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TIMING AND WHERE WE ARE NOW – OUR LOCATION IN THE HUNDRED-THOUSAND YEAR CLIMATE OSCILLATION
All climatic changes must be analyzed in an adequate time perspective, otherwise it may turn out that the analysis might either deal with just a weather pattern changes or it will fail to enhance the possible oscillatory nature of climate changes and, consequently, will not take very important determinants into consideration. The recent contemporary global warming discussion is especially tainted with this kind of poor analytic approach. The contemporary global warming analyses almost always lack consideration of data from sufficiently long ago. Who, of wider public ever heard from media about the Medieval Warming, Roman Warming, Minoan Warming, all global warming cycles that happened before with regular millennial intervals that clearly indicate their oscillatory nature? Instead of that we hear about some mysterious "stable climates" (and that apparently we have rights to them [sic!]), "hockey sticks" and a pile of such similar nonsense.
I would like to open that perspective using the following set of figures in the form of timeline shown in proportional scale. I hope it will facilitate to position the point we are currently standing at and what happened behind our time in the climate history. That will help us to realize how changeable the climate has been in ages and how much of a fallacy the idea of a stable climate it is.
Let us see the air temperature curve of the last 120 years. The Earth’s average temperature has been generally rising so this period has been named the Contemporary Global Warming (Fig. 2.1). Now, let us extend the timeline to 180 years back. As we continue to go back in time we can see that the warming trend is part of much longer warming, one that pulled the Earth from the very deep cooling called the Dalton minimum and before it, another profound cooling called Maunder Minimum, the time in which the Baltic Sea, Thames and Seine rivers used to freeze over. As we go back in time 1000 years we realize that the low temperatures of the midst of the last millennium came after… a global warming that happened around year 1000. That period was called the Medieval Warming and was quite amazing. The coast of Greenland was plowed. The crop was mostly barley but some abandoned wheat seeds have been found as well. Grapes were picked even in southern Scotland. Europe was warm. It was a good time – the continent just emerged from the dark ages. Beautiful cathedrals were built in Western Europe. The global warming was good. The things got worse, though, when the temperature started to drop in 13th and 14th centuries. The food became scarce, wars followed and malnourished people were less resistant to sicknesses. The Black Death came and desolated the continent. Roughly half of the population of Europe died. Global cooling was bad. Well, let’s go back in time for another 1000 years. We can see (Fig. 2.2) in the beginning of that millennium there also was a global warming. It was called the Roman Global Warming and it was even stronger than the medieval one. The Roman Empire blossomed. Rome was the city of 1 million people by then. The climate was able to allow lots o food to be produced. Then, starting at around the fourth century the climate changed radically. The world started to cool down fast. The Asian steppes became cold and dry. Exodus started in the 6th century. Slavs had to run away from Eurasia. They came to Europe pushing both Germanic and Celtic tribes west. As it became unbearably cold in Scandinavia the Goths started to move south to the promise land in North Africa. Before they reached Carthage they sacked Rome bringing the West Roman empire to down. The city collapsed. The number of people went down to 60 thousand at times only to regain its million late in the 19th century (!). If we go one more millennium back we can see its beginning (and more accurate the end of the previous one) was also marked with the powerful global warming, the Minoan one. That warming was the most powerful of all three. The global temperatures were high. Agriculture thrived. There was plenty of food for everyone. Very powerful Cretian civilization flourished. Magnificent palaces were built containing sophisticated multi-floor architecture. Builders invented simple machines that helped to build them. As the millennium reached its first half the climate cooled down and, again, it contributed to collapse of the Minoan civilization.
The next figure (Fig.2.3) goes back 11,000 years back in time. It shows two groups of peaks of and a few cooling periods as well. At its beginning, we can see the curve ascending steeply which suggests its origin to be at very, very low temperature level. Now, let us go another 90 thousand years back. Now we can see that this 11 thousand year long period has been a one huge global warming. It is called an interglacial. Just before it started the Earth was a very cold place. Let us pay attention to those 4 small global warming periods at the end of that curve. We can realize now those are warming periods on top of another warming just like small waves rippling over the big one. We know them from the vacation on the seaside. Sometimes they disappear before the big wave would collapse but sometimes they last longer and disappear as soon as the big one breaks up on the beach. Let us think how a small warming may disappear. It may end up naturally turning into cool period but what will happen with it if the major warming would collapse? We may get the pattern as in the Fig. 2.4.
When I tell people that the global warming can actually happen in times of global cooling and therefore be effectively a global cooling, not warming, they look very confused but it is exactly that pattern I have in mind: global cooling may take over the global warming as the cycle that causes the latter collapses because the bigger cycle it rides upon collapses first. The paleohistory confirms that. The end of the previous interglacial happened when the Earth was much warmer than today. The Eem interglacial went through a series of global warmings on its way to demise.
I have mentioned the previous great global warmings - interglacials. Let us see how they look like. The Fig. 1.1 shows them back to the fifth one: Holocene, Eemian, Le Bouchete, MIS9 called informally the Purfleet interglacial, and the Holstein, the longest one, longer due to the double Milankovitch cycle that prompted it and virtually doubled its length. The Fig.2.5 focusess on the temperature curves of the last two interglacial periods separated by the temperature curve of the nearly hundred thousand years long ice age.
Let us now try to estimate the length of the time that is left before our interglacial will end by closely comparing it with the previous ones, especially the last one that even in the first glance seems to be so far very similar to our one – the Holocene. As we now approach the maturity time of our interglacial we currently live in, it is very important to find out to what degree its climatic history resembles the climatic history of the previous one and based on that to establish a point on the timeline we may presently live in. Even more than that: knowing that point and knowing what happened in Eem interglacial after it we will be able to project when the similar occurrences may happen in our interglacial in the future. Simply, it will give us a foundation to predict the things to come.
It looks each interglacial goes through three stages. The first one is the rapid temperature gain. It is quite possible it is a momentary incident maybe in the form of a "quite vigorous" storm. The recirculation of air masses associated with this event would be enormous. This event is definitely associated with the withdrawal of the polar masses way up north, hundreds of miles north. As the re-appearance of the mid-altitude westerly winds (called later the westerlies), a colossal heat and humidity conveyor is reconstructed and huge amounts of heat and moisture begin to be transported northbound again. Warm rains come back pouring over the glaciers which results in their much faster melting than in the previous period, the one between the glacial maximum and the interglacial onset. There have already been a few characteristically similar periods in both interglacials that account for the common mechanism they developed according to. The first is the glacial maximum achieved after 2-3 thousand of years into an interglacial. Then a post-maximum period marked with a profound cooling period. Both interglacials had them approximately within the first 6 thousand years. The end of that period was marked with the final melting of the glacial plates of both northern continents. It is not the coincidence the vigorous development of world’s civilizations started at that point as well. Then a 6 thousand year-long period followed in which global warming periods interlaced with global cooling events in roughly one thousand year intervals. The first major temperature drop happened after the fourth cooling event in the row. The Holocene has been also pretty stable over that interglacial period and also frequented with the 1000 years long warming events interlaced with the cooling ones. The last cooling events in the Holocene, the Maunder and Dalton Minima, were very profound – the temperature fell to almost coldest point in the whole interglacial (it was probably colder than in the cooling event associated with the end of the interglacial maximum period). Interestingly, the contemporary global warming represents the coming out trend from that cooling event. It looks (Fig.2.1) we have just topped our global warming, the change to global cooling will soon commence. If that cooling will see the temperature drops to lower levels than those in the Maunder Minimum that may be a sign we have entered the finishing phase of our interglacial as the characteristic of that phase is the series of the warming and cooling periods but happening on the already falling temperature curve of the whole interglacial.
If our global warming is the last global warming of the Holocene is, of course, unknown. What is probable, though, is that the oncoming global cooling may be austere, much more profound that Maunder Minimum as the greatly reduced solar forcing cycle will meet an also greatly reduced solar activity cycle which may result in a distinctive temperature drop in the near future and in the beginning of the next century. Whether the interglacial will have enough stability to come out of such aggressive cooling depends on to what degree the process of continental heat loss is advanced. The continental heat loss is an extremely important phenomenon as it is one of the root causes of the ice age return.
Similarities of both interglacials (Fig.2.6)
The occurrences to happen in Holocene in future by extrapolating the Eem history:
In this part of the work I attempted to predict the time of the end of the Holocene by comparing its features common with the previous interglacial that already happened in both and then to project the occurrences that yet did not happen in the Holocene using the previous interglacial climatic pattern. This comparison method is very suggestive but the repeatability of such time distant phenomena can be questioned. Realizing that, it prompted me to jump to the more difficult but much more interesting search for the Holocene ending this time by looking for the holy grail of the hundred-thousand year climatic oscillation – the mechanism of the cooling to warming and warming to cooling switch. Knowing the nature of the switch would not only allow us to predict all the oscillation’s patterns but also to create models that maybe at some point would allow us to precisely calculate their timing.