The Pleistocene was a time of incredible warmth at low levels of CO2

Written by Dr. Matthew Wielicki on June 6, 2023. Posted in Current News

Geologic time is divided into a hierarchical system of units that represents the vast expanse of Earth’s history

The primary divisions are based on significant events and changes in the Earth’s geological, biological, and climatic records.

The traditional divisions of geologic time are as follows, from largest to smallest:

1. Eon: The largest division of geologic time is the eon. The current eon is the Phanerozoic, which began approximately 541 million years ago and continues to the present. The Phanerozoic eon is further divided into three eras.
2. Era: An era is a subdivision of an eon and represents a significant span of time characterized by particular geological and biological events. The three eras of the Phanerozoic eon are the Paleozoic, Mesozoic, and Cenozoic.
3. Period: A period is a division of an era and is characterized by distinctive rock layers and significant changes in Earth’s life forms. For example, the Mesozoic era is divided into three periods: the Triassic, Jurassic, and Cretaceous.
4. Epoch: An epoch is a subdivision of a period and represents a relatively shorter span of time. Epochs are defined by more specific geological and biological events. The Cenozoic era, for instance, is divided into epochs such as the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene.
5. Age: An age is the smallest division of geologic time and represents an even shorter interval. Ages are typically defined based on specific rock layers, fossil assemblages, and other geological markers.

The divisions of geologic time are not evenly distributed in terms of duration. Some periods or epochs may span tens of millions of years, while others may be relatively shorter.

The precise boundaries and names of these divisions are established and refined through ongoing scientific research among Earth scientists.

The Pleistocene Epoch

The Pleistocene epoch is a significant division of geologic time that occurred within the Cenozoic era, following the Pliocene epoch and preceding the Holocene epoch, which is the current epoch. The Pleistocene epoch spanned from approximately 2.6 million years ago to about 11,700 years ago.

During the Pleistocene, Earth experienced a series of repeated glaciations and interglacial periods. Vast ice sheets covered large portions of the Northern Hemisphere, including parts of North America, Europe, and Asia.

The cycles of advancing and retreating ice sheets had a profound impact on landscapes, carving out valleys, creating moraines, and reshaping the Earth’s surface.

The Pleistocene epoch was also marked by the presence of diverse megafauna, including large mammals such as mammoths, mastodons, saber-toothed cats, and giant ground sloths. These animals adapted to the harsh climate and were well-suited for survival in tundra-like environments.

The appearance of early humans, including Homo erectus and Homo neanderthalensis, also occurred during this epoch.

Towards the end of the Pleistocene epoch, approximately 11,700 years ago, the Earth transitioned into the Holocene epoch. The retreat of the large ice sheets and the onset of warmer climatic conditions allowed for the expansion of forests and the emergence of modern plant and animal species.

The Pleistocene epoch holds significant importance for the understanding of Earth’s climate dynamics, the evolution of life, and the interactions between early humans and their environment.

Temperatures of the Pleistocene Epoch

Recently, multiple studies have shown that the Pleistocene Epoch was significantly warmer than today. In fact, on the order of 9–19 °C above contemporary values, at least in Northern Greenland.

That’s on the order of 10x the current warming of 1.5°C as reported in the journal Nature found here. One study published in 2022 in the journal Nature titled, “A 2-million-year-old ecosystem in Greenland uncovered by environmental DNA”, states…

Palaeoclimatic records show strong polar amplification with mean annual temperatures of 11–19 °C above contemporary values^3,4. The biological communities inhabiting the Arctic during this time remain poorly known because fossils are rare⁵.

Here we report an ancient environmental DNA⁶ (eDNA) record describing the rich plant and animal assemblages of the Kap København Formation in North Greenland, dated to around two million years ago.

The record shows an open boreal forest ecosystem with mixed vegetation of poplar, birch and thuja trees, as well as a variety of Arctic and boreal shrubs and herbs, many of which had not previously been detected at the site from macrofossil and pollen records.

The DNA record confirms the presence of hare and mitochondrial DNA from animals including mastodons, reindeer, rodents and geese, all ancestral to their present-day and late Pleistocene relatives.

The presence of marine species including horseshoe crab and green algae support a warmer climate than today.

Another study published in the journal Boreas titled, “An Early Pleistocene interglacial deposit at Pingorsuit, North-West Greenland”, states…

This paper reports on macrofossil analyses of a coarse detritus gyttja and peaty soil, which occurred beneath a thin cover of till and glacifluvial deposits. The sediments contained remains of vascular plants, mosses, beetles, caddisflies, midges, bryozoans, sponges and other invertebrates.

The flora includes black spruce, tree birch, boreal shrubs and wetland and aquatic taxa, which shows that mires, lakes and ponds were present in the area. We describe a new extinct waterwort species Elatine odgaardii.

The fossils were deposited in a boreal environment with a mean July air temperature that was at least 9 °C higher than at present.

Climate alarmists will warn that Northern Greenland does not represent global temperatures, however, it’s not reasonable to assume that regions that were 10x warmer than pre-industrial levels in the Pleistocene were somehow isolated from the rest of the planet.

What caused the incredible warmth during the early Pleistocene Epoch?

One thing we can rule out is elevated atmospheric CO2 concentration as highlighted in this study published in 2019 in the journal Nature titled, “Low CO₂ levels of the entire Pleistocene epoch”, which states…

Quantifying ancient atmospheric pCO₂ provides valuable insights into the interplay between greenhouse gases and global climate.

Beyond the 800-ky history uncovered by ice cores, discrepancies in both the trend and magnitude of pCO₂ changes remain among different proxy-derived results. The traditional paleosol pCO₂ paleobarometer suffers from largely unconstrained soil-respired CO₂ concentration (S(z)).

Using finely disseminated carbonates precipitated in paleosols from the Chinese Loess Plateau, here we identified that their S(z) can be quantitatively constrained by soil magnetic susceptibility.

Based on this approach, we reconstructed pCO₂ during 2.6–0.9 Ma, which documents overall low pCO₂ levels (<300 ppm) comparable with ice core records, indicating that the Earth system has operated under late Pleistocene pCO₂ levels for an extended period.

The pCO₂ levels do not show statistically significant differences across the mid-Pleistocene Transition (ca. 1.2–0.8 Ma), suggesting that CO₂ is probably not the driver of this important climatic event.

So, if it’s not elevated atmospheric CO2 concentration, what could have produced these incredibly warm temperatures?

A study published in 2014 in the journal Geophysical Research Letters (humble brag, that is one of the journals that I too have authored a manuscript in) titled, “Dynamical changes in the tropical Pacific warm pool and zonal SST gradient during the Pleistocene” states…

…if the regional radiative effects of pCO₂ were the only agent of change, tropical SST gradients should have remained similar as pCO₂ varied with time.

Instead, a new record of SST from the west Pacific shows that tropical SST gradients were different, even reversed, in the past, suggesting an important role for dynamical circulation changes.

Specifically, changes in the temperature of upwelled source water, in addition to local pCO₂ forcing, influenced tropical Pacific SST. These dynamical changes, rather than pCO₂, may have shifted the background state of the tropics and even helped set the stage for the mid-Pleistocene transition.

We show that the zonal SST gradient, which has been used to estimate past atmospheric Walker circulation strength [Koutavas et al., 2002; Wara et al., 2005; Dekens et al., 2007], increased in both the glacials and during the MPT; this evidence suggests that the MPT involved dynamical circulation changes, rather than simply a response to “top-down” pCO₂ local forcing.

So, it appears as changes in ocean circulation patterns, which could arise from enhanced equatorial upwelling, thermocline depth changes, or source water for equatorial upwelling have a significantly larger forcing on the atmospheric temperature than the concentration of CO2.

Recent studies have shown that significant amounts of heat are trapped in the oceans and this has always been attributed to “top-down” heating of the oceans due to anthropogenic GHG emissions.

However, the oceans have approximately 1000x the energy of the atmosphere. So, this is analogous to having a large campfire and then lighting a match and claiming the match is heating the campfire.

The oceans are heated by multiple sources, see this earlier post, and it appears that the changes in ocean circulation could account for 10x the amount of warming we have thus far experienced as well as act as a huge source of increased atmospheric CO2.

A source that we have no way of identifying as the oceans and atmosphere are indistinguishable isotopically. Henry’s Law would dictate that as the oceans warm they release trapped CO2 due to the temperature dependence of equations.

In summary, the early Pleistocene was on the order of 9–19 °C warmer than the present-day, in multiple locations, and at pre-industrial levels of CO2.

This incredible warmth, 10x greater than the observed warming since 1850, was likely due to changes in ocean circulation patterns.

This data highlights the relative insensitivity of surface temperature to atmospheric CO2 concentration and provides a great example of the complex nature of the climate system.

Distilling the climate system to only GHG concentrations is reductionist and ignores this amazing complexity.

With this in mind, we should have no expectation of a measurable response in surface temperatures to a reduction of atmospheric GHG concentration.

See more here substack.com

Some bold emphasis added

Please note: PSI’s position is that CO2 does not drive temperature. Our intention in publishing this article is to encourage open, honest, scientific debate.

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