Spatial distribution of trends and seasonality in the hemispheric sea ice covers: 1978-1996

We extend earlier analyses of a 8.8-year sea ice data set that described th e local seasonal variations and trends in each of the hemispheric sea ice c overs to the recently merged 18.2-year sea ice record from four satellite i nstruments. The seasonal cycle characteristics remain essentially the same as for the shorter time series, but the local trends are markedly different , in some cases reversing sign. The sign reversal reflects the lack of a co nsistent long-term trend and could be the result of localized long-term osc illations in the hemispheric sea ice covers. By combining the separate hemi spheric sea ice records into a global one, we have shown that there are sta tistically significant net decreases in the sea ice coverage on a global sc ale. The change in the global sea ice extent is -0.01 +/- 0.003 x 10(6) km( 2) per decade. The decrease in the areal coverage of the sea ice is only sl ightly smaller, so that the difference in the two, the ice-free areas withi n the packs, has no statistically significant change.