I voted for 2030-2040 based on some simplified calculations, but I think they are accurate enough to make a reasonable guess. Global average surface temperature anomaly as of 2022 is at +1.3C over the preindustrial proxy (1850-1900). The decadal rate of increase starting around 1970 was about 0.18C -- until recently. James Hansen says we should expect the next couple of decades to increase that rate to 0.27 to 0.36C per decade. (2023 is already way above that trend, but it is just one year).
Notz and Stroeve 2018 calculated that at a temperature anomaly of +1.68 C, the ASI will be in equilibrium with <1M km2 Extent in Septembers.
So with 0.38 C more warming the planet will be at the temperature where (long term) we would expect ~1M km2 September ASI Extent in most years. At the decadal rate proposed by Hansen that will only take about 11-14 years starting from 2022, thus the 1.68C anomaly would be reached by 2033 - 2036.
It does not seem likely that the 1M km2 equilibrium response would occur the first year that the anomaly reaches +1.68 C. And research indicates that the "Slow Transition" negative feedback probably still has a few years left before winter warming overwhelms increased heat loss from increased open water heading into winter, but it could start to gradually weaken by 2030.
And positive feedbacks are on the increase -- including more rain, storm activity, wave activity to break up pack ice and bring up subsurface heat, ice fracturing for more mobility and export, and thinner ice that melts faster. Those positive feedback influences are still small relative to the melt resistance of the current ASI Volume, Area, Extent, and Thickness. But as they increase they will become increasingly synergistic. For example, thinning of the average ice thickness from 1.8 to 1.7M does not change the melt rate nearly as much as thinning from 0.8 to 0.7M. Thinner ice breaks into smaller pieces with more surface area exposed to >0C seawater and air, and are more vulnerable to export.
Even if the endpoint estimate is for BOE to become possible/increasingly likely starting around 2035, the stall in the long-term downward trends that we have seen since 2012 may continue for a few more years. We all remember when the climate change deniers made a big fuss about the 15-year-long global warming "hiatus" between 1998 to 2013. Watch for increasing references to the "unchanging Arctic".
(Of course, as Carl Mears who manages the RSS satellite data said,
"If you start riding a bike on the top of a hill you are guaranteed to go downhill for a while", which is why the deniers chose to start their interest in global temperature trend at 1998, the year of a very strong El Nino temperature bump.)
It would not be surprising for the current ASI decline "hiatus" to last another 4 years to also reach 15+ years in 2027-2030. But eventually, the increasingly warm winters preceding/following increasingly warm, rainy, wavy, stormy summers working against progressively thinner, more fractured, more mobile ice will kick into high gear. Then we will all be surprised at how fast the previously slow pace of ASI evolution kicks into a high-speed transition that delivers the first BOE before 2040.
While we like to discuss when the "big change" will come, it is important to realize that a BIG change has already happened. Look at the September ASI thickness map for 1985 vs. 2023. There are many ecological and other ramifications of 4+ year old thicker vs. <1 year old thinner ice. The old Arctic that Inuit elders and folks like Peter Wadhams banged around in during their younger days already only exists in memory, and for the rest of us in data. It's hard enough to fathom such a fundamental change in data, but it must be heartbreaking for those with a more intimate physical experience of the now-deceased "old" Arctic.
Image from
https://forum.arctic-sea-ice.net/index.php/topic,2348.msg384557.html#msg384557
It is happening so fast that one does not have to be an elder to see the Arctic world shifting. The late David Barber (1960-2022) noted that the Arctic he studied in grad school (late 1980s-early 90s) was no longer there. My son worked in interior Alaska a few years ago. Young Yupik villagers could point out changes in vegetation, wildlife, and in the reliability of the frozen Yukon River as the road to the coast, that had evolved in just the previous 10 years. When the river begins to thaw that ice road becomes hazardous, which had already cost some village inhabitants their lives.
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