The evolution of climate

Since the Earth’s origin, about 5 billion years ago, there have been alternating cold periods which culminated in numerous glacial episodes that lasted millions of years, and periods of temperate or warm climate, lasting hundreds of millions of years. The climate has deeply conditioned the life of living beings inhabiting the Earth, and with each variation, plants, animals and humans have had to adapt, even to the most inhospitable environments. Therefore there have always been climatic variations over the centuries, but it is important to analyze the extent of the variations, in other words how much they influence our life and their duration. If we consider the personal experience of the life of a human being, we can observe seasonal or annual variations, for example  warmer years or years in which the rainfall was more abundant than in others. Over the centuries, in fact, there have been climatic variations that were much greater than those of today. A rise in temperature is always associated with melting Polar and Continental ice, with a consequent increase in the sea levels. In the past 500 million years, there have been variations in the sea level of even hundreds of metres, compared to the current levels (200-300 metres). However these changes took place over a very long period of time, about 300 million years, and therefore were not noticeable during the human life-span.
Sea level oscillation causes
There are several different causes involved in sea level oscillation but they are usually geological, climatic, astronomic or anthropical events.
The main ones are:

  • variations in ocean basin capacity, meaning the areas occupied by water;
  • variations in the amount of ocean water;
  • minor variations such as: sea water density, sea water desiccation, marine meteorological  parameters (atmospheric pressure and winds).

In the first case, variations in ocean basin capacity are caused by geological processes within the planet. We know that on the ocean floor there are belts called “oceanic ridges” where magma moves upwards, towards the surface swelling the earth’s crust so the mass of water is displaced with the consequent rise in sea level. This is very slow process which causes the level to vary by approximately one centimeter every thousand years so man cannot notice it in a lifetime.
Ocean water quantity variation, instead, is brought about by climatic causes: during colder weather periods, a large part of the water of the oceans is trapped in the Arctic and Antarctic glacial caps as well as in continental glaciers, while during warmer weather, the ices melt causing the sea level to rise quickly, as much as one centimeter per year.
In the past century large quantities of man made greenhouse gasses have been added to the natural causes which are bringing about climate changes at a much faster pace, and all this is having a big effect on us.

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