Fig. 1: September Antarctic sea-ice extent (SIE) trends during the satellite era (1979–2018) in current climate models participating in the Coupled Model Intercomparison Project (CMIP5).

a Trends in SIE as function of mean SIE. The grey box encompasses CMIP5 models that are close to the observed mean September SIE (OBS⁹⁷, vertical dashed line) within ±3 million km². Those models with positive or only moderate negative linear trend (within ±0.3 million km² per decade of the observed trend, horizontal dashed line) are coloured blue, the other models with stronger negative trends are coloured red. Numbers represent CMIP5 models listed to the right. b, Trends in SIE as function of average ocean resolution in the Southern Ocean (45–65° S latitudinal band). The vertical dashed line denotes the mean Rossby radius of deformation in that band (13 km), while the grey box defines its range. For the models with good representation of mean SIE, a linear relationship between trend and ocean resolution is evident, with slope significantly different from zero at the 5% level (p = 0.011). The average ocean resolution was computed for each of the CMIP5 models as the square root of the average grid cell area of all ocean model cells located in that band, according to their centre (see “Methods”). Only ensemble means are given for each CMIP5 model (an otherwise identical figure with all ensemble members is provided in Supplementary Figs. 2 and 3). HR* and LR* (orange) are results from the two high- and low-resolution AWI-CM simulations discussed in this paper, but for the later period 2019–2058. High-resolution SIE decrease is delayed compared to the low-resolution configuration (see “Methods” for a discussion of earlier trends, including 1979–2018).