Total ozone data are statistically analyzed to estimate the trend detection capability which would provide early warning of ozone depletion. Based on a worldwide sample of nine stations, an abnormal global ozone change of 0.26% per year persisting over 6 years would be judged statistically significant, if it were to occur and could not be explained by historical patterns. A resulting 1.56% early warning can limit maximum reversible depletion to 2.3%, if the cause were due to chlorofluoromethanes FC‐11 and FC‐12. The analysis shows no evidence of an abnormal global trend persisting in the 1970's. The potential exists for detecting even smaller changes by using data from all the current land‐based stations and satel