Global average temperature and Southern Ocean surface temperature are not the same thing. The latter affects sea ice extent but would have to increase a lot more to have a direct effect on Antarctic Ice Sheets. It's upwelling deep water that does the damage.
That is entirely true. And the deep water temperature will *also* be much higher in 2039 than the erroneous cold models project precisely because they have a very low climate sensitivity that is scientifically proven to be wrong.
Actually no, because heat conduction through the water column is very slow and the upwelling deep water is very old. It has not mixed with other water masses for more than a thousand years, as shown by the apparent radiocarbon ages of organisms living in it. 1/2
The important questions are how global climate change controls the amount of deep water incursion onto parts of the Antarctic continental shelf, and how efficiently it melts continental ice in the places they come into contact.
There is certainly asymmetry of ocean heat uptake in the Southern Ocean as this study shared by @umsonst.bsky.social a few months ago shows. All things being equal the deep ocean is also increasing in heat content alarmingly fast.
Deep water warming is a secondary issue to where the already relatively warm water goes. The main concern regarding changes in the deep part of the Southern Ocean is the decline in bottom water production.
All of that is detail. If the planet was 10 degrees colder or 10 degrees warmer, all of that detail is secondary. Getting the basic level of planetary heat wrong on a global scale will lead to disastrously incorrect melt rate projections.
Any melt rate calculation based on a simple function or parameterisation of climate sensitivity will almost certainly be wrong, because this would ignore the complexity of the Earth system and the physics of the processes involved.
Fully agreed.
Bottom line: anyone relying on projections from erroneous cold models that have a climate sensitivity of only 3.0C per doubling of atmospheric CO2 will be severely underestimating melt rates, regardless of the understanding or misunderstandings of melt processes.