“Long-term climate changes are those changes over Geologic time that may persist for millions of years.”
By Dr. John J. HIdore
December 6, 2017—–Long-term climate changes are those changes over Geologic time that may persist for millions of years. The intermittent ice ages that have occurred through the span of earth history are an example. The processes which have produced these long-term changes, for the most part, also take place slowly.
Regular variations in the motion of the earth as it travels around the sun explain daily and seasonal differences in the amount of solar energy arriving at the surface. However, the angle of the earth’s axis and the distance from Earth to the sun vary over time.
The obliquity of the ecliptic: This term refers to the angle of Earth’s axis in relation to the plane in which the earth revolves around the sun. This angle is not constant. On a cycle of a period of about 41,000 years, the angle varies some 1.5° about the mean of 23.1°. If the earth’s axis were perpendicular to the plane there would be equal lengths of day and night over the globe and result in little seasonal change. If the angle were greater than 23.5 there would be greater extremes in the lengths of summer and winter days and nights and to cause distinctive changes in the distribution of Earth’s climates.
Earth’s orbital eccentricity: The earth moves around the sun in an elliptical orbit; the eccentricity of the orbit is derived by comparing the path to that of a true circle. Currently the orbit is relatively close to a circle. Over the past million years, the orbit has changed from almost circular to a distinctly oblong shape. This change influences the amount of solar radiation intercepted by the earth and modifies the dates at which the solstices and equinoxes occur.
Distribution of Continents
One set of theories of climatic change deals with the location of continental land masses in relation to the position of the poles and the equator. Reconstructed maps for the Permo-Carboniferous glaciation (250 million years ago) and those of the most recent Pleistocene glaciation show that in both cases there was a concentration of land masses in the polar realms. However, there have been times when such a location occurred, but no glaciation resulted.
Intimately related to the idea of moving continents is the role of mountain building. As an explanation of this theory, one only has to think of the formation of snow and ice on Mt. Kilimanjaro located astride the equator. Geologists have long noted the relationship between times of extensive mountain-building periods and some of the ice ages. For example, both the Permo-Carboniferous and recent ice ages were preceded by extensive mountain-building periods.
Variation in the Oceans
Modern research in climatology is paying increasing attention to the role of the oceans in the climatic system. The oceans have received attention, providing in some cases the basis of entire theories of climatic change. Some of the ways in which the oceans influence the prevailing climates on Earth include the following:
1. Changes in the elevation of the land is a factor. A drop in sea level would increase the heights of the continents and enlarge land masses.
2. The oceans are less variable in temperature than the continents, and changes in the relative temperature of oceanic waters influence world climates. Variations in the energy storage in the oceans can occur because of changes in salinity, evaporation rates, and relative solar penetration.
3. Oceans play a significant role in the redistribution of energy over the earth’s surface. Ocean currents transport large amounts of heat, and any changes in their relative extent and direction of flow have a great impact on climate.
At intervals throughout the history of Earth, exceptionally large objects from space have struck the earth. When these objects struck Earth, some altered the climate tremendously for short periods and in some cases for periods of thousands of years. The boundary between the Cretaceous and Tertiary geologic periods was approximately 65 million years ago. Much evidence now points to a large object impacting the earth at this time. It certainly altered the climate. The impact produced firestorms over the earth, destroying much of the vegetation. These same fires would have removed much of the atmospheric oxygen and added large amounts of carbon dioxide.
A huge dust cloud was raised that blocked out the sun for months causing temperatures to drop. The fires also contributed a huge cloud of soot to the atmosphere. The sustained cloud of solid particles would have greatly reduced solar radiation to the ground. Precipitation would have turned into acid rain and snow as the highly sulfurous particles combined with water particles in the atmosphere.
The theories presented herein are a partial representation of those that have been suggested. Other researchers have introduced ideas ranging from the possible influence of the periodic passage of the earth through an interstellar dust cloud to variations in atmospheric water vapor caused by both natural and human activities. Despite all of these ideas, there is no single theory that can account for all of the observed events; it is evident that earth’s climates result from a spectrum of causal elements.
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