Reconciling Roles of External Forcing and Internal Variability in Arctic Sea Ice Change on Different Timescales

Abstract Two large ensemble simulations are adopted to investigate the relative contribution of external forcing and internal variability to Arctic sea ice variability on different timescales since 1960 by correcting the response error of models to external forcing using observational datasets. Our study suggests that previous approaches might overestimate the real impact of internal variability on Arctic sea ice change especially on long time scales. Our results indicate that in both March and September, internal variability plays a dominant role on all time scales over the 20th century, while the anthropogenic signal on sea ice change can be steadily and consistently detected on a time scale of more than 20 year after 2000s. We also reveal that the dominant mode of internal variability in March shows consistency across different time scales. On the contrary, the pattern of internal variability in September is highly nonuniform over the Arctic and varies across different timescales, indicating that sea ice internal variability in September at different time scales is driven by different factors.