Paleoclimatology papers

[kassy]

This is collection thread for paleoclimatology papers.

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

[kassy]

CO2 in Earth's atmosphere nearing levels of 15m years ago

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

...

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

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

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

...

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

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

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

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

[kassy]

Major New Paleoclimatology Study Shows Global Warming Has Upended 6,500 Years of Cooling
https://phys.org/news/2020-06-major-paleoclimatology-global-upended-years.html



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

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

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

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

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

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

[kassy]

Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century


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

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

Open access

[vox_mundi]

We Are Already Committed to a 3°C World
https://phys.org/news/2020-07-carbon-dioxide-earth-atmosphere-higher.html

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

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

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

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

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

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

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

[Tom_Mazanec]

And of course, CO2e is even higher than CO2.

[kassy]

Also water is wet.

None of that is paleoclimatology and hence of topic.

[KiwiGriff]

We often discus equilibrium climate sensitivity and ignore earth system sensitivity as the time scales are to large for our ape brains to cope with.


Earth system sensitivity inferred from Pliocene
modelling and data
Daniel J. Lunt1,2*, Alan M. Haywood3
, Gavin A. Schmidt4
, Ulrich Salzmann2,5, Paul J. Valdes1
and Harry J. Dowsett6

Quantifying the equilibrium response of global temperatures to an increase in atmospheric carbon dioxide concentrations is one of the cornerstones of climate research. Components of the Earth’s climate system that vary over long timescales, such as ice sheets and vegetation, could have an important effect on this temperature sensitivity, but have often been neglected.Here we use a coupled atmosphere–ocean general circulation model to simulate the climate of the mid-Pliocene warm period (about three million years ago), and analyse the forcings and feedbacks that contributed to the relatively warm temperatures.Furthermore, we compare our simulation with proxy records of mid-Pliocene sea surface temperature. Taking these lines of evidence together, we estimate that the response of the Earth system to elevated atmospheric carbon dioxide concentrations is 30–50% greater than the response based on those fast-adjusting components of the climate system that are used traditionally to estimate climate sensitivity. We conclude that targets for the long-term stabilization of atmospheric greenhouse-gas
concentrations aimed at preventing a dangerous human interference with the climate system should take into account this higher sensitivity of the Earth system.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.177.6584&rep=rep1&type=pdf

[Tom_Mazanec]

The paleoclimate papers are saying that the earth was so much warmer and the seas so much higher when CO2 was at the level it is now. But this is an underestimate of what we are facing, because the CO2e is higher still.

[kassy]

Paleoclimatology is not about what we are facing now (although it can help establish bounds).

[kassy]

ShortBrutishNasty was thoughtful enough to send a link to me about James Hansen's latest article about paleo, and model, evidence about slowing of the MOC during periods of high GMSTA, see below:

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

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

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

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

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

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

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

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

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

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

Hat tip SBN.

[pikaia]

https://advances.sciencemag.org/content/6/36/eaaz9588

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