As medium-term global average atmospheric temperature trends continue to diverge sharply from predictions based on global warming alarmists’ hypotheses about CO2’s warming effect, climate feedbacks, and computer models expressing those hypotheses, the alarmists have increasingly turned to other reasons for pursuing the economic (especially energy) policies they prefer: “weather weirding,” “extreme weather,” ocean “acidification,” “coral bleaching,” species extinction, and particularly accelerating sea level rise.

The latest such is a study recently published “in Nature newly comports to confirm 2015 fears about instability of the Totten Glacier in Eastern Antarctica. This could ‘suddenly’ raise sea level as much as 4 meters!” as Rud Istvan summarizes at Judith Curry’s blog “Climate Etc.”

Major media around the world latched onto this with scary titles and stories. But the reality is otherwise. Here’s an excerpt from Istvan, but his whole post is well worth reading:

It is helpful to understand the context for seeking evidence of alarming seal level rise (SLR) (see my previous CE post Sea Level Rise Tipping Points). SLR is not accelerating, so warmunists have searched for future ice sheet ‘tipping points’ that might cause the abrupt SLR supporting urgent CO₂ mitigation. Greenland was the initial focus; it is not cooperating because of its bowl shaped geology. See my previous post for details and references.

The West Antarctic Ice Sheet (WAIS) was the next focal point. The Ronne Ice Shelf proved pinned and stable per the above linked Tipping Points guest post. ANDRILL showed that the Ross Ice Shelf is also stable; its grounding line hasn’t shifted for about 4 millennia, ditto the Tipping Points sites linked to above. Attention then shifted to the Amundsen Embayment, where much was made in 2014 of the flowing Pine Island Glacier (PIG)–until it was pointed out PIG sits on an active volcano that has nothing to do with global warming. (There are volcanic ash layers embedded in PIG.) WAIS is not cooperating, either. So attention has now shifted to the East Antarctic Ice Sheet (EAIS) ….

Where Totten enters the Southern Ocean, it is mostly grounded in shallows <500 meters deep. This does not affect its stability (like the Ross Ice Sheet), since the first ~500 meters of Antarctic coastal seawater is basically at the freezing point. But warmer seawater below about 500 meters is melting Totten’s base at a deeptrough about 5 km wide and about 800 meters deep, discovered in 2015 [link]. This melting causes a slow retreat of the grounding line behind the trough. The annual basal melting/grounding line retreat rate is presently about 100 meters/year, (but as fast as 175 meters per year in some places according to Aitken per WaPo). It is useful to note that Aitken was an author, but not lead author, on the 2015 trough discovery paper.

This deep ocean melting process could move inland for about 150 km through the Sabrina subglacial basin (deep blue in the following figure from the 2015 paper) over about 1500 years before hitting a sub-ice rock ridge perpendicular to the glacier only about 200 meters below sea level, which would stop the melting (since melting water is below ~500 meters). Aitken et. al. 2016 estimate that this would raise sea level about 0.9 meters, or ~6 cm/century. No cause for alarm.

What Aitken et. al. 2016 reports is another fjord like deep ‘fault trench’ through this blocking ridge, which would (if water temperature stratification remained undisturbed) enable basal melting to proceed through the interior Aurora subglacial basin behind the ridge. This process would continue for about another 350 km, or about 40% back into the Totten catchment basin. Aitken et. al. also used ice-penetrating radar to probe both the Sabrina and Aurora basin floors to confirm that Totten did in fact melt back through both basins about 3 million years ago in the Pliocene (before the onset of the current ice ages), with CO2 at about 400 ppm. That was spun into the PR alarm—it happened before at 400 ppm!!! At the current melting rates this would take about 3 millennia and could raise sea level about 2.9 meters, an unalarming 10cm/century. This is probably still far too fast, since all the Aurora warming water would have to enter undisturbed through the newly reported narrow trench through the ridge.

Istvan’s analysis continues, progressively undermining cause for alarm.