How much has the sea risen so far?

Your grandparents might not have noticed the sea level rising but your grandchildren will. Photo/Warren Buckland

KIA RITE — TIME TO ACT

By Guest contributor: Dr Edgar Burns, Chair of Integrated Catchment Management Hawke's Bay.

People 'get' sea-level rise (SLR) much easier than climate change.

Water and the coast are real. You see the ocean, smell the salt, skip the stones, catch kahawai. As kids, Mum and Dad used to pick up a big packet of fish and chips. We'd all perch on driftwood on the shingly beach, hands all-in to the newspaper and tomato sauce.

Today, 50 years later, you wouldn't eat in the same spot we used to. Ask a property owner at Haumoana or Te Awanga, their house easing into the surf.

You'll soon learn SLR isn't a theory - no insurance isn't funny. Ditto storm surges. Why are we still building houses out that way?

We actually have a pretty good idea where sea-level is going. Lots of information helps forecast SLR. You might be surprised how fast it is happening right now in 2022. Projections are based on accurate year-by-year measurements since pre-1900.

I could give you the numbers, but let me give you a picture. The palm of my left hand is less than 10 centimetres(4 inches) across. Since your grandparents and parents' lifetimes, that's how much the sea has risen in the 20th century, all around the world, not just New Zealand. Not so much, eh? Feet still get wet? Sure. Still catch fish? Sure.

Now take my other hand; the width of my right palm is obviously the same as my left. Well, that's how much the sea has risen in our lifetime - in the quarter-century since the 1990s. What were you doing on the coast in 2000? Seeing in the new millennium?

In these diagrams, each hand summarises NASA's historical SLR records. You can find copies of these graphs on NASA's website. It is the upward trend that is very telling.

The 3.4 millimetres per year does not seem much. But it is increasing year-on-year as the climate heats up. Try doing some simple multiplication. Remember, the trend is upward, and in parts of our coastline land is subsiding, so any figure you come up with is under-reporting the situation.

It's no secret in these graphs that SLR in the latest quarter-century is four times the rate compared to the whole twentieth century. That is, SLR is not just happening - it is speeding up.

Dr Edgar Burns is Chair of Integrated Catchment Management Hawke's Bay.

How far will SLR go? We don't know, but a lot further than most people realise. In the end, seawalls won't be enough. Talk to the Te Awanga folk about that.

SLR is fueled by the heat-trapping greenhouse gases we keep putting into the atmosphere. These gases, like carbon dioxide and methane, cause heating. Heating causes SLR (and other things). We must add to this future, sudden not just gradual SLR from melting polar ice sheets. The social impacts will be huge.

Your grandparents didn't notice, but your grandchildren will.

In Hawke's Bay, with over 350 kilometres of coastline, we are going to need to make complex decisions about what should happen; what we should protect, if and when we should retreat from the coastline and how we will fund those initiatives.

The Clifton to Tangoio Coastal Hazards Strategy 2120 outlines this work. Find out more at hbcoast.co.nz