The most dramatic loss of ice in recent years has been the decline of summer sea ice in the Arctic Ocean. Between 1953 and 2006, the area covered by sea ice in September shrunk by 7.8 percent per decade, more than three times as fast as the average rate simulated by climate models. Researchers were further stunned in the summer of 2007 when Arctic sea ice extent plummeted to the lowest level ever measured, more than 20 percent below the 2005 record.
This decline is rapidly changing the geopolitics of the Arctic region, opening the Northwest Passage for the first time in recorded history and triggering a scramble among governments to claim large swaths of the potentially resource-rich Arctic sea floor. An important factor behind the sudden drop in ice cover in 2007 was that the sea ice at the start of the spring melt-season was thinner and less extensive than usual.
The fact that the ice was unable to fully recover over winter has led researchers to suggest that a tipping point has already been reached: many now believe the summer Arctic Ocean could be ice-free by 2030, decades earlier than previously thought possible. Arctic sea ice both reflects sunlight and acts as an insulating layer between the relatively warm ocean and the colder atmosphere. As it melts away, these cooling effects disappear, warming the region still further. Sea-ice decline may therefore be part of the reason why average Arctic temperatures have risen at almost twice the global rate in the last 100 years.