The industrial companies have begun to spread into the atmosphere carbon dioxide and other greenhouse gases with the introduction of manufacturing plants and coal-fired power stations, whose emissions are then added to those of motor vehicles. In those circumstances, only who lived in the industrial sector is responsible for the accumulation of greenhouse gases into the atmosphere and for the trend towards global warming?
Things are not really so. Certainly the industrial activities have contributed greatly, but there are other natural factors that influence the climate.
Since the seventies is recognised that what dominate the global climate is the long term (by millions of years) three variations of the Earth rotation around the Sun called Milankovich cycles.
The precession of the equinoxes is a gradual shift of the Earth's rotation axis. This motion is caused secondary by the gravity attraction of the Moon and the Sun that tends to change the direction of them and describe, clockwise, the surface of a cone in little more than 23000 years.
Tilt: the angle of the Earth's axis relative to the plane of its orbit varies between 21.5 and 24.5 degrees over a period of 41,000 years...
Eccentricity: the shape of the Earth's orbit around the Sun. The eccentricity varies over about 100,000 years between slightly more or less elliptical.
As a result of these orbital cycles the amount of solar radiation reaching the various parts of the globe in a given season, can vary by more than ten percent. Over the past three million years, these changes in the amount of sunlight that reached the surface of the planet have produced a long sequence of glaciations separated by brief warmer periods.
While it revolves around its axis, Earth waves as a gyroscope.
A carrot ice recovered three kilometers long in the nineties of the last century from the Vostok station in Antarctica contained ancient air bubbles that revealed the composition of the atmosphere in the last eight hundred thousand years.
The natural variations of earth’s orbit change the sunlight that reaches the globe and cause strong fluctuations in atmospheric concentrations of methane and carbon dioxide.
The Vostok cores tell us that concentrations of methane into the atmosphere have increased and decreased in the last three hundred and fifty thousand years, in perfect harmony with the ups and downs of solar radiation, induced by precession in the north.
Concentrations of carbon dioxide are varied depending on the precession, the variation of the tilt of Earth's rotation and orbital shape of the planet. These cycles occur every 41000 and 11000 years. For reasons still not entirely clear, global concentrations of these greenhouse gases cause almost exclusively changes that occur during the summer in the northern hemisphere, where focuses most of the continental masses. The peak of summer heat in the northern occur every twenty-two thousand years, when the northern summer coincides with the Earth’s moving closer to the Sun and the northern hemisphere receives the maximum light. The summer heat instead reaches the minimum eleven thousand years later, after the Earth's axis has made half a revolution. The hemisphere receives the least sunlight summer because the Earth and the Sun are at the maximum distance.
In summary, cores of Vostok tell us that despite the wide fluctuations had in the past, the climate has maintained a regularity that reflected changes into that of Earth’s orbit, ranging between two stages of apparent balance, a cold glacial period and another warm period. This has happened in the last eight hundred thousand years.
Today, however, is no longer so, in fact the human activities have changed forever the natural cycles and, with a certainty, our impact on the environment will grow more and more. We can not go back. We can, however, studying the transformation process in place, learn to control it and groped handle with the choices of politics and with the laws of physics. People will say, what has it got to do to with physics? Physics have to do a lot!
Summary of Milankovich cycles…
Nessun commento:
Posta un commento