Climate Change

This entry reviews climate change records on all timescales—instrumental, historical, and geological—and their primary causes. The characteristics of glacial phases are detailed, followed by a discussion of the climate of the Holocene and the past millennium.

Changes of climate operate over all timescales. For convenience, we may recognize variations as decadal to century, millennial, 104 to 106 yrs. (years), and ≥108 yrs., each with its dominant forcing factors. Solar variability, volcanism, and changes in atmospheric composition occur on all [Page 456]timescales. Astronomical changes in Earth's orbital characteristics occur for more than 20,000 to 400,000 yrs. with distinct periodicities; these are about 23,000 yrs. (precession of the equinox), 41,000 yrs. (axial tilt of Earth), and 100,000 and 400,000 yrs. (orbital eccentricity of Earth). Geological processes of continental ...