Grand Strategy Annex

19th June 2016

Post with 18 notes

The Advent of the Holocene

At a time when we are contemplating whether we have entered a new geological epoch, the Anthropocene Epoch, it would be instructive to consider the last time a new geological epoch began, and this was the advent of the Holocene. 

Some geological periodizations are more significant than others. The Holocene is a new geological epoch, but it takes place within the larger climatological pattern we call the Quaternary glaciation. The Quaternary period is a more comprehensive classification of geological time, and includes within it both the Pleistocene and the Holocene – and, presumably, will also include the Anthropocene (unless it is determined millions of years from now that the Anthropocene was not merely the beginning of a new epoch, but also the beginning of a period, era, or aeon). The Quaternary glaciation is a colder period, i.e., an ice age, that has been repeatedly interrupted by shorter periods of warming. The Holocene is the latest warming period to interrupt the Quaternary glaciation.

That we understand as much as we do of the large scale patterns of geological and climatological history is remarkable, but there remains much that we do not understand. What we do understand so far is that the advent of the Holocene can be dated with surprising precision for a geological epoch, starting about 11,700 years ago.

What we do not yet clearly understand is a number of climatological fluctuations that preceded the advent of the Holocene. Because the last ice age was relatively recent in terms of geological time, we have comparatively more data about climate fluctuations during the last ice age before the Holocene. These fluctuations include the Oldest Dryas stadial  (cooling from 18,050-15,050 BP), the Bølling interstadial (warming from 14,650 to 14,000 BP), the Older Dryas stadial (cooling from 14,000 to 13,600 BP), the Allerød interstadial (warming from 13,600 to 12,900 BP), and the Younger Dryas stadial (cooling from 12,900 to 11,640 BP).

Because of early dating techniques such as the Blytt–Sernander system for dating the layers in peat bogs, tree ring chronology (i.e., dendrochronology), and varve chronology, which studies the annual patterns of glacial melt, scientists were studying the transition from the last ice age to the Holocene before technologies for C-14 dating and ice coring became available. With a hundred years or more of data available, our knowledge of this transition is fairly detailed, but explanations are still lacking. We know what happened, but we don’t know why it happened in the way that it happened. That is to say, we often lack causal mechanisms to explain sequences of climatological events. 

The Younger Dryas impact hypothesis (which, if it happened, happened about 12,800 years ago) – that the Earth was struck by a large extraterrestrial body – has been proposed to explain the sudden cooling prior to the advent of the Holocene. Of course, Earth has been subject to impacts of extraterrestrial bodies since its formation. Indeed, Earth would not exist had not a large amount of matter gathered together, which means that the Earth itself is the result of an ancient process of bodies in space impacting on each other. Some of these impacts are quite large, as in the case of the impact hypothesized to have resulted in the formation of the moon (in which case the impactor was almost the size of Mars), while many more frequent impacts involve bodies so small they have left no trace. So it is tempting to assign a climatological change to an impact, but the evidence for a Younger Dryas impact is not particularly strong at the present time. Positing a major impact without solid evidence is a little bit like invoking a deus ex machina – the plot is resolved, but not entirely satisfactorily.

We should not be surprised that we do not yet understand climatological fluctuations, as the planet is a complex system subject to chaotic interactions of many different factors. For example, in addition to the regular patterns of changing insolation known as Milankovitch cycles – Earth’s axial tilt, axial precession, orbital eccentricity, and orbital precession (which I have previously characterized as Speciation Pumps) – there are other semi-regular climatological patterns that result not from the orientation of the Earth in relation to the sun, but from oceanic and atmospheric flows. Beyond obvious examples such as the Humboldt Current and the Gulf Stream, and recurring events that appear in the news because of their economic impact, such as the El Niño–Southern Oscillation (ENSO), there are lesser known oceanic regularities such as the Thermohaline circulation (THC) and Atlantic Multidecadal Oscillation (AMO).

With variations in the amount of sunlight reaching the surface of the earth (insolation), variations in the amount of sunlight reflected back into space due to clouds, snow, and ice (albedo), and large scale interactions with atmospheric and oceanic flows, not to mention whatever the present positions of the continents are due to the supercontinent cycle, even the best supercomputer available at the present time would have difficulty calculating these interactions, and even if we had the supercomputer time available to us, we don’t have enough data points to model the global climate effectively.  

Tagged: Holocenegeological epochAnthropoceneYounger Dryasinsolationalbedoclimate scienceclimatologyice age