After so much cold ... finally a bit of heat arrives
We will talk about the trend of Temperaturestarting from 10,000 years BC Why this limit, which after all, compared to the presence of man on Earth, is a very small thing? Perhaps it is difficult to reconstruct the changes in temperature in previous eras? It would not be enough to go back two or three thousand years to know the "rules", if there are any, with which the climate has changed in the past, so as to be able, as far as possible, to see what awaits us in the near future and to reassure those who cry out"it has never been as hot as this year"or those who exasperating the"earth effect"herald the melting of the glaciers and consequent floods.
The choice of a period of twelve thousand years was made because it is connected with a great climatic event: the end of the Ice Age, which took place after more than 850,000 years of frost established with alternating phases, in the northern hemisphere, in particular in Europe.
It was not the only glaciation in the history of the Earth, but undoubtedly the most important for humanity, since it is during this period (Quaternary Era) that Homo sapiens appeared and, more fascinatingly, the selection for get to modern man.
Before examining the trend of temperatures in the various periods it should be borne in mind that there is a substantial one difference between "meteorological trends" and "climatic trends", while often there is a great confusion between the two entities. In fact, the variations recorded within a few decades only authorize considerations of a meteorological nature, even if they highlight excursions of different degrees. In these cases we cannot speak of climatic variations and much less risk forecasts on the climate even at a short distance.
Because we can instead speak of excursions and weather forecast it is necessary to be in the presence of direct or indirect observations relating to several decades, taking into account the variations in average temperatures. Important climatic changes occur, as regards the temperature, with variations of 3 or 4 degrees.
It should definitely be pointed out that variations in temperatures are not the only parameters to be taken into consideration to ascertain and evaluate both meteorological and climatic changes.
Naturally, the climate in the last 12,000 years has undergone various fluctuations that allow us to divide the time spent in different periods, characterized by warm climates alternating with returns of icy climates. These periods can only be defined a posteriori, so much so that it is difficult to define whether today we are going through a glacial or interglacial climate excursion.
Broadly speaking, the trend of the past climate can be divided into the following periods:
- the hottest period experienced by humanity is that between 10,000 and 1,000 BC. with the peak between the 5th and 4th millennium BC During this time, the Great Ancient Civilizations;
- a second relatively mild period, separated by a brief rigid phase from the previous one, occurred between the end of the 1st millennium BC. and 1400 AD, which mainly affected the Middle Ages;
- with 1400 there was a return of frost throughout Europe with influence on the southernmost latitudes. This phase has been defined "The little ice age"which is believed to have ended in the late 1800s, but it is not excluded that it still continues today.
Before discussing the different periods, it will be appropriate, at least in broad terms, to consider the climatic variations and the consequences that may have occurred with regard to man and his activities.
As indicated in the Ice Age card, between 10,000 and 9,000 years BC man in the Northern Hemisphere came out of difficult living conditions, not only for climatic reasons, but also because the means of defense and the tools for basic necessities were really crude and of limited effectiveness.
Coinciding with the gradual warming that was taking place in the northern hemisphere we have the first and perhaps the most important Revolution of Humanity, in fact in the Evolution of Humanity other factors in addition to the climatic ones were decisive, but if we consider that during the glaciation the Palaeolithic man lived only thanks to the hunting and gathering of plant products that spontaneously grew in the most favored areas, it is only with climate change that humans discovered and perfected two truly revolutionary activities: agriculture and animal husbandry.
Millennium after millennium, the temperature continued to rise until it reached its peak during the sixth millennium BC, accompanied by another no less important climatic phenomenon: increased humiditysuch as to maintain the balance of all the other factors that have always characterized the ecological system of this Great Greenhousewhich is the terrestrial globe. L'greenhouse effect, nowadays often misquoted and to demonize it, it is linked to the ecosystem that has been established on Earth since the earliest times and which still allows the development and survival of the plant and animal kingdom including mankind today.
As the temperature increases, evaporation increases and consequently the humidity rate rises, so that precipitation intensifies. Obviously there is an increase in the waters of the rivers, the flow of which is also affected by the thawing of the glaciers, with consequent possible, but certainly not, sea level rise, as is argued today by those who formulate catastrophic forecasts for the more or less immediate future.
Also in this case nature to maintain a certain balance makes use of effects of opposite sign, in order to have compensations between the phenomena in the final result. In fact, the rise in sea level is not related to precipitation, as there is a balance between evaporation and precipitation, but is linked to the thawing of the glaciers and therefore a greater presence of water in the basins. However, a sea level rise in proportion to the volume of melted ice has not always been observed as there are factors that can reduce or cancel the extent of the rise. First of all in geology it is not always possible to establish in the case of sea ingress on dry land whether the cause was the sea level rise or rather a lowering of the region, as well as in the case of sea water withdrawal it could be due to an actual withdrawal of water, due to evaporation or less precipitation, or rather to a lifting of the mainland. In many cases it is the concomitance of the two phenomena that determines the final effect.
Going into more detailed considerations regarding the melting of glaciers, the following should be noted:
- the lands on which enormous masses of ice stand are subjected to considerable pressures which, with the melting of the ice, are considerably reduced, so that they rise even several tens of meters. All the coasts of the Mediterranean are characterized by esplanades far above the current sea level, commonly classified "marine terraces";
- another argument put forward by those who fear the rising of the sea to the point of submerging extensive lands, is that of the melting of icebergs in the northern latitudes. Undoubtedly, their contribution can be given, but taking into account that almost the entire volume of the iceberg, being already submerged in the sea, contributes to determining the sea level before melting. Another important factor is that the volume of the resulting water since thaw it represents 85% of the volume of the iceberg, therefore there will be a small contribution to the rise in the level due to the emerged part equal to 1/10 of the entire iceberg;
- any significant increase in marine waters will cause subsidence movements of the sea beds, the extent of which depends on many factors linked to the geology of the area, but which in any case constitutes a compensatory element for any increases in sea levels;
- certainly those coastal and river areas, which human intervention for social or economic reasons has decidedly modified with reclamation works or infrastructures, not always respecting the environmental structure resulting from balances achieved over so many millennia, can easily be again covered by marine or brackish waters. Of course this prospect will not please the descendants of those who many decades ago had reclaimed marshy areas such as the Pontine plain, the Polesine, etc., but it should not be swear at Nature, because conditions pre-existing to human intervention have been restored as well as one should not seek an alibi in pollution, because they are events that have occurred for hundreds of millions of years, when there was no activity to pollute Nature.
Dr. Pio Petrocchi