Abstract
The trends in the sea ice cover in the two hemispheres have been observed to be asymmetric with the rate of change in the Arctic being negative at −3.8 % per decade while that of the Antarctic is positive at 1.7 % per decade. These observations are confirmed in this study through analyses of a more robust data set that has been enhanced for better consistency and updated for improved statistics. With reports of anthropogenic global warming such phenomenon appears physically counter intuitive but trend studies of surface temperature over the same time period show the occurrence of a similar asymmetry. Satellite surface temperature data show that while global warming is strong and dominant in the Arctic, it is relatively minor in the Antarctic with the trends in sea ice covered areas and surrounding ice free regions observed to be even negative. A strong correlation of ice extent with surface temperature is observed, especially during the growth season, and the observed trends in the sea ice cover are coherent with the trends in surface temperature. The trend of global averages of the ice cover is negative but modest and is consistent and compatible with the positive but modest trend in global surface temperature. A continuation of the trend would mean the disappearance of summer ice by the end of the century but modelling projections indicate that the summer ice could be salvaged if anthropogenic greenhouse gases in the atmosphere are kept constant at the current level.
Highlights
Sea ice has been regarded as a key component of the Earth’s climate system
The observation of the seasonal and interannual variability of the sea ice cover was made possible through the use of data from a series of passive microwave sensors that started with the NASA/Nimbus-7 SMMR
These results should suggest an asymmetry in the trends of sea ice cover in the two hemispheres considering the high correlation of the two variables
Summary
Sea ice has been regarded as a key component of the Earth’s climate system It covers about 6% of the World’s oceans and affects the system in many ways. It is important to look at these changes from a global perspective since the trend in the ice cover in the Antarctic is going the opposite ways (Cavalieri et al, 1997) Such asymmetry has been postulated to be caused by various factors including the increase in snow precipitation in the Antarctic, the freshening of water in the region due to increases in the melt of ice shelves (Jacobs, 2006) and the occurrence of the ozone hole that tended to cause a deepening of the lows in the West Antarctic region (Turner et al, 2009). Changes in the sea ice cover, using a sea ice data set that has been enhanced for better consistency and updated for improved statistics, has been evaluated in conjunction with observed changes in surface temperature to gain insight into the phenomenon and improved understanding of the state and future of the sea ice cover
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