Skating on Thinning Ice

Sea ice is a sensitive indicator of climate change - if global climate were warming, then the amount of permanent sea ice in the Arctic should decrease. Satellite measurements and surface observations have shown that at least the area extent of Northern Hemisphere sea ice has been decreasing for almost 50 years. Two reports present new measurements and analysis of changes in Arctic sea ice. Iohannessen et al. measured the areal extent of the perennial Arctic sea ice pack and found that the area of the multiyear ice has decreased by more than twice as much of that of total sea ice. This change in ice cover has been accompanied by a decrease in ice thickness, which suggests that the heat and fresh water balances of the Arctic may be changing in significant ways. Vinnikov, et al. have examined the decrease in areal extent of sea ice. They combined five separate date sets and two independent climate models to test, whether these sea ice reductions can be attributed to natural climate variations. The model results suggest that the probability of this change is less than 2 percent for the last 20 years and that the decreases seen should continue during the next century. They conclude that the observed decrease in Northern Hemisphere sea ice is probably a result of anthropogenically driven global warming.

- Science, vol. 286 №5446 p. 1813

1. How does sea ice indicate climate change?

2. What was the result of the Yohannessen’s measurement of the areal extent of the Arctic ice pack?

3. What are the perspectives of natural climate variations according to Vinnikov, et al.?

Вариант 2

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