Ocean & Lake Sediments: Scientists take core samples of ocean and lake sediments. In addition to pollen, fossils and chemicals embedded in the sediment are analyzed to determine the climate in the past.
Microbial Data: Foraminifera and diatoms are commonly used microbial climate proxies. Both are aquatic organisms with shells. Foraminifera shells are made up of calcium carbonate (CaCO3) and diatom shells are composed of silicon dioxide (SiO2). In warmer water environments, the shells will be richer in O-18 and in colder conditions,
O-16 will prevail.
Paleoclimatologists weave together the data from all of these sources in an attempt to create a history of the Earth’s climate. Proxy records are coordinated with current data and the historical record, usually using computer models. They also use the models to predict future climate.