No one really knows how the concentrations of atmospheric carbon dioxide have changed in the distant past, because we have only been directly measuring it since 1955.

Question

Quizplus · Accepted Answer

Scientists can estimate past concentrations of atmospheric carbon dioxide (CO2) using indirect methods, such as analyzing air bubbles trapped in ice cores, which can provide data going back hundreds of thousands of years.

No One Really Knows How the Concentrations of Atmospheric Carbon