The most direct sources of consistent, repetitive information on the polar sea ice covers are satellite passive microwave sensors. Previous studies using microwave data have detected decreases in Arctic ice extent and ice area, but no significant changes in the Antarctic. Here we analyze microwave data 1978–1995, to identify changes in ice extent, ice area, and overall ice concentration. We find continued decreases in the Arctic ice extent and ice area, and establish a decrease in the overall ice concentration. We also include a seasonal analysis of the Arctic ice cover, which reveals the greatest decreases to be in summer. The relatively large summer decreases imply a reduction in the multi-year ice area, suggesting reduced ice thickness. These findings have considerable implications for global warming and are important for polar operations.
The polar regions are generally regarded as particularly sensitive to the potential warming related to increases in global greenhouse gases. Simulations of greenhouse warming scenarios using general circulation models (GCMs) usually indicate amplified warming in the polar regions, particularly the Arctic (Stouffer et al., 1989), including a substantial retreat of the sea ice cover (Senior and Mitchell, 1993). Some models even show the complete or near-complete removal of the sea ice cover in summer (Manabe et al., 1992) Recent time-dependent greenhouse warming simulations indicate that within the next two decades, the greenhouse signal should become detectable over the natural variability (Cubasch et al., 1995). Observational studies of Arctic and Antarctic sea ice could thus be useful for detecting climate change (Walsh, 1991 and 1995). Trends in the sea ice covers would also be important for operations in the polar regions. Polar transport is generally limited to specific regions and seasons. Reductions in the ice cover could facilitate transport through, for example, the Northern Sea Route (Johannessen et al., 1994).
