Scientists have long discussed the driving forces behind the large climatic fluctuations between the glacial and interglacial phases the last 2-3 million years. Most scientists agree that astronomical factors have influenced the major climate variations on Earth, factors that affect the Earth's surface and insolation against distribution of energy. These are called Milankovitch factors, named after the Serbian scientist Milutin Milankovitch, who already in the 1920’s could calculate how the Earth's position relative to the Sun varied at a certain cyclicity. This variation is due to the sum of the following three factors: The shape of the Earth’s orbital path varies from being nearly circular to weakly elliptical with a cyclicity of between 100 000 and 400 000 years. Earth’s axis varies in inclination between 22.1˚ and 24.5˚ and changes with a periodicity of 41 000 years.
It is the inclination of Earth’s results in our seasons and causes the Arctic Circle to move. Precession shows how the Earth is wobbling around like a top that is losing speed while it spins on its axis.
A climate record (or archive) can be viewed as a set of clues that tell you something about the Earth's past climate. Glaciers, sea ice, temperatures, precipitation, wind and other natural environmental elements react to climate change to become stronger, weaker, bigger, smaller, more frequent, etc. Hence, climate records will be found in nature in glaciers, seafloor sediments, lake bottoms, or on land. On land, such clues may be found in places such as in glaciers, marine sediments, stalactites and in marshes.
Glaciers and sediments consist of many layers, each of which represent specific past events or periods. Sediments and snow are deposited in layers so that younger layers lie on top of older layers. For example, Greenland’s inland ice sheet, which is nearly 3,000 meters at its thickest point, has layers nearly 130 000 years old that lie close to the bottom. Similarly, sediments buried deepest at the bottom of the sea or lakes are the oldest. Researchers can take core samples from ice and sediments, that allow them to analyze a continuous sample, from bottom to top. Sediments from the seabed are collected using different types of core sampling tools that carried on research vessels.
Important sources of climate information are the fossils of single celled animals and plants that lived in sea, then sank to the bottom and were buried in sediments after they died. Dinoflagellates and foraminifera are examples of such fossil groups.
By looking at the conditions presently found where the same species live today, one may estimate factors such as temperature, salinity and currents of the environment where fossils were deposited. If we can determine the age of the sediments or fossils, we can estimate the date or period when certain conditions existed. By combining data from different climate records, on land and in the sea, we can get a regional picture of climate history and the past environment.