Just a quick first review of PIOMAS data from 1978 to 2021. The results of this preliminary data-dive are what I had expected, which is not good.
The PIOMAS gridded data allows calculation of metrics such as regional volume, thickness, amongst a whole load more. So here's a quick perusal of what the PIOMAS shows, and in a nutshell, my prior expectations are correct, the sea ice pack in the Arctic Ocean is radically different from the past, there has been no recovery from either the 2007 or 2010 volume loss events. Were they tipping points? Not sure on that, I am pondering Critical Slowing and will have more to say on that.
Firstly, the Arctic Ocean is Beaufort, Chukchi, East Siberian Sea, Kara, Laptev and Central regions of the Arctic Ocean. The graph below is average thickness for that region.
"Given the strong thickness–growth feedback of sea ice (Bitz and Roe 2004), where in a warming climate we can expect the thicker MY ice to thin at a greater rate than the thinner FY ice, and the fact that the ratio of MY to FY ice entering into the MY ice category each year is decreasing, it is likely that the difference between FY and MY ice survival ratios will decrease in a warming climate. If this occurs, the Arctic sea ice system would move toward a regime of decreased memory and decreased sensitivity to climate forcing..."
Here the darker the line is the older, and we can see the old ice-pack in dark blue, with the more recent ice pack thickness distribution shown is whiter, lighter blue.
These are two highly distinct systems within the Arctic Ocean's ice pack, the older having more thick mechanically deformed ice, while now the ice confirms to a sharp peak of thickness around 2m thick. And what governs the growth of that ice is winter cold.
I'm not going looking, but I'm fairly sure what is left of the denialists will be claiming that the sea ice doomers were wrong. Well the doomers were, there was no rapid crash, the extrapolation of curves turned out to lack detail, detail that was apparent from as early as 2004 when Bitz and Roe published "A Mechanism for the High Rate of Sea Ice Thinning in the Arctic Ocean." But anyone viewing this as meaning there is no cause for concern is an idiot.
The Arctic has transitioned with the ocean covered by a new type of ice pack, open water formation is worryingly high, especially as the open water will be warming seas right over the East Siberian Shelf with its seabed store of methane. The massive open water formation efficiency now produces a situation where massive energy is stored in the ice/ocean reservoir only to be released into the autumn (I've not checked on that yet but it will be).
In essence, the volume loss from the thicker older ice has dropped the Arctic sea ice into a new stable 'potential well' and to get back where it was is a steeper climb of action and effort than it took to get here.