Marine heatwaves forecast to devastate

Marine heatwaves now (left) and predicted in 2100.
Marine heatwaves now (left) and predicted in 2100.
The southern tip of the South Island is likely to experience severe marine heatwaves lasting more than a year by the end of this century, having disastrous implications for the local marine ecosystems, new Niwa research shows.

Last week, Niwa statistics showed record-breaking sea temperatures during the recent summer of 2021-22.

Off the back of that, the organisation has unveiled new research showing New Zealand could experience very long and very severe marine heatwaves by 2100.

Marine heatwaves occur when water temperatures stay in the warmest 10% of historical observations for at least five days, and they are already becoming a common experience for New Zealanders.

Research from the Deep South Challenge shows New Zealand has about 40 marine heatwave days per year at present, but that will increase to between 80 days (low emissions, best-case scenario) and 170 days (high emissions, worst-case scenario).

Research lead and Niwa ocean modeller Dr Erik Behrens said for some regions, such as the southern tip of the South Island, there was a high chance that marine heatwaves would start to last more than a year.

For coastal waters, average marine heatwave intensities would increase by 20% (best case) to 100% (worst case) by the end of the century.

"For the North Island, this means an average marine heatwave could be between 0.5degC to 2degC more intense than they are today."

Dr Behrens said the chance of marine heatwaves becoming a permanent fixture was worrying.

"We’re just coming off the back of one of our most intense marine heatwaves, like what we experienced in 2017. Our work indicates that this will start to become the norm as time goes on.

"Marine heatwaves can have significant impacts both at sea and on land. They kill off corals, disturb ecosystems, and can also pose a problem for fishing and aquaculture, as well as contributing to land heatwaves and climate extremes across the country."

Terra Moana marine consultancy partner Tony Craig said both industry and recreational fishers were already noticing changes in the kinds of species that were caught and where.

"It’s hard to see current fisheries being resilient enough to withstand increases between 80% and 100% of median marine heatwave intensities by the end of the century," he said.

Deep South Challenge climate change knowledge broker Kate Turner said the projections highlighted the need to start adapting to our changing climate now.

"Organisations, iwi and hapu, councils and communities up and down the country are experiencing these impacts already.

"We need to really focus on how we can support their adaptation planning today," she said.


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