From where is the history of average global temperature over the last 160,000 years derived?

The history of average global temperature over the last 160,000 years is primarily derived from isotopic analysis of ice layers. Ice cores, particularly those retrieved from regions like Antarctica and Greenland, encapsulate air bubbles from different periods in history. By analyzing the isotopes of oxygen and hydrogen present in the ice, scientists can infer past temperatures.

The isotopic ratios vary with temperature; for example, during warmer periods, certain isotopes become more prevalent in the ice. This correlation enables researchers to create temperature records that span back tens of thousands of years. The data extracted from ice cores paint a detailed picture of climate fluctuations, enabling a better understanding of past climate conditions and how they relate to current trends in global temperatures.

While ocean sediment cores, tree ring analysis, and atmospheric models also provide valuable climate data, they serve different purposes or cover different time scales and are not as directly correlated with the average global temperature records over that specific 160,000-year period as the isotopic analysis of ice layers is.