Variability of the Earth’s Climate

Abstract

The overall heat balance of the surface of the Earth is dictated by a number of factors. Three important elements are:

• Rate at which solar energy impinges on the Earth.

• Fraction of solar energy reflected by the Earth into space (albedo ).

• Effect of greenhouse gases (particularly water vapor , CO₂, and CH₄) in the atmosphere in absorbing and reemitting radiation emitted by the Earth.

There is evidence that over hundreds of millions of years, the Earth has undergone wide variations in climate. In this book, however, we concentrate on the occurrence of Ice Ages and Interglacials over the past ~800,000 years. These quasi-cyclic climate variations apparently began about 3,000,000 years ago (ya), but the duration and depth of the cold periods increased as time progressed. We refer to these cold periods as “Ice Ages.”