11 Apr 2023

Why is Antarctic sea ice vanishing?

From The Detail, 5:00 am on 11 April 2023

Researchers in our southernmost continent were shocked to find stretches of sea ice disappearing, and while they don't know why it's happening, the consequences could be catastrophic.

Four scientists in Antarctica, wearing orange and black jackets. They are standing around a piece of silver equipment.

Documenting the intact structure of the sub-ice platelet layer as recovered by the sampling system, (from left) Greg Leonard, Natalie Robinson (on ladder), Steve Parker and Ken Ryan. Photo: Supplied/Brett Grant

Setting up camp in Antarctica's McMurdo Sound is always full of uncertainty, with blizzards whipping up the snow and ice, changing the landscape.    

But for NIWA oceanographer Dr Natalie Robinson, last October's annual sea ice research trip was unlike any of her previous 19 expeditions there. The changes she saw were drastic.

"It was an eye opener," she says. "It was completely unprecedented."

During preparations for the camp, Wellington-based Robinson kept an eye on the sea ice over winter, expecting to see it grow as it normally would. But a series of southerly storms over that time had created unusual conditions in the Ross Sea region, blowing the sea ice offshore. 

The team from the Antarctic Science Platform's sea ice research programme were facing the prospect of having no ice that was strong or thick enough to camp on, or for vehicles to travel on.

By late August, their plans were still up in the air, because there was no sea ice.

Then the weather changed and the team were able to work around the conditions, and set up camp in a different spot near Scott Base. But Robinson and other scientists are now looking at what was behind the sudden, drastic change - in what could be a glimpse into a future, with less sea ice in this part of Antarctica. 

Despite the restrictions of working in a tighter field site, Robinson says the trip was critical.

"Even though it might not be a scenario that we expect to see in another few years again, it's certainly moving towards a scenario that we are expecting. That would be sea ice forming later in the season, forming thinner and ultimately perhaps to a lesser extent as you go northward as well."

Three scientists in Antarctica, wearing black and orange jackets. They surround a yellow piece of equipment.

(Left to right) Lars Smedsrud (University of Bergen, Norway), Inga Smith (University of Otago) and Britney Schmidt (Cornell University, USA) inspect frazil ice that has formed on Icefin, 3 November 2021. Photo: Supplied/Andy Mullen

Robinson tells The Detail what differences her team of researchers discovered when they camped on the ice, and why she thinks more attention must be given to the role of Antarctic sea ice in keeping the planet cool and species like the emperor penguin alive.

"We have an opportunity as a society to make things better than they would otherwise be. The window for that opportunity is closing because there are thresholds that are going to be met and we cannot reverse them."

She is one of more than 100 scientists working in unison on the Antarctic Science Platform on climate change questions. The work they're doing ranges from field work to analysis and modelling.

Otago University physicist Dr Inga Smith, who specialises in sea ice, explains to The Detail how the last year's events have affected her own research, and why she is still waiting to get her hands on the blocks of ice that were flown out from Antarctica months ago. 

The overall aim of Smith's research is to understand how Antarctic sea ice will change over the next century. She is looking for critical thresholds or "tipping points" for Antarctic sea ice survival that will be crossed in the future of warmer temperatures and higher carbon dioxide levels.

At its maximum, in September, Antarctic sea ice covers 19 to 20 million square kilometres of the Southern Ocean, four percent of the Earth's surface. It shrinks to three to four million square kilometres in February.

But Smith says that in the last two years the sea ice has been much more diminished. 

"What we've been looking at is, what's the baseline? What was unusual about 2022 - at least in our recent experience - the baseline was that there was always ice for 15 to 30 kilometres out, that vehicles could be driven out, that equipment could be deployed on, but that wasn't the case last winter."

Smith says the climate models predict that as the world warms, there'll be less Antarctic sea ice.

"Around the whole of Antarctica in the last two years, the summer sea ice has been at record lows...and people are still investigating exactly what's happened."

Find out more about what's at stake by listening to the full episode.

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