By way of a change we start this month’s look at all things Arctic with some sea ice statistical analysis. Anthony Watts’ Arctic porky pie production line has been speeding up recently, and I am not the only one who has noticed. As part of his takedown of the latest “skeptical” allegations against the United Kingdom Met Office Tamino has been looking at trends in Arctic sea ice extent over at his “Open Mind” blog:
First and foremost, the yearly minimum is only one day out of the year. We have sea ice extent data throughout the year, and what happens during the rest of the year counts. Instead of using the annual minimum, let’s use the annual average. To avoid losing the most recent data, I’ll compute the yearly average for October through the following September rather than the usual (but arbitrary) January through December. I’ll also omit October 1978 through September 1979 because that year is incomplete. I get this:
The annual averages show much less fluctuation than the annual minima, so we can estimate things like rates of change with greater precision. I find that there is statistical evidence that the rate changed over time. One model of such changes uses three straight-line segments with their changes chosen to best-fit the data, like this:
Much more detail can be found over at Open Mind, but as I pointed out in the comments:
[Edit – October 5th]
There is indeed some research… [into a factor that might have caused the ice to stabilize since 2007]. By way of example, we have been discussing “The Slow Transition” over on the Arctic Sea Ice Forum since 2014. If you want to dig deeper then please see this 2011 paper by Armour et. al.:
“We can expect the thicker MY ice to thin at a greater rate than the thinner FY ice.”
The NSIDC have now published their post minimum episode of Arctic Sea Ice News:
The summer melt season has come to a modest end. The summer of 2021 was relatively cool compared to the most recent years and September extent was the highest since 2014. It was nevertheless an eventful summer, with many twists and turns.
Arctic sea ice extent for September averaged 4.92 million square kilometers (1.90 million square miles), the twelfth lowest in the 43-year satellite record. This is 1.35 million square kilometers (521,000 square miles) above the record low set in September 2012, and 1.49 million square kilometers (575,000 square miles) below the 1981 to 2010 average. The last 15 years (2007 to 2021) have had the 15 lowest September extents in the record.
Amongst numerous other things the NSIDC point out that:
[Edit – October 8th]
Despite September total ice extent being high compared to recent years, the amount of multiyear ice as assessed from ice age reached a near-record low, with an extent of only 1.29 million square kilometers (498,000 square miles), just slightly above the value of 1.27 million square kilometers (490,000 square miles) at the end of the 2012 melt season.
Here are the first results this Autumn from AWI’s flavour of CryoSat-2 Arctic sea ice thickness data. Note that the thickness palette is compressed further than is usual in our winter and spring updates:[Edit – October 11th]
An AMSR2 animation of the sea ice cover along the Northern Sea Route this summer. The “choke point” at the Vilkitsky Strait has “closed” much earlier than last year:
Here’s the current AARI sea ice chart for the area, dated October 8th:
The University of Bremen have restarted SMOS coverage of the Arctic, so here’s their current “thin ice thickness” map for the Vilkitsky Strait and the rest of the Arctic Ocean:[Edit – October 12th]
The Polar Science Center has released the PIOMAS volume data for September:
Average Arctic sea ice volume in September 2021 was 4,760 km3. This value is the 8th lowest on record for September about 1000 km^3 above the record set in 2012. Monthly ice volume was 72% below the maximum in 1979 and 55% below the mean value for 1979-2020. Average September 2021 ice volume was about 0.7 sigma above the 1979-2020 trend line. September ice melt was fairly normal for recent years but the mean ice thickness for September (above 15 cm thickness) was near a record low suggesting that the ice was spread out over a wider area.
Here too are the updated volume trends, now including September 2021:[Edit – October 13th]
Here’s an animation of Arctic sea ice age from the 2015 minimum extent in September until the 2021 minimum:[Edit – October 17th]
Something to watch with much interest over the next few days:[Edit – October 18th]
An analysis of the 2021 Arctic sea ice melting season from Walt Meier of the NSIDC, and a discussion about Bering Sea ice conditions from Rick Thoman of the University of Alaska:
Watch this space!