Catastrophic Sea Level Rise Possible within Our Lifetime? Yes, Here’s How
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]’.
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.
Isabelle Bond is a climate security analyst with ASPI’s Climate and Security Policy Centre. This article is published courtesy of the Australian Strategic Policy Institute (ASPI).
