/ice-age-weather-balloon-probes-ancient-temperatures-high-atmosphere
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kassy

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Re: Paleoclimatology papers
« Reply #68 on: October 05, 2022, 02:44:20 PM »
The last 12,000 years show a more complex climate history than previously thought


We rely on climate models to predict the future, but models cannot be fully tested as climate observations rarely extend back more than 150 years. Understanding the Earth's past climate history across a longer period gives us an invaluable opportunity to test climate models on longer timescales and reduce uncertainties in climate predictions.

In this context, changes in the average surface temperature of the Earth during the current interglacial Epoch, the Holocene (approximately the past 12,000 years), have been thoroughly debated over the past decades. Reconstructions of past temperature seem to indicate that global mean temperature showed a maximum around 6,000 years ago and has cooled until the onset of the current climate crisis during the industrial revolution. Climate model simulations, on the other hand, suggest continuous warming since the start of the Holocene. In 2014, researchers named this major mismatch between models and past climate observations the "Holocene Temperature Conundrum."

In this new study published in Nature Communications, scientists used the largest available database of past temperature reconstructions extending back 12,000 years to carefully investigate the geographic pattern of temperature change during the Holocene. Olivier Cartapanis and colleagues find that, contrary to previously thought, there is no globally synchronous warm period during the Holocene. Instead, the warmest temperatures are found at different times not only in different regions but also between the ocean and on land. This questions how meaningful comparisons of the global mean temperature between reconstructions and models actually are.

According to the lead author Olivier Cartapanis, "the results challenge the paradigm of a Holocene Thermal Maximum occurring at the same time worldwide." And, while the warmest temperature was reached between 4,000 and 8,000 years ago in western Europe and northern America, the surface ocean temperature cooled since about 10,000 years ago at mid-high latitudes and remained stable in the tropics. The regional variability in the timing of maximum temperature suggests that high latitude insolation and ice extent played major roles in driving climate changes throughout the Holocene.

Lukas Jonkers, co-author of the study and researcher at the MARUM—Center for Marine Environmental Sciences in Bremen, Germany, says, "Because ecosystems and people do not experience the mean temperature of the Earth, but are affected by regional and local changes in climate, models need to get the spatial and temporal patterns of climate change right in order to guide policy makers."

...

https://phys.org/news/2022-10-years-complex-climate-history-previously.html

Open access:

Complex spatio-temporal structure of the Holocene Thermal Maximum
https://www.nature.com/articles/s41467-022-33362-1
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kassy

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Re: Paleoclimatology papers
« Reply #69 on: February 19, 2023, 12:56:45 PM »
Palaeoecology: Explaining marine species richness at the Equator


Ancient climate change may have driven the development of latitudinally skewed patterns of planktonic marine biodiversity that are still apparent today, two papers published in this week’s Nature suggest. The studies, which help to explain how marine biodiversity is generated and maintained over millions of years, may contribute to predictions of how today’s marine ecosystems are likely to respond to future climate change.

Species richness increases from the poles to the tropics, but the mechanisms that drive this latitudinal diversity gradient are disputed. Understanding the drivers of global species distribution may help us to predict the potential impacts of global change on biodiversity and how they may affect ecosystem services that are fundamental to the health, livelihood and wellbeing of billions of people.

Two studies in Nature assess changes in planktonic foraminifera, a group of shelled, unicellular organisms that float in the water column and can become preserved as fossils. Adam Woodhouse, Anshuman Swain and colleagues studied a recently developed global dataset of these fossils to reveal that the latitudinal ranges of planktonic foraminifera have shifted markedly towards the Equator over the past 8 million years, in response to the formation of polar ice sheets. However, these ranges may be shifting polewards again in response to climate change related to human activity.

In a separate paper, Erin Saupe and colleagues combine a record of planktonic fossils extending back 40 million years with palaeoclimate models. Their analyses reveal that the latitudinal gradient may have started to emerge around 15 million years ago, as the Earth’s climate began to cool. The authors also suggest that the gradient may have been driven by the structure of the water column (how the water varies from the surface to the bottom). Higher rates of speciation are likely to occur at lower latitudes, where there is more temperature variation by depth, they say.

Together, these studies add to our understanding the evolution of marine diversity gradients on long time scales.

http://www.natureasia.com/en/research/highlight/14382

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kassy

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Re: Paleoclimatology papers
« Reply #70 on: February 19, 2023, 09:13:06 PM »
Early forests did not significantly change the atmospheric CO2


Scientists have discovered that the atmosphere contained far less CO2 than previously thought when forests emerged on our planet, the new study has important implications for understanding how land plants affect the climate.

...

Earth's continents were colonized by tall trees and forests about 385 million years ago. Before then, shallow shrub-like plants with vascular tissue, stems, shallow roots, and no flowers had invaded the land. Textbooks tell us that the atmosphere at that time had far higher CO2 levels than today and that an intense greenhouse effect led to a much warmer climate. The emergence of forests was previously thought to promote CO2 removal from the atmosphere, driving the Earth into a long cool period with ice cover at the poles.

Reconstructing atmospheric CO2 levels in the geological past is difficult and has previously relied on proxies that also depend on parameters that had to be assumed. Climate scientists agree that CO2 plays a crucial role in shaping Earth's climate both today and in the past. Therefore, a grand challenge for Earth scientist is to understand what has controlled the abundance CO2 in the atmosphere.

"We calibrated a mechanistic model for the gas-exchange between plant leaves and the ambient air to the oldest lineage of vascular land plants, namely clubmosses. With this approach, we could calculate the CO2 level in the air solely from observations made on the plant material," tells associate professor Tais W. Dahl from the Globe institute at University of Copenhagen, who led the study in collaboration with an international team of researchers from Germany, Saudi Arabia, UK, and USA.

The new method builds on three observations that can be made both in living plants and fossil plant tissue, including the ratio of two stable carbon isotopes and the size and density of stomata (pore openings) through which CO2 is taken up by the plant. The researchers calibrated the method in living clubmosses and found that this approach can accurately reproduce ambient CO2 levels in the greenhouse.

"The newly calibrated method to study CO2 levels from the geological record is superior to previous approaches that produce estimates with unbound error bars simply because they depend on parameters that cannot be independently constrained in the geological record," says Barry Lomax Professor at University of Nottingham and a co-author on the study.

The research team applied the method to some of the oldest vascular plant fossils that lived before and after trees evolved on our planet and discovered that the ratio of the two stable carbon isotopes, carbon-13 and carbon-12, is very similar to that of modern plants. Further, the stomata density and size were also very similar to that observed in their living descendants. These observations kickstarted a more thorough investigation of the early CO2 record.

Dahl and colleagues collected data from 66 fossils of three distinct species of club mosses found in 9 different localities worldwide 410 to 380 million years in age. In all cases, the atmospheric CO2 levels were only 30-70% higher (~525 -- 715 ppm) than today (~415 ppm). This is far lower than previously thought (2000-8000 ppm). Ppm stands for parts-per-million and is the unit used to measure carbon dioxide concentrations in air.

The team utilized a paleoclimate model to show that Earth was a temperate planet with mean tropical surface air temperatures of 24.1-24.6°C.

"We used a fully coupled atmosphere-ocean model to find that Earth had ice-covered poles when forests emerged. Yet, land plants could thrive in the tropical, subtropical and temperate zones," explains Georg Feulner from the Potsdam Institute for Climate in Germany, who co-authored the study.

The new study suggest that trees actually play an insignificant role on atmospheric CO2 levels over longer time scales because early trees had deeper root systems and produced more developed soils that are associated with lower nutrient loss. With more efficient nutrient recycling in soils, trees actually have a smaller weathering demand than the shallow shrub-like vegetation that came before them. This idea goes against previous thinking that trees with deeper root system promoted CO2 removal through enhanced chemical weathering and dissolution of silicate rocks.

Dahl and colleagues used Earth system models to show that primitive shrub-like vascular plants could have caused a massive decline in atmospheric CO2 earlier in history, when they first spread on the continents. The model shows that vascular ecosystem would have simultaneously led to a rise in atmospheric O2 levels.

https://www.sciencedaily.com/releases/2022/12/221220112418.htm

I put this in Earth though time but i keep thinking about the bolded part.
So we finally have a measurement for atmospheric CO2 and that puts a big constraint on the numbers we use which used to be way bigger.

I think this probably holds true for most scenarios which implies there is way less budget left but of course we do not have the data for other big excursions yet. But there is no reason the same pattern would not show up.
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kassy

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Re: Paleoclimatology papers
« Reply #71 on: February 20, 2023, 03:12:51 PM »
Climate: Lessons from the latest global warming


56 million years ago, the Earth experienced one of the largest and most rapid climate warming events in its history: the Paleocene-Eocene Thermal Maximum (PETM), which has similarities to current and future warming. This episode saw global temperatures rise by 5-8°C. It was marked by an increase in the seasonality of rainfalls, which led to the movement of large quantities of clay into the ocean, making it uninhabitable for certain living species. This scenario could be repeated today. This is what a team from the University of Geneva (UNIGE) has revealed, thanks to the analysis of sediments taken from the deep waters of the Gulf of Mexico. These results can be found in the journal Geology.

The Paleocene-Eocene Thermal Maximum (PETM), which occurred 56 million years ago, is the largest and most rapid climatic disturbance of the Cenozoic era (65.5 million years ago to the present day). Exceptional both in terms of its amplitude (5-8°C increase) and its suddenness (5,000 years, a very short time on a geological scale), this episode was marked by a warming of temperatures on a global scale. It lasted for about 200 000 years and led to numerous marine and terrestrial extinctions.

It would have been caused by a high concentration of carbon dioxide -- the famous CO2 -- and methane in the atmosphere, two powerful greenhouse gases. As is the case currently, these gases may have been released by several phenomena, certainly in combination: the release of methane hydrates trapped on the seabed, the sudden and significant melting of the permafrost, and the injection of magma into the organic sediments of the western edge of Norway. The origin of these processes is still under debate. The impact of a meteorite and/or the effects of intense volcanic activity in the depths of the North Atlantic could be responsible.

A geological ''archive'' of unprecedented quality

Because of the many similarities between the PETM and the current warming, the geological remains of this period are being closely studied by scientists. A team from the UNIGE is now reporting new elements. ''The objective of our study was to investigate the influence of these climatic changes on sedimentary systems, i.e. on the processes of sediment formation and deposition, and to understand how these changes could have been transmitted from the atmosphere to the depths of the ocean,'' explains Lucas Vimpere, a post-doctoral scholar at the Section of Earth and Environmental Sciences of the UNIGE's Faculty of Science and first author of the study.

The researchers analysed sediments taken from more than 8km deep in the Gulf of Mexico. This basin acts as a giant ''sink'' into which material eroded and transported from the North American continent over millions of years is discharged. ''For reasons of cost and infrastructure, the sediments used to study the PETM are generally taken from shallow marine or continental environments. Thanks to the collaboration of an oil company, we were able to obtain a sample of unprecedented quality, without any alteration'', says the researcher. The 543-metre-long core contains a 180-metre-thick PETM sedimentary record, making it the most complete geological ''archive'' of this period in the world.

More clay on the ocean floor

The UNIGE scientists found that it was composed first of a large layer of clay and then of a layer of sand, a counter-intuitive result. ''At the time of the PETM, we thought that there had been more precipitation, and therefore more erosion, and that large quantities of sand had then been transported first by the fluvial systems into the oceans. However, thanks to our sample, we were able to determine that it was the clays and not the sands that were transported in the first instance'', explains Sébastien Castelltort, full professor at the Earth and Environmental Sciences Section of the UNIGE Faculty of Science, and last author of the study.

This established that the period was not marked by an increase in the annual rate of precipitation but by an increase in its seasonality and intensity. ''This resulted in increased mobility of the river channels -- the deepest areas of a river -- which in turn transported large quantities of fluvial clays deposited on the adjacent alluvial plains to the ocean depths. We can now consider the presence of clay in deep basins as a marker of increased rainfall seasonality,'' says Lucas Vimpere. The phenomenon has led to an increase in ocean turbidity that is harmful to marine life, especially corals.

''The PETM is a potential analogue of current warming. As recent IPCC reports show, we are also now seeing an increase in the seasonality and intensity of rainfall. As our study shows, this is likely to destabilise sedimentary systems in the same way as during the PETM and with the same consequences for the oceans and living species,'' explains Lucas Vimpere. These new data can now be integrated into modelling aimed at predicting the evolution and consequences of global warming.

https://www.sciencedaily.com/releases/2023/02/230216172224.htm
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kassy

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Re: Paleoclimatology papers
« Reply #72 on: April 10, 2023, 07:19:30 PM »
Past extreme climate warming triggered by tipping points, study finds

Can a rapid warming of Earth trigger tipping points in our climate? For decades scientists have debated if today's warming can strongly amplify itself by triggering a catastrophic release of greenhouse gases. New research, published in Science Advances, now presents evidence that such tipping points did occur in Earth's history. The researchers show that tipping points triggered three periods of extreme warming in the distant past, millions of years ago.

...

The new research now shows for the first time that rapid global warming phases in the geological past, between 56 and 52 million years ago, were indeed caused by climate tipping points. It was already known that large amounts of CO2 and methane were released into the atmosphere during these phases, amplifying warming. This, in turn, destabilized other carbon reservoirs, triggering the release of more carbon. Global temperatures spiked even further—and this allowed the chain reaction to continue.

The research, a remarkable collaboration between mathematicians and Earth scientists from Wageningen University & Research and Utrecht University, shows that the sturdiness of the climate system decreased in the time period leading up to the phases of extreme warming. "This is exactly what you would expect to see if release of carbon was caused by a carbon cycle tipping point," explains mathematician Shruti Setty, Ph.D. candidate at Wageningen University & Research and first author of the paper.

...

https://phys.org/news/2023-04-extreme-climate-triggered.html

paper:

Loss of Earth system resilience during early Eocene transient global warming events

Abstract
Superimposed on long-term late Paleocene–early Eocene warming (~59 to 52 million years ago), Earth’s climate experienced a series of abrupt perturbations, characterized by massive carbon input into the ocean-atmosphere system and global warming. Here, we examine the three most punctuated events of this period, the Paleocene-Eocene Thermal Maximum and Eocene Thermal Maximum 2 and 3, to probe whether they were initiated by climate-driven carbon cycle tipping points. Specifically, we analyze the dynamics of climate and carbon cycle indicators acquired from marine sediments to detect changes in Earth system resilience and to identify positive feedbacks. Our analyses suggest a loss of Earth system resilience toward all three events. Moreover, dynamic convergent cross mapping reveals intensifying coupling between the carbon cycle and climate during the long-term warming trend, supporting increasingly dominant climate forcing of carbon cycle dynamics during the Early Eocene Climatic Optimum when these recurrent global warming events became more frequent.

https://www.science.org/doi/10.1126/sciadv.ade5466

The technical bit is rather dry and the bulk of the paper.

Of course we know all this because we know the order events progressed in.
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sidd

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Re: Paleoclimatology papers
« Reply #73 on: April 11, 2023, 06:05:07 AM »
Thanks for the reference. I have previously used the Sugihara treatment of  CCM elsewhere, and have referred to one of the authors,  van Nes, in this forum.

sidd

kassy

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Re: Paleoclimatology papers
« Reply #74 on: May 16, 2023, 10:52:54 PM »
How One 'Warm Ice Age' Permanently Changed Climate Cycles

In recent geological history, 90,000 of every 100,000 years have been ice ages. It's been 12,000 years since the last one so we may be due.

Or not. Climate science has a few rules but a lot of exceptions and 700,000 years ago a big exception occurred. At that time the planet experienced a “warm ice age” and it permanently changed the climate cycles on Earth. Though it became warmer and with more rain, the polar glaciers also expanded. Geological data in combination with computer simulations published in Nature Communications hopes to lend insight into this paradox.

Glacial periods – ice ages -are characterized by the development of large ice sheets in the Northern Hemisphere. As Neandertal-Denisovan ancestors of modern humans were spreading across the globe, these phases began to shift between distinct glacial and warm periods about every 100,000 years.

Prior to that, the Earth’s climate was governed by 40,000-year cycles with shorter and weaker glacial periods. The change in the climate cycles occurred in the Middle Pleistocene Transition period, which began approximately 1.2 million years ago and ended about 670,000 years ago.

Why the shift? Early humans certainly were not impacting the climate in any meaningful way but the mechanisms responsible for this critical change in the global climate rhythm remain largely unknown. They're not variations in the orbital parameters governing the Earth’s climate but the recently identified ‘warm ice age’, which caused the accumulation of excess continental ice may hold clues.

For their investigations, the researchers used new climate records from a drill core off Portugal and loess records from the Chinese Plateau. The data was then fed into computer simulations. The models show a long-term warming and wetting trend in both subtropical regions for the past 800,000 to 670,000 years. Contemporaneous with this last ice age in the Middle Pleistocene Transition period, the sea surface temperatures in the North Atlantic and tropical North Pacific were warmer than in the preceding interglacial, the phase between the two ice ages.

This led to higher moisture production and rainfall in Southwest Europe, the expansion of Mediterranean forests, and an enhanced summer monsoon in East Asia. The moisture also reached the polar regions where it contributed to the expansion of the Northern Eurasian ice sheets. “They persisted for some time and heralded in the phase of sustained and far-reaching ice-age glaciation that lasted until the late Pleistocene.

Such expansion of the continental glaciers was necessary to trigger the shift from the 40,000-year cycles to the 100,000-year cycles we experience today, which was critical for the Earth’s later climate evolution.

https://www.science20.com/news_staff/how_one_warm_ice_age_permanently_changed_climate_cycles-256629

Moist and warm conditions in Eurasia during the last glacial of the Middle Pleistocene Transition

Abstract
The end of the Middle Pleistocene Transition (MPT, ~ 800-670 thousand years before present, ka) was characterised by the emergence of large glacial ice-sheets associated with anomalously warm North Atlantic sea surface temperatures enhancing moisture production. Still, the direction and intensity of moisture transport across Eurasia towards potential ice-sheets is poorly constrained. To reconstruct late MPT moisture production and dispersal, we combine records of upper ocean temperature and pollen-based Mediterranean forest cover, a tracer of westerlies and precipitation, from a subtropical drill-core collected off South-West Iberia, with records of East Asia summer monsoon (EASM) strength and West Pacific surface temperatures, and model simulations. Here we show that south-western European winter precipitation and EASM strength reached high levels during the Marine Isotope Stage 18 glacial. This anomalous situation was caused by nearly-continuous moisture supply from both oceans and its transport to higher latitudes through the westerlies, likely fuelling the accelerated expansion of northern hemisphere ice-sheets during the late MPT.

https://www.nature.com/articles/s41467-023-38337-4
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kassy

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Re: Paleoclimatology papers
« Reply #75 on: May 22, 2023, 11:37:33 AM »
About 13,000 years ago, the water outflow from the Mediterranean to the Atlantic Ocean was twice that of today’s


About 13,000 years ago, a climate crisis caused a global drop in temperatures in the northern hemisphere. This episode of intense cold, known as the Younger Dryas, also caused severe aridity across the Mediterranean basin, which had a major impact on terrestrial and marine ecosystems. But what do we know about the impact of this climate change on water circulation in the Mediterranean?

During the Younger Dryas, the flow of water masses from the eastern Mediterranean to the Atlantic Ocean through the Strait of Gibraltar doubled, according to a study published in Nature's Communications Earth & Environment journal. The work has applied the innovative technique of neodymium (Nd) isotopes to reconstruct the conditions in the Mediterranean since the last deglaciation, some 14,000 years ago.

...

The Younger Dryas was the most intense climate change of the last 13,000 years and the most far-reaching on a planetary scale. Its end marked the end of the Holocene, the interglacial period in which we find ourselves today. "There has also been climate variability during the Holocene, such as the episodes known as the Little Ice Age, the Medieval Climatic Anomaly or the Roman Warm Period. However, this climate variability had a lower relative intensity with different regional climatic expressions, without the capacity to generate changes on a global scale," says Professor Isabel Cacho, from the UB Department of Earth and Ocean Dynamics.

The paper also analyses the last sapropel, a Holocene episode after the Younger Dryas linked to an extraordinary increase in rainfall in the Mediterranean region, especially in North Africa. The study provides the first quantification of changes in the deep circulation of the eastern Mediterranean during this episode, and it has estimated that it was reduced by up to a quarter compared to the Younger Dryas. Still, the experts explain that the impact this event may have had on the oceanography of the North Atlantic is unknown.

The new study supports the hypothesis that increased salt input from the Mediterranean into Atlantic waters during the Younger Dryas was key to reactivating the North Atlantic circulation: this led to a rapid warming in Europe and the Mediterranean, which marked the beginning of the Holocene.

"Mediterranean water masses are one of the primary sources of salt in the North Atlantic. Water salinity is an important factor in oceanography, as it determines the density of water masses. It is therefore a key process in the formation of deep waters in the Atlantic Ocean and is the driver of global ocean circulation," says researcher Sergio Trias-Navarro.

...

https://www.sciencedaily.com/releases/2023/05/230516115529.htm
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J Cartmill

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Re: Paleoclimatology papers
« Reply #76 on: May 22, 2023, 01:31:43 PM »
There was an idea proposed back in 1997 to build a dam across the Straits of Gibralter to regulate the flow of high salinity Mediterranean water.

Quote
If the Mediterranean Sea continues to increase in salinity, shifting climatic patterns throughout the world may cause high-latitude areas in Canada to glaciate within the next century. The Mediterranean is starved of freshwater by human activities: most of the annual flow of the Nile River is now used for irrigation and no longer enters the sea. The sea surface evaporation losses are also increasing as the surface warms due to rising CO2 concentrations in the atmosphere. Consequently, the Mediterranean hydrologic deficit is steadily increasing. The deficit is the difference between the larger amount of water lost by evaporation and the smaller amount received from rainfall and river inputs. The difference is made up by a two-way exchange of water with the Atlantic at Gibraltar. Barring a significant change in regional atmospheric circulation, these two human modifications of the environment will cause the salinity of the Mediterranean to increase for some time as fossil fuels are consumed.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/97EO00180

trm1958

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Re: Paleoclimatology papers
« Reply #77 on: May 22, 2023, 05:11:14 PM »
Quote
Its end marked the end of the Holocene, the interglacial period in which we find ourselves today.
I take it you mean the beginning, kassy.

kassy

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Re: Paleoclimatology papers
« Reply #78 on: June 13, 2023, 05:58:43 PM »
Yes indeed.

Seasonal sea ice persisted through the Holocene Thermal Maximum at 80°N

Abstract
The cryospheric response to climatic warming responsible for recent Arctic sea ice decline can be elucidated using marine geological archives which offer an important long-term perspective. The Holocene Thermal Maximum, between 10 and 6 thousand years ago, provides an opportunity to investigate sea ice during a warmer-than-present interval. Here we use organic biomarkers and benthic foraminiferal stable isotope data from two sediment cores in the northernmost Barents Sea (>80 °N) to reconstruct seasonal sea ice between 11.7 and 9.1 thousand years ago. We identify the continued persistence of sea-ice biomarkers which suggest spring sea ice concentrations as high as 55%. During the same period, high foraminiferal oxygen stable isotopes and elevated phytoplankton biomarker concentrations indicate the influence of warm Atlantic-derived bottom water and peak biological productivity, respectively. We conclude that seasonal sea ice persisted in the northern Barents Sea during the Holocene Thermal Maximum, despite warmer-than-present conditions and Atlantic Water inflow.

https://www.nature.com/articles/s43247-021-00191-x

Open access.
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kassy

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Re: Paleoclimatology papers
« Reply #79 on: August 05, 2023, 07:48:54 PM »
Was the Medieval Era Warmer Than Now? New Tree Ring Study Offers Insight


A new study of tree rings in Scandinavia is helping to resolve a longstanding question about the Medieval Warm Period.

Past studies of tree rings had indicated that the Medieval period was as warm or warmer than today, but climate models found otherwise. Climate deniers have long pointed to the tree-ring data to suggest the current period of warming is not without precedent.

The new tree-ring study, which used more precise methods than prior research, agrees with the climate models.

For the study, researchers gathered data from 188 Scots pines, both living and dead, in Sweden and Finland. While past studies largely looked only at the width and density of rings, the new study analyzed tree rings at a microscopic level, examining 50 million tree cells to infer changes in temperature — cell walls tend to grow thicker in hotter weather, which is why a darker layer of each ring forms in late summer.

Researchers used the tree ring data to reconstruct summer temperatures, finding that Scandinavia is now warmer than at any point in the past 1,200 years. The findings, published in Nature, line up with the climate models, highlighting the impact of human-caused warming.

“This means that there are now two independent accounts of the regional climate that both find lower temperatures during the Medieval, providing new evidence that this phase was not as warm as previously thought,” lead author Jesper Björklund, of the Swiss Federal Institute for Forest, Snow, and Landscape Research, said in a statement. “Instead, both show that the current warming is unprecedented, at least in the past millennium.”

https://e360.yale.edu/digest/tree-ring-study-medieval-warm-period

https://www.nature.com/articles/s41586-023-06176-4

paywalled
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kassy

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Re: Paleoclimatology papers
« Reply #80 on: December 09, 2023, 11:01:19 PM »
Climate change will increase wildfire risk and lengthen fire seasons

oday atmospheric carbon dioxide is at its highest level in at least several million years thanks to widespread combustion of fossil fuels by humans over the past couple centuries.

But where does 419 parts per million (ppm) -- the current concentration of the greenhouse gas in the atmosphere -- fit in Earth's history?

That's a question an international community of scientists, featuring key contributions by University of Utah geologists, is sorting out by examining a plethora of markers in the geologic record that offer clues about the contents of ancient atmospheres. Their initial study was published this week in the journal Science, reconstructing CO2 concentrations going back through the Cenozoic, the era that began with the demise dinosaurs and rise of mammals 66 million years ago.

Glaciers contain air bubbles, providing scientists direct evidence of CO2 levels going back 800,000 years, according to U geology professor Gabe Bowen, one of the study's corresponding authors. But this record does not extend very deep into the geological past.

"Once you lose the ice cores, you lose direct evidence. You no longer have samples of atmospheric gas that you can analyze," Bowen said. "So you have to rely on indirect evidence, what we call proxies. And those proxies are tough to work with because they are indirect."

"Proxies" in the geologic record

These proxies include isotopes in minerals, the morphology of fossilized leaves and other lines of geological evidence that reflect atmospheric chemistry. One of the proxies stems from the foundational discoveries of U geologist Thure Cerling, himself a co-author on the new study, whose past research determined carbon isotopes in ancient soils are indicative of past CO2 levels.

But the strength of these proxies vary and most cover narrow slices of the past. The research team, called the Cenozoic CO2 Proxy Integration Project, or CenCO2PIP, and organized by Columbia University climate scientist Bärbel Hönisch, set out to evaluate, categorize and integrate available proxies to create a high-fidelity record of atmospheric CO2.

"This represents some of the most inclusive and statistically refined approaches to interpreting CO2 over the last 66 million years," said co-author Dustin Harper, a U postdoctoral researcher in Bowen's lab. "Some of the new takeaways are we're able to combine multiple proxies from different archives of sediment, whether that's in the ocean or on land, and that really hasn't been done at this scale."

The new research is a community effort involving some 90 scientists from 16 countries. Funded by dozens of grants from multiple agencies, the group hopes to eventually reconstruct the CO2 record back 540 million years to the dawn of complex life.

At the start of the Industrial Revolution -- when humans began burning to coal, then oil and gas to fuel their economies -- atmospheric CO2 was around 280 ppm. The heat-trapping gas is released into the air when these fossil fuels burn.

Looking forward, concentrations are expected to climb up to 600 to 1,000 ppm by the year 2100, depending on the rate of future emissions. It is not clear exactly how these future levels will influence the climate.

But having a reliable map of past CO2 levels could help scientists more accurately predict what future climates may look like, according to U biology professor William Anderegg, director the U's Wilkes Center for Climate & Policy.

"This is an incredibly important synthesis and has implications for future climate change as well, particularly the key processes and components of the Earth system that we need to understand to project the speed and magnitude of climate change," Anderegg said.

Today's 419 ppm is the highest CO2 in 14 million years

At times in the past when Earth was a far warmer place, levels of CO2 were much higher than now. Still, the 419 ppm recorded today represents a steep and perhaps dangerous spike and is unprecedented in recent geologic history.

"By 8 million years before present, there's maybe a 5% chance that CO2 levels were higher than today," Bowen said, "but really we have to go back 14 million years before we see levels we think were like today."

In other words, human activity has significantly altered the atmosphere within the span of a few generations. As a result, climate systems around the globe are showing alarming signs of disruption, such as powerful storms, prolonged drought, deadly heat waves and ocean acidification.

A solid understanding of atmospheric CO2 variation through geological time is also essential to deciphering and learning from various features of Earth's history. Changes in atmospheric CO2 and climate likely contributed to mass extinctions, as well as evolutionary innovations.

During the Cenozoic, for example, long-term declines in CO2 and associated climate cooling may have driven changes to plant physiology, species competition and dominance, which in turn impacted mammalian evolution.

"A more refined understanding of past trends in CO2 is therefore central to understanding how modern species and ecosystems arose and may fare in the future," the study states.

https://www.sciencedaily.com/releases/2023/12/231207160421.htm

RESULTS
The resulting reconstruction illustrates a more quantitatively robust relationship between CO2 and global surface temperature, yielding greater clarity and confidence than previous syntheses. The new record suggests that early Cenozoic “hothouse” CO2 concentrations peaked around 1600 ppm at ~51 Ma. Near 33.9 Ma, the onset of continent-wide Antarctic glaciation coincided with an atmospheric CO2 concentration of 720 ppm. By ~32 Ma, atmospheric CO2 had dropped to 550 ppm, and this value coincided with the onset of radiation in plants with carbon-concentrating mechanisms that populate grasslands and deserts today. CO2 remained below this threshold for the remainder of the Cenozoic and continued its long-term decrease toward the present. Along this trajectory, the middle Miocene (~16 Ma) marks the last time that CO2 concentrations were consistently higher than at present; Greenland was not yet glaciated at that time, and independent estimates suggest that sea level was some 50 m higher than today. Values eventually dropped below 270 ppm at the Plio-Pleistocene boundary (2.6 Ma), when Earth approached our current “icehouse” state of bipolar glaciation. This and other climatic implications of the revised CO2 curve, including the evolution of the cryosphere, flora, and fauna, along with the cross-disciplinary data assessment process, are detailed in the full online article.

https://www.science.org/doi/10.1126/science.adi5177
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vox_mundi

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Re: Paleoclimatology papers
« Reply #81 on: February 15, 2024, 05:01:51 PM »
Passing Stars Altered Orbital Evolution of Earth and Other Planets, Astronomers Find
https://phys.org/news/2024-02-stars-orbital-evolution-earth-planets.html



Stars that pass by our solar system have altered the long-term orbital evolution of planets, including Earth, and, by extension, modified our climate.

"One reason this is important is because the geologic record shows that changes in the Earth's orbital eccentricity accompany fluctuations in the Earth's climate. If we want to best search for the causes of ancient climate anomalies, it is important to have an idea of what Earth's orbit looked like during those episodes," Kaib said.

"One example of such an episode is the Paleocene-Eocene Thermal Maximum 56 million years ago, where the Earth's temperature rose 5-8 degrees centigrade. It has already been proposed that Earth's orbital eccentricity was notably high during this event, but our results show that passing stars make detailed predictions of Earth's past orbital evolution at this time highly uncertain, and a broader spectrum of orbital behavior is possible than previously thought."



As the sun and other stars orbit the center of the Milky Way, they inevitably can pass near one another, sometimes within tens of thousands of au, 1 au being the distance from the Earth to the sun. These events are called stellar encounters. For instance, a star passes within 50,000 au of the sun every 1 million years on average, and a star passes within 10,000 au of the sun every 20 million years on average. This study's simulations include these types of events, whereas most prior similar simulations do not.

One major reason the Earth's orbital eccentricity fluctuates over time is because it receives regular perturbations from the giant planets of our solar system (Jupiter, Saturn, Uranus, and Neptune). As stars pass near our solar system, they perturb the giant planet's orbits, which consequently then alters the orbital trajectory of the Earth. Thus, the giant planets serve as a link between the Earth and passing stars.

Kaib said that when simulations include stellar passages, we find that orbital uncertainties grow even faster, and the time horizon beyond which these backward simulations' predictions become unreliable is more recent than thought.

This means two things: There are past epochs in Earth's history where our confidence in what Earth's orbit looked like (for example, its eccentricity or degree of circularity) has been too high, and the real orbital state is not known, and the effects of passing stars make regimes of orbital evolution (extended periods of particularly high or low eccentricity) possible that past models did not predict.

"Given these results, we have also identified one known recent stellar passage, the sun-like star HD 7977, which occurred 2.8 million years ago, that is potentially powerful enough to alter simulations' predictions of what Earth's orbit was like beyond approximately 50 million years ago," Kaib said.

The current observational uncertainty of HD 7977's closest encounter distance is large, however, ranging from 4,000 au to 31,000 au. "For larger encounter distances, HD 7977 would not have a significant impact on Earth's encounter distance. Near the smaller end of the range, however, it would likely alter our predictions of Earth's past orbit," Kaib said.

Nathan A. Kaib et al, Passing Stars as an Important Driver of Paleoclimate and the Solar System's Orbital Evolution, The Astrophysical Journal Letters, (2024)
https://iopscience.iop.org/article/10.3847/2041-8213/ad24fb
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― anonymous

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late