The Changing Sea Ice Cover in the Warming Arctic

Global surface temperatures increased by about 0.8 oC during the last century while Arctic temperatures increased at a higher rate of about 0.6 oC per decade since 1981. This is consistent with the expected amplification of global signals in the Arctic on account of ice-albedo feedback. This amplified signal is reflected in the perennial ice cover (or ice that survives the summer) which has been rapidly declining at almost 10% per decade. The perennial ice cover consists mainly of thick multiyear ice floes and a continued retreat could lead to a blue Arctic Ocean in summer and profound changes in the environment and ecology of the region. However, warming due to increases in greenhouse gases in the atmosphere is supposed to be most apparent in winter when long wave radiation is most dominant during the period of darkness but the maximum extent of the sea ice cover has been declining at the modest rate of only 1.5% per decade during the winter. This phenomenon is likely to change soon since drastic reductions in the maximum extent of the winter ice cover and associated warming in the regions of largest retreat are observed in 2005 and 2006. The winter decline also shows reductions in the eastern (Barents Sea) region making the perennial ice cover even more vulnerable. Strong correlations of the winter ice anomalies with surface temperature anomalies and wind circulation patterns are observed. The negative trend in the winter ice cover is likely to continue in the near future since the length of the ice growth season has been declining since the beginning of the satellite era and there is the expected impact of surface warming on account of the ice-albedo feedback. A real signal associated with increasing greenhouse gases in the atmosphere may have finally arrived in the Arctic.