‘Runaway ice loss causing rapid and catastrophic sea level rise is possible within our lifetime,’ according to a joint emergency statement released by more than 300 scientists at the inaugural Australian Antarctic Research Conference in Hobart last month.
‘The East Antarctic ice sheet alone,’ the scientists stated, ‘holds enough water to raise global sea levels by approximately 50 metres.’
This prospect of near-term runaway sea level rise is considerably more serious than sea level projections issued by the Intergovernmental Panel on Climate Change (IPCC), which forecast an average 40 centimetre rise under the best-case emissions scenario by the end of the century and 70 centimetres under the worst-case scenario—the trajectory on which we are currently tracking.
The explanation for this discrepancy is acknowledged, though often overlooked, within the depths of IPCC reports: positive feedback loops. These processes are too complex to be fully integrated into current global climate models, which means they aren’t accounted for in sea level rise projections.
The resulting blind spots could be pivotal.
As such, the need for climate experts to advise the government on strategic planning and risk management is becoming urgent. This is especially true for our intelligence and national security communities. We cannot make and follow plans that rely solely on model projections. Rather, models must be contextualised by climate experts to ensure that critical feedback loops such as marine ice sheet and ice cliff instability are properly accounted for—and hence that resulting threats are managed.
Given that about half of all Australians live within seven kilometres of the coast, the impacts of runaway ice loss on Australia’s domestic security would be immense. For context, greater Sydney’s average elevation is 53 metres above sea level; Melbourne’s is 49 metres; Brisbane’s is 45 metres; and Perth’s is 26 metres.
These cities would become uninhabitable, mostly because of direct inundation, but also due to coastline retreat from storm surges and erosion. The latter cannot be overstated. As one centimetre of sea level rise results in an average coastline retreat of one metre, a 50 metre sea level rise would cause coastlines to retreat by several kilometres. Hence, even the areas of higher elevation within Australia’s most populous cities would be in a serious predicament.
Without planning and preparation, the security and strategic ramifications of this would be catastrophic. This is even before we account for regional implications, considering that Asia has the largest near-coastal population in the world.
As the IPCC has stated, rapid and irreversible ice loss due to marine ice sheet instability and marine ice cliff instability could ‘lead to a collapse of … Antarctic Ice Sheet[s]’.
Note: figures show the two phenomena of ice sheet instability (a) and ice cliff instability (b), not a progression over time.
Marine ice sheet instability results mostly from the retreat of grounding lines—the points where the ice sheet meets the ocean floor. Over thousands of years, the weight of the Antarctic ice sheet has pressed down on the land beneath it, effectively deforming the earth’s crust and creating a deep basin that slopes into the continent’s interior—a process known as isostatic adjustment.
Many of the ice sheet’s grounding lines are poised on high points behind which the land drops away in downhill—or ‘retrograde’—slopes. As the ice at these grounding lines is exposed to warmer ocean waters and melts, two crucial things happen. As grounding lines retreat further down these retrograde slopes, the ice sheet’s ocean-exposed surface area becomes larger. Second, because the ice that sits above the newly retreated grounding line is thicker and heavier, more pressure is exerted – accelerating melting as higher pressure lowers the melting point of ice.
Together, these phenomena can create a positive feedback loop as the volume of ice melting continuously accelerates.
The second process, marine ice cliff instability, is driven by the disintegration of ice shelves—the floating extensions of the ice sheet that form when land ice flows into the ocean, creating large ice ‘tongues’ that float on the water’s surface. These ice shelves act as a buttress, slowing the flow of the ice sheet into the ocean. When this buttressing mechanism is weakened or removed due to ocean and atmospheric warming, the flow of the ice sheet into the ocean accelerates.
Furthermore, the retreat of ice shelves continues to expose taller and taller ice cliffs, which are prone to a self-reinforcing cycle of instability. Ice cliffs are vulnerable to structural failure when stress exceeds the strength of the ice. That is, taller cliffs are more likely to collapse under their own weight. And without the protective effect of the ice shelf, the ice sheet also becomes subjected to greater wave energy, accelerating ice loss through increased calving events.
Because of the complexity of these ice sheet dynamics, these processes are currently unable to be incorporated into global climate models, resulting in projection blind spots and, hence, the above discrepancy between IPCC sea level rise model projections and the dire warnings of climate experts.
Last month’s warning is consistent with the unexpected collapse of parts of the Antarctic ice sheet, and the accelerated loss of their mass, observed over the last couple of decades—from the sudden collapse of the Larson B ice shelf earlier this century, to the New York City-sized ice shelf that collapsed in 2022.
This is not to say climate models are not useful. They perform well at projecting average changes in relation to past climate. However, they function poorly at anticipating events that wouldn’t have been possible in a world without climate change.
The temptation to leave decisions regarding climate preparedness to the ‘impartial’ realm of statistical evidence is flawed and, in fact, dangerous.
It also demonstrates the propensity to disregard one of strategy’s oldest axioms—the crucial nature of interaction. That is, strategy is not merely the execution of a plan.
If we want effective strategic planning, we cannot rely on model projections alone. To ensure we are adaptable and flexible in the event of runaway sea level rise, projections need to be continually put into context by climate experts. Otherwise, even our best plans won’t survive contact with reality.
An overreliance on statistical evidence at the expense of physical knowledge and expertise risks having the world forge ahead none the wiser, while the thresholds of feedback processes such as marine ice sheet and marine ice cliff instability are crossed. The real kicker is that they might have been crossed already.
