National guidance published by the Ministry for the Environment projected 0.46–1.05m of sea-level rise by 2100, depending on how quickly people and governments cut carbon emissions. You might expect the oceans around Aotearoa would rise evenly, like a filling bath - and indeed, that’s what most of our coastal planning assumes will happen. That’s the kind of extreme flooding that, today, is considered rare - and it’s big enough to gouge the city’s seawalls. Surprisingly, small amounts of sea level rise can have devastating impacts: research for former Parliamentary Commissioner for the Environment Jan Wright found just 30 centimetres higher seas would turn a one-in-100 year flood event in Wellington into an annual event for the capital.

Add the two together and you get double the global average rate of sea level rise. This gravelly piece of seaside is sinking up to 3.8mm a year, coincidentally about the same amount (3.5mm) that the sea around New Zealand is rising. Take Lowry Bay, a narrow, rocky swimming beach in Wellington’s Lower Hutt, around the coast from Petone. However, new measurements of these movements - released publicly today, for every 2km of New Zealand’s coastline - drastically change how long many communities have to prepare for coastal floods. None of these movements is big enough to bother the average resident as they go about their daily lives - they amount to just 0-4mm of movement a year. In the space of just 2km of shoreline, Thames goes from rising, to sinking, to rising again. The tiny settlement of Pīkowai (between Te Puke and Matatā in the Bay of Plenty) is rising fast, in geological terms, while Thames is on a veritable roller-coaster ride. In contrast, much of Tauranga is standing still or even rising gradually out of the ocean.

So is much of Wellington, bits of Christchurch, most of the Wairarapa coast and land around Napier airport. You might not notice if you’re strolling along the harbour, but much of Auckland is sinking.

The sinking city map