A glimpse of the Future
There is good evidence that the next cyclical advance of Pleistocene ice will occur within the next thousand years or so. This will be a catastrophe for humanity, but I am optimistic enough to suppose that, as a species, we will survive. Our few remaining short-lived descendants, as they shiver before a fire at the mouth of their cave after a long day’s hunting in the snow, will tell each other stories of a legendary past when their long-lived ancestors enjoyed a life of abundance in a former golden age – the Happy Holocene.
Meanwhile, back in the Holocene.
The International Union of Geological Sciences (IUGS), founded in 1961, is the peak governing body of geology. Under its aegis are a number of Commissions covering such things as Structure and Tectonics, Geochemistry, Ethics, History of Geology, Geological Education and so on.
The oldest and probably the most important of these Commissions is the International Commission on Stratigraphy (ICS) which is tasked with responsibility for the subdivision of geological time going back 4.6 billion years (4.6 Ga). The subdivisions are based on the stratigraphic record – the sequential accumulation of sediments and the fossil remains (if any) within them. Boundaries between subdivisions are based on significant continental or world-wide, geologically rapid, transitions in the overall depositional environment. Localities where these key transitions are well exposed are referenced as type-localities and dated by isotopic methods. Each distinctive rock/fossil assemblage (subdivision) is given a name, thus reifying it a “thing”. Many of the names go back more than 200 years and reflect the happenstance of early geological research (see my post, The Invention of the Paleozoic).
On a stratigraphic chart, subdivisions are organised by nested hierarchies of ever smaller intervals of time. Each step of the classification scheme is given a formal name. Eons (sometimes called Eonthems) are the longest: there are four of these in the 4.6 Ga geological record. Together, these four Eons are subdivided into fifteen Eras (Erathems), and these fifteen Eras contain twenty-six Periods (Systems). The Periods contain 38 Epochs (Series), and the Epochs themselves contain over a 100 Stages. A Stage is the shortest time interval in the classification.
If we consider the stratigraphic column as a Library, then the Eons are books, the Eras chapters, the Periods paragraphs, the Epochs sentences, and the Stages, words. The last words of the last paragraph of the last chapter of the last book in the library are: “to be continued…”
The most recent time subdivisions at the top of the ICS chart are the topic of this post.
To carry out their task, the ICS created a number of Sub Commissions, each responsible for one of the 26 Periods in the stratigraphic record. The most recent Period, the one we live in today, is known as the Quaternary and began 2.58 million years (2.58 Ma) ago. According to the ICS Sub Commission for the Quaternary (SQS), the Quaternary is made up of two Epochs: the Pleistocene from 2.58 Ma to o.0117 Ma, and the Holocene from 0.0117 Ma to present.
Geological subdivisions of the recent past, according to the ICS. Redrawn from their official chart at https://stratigraphy.org. Click for a larger image.
I take serious issue with this part of the ICS classification.
The lower boundary of the Pleistocene Epoch of the Quaternary Period is unequivocally defined by the start of an Ice Age when temperatures plummeted, and kilometer-thick ice became generally established over land and sea at high- to mid-latitude areas around both poles. Glacial conditions like these ruled for around 80% of Pleistocene time, broken only by shorter periods of relatively warmer conditions and ice retreat called interglacials. The upper boundary of the Pleistocene will therefore, logically, be when this pattern ends. There is no evidence that has happened yet. Considering the duration of previous Ice Ages, each of which lasted tens of millions of years (such as the one at the end of the Ordovician Era around 440 Ma, or that near the end of the Permian Era around 250 Ma), ours has probably many millions of years to run (see my post, Climate Change Explained in Three Graphs). The general cold temperatures of the Pleistocene are not becoming less extreme with time: quite the opposite. The evidence shows that the last few glacial advances have been the coldest and most extensive of the entire Epoch.
The Holocene is a period of ice retreat, relatively warm global temperature and sea level rise. Pleistocene geological records show at least 45 such temporary retreats of ice called interglacials. Depending upon how their start and end dates are defined, Interglacials together make up around 20% of Pleistocene time. The warm weather and glacial retreat of the Holocene is not significantly different (at least, so far) from any of the numerous previous interglacials.
But, according to the ICS, and with approval of the IUGS, the Pleistocene Epoch (Ice Age) finished, terminated and collapsed forever 11,700 years (0.0117 Ma) ago, to be replaced by the Holocene Epoch. These august bodies must therefore consider that the Holocene warm episode is fundamentally different from the dozens of interglacials that preceded it. There is no evidence for this.
If the Holocene is a separate Epoch within the Quaternary, then, logically, all the previous interglacials and glacials of the Quaternary should be judged as Epochs also. That would mean abolishing a single Pleistocene Epoch and replacing it with more than 45 Epochs, thus creating for the Quaternary Period more Epochs than there are in all the other Periods of the stratigraphic record combined. An absurd proposition. In this dilemma, the ICS appears to be trapped in an epistemological maze with no clear roadmap to follow.
But are the ICS correct? It will be another 10,000 years before we can be 100% certain of the answer to that question. But we don’t need to wait that long. Based on the evidence available today, I am more than 90% certain we are still living within the Pleistocene Ice Age and the glaciers will return.
Here is the most compelling of that evidence…
Antarctic ice core data from www.climatedata.info Click for a larger image
The graph (A) shows changes in air temperature (blue) and CO2 concentration (red) over Antarctica, as measured in the Vostok and EPICA ice cores. Broadly similar graphs can be produced for other regions of the globe. The graph begins (at left) 450,000 years ago (0.45 Ma) and continues to present day. This represents the last 20% of the Pleistocene. Five upward spikes of the graph are apparent: these are episodes of ice retreat – the last two labeled as “Eemian” and “Holocene”. There are two other important takeaways from this graph: there is good correlation between temperature and CO2 and, the peaks and troughs of CO2 lag the peaks and troughs of temperature by 500-1000 years. This tells us that whereas temperature might credibly be controlling CO2, CO2 cannot be controlling temperature (since an effect cannot precede its cause).
Greenland ice core data from Vinther et al 2009: https://www.nature.com/articles/nature08355. Macassar Strait sea-floor sediment data from Rosenthal et al 2013 http://science.sciencemag.org/content/342/6158/617. Compilation of the two data sets by Andy May Click for a larger image
The graph (B), above, shows air and sea temperatures over the past 10,000 years – the last 85% of the Holocene. These are compiled from ice core data from Greenland (orange) and sea-floor sediment data from the Eastern Pacific (black). The good correlation of temperatures between two regions on opposite sides of the globe, based 0n two completely different types of deposit, is compelling.
From the graph we can see a steep initial rise in Holocene temperature to a maximum around 6-9000 years before present (known as The Holocene Climate Optimum) followed by a slow and gradual decline to a deep trough in temperature from around 200 to 800 years BP (known as The Little Ice Age). Comparing graphs A and B (allowing for their different vertical scales), all the interglacials of the Pleistocene for which we have sufficient resolution show a similar strongly skewed pattern. The relentless decline in global temperature following the Holocene Climate Optimum matches this pattern and is an ominous pointer to the next cyclical glacial advance.
On the Greenland data, Graph B clearly shows a spike temperature at the extreme right. This is the Modern Warm Period and the subject of much current existential angst and bloviating from politicians, the media and not a few scientists. But, as is evident from this graph, the Modern Warm Period is not unprecedented for the Holocene.
The members of the ICS apparently consider that, starting from the time of the cultural Neolithic Revolution (made possible by the warmth of the early Holocene), humans have caused sufficiently large changes to global sedimentary processes to justify raising the status of the Holocene from merely the most recent of the many Pleistocene interglacials, to a unique stratigraphic Epoch in its own right.
This is a controversial and debatable proposition. As the late, great Carl Sagan wrote in 1979: “Extraordinary claims require extraordinary evidence”.
Astonishingly, in 2019, the ICS made another proposal to their governing body, the IUGS. They advocated the creation of a brand-new Epoch to succeed the Holocene Epoch. This Epoch was to be called the “Anthropocene”, a neologism cobbled together from two Greek words meaning roughly: “The New Age of Man”. It was supposed to have started around 1950AD.
This is equivalent to a declaration made in 1946 that the establishment of the United Nations will lead to a new epoch of Global Peace (Pax Americana?) that will last for 10,000 years.
To their credit, the IUGS, in a near-unanimous vote, rejected the Anthropocene proposal of the ICS.
I strongly suspect that the stratigraphic proposals of the ICS concerning the Holocene and Anthropocene were influenced by the current scientific conceit that the effects of modern human activities are strong enough to overwhelm all other natural earth forces that have controlled sedimentary deposition around the globe for billions of years.
Our remote descendants may well think otherwise.