Drowning dreams: What will happen when the seas rise?

A storm surge is a slow-moving bulge in the sea’s surface, like the massive swelling that sank the Wahine in 1968. Rising sea levels set a higher baseline for storm surges, pushing them further inland.

King tides, storm surges and rogue waves are already reaching deeper into Aotearoa and these coastal floods will get longer, larger and more frequent with climate change, reports on the threat from sea levels say.

Some places will be hit worse than others; it depends on local factors like the contour of the shore, the size of sand dunes and engineered protections, like seawalls.

Scientists can’t tell us where sea levels will end up, because they don’t know how much more greenhouse gas we’ll pump into the atmosphere, or at what point the Antarctic ice sheets could tip into unstoppable decline (although there’s evidence it may be around 2C of warming).

Today’s once-in-a-century high tide is going to be breached every four years in Auckland, and every year in Christchurch and Wellington, after just 30cm of sea level rise.

What they do know is that today’s extreme is going to become normal. Auckland and Wellington recorded their highest-ever sea levels in 2011 and 2013 respectively, based on records going back (respectively) 100 and 50 years. Today’s once-in-a-century high tide is going to be breached every four years in Auckland, and every year in Christchurch and Wellington, after just 30cm of sea level rise, the Parliamentary Commissioner for the Environment noted in her 2015 report.

By the time we have 70cm of added sea level, every high tide at the Port of Wellington will be higher than today’s once-in-a-century tide. That doesn’t include any increased frequency of storm surges caused by warming oceans.

Rising tides will hasten erosion, and first to retreat will be already-disappearing beaches, like Haumoana in the Hawke's Bay. It won’t be easy to save them, because breakwaters built to protect one beach might lead to greater erosion down the coast by disrupting the natural flow of sediment. Piling rocks along our beaches may protect the land behind it, but at the cost of sacrificing the sandy shore that attracted people to build there in the first place.

Planning ahead won’t change the reality of rising sea levels, but it will give people more options for adapting.

Read more: Billions at stake as govt mulls sea level rules

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