Variability and Trends in Antarctic Surface Temperatures from In Situ and Satellite Infrared Measurements.

The surface air temperatures observed from stations in Antarctica have been shown to have predominantly positive trends that are as high as 0.5°C decade¹ along the Antarctic Peninsula. To evaluate whether the trends are caused by a local or large-scale phenomenon in the Antarctic region, surface temperatures inferred from infrared satellite data from 1979 to 1998 have been analyzed in combination with data from 21 stations that have long record lengths. The surface temperatures derived from infrared data are coherent spatially and temporally and are shown to agree well with Antarctic station data with a correlation coefficient of 0.98 and a standard deviation of about 3°C. The trend analysis on station data yielded on the average 0.012 ± 0.008°C yr¹ and 0.008 ± 0.025°C yr¹ for the 45- and 20-yr record, respectively. The latter reasonably agrees with the trend of 0.042 ± 0.067°C yr¹ inferred from the satellite 20-yr record. The 20-yr record length is shown to be about the minimum length required for a meaningful trend analysis study. However, interannual fluctuations of the temperatures are large and the 95% confidence level for the satellite trends ranges from 0.177 to 0.094°C yr¹ for the Antarctic ice sheet. Nevertheless, the observed cooling is intriguing, especially since it is compatible with the observed trend in the sea ice cover. In the sea ice regions, the northernmost positions of the ice edge are shown to be influenced by alternating warm and cold anomalies around the continent. The pattern of these anomalies is consistent with that of the Antarctic circumpolar wave but with predominantly mode-3 instead of mode-2 wave as reported previously.