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Marine heatwave is looking likely

Popular holiday spot Castlepoint, on the Wairarapa east coast. PHOTO/FILE

Coastal sea temperatures have already risen far above average, signalling another year with a marine heatwave.

National Institute for Water and Atmospheric Research [Niwa] meteorologist Ben Noll said that water temperatures had ranged from 1.1 degrees Celsius to 1.4 degrees Celsius above average for November.

Noll said daily sea surface temperatures were more than 3C above average around the western and northern North Island and eastern South Island over the last week.

This comes as Wairarapa became one of the driest places in New Zealand last week.

Noll said marine heatwave conditions, classified when the sea temperature is above the 90th percentile for at least five days, had been observed in waters offshore of all regions of New Zealand – including Wairarapa.

“This is comparable to the conditions observed in November 2017, which marked the beginning of an unprecedented marine heatwave around the country and in the Tasman Sea.”

He said frequent patterns of high pressure near and south of New Zealand during November had caused more frequent sub-tropical, northeasterly winds than normal.

“Reduced wind speeds through the month have prevented colder, subsurface ocean waters from getting mixed up to the surface.

In addition, sunshine has generally been above normal, which has helped to heat the ocean surface.”

Noll said marine heatwaves were becoming increasingly frequent in a warmer climate with 963 marine heatwave days experienced in New Zealand region from 2010 to 2019 compared with 366 from 2000 to 2009.

Niwa research has found that our oceans have been getting warmer and more acidic. Scientists have been focusing on how these changes threaten life under the sea.

Research made public in 2019 by Niwa oceanographer Phil Sutton showed the surface waters of New Zealand were significantly warmer than they were 30 years ago.

Sutton said species that usually lived in tropical waters were widening their ranges and displacing other species

“Mobile marine life can escape the warmer temperatures, but sedentary plants and animals will be hardest hit.

“The impacts are there for aquaculture as well, with warmer waters making it more difficult to grow some finfish or shellfish.”

He said increasing frequency of marine heatwaves were another indication that the earth’s climate system was starting to change.

“Individual warm seasons have always occurred, but in future there will be more of them, and they will keep getting warmer,” Sutton said.

“A sobering thought is that even if we somehow managed to turn global warming off right now, the atmosphere would keep warming for some years to come because of the heat that’s stored in the ocean.”

Niwa said more than 90 per cent of the excess heat generated because of global warming had been absorbed by the oceans, and about 40 per cent of the carbon dioxide produced by humans in the past 50 years had ended up in our seas.

On a shorter outlook, Metservice predicted seas to become increasingly rough on Wairarapa’s east coast this week.

By Friday, northeast winds would reach 25 knots with seas becoming rough.

Niwa’s seasonal climate outlook has explained the likelihood of warm seas continuing through the season and their impact on the summer ahead.

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