Citizen Science – sea level change and what it means for New Zealanders

31 January 2014

Welcome to the first of our Citizen Science articles around the King Tides Auckland Initiative.

Climate change is happening and sea levels are on the rise, but what does it all mean?

We chatted to Dr Scott Stephens at NIWA, expert on coastal and estuarine physical processes, about the science behind rising sea levels and what it means for New Zealanders.

How do we know that sea levels are rising?

Analysis of reliable sea-level gauges worldwide has shown that sea-level has been rising at a steady rate of about 17 cm per century over the last 100–150 years. Modern satellite records collected since 1993 also show that sea-level is rising worldwide.

What is causing sea levels to rise?

Scientists have shown that sea-level rise over the last 100–150 years is linked to the release of heat-trapping (green-house) gases into the atmosphere from the burning of fossil fuels (e.g. oil and coal) and other human and natural activities. This has caused the oceans to warm, causing thermal expansion of the water that is raising sea level. The melting of ice in glaciers and from the poles is also causing the sea level to rise as it flows into the oceans.

How much are sea levels expected to rise in New Zealand in the near future?

To help plan for sea-level rise, scientists suggest that sea-level rise of about 0.7 m is plausible by the year 2115 (100-years from now) in New Zealand, but the effects of even higher sea level rise should also be considered.

What can we do about it?

Although we can’t immediately stop sea-level rise, we can make wise decisions to plan for and adapt to the rising sea, to prevent problems such as coastal flooding, both within our lifetimes and for future generations.

To reduce the rate of sea-level rise and eventually stop it will require global cooperation to reduce green-house gas emissions and re-plant forests that absorb atmospheric carbon. We can play our part as individuals through by making lifestyle choices that reduce carbon emissions, such as car-pooling or cycling, or buying local products.

What information do King Tides give us about sea level rise?

King tides are very high tides that occur every 7 months when the gravitational attraction of the sun and moon combine at the same time that the moon is closest to earth in its orbit. During King Tides we can watch the sea reach a considerably higher elevation than usual (about 0.5 m above an average high tide and 0.1–0.2 m above a mean high-water springs). During King Tides we observe flooding of coastal land that does not normally occur, and so helps us imagine the effect that sea-level rise might have. It also teaches us that we are already vulnerable to the sea in many locations.

How high can we expect the King Tides this Sunday to be?

We can expect the King Tides this Sunday to be about 0.5–0.6 m above an average high tide and 0.1– 0.2 m above the mean high-water springs elevation (which is the elevation reached by regular spring tides that peak every fortnight).

Why do you think the King Tides Auckland initiative is important?

The King Tides Auckland initiative is a great way to raise awareness that our coastal lifestyle is already vulnerable to coastal inundation and will become increasingly impacted by future sea-level rise. This raised awareness will hopefully lead to support for wise decision-making for the future.