Paleoclimate is the variation of the climate in past geologic times, prior to instrumental measurements. Paleoclimate is expressed by its parameters—paleotemperature, precipitation in the past, circulation, sea surface temperature (SST), and sea level.

The general state of the earth's climate is dependent upon the amount of energy the earth receives from the solar 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 the global energy balance (climate forcing). Climate forcing processes can be divided into internal and external types. External processes include variations in Earth's orbit around the Sun. These variations change the amount of energy received from the Sun, and also cause variations of the distribution of sunlight reaching the earth's surface. Long periods of solar luminosity variations cause variations of the global climate, although lower...