Quaternary or glacial era

Major climate variations have taken place during the Quaternary period (the past 2,5 million years), which is when man made his first appearance on Earth, caused by the massive expansion of the polar caps approximately every 100 thousand years, that made the sea level decrease by as much as 120 – 140 meters below what it is today.
We must bear in mind that the last glaciation allowed man to spread all over the world, thanks to the spits of dry land emerging from the lowered sea level.
These periods were followed by other warmer ones with temperatures which were similar to the ones we have today which allowed the ice to melt and consequently increase the sea level.
Shortly before the beginning of the Quaternary because of the tectonic plates which allows vast areas of dry land to shift, the distance between south America, Africa and the Antarctic continent induced an ocean current similar to a gigantic “river” moving a volume of water 100 times the size of the Amazon River. This river submerged from the north Atlantic, reaching the ocean floor and traveling the whole length of the Atlantic Ocean from north to south going around Africa to then spread into the Indian Ocean while part of it went as far as the Pacific Ocean. This enormous volume of water is still moving today and acts as a huge conveyor belt for heat, as though it were a gigantic air conditioning system  that controls the weather on Earth. When the hot current reaches as far north as Iceland it encounters the cold winds from Canada so it cools off, releasing the heat into the air and mitigating the effect that these winds would have on northern Europe.
With the evaporation water becomes more dense and tends to sink, generating a cold deep current. The amount of heat carried by this enormous “conveyor belt” depends obviously on how much is stored during its formation. At present the “conveyor belt” is near Iceland, but its latitude can vary, oscillating to the point of interruption, thus causing a break down of the heat distribution system.
As time passes, the sun’s heat reaching the surface of Earth and the sea, changes according to the orbital parameters of our Planet.
There are three main causes for latitude variations.
Shift in the axis inclination of Earth’s rotation. The Earth’s axis inclination has a slow oscillation that goes from 21,8° to 24,4° in a stable period spanning approximately 40,000 years. Currently the angle is 23.45° and is decreasing, thus diminishing the contrast between summers and winters.
Changes in the eccentricity of Earth’s orbit. The planet’s orbit changes from an almost perfect circumference to a marked ellipse. When it is an ellipse, the planet is closer to the sun, otherwise, it is more distant. A complete orbital cycle going from an almost round orbit to an ellipse one and vice versa, takes 100,000 years.
Precession of the equinoxes. This is the celestial phenomenon whereby the axis of our planet goes a complete circle around an imaginary cone every 26,000 years. This is the reason why the seasons have a slow tendency to come sooner and be modified. The same thing happens when one spins a spinning top which in fact is very difficult to keep straight with its axis perfectly perpendicular to the ground. It is more likely to have an eccentric spinning motion and its point will gradually design a cone as it goes around. Something similar happens to our planet although the forces that cause this are obviously different.
Therefore, over thousands of years, Earth changes its position with respect to the sun to then start all over again every 26,000, 40,000 and 100,000 years. The combination of these three elements will modify the amount of energy(Watt per m2): when the point of no return is reached, the heat is so intense that the glaciers melt and reach a peak, whereby the climate is similar to what we have nowadays and lasts for a time span ranging from 6,000 to 13,000 years, until Earth’s geometry gradually changes causing glaciers to build back up quite quickly (within just a few hundred years).

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