Rate of sea-level rise around New Zealand doubles in 60 years - Stats NZ

Lyttleton Harbour, Banks Peninsula. Photo / Banks Peninsula District Council

By RNZ

The rate of sea-level rise around Aotearoa New Zealand has doubled in recent decades compared with the first half of the last century, Stats NZ says.

Stats New Zealand recently updated its coastal sea-level rise environmental indicator and found that relative annual sea levels had risen faster over the last 60 years at four coastal monitoring sites.

Stats NZ environmental and agricultural statistics senior manager Michele Lloyd said the rate had nearly doubled in the last 60 years.

"Sea levels rose faster over the last 60 years, 1961 to 2020, compared with the previous 60 years, 1901 to 1960, at four main sites with records dating back to the 1890s and 1900s: Auckland, Wellington, Lyttelton and Dunedin.

The rate of sea level rise has doubled in the 60 years to 2020 at three out of the four sites, Wellington, Lyttelton and Dunedin, compared with the mean rate from 1901 through to 1960.

Out of the locations monitored for the last 120 years, Lyttelton had seen the highest long-term trend in relative sea-level rise, at 2.24mm/year.

And between 1961 and 2020, the largest increase in the rate of mean sea-level rise was observed in Wellington.

Stats NZ said the relative sea-level rise included any local or regional changes in vertical land movement up or down. This could be caused by land sinking or rising due to geological causes, as well as human activity.

However, climate change was one of the main causes of sea-level rise - and it was likely to continue to contribute to the rise.

"Future climate change projections indicate that sea levels will continue to rise. Rising sea levels affect coastal communities, infrastructure, coastal habitats, and biodiversity," Lloyd said.

What causes sea-level rise?

Climate change was one of the main causes of sea-level rise, Stats NZ said.

"As greenhouse gas emissions warm the Earth's atmosphere, heat is absorbed by the ocean.

"The expansion of seawater as it warms, combined with increased sea volume caused by the melting of glaciers and ice sheets, contribute to sea-level rise."

- RNZ