Causes of Climate Change
The general state of the Earth's climate is dependent upon the amount of energy stored by the climate system, and in particular the balance between the amount of energy the Earth receives from the Sun, in the form of light and ultraviolet radiation, and the amount of energy the Earth releases back to space, in the form of infrared heat energy. Causes of climate change involve any process that can alter this global energy balance. Scientists call this "climate forcing". Climate forcing "forces" the climate to change.
The are many climate forcing processes, but broadly speaking, they can be separated into internal and external types. External processes operate outside planet Earth, and includes changes in the global energy balance due to variations in the Earths orbit around the Sun, and changes in the amount of energy received from the Sun. Internal processes operates from within the Earth's climate system, and include changes in the global energy balance due to changes in ocean circulation or changes in the composition of the atmosphere. Other climate forcing processes include the impacts of large volcanic eruptions and collisions with comets or meteorites.
Luckily, the Earth is not hit by large comets or meteorites very often, perhaps every 20 to 30 million years or so, and therefore their associated climate changes occur rarely throughout Earth History. However, other causes of climate change influence the Earth on much shorter time scales, with changes sometimes occurring within a single generation. Indeed, our present pollution of the atmosphere with greenhouse gases may be causing the global climate to change. This man-made climate change has become known as global warming.