Excerpt from the Southwest Climate Change Network, written by Zack Guido, University of Arizona
At numerous times in the geologic past, the Earth’s astronomical position reduced the amount of solar energy striking the atmosphere, causing massive ice sheets to grow. The cause of these cooling periods, and the subsequent warmer periods, was a change in the amount of solar energy available to power the climate system.
The climate system evolves in part due to changes in external factors that affect the amount of solar radiation available to drive the climate. These factors are called "forcings" and include solar variations, cycles in the Earth’s position in space, volcanic eruptions, and changes in the atmospheric concentrations of greenhouse gases. All of these phenomena change the radiation balance, which has a direct influence on climate. They also cause secondary changes known as "feedbacks," such as an increase or decrease in the size of ice sheets and the cloud cover, which in turn magnifies or lessens climate change.
To identify how and to what degree human actions alter the climate, it is important to understand the principal drivers of climate. They include:
- Incoming Solar Radiation
- Variations in the Sun's Solar Emissions
- Greenhouse Gases
- Volcanic Eruptions and Aerosols
- Climate Control Feedbacks
Adapted for eXtension.org by Michael Crimmins, University of Arizona
External Links
Southwest Climate Change Network
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