As reported by the US National Snow and Ice Data Center (NSIDC), the minimum extent of Arctic sea ice is decreasing at a rate of 13.1% per decade. This year, the summer minimum ice sheet has been the twelfth lowest in records – last 43 years – and has shrunk to 4.72 million square kilometers (measured on September 16).
Due to a cool and cloudy Arctic summer, this year's annual low was the highest since 2014 – ice covered nearly 1 million square kilometers more than last year's extent. "Even with global warming and the general downward trend in sea ice, there is still natural variability ," explains Walt Meier, principal research scientist at the NSIDC, which is based at the University of Colorado Boulder, in a note that just published the journal Nature.
The summer of 2021 has been colder and cloudy than normal, due in part to low atmospheric pressure patterns in the Northern Hemisphere.
In June and July, weak low pressure in the central Arctic prevented warmer southerly winds from entering the area. This kept the air cool and prevented some of the ice from melting. The low pressure also causes the formation of clouds that block sunlight. This can further slow down the merge.
The researchers recall that, although in certain years there may be more ice than usual in the low season after the summer, the trend is downward. "Including this year, the last 15 years have had the 15 lowest minimum Arctic extensions on record," Meier recalled.
