The leakage of stored and transported CO2 is a risk for geological sequestration technology.One of the most challenging problems is to recognize and determine CO2 leakage signal in the complex atmosphere background.In this work,a time series model was proposed to forecast the atmospheric CO2 variation and the approximation error of the model was utilized to recognize the leakage.First,the fitting neural network trained with recently past CO2 data was applied to predict the daily atmospheric CO2.Further,the recurrent nonlinear autoregressive with exogenous input (NARX) model was adopted to get more accurate prediction.Compared with fitting neural network,the approximation errors of NARX have a clearer baseline,and the abnormal leakage signal can be seized more easily even in small release cases.Hence,the fitting approximation of time series prediction model is a potential excellent method to capture atmospheric abnormal signal for CO2 storage and transportation technologies.