Energy > Climate Change
April 2022
Has the earth’s climate changed before?
This article is part of our series focused on the causes and consequences of a warming planet
The earth’s climate has changed many times over its long history. Two of the major causes of these changes are the shifting of the earth’s land masses and variations in the position of the earth relative to the sun.
The earth’s crust is composed of tectonic plates which cause continents to drift. Millions of years ago there was just one huge continent called Pangea. Due to shifting tectonic plates, this huge land mass gradually broke apart forming the continents we see today. These changes impacted the earth’s climate.
As continents moved toward the poles, snow and ice collected on the land. The white surface reflected most of the sunlight back into space leaving little light to be absorbed by the earth as heat. So, as the land moved towards the poles, the poles became colder.
At one time, South America and Antarctica were connected. When they broke apart, it allowed an ocean current to form that circled Antarctica. The ocean current blocked warm Equatorial water from reaching Antarctica resulting in the cooling of Antarctica and the development of an ice sheet over the continent.
Slight variations in the position of the earth relative to the sun impact temperature because of the change in the amount, angle, and timing of sunlight striking the earth’s surface. The climatic movement of the earth in and out of ice ages is partially due to these variations.
The orbit of the earth around the sun is not an unchanging circle. Rather, it is an ellipse that gradually changes in shape over time. This variation in the earth’s orbit causes a change in the distance from the earth to the sun and impacts the amount of sunlight reaching the earth’s surface.
Another variation is the tilt of the earth’s axis relative to the sun. The tilt changes slowly over time, varying from 22 to 25 degrees. A change in the earth’s tilt impacts the angle at which sunlight strikes the earth’s surface.
A third variation is a very slow wobble of the earth’s axis. The wobble is similar to that of a spinning top. If we were to look into the night sky 13,000 years ago, we would see the North Star but it would be a different star than it is today because of the earth’s wobble.
Although the earth’s climate has changed before, these changes have occurred over extremely long periods of time. They have virtually no impact on the rapid changes in temperature and climate the earth has experienced.
See the Ag Decision Maker website for more from this series.
Don Hofstrand, retired extension agricultural business specialist, agdm@iastate.edu
Reviewed by Dr. Eugene Takle, retired professor emeritus Iowa State University
