Yes. Earth has experienced cold periods (informally referred to as “ice ages,” or "glacials") and warm periods (“interglacials”) on roughly 100,000-year cycles for at least the last 1 million years. The last of these ice age glaciations peaked* around 20,000 years ago. Over the course of these cycles, global average temperatures warmed or cooled anywhere from 3° to perhaps as much as 8° Celsius (5°-15° Fahrenheit). It was partly through their attempts to understand what caused and ended previous ice ages that climate scientists came to understand the dominant role that carbon dioxide plays in Earth’s climate system, and the...