The relative contribution of external forcing and internal climate variability to Arctic sea ice changes remains a controversial topic. To account for the bias of climate models in estimating the externally forced signal, we use two large ensemble simulations combined with optimal fingerprint method and find that previous approaches might overestimate the real impact of internal variability on Arctic sea ice change especially on lont time sclaes. Our results indicate that in both March and September, internal variability plays a dominant role on all time sclaes over the 20th century, while the anthropogenic signal on sea ice chage can be steadily and consistently detected on a timescale of more than 20 year after 2000s. We alos find that the pattern of internal variability in September is highly nonuniform over Arctic and varies across different timescales, indicating that sea ice internal variability in September at differernt timescales is driven by differernt factos. The local and remote factors on sea ice decadal variability also needs to be further discussed. 

Arctic sea ice; Decadal variability; Large ensembles; Internal variability