So what is the connection between pollen and climate change? All flowering plants produce pollen grains. Their distinctive shapes can be used to identify the type of plant from which they came. Since pollen grains are well preserved in the sediment layers in the bottom of a pond, lake or ocean, an analysis of the pollen grains in each layer tell us what kinds of plants were growing at the time the sediment was deposited. Pollen and spores are critical parts of the life cycles of vascular and, because they have very resistant walls, pollen and spores typically are the most abundant, easily identifiable, and best preserved plant remains in sediments and sedimentary rocks.
Relative dating using pollen is possible by comparing between stratified deposits the number of pollen types that have occurred during their formation because of changing environmental conditions. At a simple level an older deposit will contain pollen representing older plant communities. Over time, though the formation processes of the sediment deposit may not alter, vegetation changes due to climatic or human influence will result in different range of preserved pollen.
The most common method of extracting pollen samples is by core sampling sediments, and taxa (plant groups) along with concentrations of pollen are used as indicators of environmental settings. Pollen is widely distributed, produced in vast quantities (one pine branch can produce 350 million pollen grains), easily recognisable and very resistant to decay (some pollen in East Africa goes back 3 million years). The fluctuating type and distribution of pollen assists in interpreting local and regional histories of vegetation and climate.
From deep-sea cores we can obtain samples of foraminifera, pollen and dust from below the ocean floor. The abundance and biodiversity of foraminifers give clues to past sea temperatures and the dust can be dated. Most palaeoclimatolgy study relies on proxy (substitute) records like ice core, deep-sea drilling and pollen samples as actual records are not available from prehistory. By using data from these sources a climate model for the Pleistocene can be detailed, which obviously varies from continent to continent, and region to region.