First-of-its-kind study: How Antarctica’s melting ice sheet could change NZ’s climate patterns

• A first-of-its-kind study suggests the ongoing melting of Antarctica’s vast ice sheet could have direct implications for sea and air temperatures around New Zealand in the future.
• The new research aims to fill a gap in current state-of-the-art climate models, which don’t factor in assumptions about ice from the sheet covering the frozen continent.
• It finds the massive amounts of meltwater could influence ocean temperatures around New Zealand – and also the number of extra-hot days decades from now.

A first-of-its-kind study suggests the worsening melting of Antarctica’s vast ice sheet could directly drive shifts in New Zealand’s local climate patterns.

The new study also indicates massive amounts of meltwater from the frozen continent might counteract climate change-driven ocean warming around New Zealand, while slightly reducing the number of extra-hot days projected in future.

But its authors stress Antarctica’s accelerating ice loss – now totalling some 500 billion tonnes each year – should be viewed as anything but positive, given its worrying and myriad implications for the earth system.

The New Zealand, UK and German research team investigated a gap in state-of-the-art climate models, which projected future scenarios without factoring in assumptions of melting from the thick ice sheet that sits upon Antarctica’s land area.

“In reality, we know that the ice sheet has been losing mass over the last few decades and will only lose more into the future as the planet warms,” said lead author Dr Andrew Pauling, of the University of Otago’s Department of Physics.

“The fact that models do not include this effect means that they are missing the resulting input of freshwater to the Southern Ocean.”

Earlier studies have shown when that injection of freshwater was accounted for, it meant more cooling of the Southern Ocean’s surface and more sea ice around the frozen continent.

“Given New Zealand’s proximity to Antarctica and the Southern Ocean, we were interested to see if including this missing freshwater would also impact our climate,” Pauling said.

“Many studies have looked at the impact of this freshwater on the ocean and sea ice around Antarctica, and on the wider global climate, but our study is the first to look at the specific effects on New Zealand.”

The group’s modelling ultimately showed as New Zealand headed toward a warmer future climate, the meltwater resulted in less warming than otherwise would be observed.

“That is, it doesn’t result in cooling overall, there’s just less warming than there would otherwise have been.”

Adding the meltwater into simulations led to cooler sea surface temperatures southeast of New Zealand, particularly in winter and spring.

The study particularly explored the implications for the subtropical front – a narrow band of ocean near New Zealand that typically varies in temperature by several degrees.

Meltwater from Antarctica's ice sheet could slightly influence how many extra-hot days – those over 25C – New Zealand experiences in the future.

“The exact position of this front is important for marine life, as temperatures to the north of it are substantially warmer than those to the south.”

As the planet heated, that front was projected to move south – but incorporating the missing meltwater offset that shift by a small amount, meaning slightly less potential impact on marine life and fisheries.

The researchers also examined the effect on extreme heat, which is likely to become increasingly frequent over coming decades.

“Without considering meltwater, the climate models used in our study predict that the number of hot days over 25C in New Zealand will increase by about 27 days per year by the end of the century,” Pauling said.

“However, with the inclusion of Antarctic meltwater, this increase is slightly reduced – by about two days annually on average – with the biggest effects seen in the North Island.”

Pauling pointed out that there remained uncertainties about just how much of the ice sheet, measuring several kilometres thick, was likely to melt.

“First, it depends on how much warming we will experience in the future, which depends largely on the choices we make globally about our CO2 emissions.”

Then, there were questions surrounding the physics of the ice itself: particularly when it came to understanding how swiftly the ice might flow toward the ocean – or how it might collapse.

“There’s also uncertainty in exactly what the local temperature change in the ocean around Antarctica will be for a given rise in global average temperature,” he said.

“This is important, since most of the melting occurs where the ocean is in contact with the ice at the coast.

“The amount of melt is important to get right because melting Antarctic ice will have a large impact on sea level changes in the future, as well as impacts on climate such as those shown in our study.”

The new research, published in the scientific journal Geophysical Research Letters, was funded by the Deep South National Science Challenge and the Antarctic Science Platform, with high-performance computing facilities provided by New Zealand eScience Infrastructure (NeSI).

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.

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