To date, in modern human history (and since 11,000 years ago), the annual snow engine has been idle enough to AVOID glacial expansion under the moribund equilibrium. Turning the Arctic Ocean ice-free will change that. When the land becomes the primary area of "cryospheric battery" for which the atmosphere gets more bang for its buck, I think it is possible we see primary annual ice-mass gain transfer from the ocean to the land, a process that is already underway. This eliminates the impact of warm Arctic waters on albedo, as well (from a net perspective, a la Daisyworld, and the system will indeed optimize for efficiency in this case as well)
I don't disagree with the overall picture expressed in this post, but I'm not sure there's enough time for a meaningful glacial expansion. The Younger Dryas example is very interesting, but crucially, this occurred at a time when global temps were lower. Now we are on this trajectory headed higher than even the conditions of the Eemian.
There will certainly be extremes of snow extending further out of the NHEM winter season. I tend to think of it as the system fighting back, a negative feedback to global warming. This is a system at the breaking point. The incredible stability of the past 10,000 years of weather gives some indication that it is hard to break. This also suggests that once broken, it will be very hard to get back.
I think the problem is that as the state-shift occurs the dual vortices are going to get much stronger. Winter is going to start earlier and last later for certain regions.
But what happens when we hit BOE and the re-icing is minimal? Like, 1M KM^2 minimum, on October 1st, with only 3-4M KM^2 in extent by New Years? At that point volume is going to barely recover.
But you know what will be taking up the slack? The snowfall on the continents. In fact the warmer the Arctic gets while Greenland is extant, the more snow will fall. We have melted .1% of Greenland since 2000. .1%!!!! In 20 years!!!! We are not getting to 10% let alone 5%, IMO.
The yearly anomalies for 2019 are going to be the most extreme since the 1970s or earlier across the United States. Parts of the Dakotas and Montana are going to finish -3/-4C for the YEAR. ! The highest maximums on the positive side are now substantially less relatively impressive than the colder minimums on the negative side. And that is with only .1% of Greenland gone!
What is going to happen next? The continental snowfall increase is going to start worsening exponentially as more and more open water persists each year. We are going to hit an annual max of 5,000 KM^3, then 6,000, then 7,000, then 10,000KM^3.
Around that point the annual cryospheric mass balance will probably shift to snow versus sea ice and we will see the first year with snow persisting in the higher elevations of North America through summer. That same summer could very well be the BOE up north. From that point the residual snowpack across the continents has an expanded baseline to grow on during summertime, through solstice, and it begins increasing exponentially in depth and water content. By the third or fourth year as the snows have spread, May, June, July, and August become the prime time for snowfall accumulation in the glacial zone, with the contrast between the GHG-enhanced oceanic warming and the albedo-cooled continental interior sufficient to result in quasi-permanent mega-storms in the flux regions of the -500MB vortices over Hudson Bay and the Kara (this is how Hansen's mega-storms occurred).
I think it is important to note that while each autumn will revert to the dual-vortex state mentioned by sark, without the sea ice, momentum is (IMO) on North America's side by springtime due to its positioning near Greenland, especially as sea ice dwindles further near Eurasia. If Hudson Bay becomes a bastion of MYI, which it will if snow begins building across North America's higher elevations, the Kara vortex will collapse by April or May as Eurasia is overwhelmed by the raw impact of continental heatwaves (since CO2 is still 420ppm or at that point, 435ppm or whatever).
The North American vortex will persist through the summer until a new Eurasian vortex again appears in the fall. So Eurasia becomes the focus of massive summertime heatwaves and an extension of major positive height anomalies while the opposite occurs in North America (much of Eurasia will eventually follow into perpetual winter as the NAmerican pack expands dramatically each year but it will take some time since concurrent with North America's cooling, there is a decent chance that through all of this the Arctic Ocean will STILL BE WARMING).
The coupling of the vortex, snowfall, sea ice, and residual ice sheet (Greenland) is likely to result in a much earlier "winter" for North America than Eurasia, and this event sequence is also confirmed by the staggering of the arrival of previous cold periods per geological records (it generally goes North America -> NW Europe -> Eurasia -> East Asia). So while the two vortices we are seeing form are quite interesting, I think the North American vortex is the more anomalous, and will eventually become more dominant on an inter-annual basis, at least for a few decades.