The US National Snow and Ice Data Center has reported on 27th September that Arctic sea ice appears to have reached its annual minimum extent on 19th September. On that day it covered an area of 4.60 million square kilometers (1.78 million square miles). This year’s minimum was the third-lowest in the satellite record, after 2007 and 2008. In fact, this is only the third time in the satellite record that ice extent has fallen below 5 million square kilometers (1.93 million square miles), and all those occurrences have been within the past four years.
Despite a late start to the melt season, the ice extent declined rapidly thereafter, with record daily average ice loss rates for the Arctic as a whole for May and June. During these months high pressure dominated the Beaufort Sea with low pressure over Siberia, a pattern known as dipole anomaly. Winds associated with this pattern helped speed up ice loss by pushing ice away from the coast and promoting melt. The pattern broke down in July with low-pressure cells bringing cooler and cloudier conditions over the Arctic Ocean, but returned in August when air temperatures were 1 to 3 degrees Celsius (1.8 to 5.4 degrees Fahrenheit) above normal in the Beaufort and Chukchi seas and below normal over the Barents and Kara Seas.
While the sea ice extent in the Arctic has been below average in the Antarctic it has been above average. Sea ice extent in the Antarctic has been unusually high in recent years, both in summer and winter. Overall, the Antarctic is showing small positive trends in total extent.