Comment permalink

Change is all around us these days. There is no escape from it, and that applies to changes to the shimmering blue briny that is also all round us.

Think of change and it is mostly in relation to those things close by us, which can affect our communities, our lives and jobs, and our environment. It is also generally about transformations on land, which of course is where most of us live.

When we look out to sea, it just looks so vast, so constant and unchanging a force and feature of our world, that it is difficult to imagine it too could be changing significantly in ways that, until relatively recently, were either poorly understood or unknown.

If you zoom in closer, you can see the oceans are always in a state of flux, relentlessly swirling, pushed this way and that by weather and the shape of the land. But those changes are largely predictable and cyclic.

One day the sea appears grey and stormy, its angry waves flecked with white caps; the next it is a gently rippling aquamarine pool; the following, a mirror-like azure millpond. But the rhythms are always there — the waves keep rolling in and crashing on the shore, and the tides keep endlessly lifting and dropping the sea.

It’s the predictability of those patterns, the fact they happen no matter what else is going on, that makes the sea seem somehow inviolable and above it all. So it comes as an especially hard blow to find out mankind’s actions are now having significant effects on the salty marine engine that drives life on our planet.

This week, for a change, the news columns have been full of something different from Covid-19, the war in Ukraine, and moronic crime and violence. Instead, we have had the frightening prospects brought home to us about climate change-induced sea-level rise around New Zealand in the decades ahead.

In a massive and critical piece of work, scientists from the NZ SeaRise programme have projected likely sea-level rise up to the year 2300 for every 2km of the coast.

Led by Prof Tim Naish of Te Herenga Waka — Victoria University of Wellington and Associate Prof Richard Levy of GNS Science, the analysis takes into account land movement through subsidence and uplift, and the contribution of climate-driven sea-level change, to calculate probable local sea-level rises.

The new figures confirm previous guidance that for the highly vulnerable South Dunedin, sea-level rise of up to 35cm is likely by 2050-60, and possibly as much as 1.12m by 2100, but dependent on global greenhouse gas emissions.

The story is considerably worse for other parts of the New Zealand coast, particularly around Wellington and Wairarapa, where land subsidence due to tectonic action means sea level could rise by more than 1.5m by 2100.

The authors say global sea-level rise is accelerating, due to the expansion of warmer oceans and ice melt. On average the increase was 1.7mm per year from 1901 to 2010, but from 1993 to 2016 the seas rose at an average rate of 3.4mm a year.

Marine heatwaves, such as the one currently being experienced, are also changing what is in the seas around New Zealand. This week, the Moana Project warned that all coastal waters, except around Otago Peninsula, are in a state of heatwave and expected to stay that way for at least another week, with sea-surface temperatures at least 1degC above average.

No wonder then that the distribution of fish species in our waters is changing and unusual visitors are washing up on our shores. Warmer seas also mean it will become easier for tropical algae to invade and disrupt endemic ecosystems.

It may look the same out there as it always has. But a sea change is literally taking place — just another reminder of how humanity is wrecking the world.