The earth's climate has changed historically as a result of natural processes or one-off events. Natural cycles of the earth's orbit, occurring over tens to hundreds of thousands of years, have resulted in periods of cooling (ice ages) and warming (interglacials), causing ice caps and glaciers to grow and shrink as a result of changes to the level of the sun's energy received by the earth. Other cycles, such as El Nino, occur on much shorter timeframes and have more localised impacts on climate. One off events such as volcanic eruptions or meteorites have resulted in large quantities of dust being released to the atmosphere, reducing the sun's energy received by the earth and reducing temperature.
Throughout our planet's history, the climate has changed as a result of natural processes and these natural processes continue to effect the climate today. Understanding how the ocean, land and atmosphere have been effected by historic natural climate change allows us to develop an understanding of the interactions between climate and these earth systems, as well as distinguish between climate change that is natural and that which is a result of human activity. Natural climate change can be divided into three broad categories: (i) one-off events; (ii) short-term patterns; and (iii) long-term patterns. Each is discussed in more detail below.
Volcanic eruptions release particulates in the air, which act to reduce the solar radiation that reaches the earth's surface, with an associated cooling effect. Click here for more information.
El Nino (or the El Nino Southern Oscillation ("ENSO")) is a pattern that occurs every two to seven years associated with a warming of the central and east central equatorial Pacific and areas of high pressure in the Western Pacific and lower pressures in the East, compared with average norms. This has typically caused drier periods in Indonesia, Australia and India and wetter weather in Central and South America. Click here for more details
Sunspots are areas of increased solar activity. During a sunspot period, the level of solar irradiation received by the earth can increase, with an associated increase in temperatures. Click here for more detail.
Milankovitch cycles are long-term, natural cycles of changing levels and distributions of solar irradiation reaching the earth as a result of changes to the shape of the earth's orbit, variability in the tilt of the earth on it's axis and the precession of the earth's axis in a gyroscopic motion. Click here for more information.
