182 Ecology and Applied Environmental Science
a basic period of about 100,000 years, one part of which corresponds to
a warm period with climatic conditions similar to the ones we have today,
while the rest corresponds to a cold glacial period. As the Earth rotates
around its axis and around the sun, various periodic variations occur that
bring about changes to the intensity of solar radiation which falls on every
spot of the planet. The variations are due to gravitational influences of
other planets, tides etc. The change in the eccentricity of the Earth’s orbit
has taken place in a period between 90,000 and 100,000 years. The change
in the obliquity of the ecliptic, or axial, tilt has taken place in a period of
about 40,000 years. The Earth’s orbit tilt changes with a period of approximately 70,000 years. The direction change of the rotation axis has a period
of about 20,000 years. The Milankovitch cycles are the collective outcome
of the influence exerted on the climate by the changes of the Earth’s movements. However, the correlation between astronomic variations and climatic changes cannot be considered complete for the time being. Today,
approximately 10,000 years since the last glacial period, we are going
through a warm period, the duration of which there is no satisfactory
forecast. It is probable, on a geological scale, that the planet is approaching a new glacial era. It has been calculated that in about 30,000 years,
Earth’s orbit will have changed enough to reduce sunlight in the Northern
Hemisphere to the levels that led to the last ice age. In any case, the study
of the climate’s course during the last 130,000 years allows the representation of the conditions that prevailed at the end of the previous warm period
and the phenomena that followed, as for example the gradual covering of
North Europe with ice, the gradual replacement of South Europe’s forests
by steppes etc.
In addition to the fluctuation that corresponds to the great climatic cycle
of the last 100,000 years, it has been ascertained that the climate during
the post-glacial period presented a series of smaller fluctuations for which
there are no satisfactory explanations. We are talking about an alternation of warm-rainy periods and cold-dry ones, the average temperatures of
which did not differ by more than 2°C. Those differences, however, were
enough to significantly influence the vegetation, fauna, soil and waters,
which had an important impact on the corresponding historical periods.
According to certain views, the warm periods were eras of flourish and economic prosperity for humanity, while the cold ones brought years of misery
and economic retardation. According to these views, the era of prosperity
of primitive peoples that corresponds to the myth of Eden, the decline of
great kingdoms in Mesopotamia, Egypt and the Indies, the development
and amassment of capital during the Middle Ages in Europe and North
Africa (Medieval Warm Period) or certain phenomena of economic deceleration and retardation that were observed during the period called Little
Ice Age (about 1450–1850) could be explained.
a basic period of about 100,000 years, one part of which corresponds to
a warm period with climatic conditions similar to the ones we have today,
while the rest corresponds to a cold glacial period. As the Earth rotates
around its axis and around the sun, various periodic variations occur that
bring about changes to the intensity of solar radiation which falls on every
spot of the planet. The variations are due to gravitational influences of
other planets, tides etc. The change in the eccentricity of the Earth’s orbit
has taken place in a period between 90,000 and 100,000 years. The change
in the obliquity of the ecliptic, or axial, tilt has taken place in a period of
about 40,000 years. The Earth’s orbit tilt changes with a period of approximately 70,000 years. The direction change of the rotation axis has a period
of about 20,000 years. The Milankovitch cycles are the collective outcome
of the influence exerted on the climate by the changes of the Earth’s movements. However, the correlation between astronomic variations and climatic changes cannot be considered complete for the time being. Today,
approximately 10,000 years since the last glacial period, we are going
through a warm period, the duration of which there is no satisfactory
forecast. It is probable, on a geological scale, that the planet is approaching a new glacial era. It has been calculated that in about 30,000 years,
Earth’s orbit will have changed enough to reduce sunlight in the Northern
Hemisphere to the levels that led to the last ice age. In any case, the study
of the climate’s course during the last 130,000 years allows the representation of the conditions that prevailed at the end of the previous warm period
and the phenomena that followed, as for example the gradual covering of
North Europe with ice, the gradual replacement of South Europe’s forests
by steppes etc.
In addition to the fluctuation that corresponds to the great climatic cycle
of the last 100,000 years, it has been ascertained that the climate during
the post-glacial period presented a series of smaller fluctuations for which
there are no satisfactory explanations. We are talking about an alternation of warm-rainy periods and cold-dry ones, the average temperatures of
which did not differ by more than 2°C. Those differences, however, were
enough to significantly influence the vegetation, fauna, soil and waters,
which had an important impact on the corresponding historical periods.
According to certain views, the warm periods were eras of flourish and economic prosperity for humanity, while the cold ones brought years of misery
and economic retardation. According to these views, the era of prosperity
of primitive peoples that corresponds to the myth of Eden, the decline of
great kingdoms in Mesopotamia, Egypt and the Indies, the development
and amassment of capital during the Middle Ages in Europe and North
Africa (Medieval Warm Period) or certain phenomena of economic deceleration and retardation that were observed during the period called Little
Ice Age (about 1450–1850) could be explained.