Chapter 3 - Arctic Sea Ice

Abstract

The Arctic sea ice has been in decline during the last three decades, and the Arctic summer sea ice extent has never been as low as at present during the last 1450years. Natural variability alone cannot explain the recent observed decrease. There is a direct physical argument that climate change causes a decrease of sea ice: an increase of atmospheric CO2 leads to an increase in long-wave radiation resulting in an increase of ice melt. Climate model studies allow us to discriminate between the impact of natural variability and the impact of climate change on the observed sea ice decline. Current models indicate that both impacts are of similar magnitude. While the precise ratio is uncertain due the dependency on the level of sophistication of the model and how well key processes are included, there is evidence that the Arctic sea ice decrease is at least to some extent caused by climate warming. Due to its fast response to external drivers, the Arctic sea ice is a prominent indicator of climate change.