To understand changes in climate, knowledge about Earth’s past climates is needed. Since instrument weather records only exist for a couple hundred years, methods were developed which allows a person to infer Earth’s past climates. These records become less accurate the further they go back in time. However, they describe our planet as being much warmer than today. Significant changes have occurred on our planet including hot periods with no polar ice, and cold periods with extensive ice sheets. This chapter explores Earth’s past climates, how these past climates were determined, and what natural variability is present today that influences climate.

Chapter objectives:

1. Explain how scientists determine Earth’s past climates.

2. Describe the variations in Earth’s past climates.

3. Understand how Milankovich cycles caused Earth’s glacial and interglacial periods.

4. Describe ENSO and its influence on seasonal weather conditions.