What evidence do ice cores provide about carbon dioxide and methane during glacial cycles?

Ice cores provide critical evidence of past climate conditions by trapping ancient air in bubbles as snow is compressed into glacial ice. By analyzing these trapped air bubbles, scientists have determined that atmospheric concentrations of the greenhouse gases carbon dioxide and methane fluctuated significantly in correlation with glacial cycles.12

Specifically, ice core records show that the levels of both carbon dioxide and methane were much lower during glacial periods—even lower than pre-industrial levels—and peaked during interglacial periods. This evidence indicates that greenhouse gas concentrations are closely linked to the Earth's climate system. The reduction of these gases during the transition to a glacial phase acts as a feedback process that reinforces and amplifies cooling, while the reverse occurs during the transition to interglacial periods. Understanding these dynamics is essential for researchers studying the complex interplay between atmospheric chemistry, ice sheet dynamics, and global climate change.21