Sensitivity analysis of the long-term trend in Antarctic sea ice extent

There is a rapid diminishing ice extent in the Arctic but an opposite trend in Antarctic. The observed Antarctic sea ice extent to be expanding at a statistically significant rate 16.5±3.5×103km2yr-1 (IPCC 2013), reported by the IPCC AR5, whereas the trend is statistically insignificant at a rate of 5.6±9.2×103km2yr-1 in IPCC AR4 (IPCC 2007). The trends are derived from a long time series of passive microwave data, covering both the South Pole and the North Pole regions almost daily since 1970s. The sea ice concentration (proportion of ice area in a pixel) has been retrieved from the brightness temperature of passive microwave data, and the sea ice extent is defined as the area of ice that has an ice concentration no less than 15% (to avoid weather filtering issues near the ice edge). In an conventional way, the daily extents are averaged to monthly mean values, on the basis of those, monthly deviations are derived and linear regression model is applied to determine the rate (Parkinson and Cavalieri 2012). During this process, uncertainties from sensor transitions, processing method update, the addition of new data sources and the choice for a statistical method can all influence the final result (Cavalieri et al. 2012; Eisenman et al. 2014).