"Continuous monitoring of the polar regions by satellites has shown that sea ice extent (SIE) in the Antarctic has increased slightly since 1979. By contrast, climate model simulations including all major anthropogenic and natural climate influences simulate an average decrease in SIE since 1979. Here we take a longer view and assess the consistency of observed and simulated changes in Antarctic SIE using recently recovered satellite-based estimates of Antarctic SIE for September 1964 and May–July 1966, hence extending the current observational record from 35 to 50 years. While there is evidence of inconsistency between observed trends in Antarctic SIE and those simulated since 1979, particularly in models with realistic interannual variability, the observed trends since the mid-1960s fall within the 5–95% range of simulated trends. Thus our results broadly support the hypothesis that the recent increase in Antarctic SIE is due to internal variability, though the reasons for the inconsistency in simulated and observed changes since 1979 remain to be determined."