Measurements of methyl chloride (CH₃Cl) in Antarctic polar ice and firn air are used to describe the variability of atmospheric CH₃Cl during the past 300 years. Firn air results from South Pole and Siple Dome suggest that the atmospheric abundance of CH₃Cl increased by about 10% in the 50 years prior to 1990. Ice core measurements from Siple Dome provide evidence for a cyclic natural variability on the order of 10%, with a period of about 110 years in phase with the 20th century rise inferred from firn air. Thus, the CH₃Cl increase measured in firn air may largely be a result of natural processes, which may continue to affect the atmospheric CH₃Cl burden during the 21st century.