Figure 2.16: Monthly Antarctic
sea-ice extent anomalies, 1973 to 2000, relative to 1973 to 1996. The data are
a blend of National Ice Center (NIC) chart-derived data (Knight, 1984), Goddard
Space Flight Center satellite passive-microwave (Scanning Multichannel Microwave
Radiometer (SMMR) and Special Sensor Microwave/Imager (SSM/I)) derived data (Cavalieri
et al., 1997) and National Centers for Environmental Prediction satellite passive-microwave
derived data (Grumbine, 1996). It is uncertain as to whether the decrease in interannual
variability of sea ice after about 1988 is real or an observing bias.