Sea levels around New Zealand rose twice as fast in the past 60 years as they did in the first half of last century, with climate change flagged as the primary culprit.
Stats NZ’s recently updated coastal sea level rise indicator shows the rate doubled between 1961 and 2020, compared with the mean rate from 1901-1960, at three of the four sites monitored – Wellington, Lyttelton and Dunedin.
The capital city, Wellington, experienced the largest increase over the past 60 years, of 2.84mm a year, while Lyttelton, near Christchurch, had the highest overall trend over the past 120 years, at 2.24mm a year.
The measure took into account any local changes in vertical land movement, which can be caused by geological processes or human activity that causes subsidence.
Climate change was cited as one of the main causes of the sea level rise. As greenhouse gas emissions warm the Earth’s atmosphere, heat is absorbed by the ocean, Stats NZ said, adding that the expansion of sea water as it warms, combined with increased sea volume caused by the melting of glaciers and ice sheets, all contribute to sea level rise.
“Future climate change projections indicate that sea levels will continue to rise,” said Michele Lloyd, Stats NZ’s environmental and agricultural spokesperson. “Rising sea levels affect coastal communities, infrastructure, coastal habitats, and biodiversity.”
New Zealand’s coastline is vast and many houses are built near the shore – one in seven residents, or 675,000 people, live in areas prone to flooding, while another 72,065 live in areas projected to be subject to extreme sea level rise.
A 2020 government-funded report by Deep South Challenge – a national science collaboration – found at least 10,000 homes in New Zealand’s biggest cities would be in effect uninsurable by 2050, while Local Government New Zealand estimates the amount of local infrastructure exposed to sea level rise to be about $14bn.
The question of “managed retreat” – who foots the bill when sea level rise or flooding renders a community unsafe or uninsurable – has become increasingly pressing in New Zealand. The government has committed to legislation on managed retreat by the end of 2023. Meanwhile, last month, it released the country’s first national plan to prepare for climate driven disasters, including rising seas.
