Arctic Sea Ice Decline in 2015

The surface ice in the Arctic has been melting to historic low levels every year for the last several years. The graph above shows the first ten years in the National Snow & Ice Data Center records, meant to indicate what Arctic Sea Ice "normally" does as it melts off during the northern warm months. The thick black line is the average over 1981-2010, and grey shaded area shows two standard deviations above and below that line. The blue line tracking along the lower end of the 2SD shaded area is the ice extent this year. During the period when sea ice is at its maximum, this year's ice was low. This does not reliably predict the ultimate September minimum, but it is interesting that the sea ice extent is following an extreme course.

I'm reluctant to say anything about what will happen this year. The melting rate could slow, storms that may play a role in diminishing sea surface ice in the Arctic may not play a big role. Or, the rate of melt could increase and all the various factors that determine a year's minimum could drive the ice off the sea to the extent that we have a record low. It would be very hard to beat the 2012 minimum extent, as that was an extreme year. But, that extreme year, show on the figure below, was not as low at the present time as the current extent.

The volume of sea ice is in some ways more important than the area it covers, because this reflects the overall Earth's surface heat imbalance resulting from the human-induced greenhouse effect. Volume includes both new ice (formed over the previous winter) and old ice that does not melt at all in a given year. This old ice probably serves the role of keeping some of the new ice stable so it melts less, so there is a feedback. The more the volume reduces, the more the surface area may reduce, depending on various conditions.

Andy Lee Robinson has created, and regularly updated, an amazing graphic showing the change over time in Arctic sea ice volume.