After a period of rapid ice loss through the first half of June, sea ice extent is now slightly below 2010 levels, the previous record low at this time of year. Sea level pressure patterns have been favorable for the retreat of sea ice for much of the past month.
Overview of conditions
On June 18, the five-day average sea ice extent was 10.62 million square kilometers (4.10 million square miles). This was 31,000 square kilometers (12,000 square miles) below the same day in 2010, the record low for the day and 824,000 square kilometers (318,000 square miles) below the same day in 2007, the year of record low September extent.
Conditions in context
The main contributors to the unusually rapid ice loss to this point in June are the disappearance of most of the winter sea ice in the Bering Sea, rapid ice loss in the Barents and Kara Seas, and early development of open water areas in the Beaufort and Laptev Seas north of Alaska and Siberia.
Recent ice loss rates have been 100,000 to 150,000 square kilometers (38,600 to 57,900 square miles) per day, which is more than double the climatological rate.
Sea level pressure favors the advection of ice
A pattern of high pressure over the Beaufort Sea and low pressure over the Laptev Sea has been present for the past few weeks. This pattern is favorable for summer ice loss, by advecting warm winds from the south (in eastern Asia) to melt the ice and transport it away from the coastlines in Siberia and Alaska. The high pressure over the Beaufort leads to generally clear skies, and temperatures are now above freezing over much of the Arctic pack. Snow cover in the far north is nearly gone, earlier than normal, allowing the coastal land to warm faster.
Early melt onset, and clear skies near the solstice are favorable conditions for more rapid melting, and warming of the ocean in open-water areas. The persistence of this type of pressure pattern throughout summer 2007 was a major factor toward causing the record low September extent that year. Conversely, in 2010, the patterns were not as favorable for loss of ice and the seasonal decline slowed later in the summer, and the extent did not approach the record low levels of 2007.
While these patterns and conditions have looked similar to 2007, over the last couple days the high pressure pattern over the Beaufort Sea has broken down. And while the extent is at a record low for the date, it is still early in the melt season. Changing weather patterns throughout the summer will affect the exact trajectory of the sea ice extent through the rest of the melt season.