Why 2m not 1m of sea-level rise must be new benchmark for major coastal development

Rapid collapse of Antarctic glaciers causing up to 3.3m of sea level rise is plausible

In previous posts, I have been critical of the Thames-Coromandel District Council for its failure to take account of the latest projections of sea-level rise when considering major coastal development. Recent US reports and the latest draft Guidelines from the Ministry for the Environment suggest a “stress test” of around 2 m of sea-level rise should be applied to greenfield coastal development.  The Council has willfully ignored these projections. For the Whitianga town upgrade project the Council considered just 0.5 m, for the Whitianga Waterways coastal subdivision they accepted consultant’s recommendations to consider 1 m, and for the proposed apartments on the Thames foreshore the Council didn’t even bother to require an update of projections made 15 years earlier of half a metre of sea-level rise!

Why should up to 2 m now be considered? The answer lies in recent research on the Antarctic ice sheets, and a potentially catastrophic process called marine ice cliff instability. A recent article by Eric Holthaus in Grist Magazine is the best summary I have read. Please take the time to read the full article or the extracts which I have quoted below and/or watch this excellent video clip.

“There’s no doubt this ice will melt as the world warms. The vital question is when.

In the past few years, scientists have identified marine ice-cliff instability as a feedback loop that could kickstart the disintegration of the entire West Antarctic ice sheet this century — much more quickly than previously thought.  Instead of a 1m increase in ocean levels by the end of the century, 1.8m was more likely, according to DeConto and Pollard’s findings.

But if carbon emissions continue to track on something resembling a worst-case scenario, the full 3.35m of ice locked in West Antarctica might be freed up, their study showed. The glaciers of Pine Island Bay are two of the largest and fastest-melting in Antarctica. Together, they act as a plug holding back enough ice to pour 3.35m of sea-level rise into the world’s oceans

The ocean floor gets deeper toward the centre of this part of Antarctica, so each new iceberg that breaks away exposes taller and taller cliffs. Ice gets so heavy that these taller cliffs can’t support their own weight. Once they start to crumble, the destruction would be an unstoppable amount that would submerge every coastal city on the planet. A wholesale collapse of Pine Island and Thwaites would set off a catastrophe. 

Previous models suggested that it would take hundreds or thousands of years for sea-level rise of that magnitude to occur. But once they accounted for marine ice-cliff instability, DeConto and Pollard’s model pointed toward a catastrophe if the world maintains a “business as usual” path — meaning we don’t dramatically reduce carbon emissions.

In West Antarctica, scientists have discovered the engine of catastrophe.   “It could happen faster or slower, I don’t think we really know yet,” says Jeremy Bassis, a leading ice sheet scientist at the University of Michigan. “But it’s within the realm of possibility, and that’s kind of a scary thing.”

There’s a recurring theme throughout these scientists’ findings in Antarctica: What we do now will determine how quickly Pine Island and Thwaites collapse. A fast transition away from fossil fuels in the next few decades could be enough to put off rapid sea-level rise for centuries. That’s a decision worth countless trillions of dollars and millions of lives.”