some squiggles and icecubs and a skidoo on a purple zany WORK WEEK background

Image: Archi Banal

ScienceMarch 19, 2023

I am a polar oceanographer – this is what I do

Guest Post

Image: Archi Banal

From his office at NIWA headquarters in Wellington, scientist Craig Stewart gets updates from the Southern Ocean, where climate change is starting to melt the ice shelves.

All week on The Spinoff we’re delving into our relationship with the world of work in Aotearoa. For more Work Week stories, click here.

I’m a polar oceanographer who has been working in Antarctic science for two decades. My first trip to Antarctica was with the British Antarctic Survey in 2001; since then, I’ve done perhaps a dozen polar trips, with different objectives. But the themes for me have been using radar to measure the thickness of the ice shelf and using moorings to measure the ocean underneath.

The last time I went down was in the 2021-2022 summer season. We were camping at the far side of the Ross Ice Shelf, 900 km in a straight line from Scott Base. That’s about a four hour flight on a small plane with a landing in the middle to refuel. You don’t get much further from home for that, or from spare parts for that matter. We were establishing a mooring site, drilling through the ice shelf to put instruments in the ocean underneath. Communications have improved since I first went south – we were able to send and receive emails this time, although not attachments.

It’s a huge contrast from my life of commuting into work in Wellington. It’s all the obvious things – you’re totally isolated, you have to be really well prepared. What I do on a weekly basis, going into the office to look at my computer all day, is not that different from a lot of other people. But when I sit in my office I’m thinking about that next season, how we can have everything we need, how we can best do it. How far can we travel in a day on the Ski-Doo? What is all the software and hardware we’ll need? Will the batteries for the instruments last in cold temperatures? It’s easy to underestimate how much preparation is required, but it’s a significant part of the job.

grainy hazy sorta vintage vibes of BIG OLD mountains and ice ice ice and a silohetted figure with a skidoo — Craig Stewart at the Rutford Ice Stream in Antarctica in 2001 (Photo: supplied)

Because it’s so far away and inaccessible, it’s really difficult to fix things when they go wrong. You have to think ahead a lot. For example, I’ve had a few specific problems with instruments not working lately, and you can’t just go and fix them. We can still get information, and Antarctica New Zealand did a great job servicing some of these, but we couldn’t get to all the sites before the helicopter returned to New Zealand for winter. The rest will have to wait for November, when we can next reach the sites. Things are even tougher when the instruments are under the ice shelf.

One of my projects is to characterise how the basal melting of the Ross Ice Shelf, where warm water melts it from underneath, varies in different seasons. So we’ve installed 12 radar instruments that were custom built to measure the thickness of ice shelves, powered by a solar panel. They take a shot every hour, and it’s remarkable to me that the technology works, that those measurements get emailed to me while I sit at my desk in Wellington. That’s really pleasing, when the technology works well – 15 years ago, that wasn’t something we could do.

Taking these measurements is important, because the Antarctic ice sheet is thinning. Picture a pile of snow where it’s so heavy in the middle that it slides inwards and out, pushing between mountains and eventually flowing over the sea. These floating fringes, called ice shelves, are incredibly sensitive to changes in the ocean. The areas in Antarctica where the change is most rapid is where warm water is getting in under the floating ice shelf and melting it from underneath. Measurements help us to understand the vagaries of the ocean, helping us improve future predictions of how the Antarctic ice sheet will respond to warming oceans.

endlessly blue sky and that impossible gleaming horizon. in the centre of the frame, a scientist in a red coat cups a mug in his hands. it is very sunny, very empty, very cold — Craig Stewart takes a tea break on the Ronne Ice Shelf (Photo: supplied)

I think about climate change all the time; it’s something I’ve been aware of for more than 20 years – I remember mentioning it in my interview before my first trip to Antarctica. It’s one of the things that motivates me to do the work; we know enough that we need to make major changes to our lifestyles. We should be very concerned. There are huge amounts of questions about how climate change will happen that we need to answer, too, which is why this science matters.

I also think about the carbon cost of the fieldwork itself, which can be high. You fly to Antarctica, there’s fuel use from the Ski-Doo and the helicopter. I feel that fuel use is justified in terms of the knowledge we gain through the work, but as scientists, it’s something we should think carefully about.

You do get some great stories. The first time I went to Antarctica, bad weather meant I was stuck in the Falkland Islands for three weeks. Then I spent 11 weeks with only one other person, camping on the ice shelf in a group of two. He had a bit of a reputation; on Christmas I unwrapped two angels that my lovely family had sent and he said “Crikey! I don’t believe in Christmas”. Some of the equipment is the same as what early polar explorers used; the Scott Polar Tents are heavy, but in a howling polar storm you’re pretty happy to be inside one, and with the British Antarctic Survey, we used Primus stoves and wooden Nansen sledges, which haven’t changed much either.

I have an engineering background, and I studied oceanography for my Masters and PhD. I think what I like most about my job is the variety, that I can do science and write programmes to analyse data, and be involved in hands-on, technical stuff, like sorting out the battery and solar panels on the radar and going to Antarctica to do fieldwork physically. I’m lucky that I get to do lots of types of work – it keeps things interesting!

– As told to Shanti Mathias

Keep going!

Cyclone Gabrielle barrels towards Aotearoa in February 2023 (via earth.nullschool.net)

ScienceMarch 15, 2023

‘Rapid reaction force’ of global scientists reveal findings on climate change role in Cyclone Gabrielle

Toby Manhire

Editor-at-large

Cyclone Gabrielle barrels towards Aotearoa in February 2023 (via earth.nullschool.net)

Observational results point to climate impacts, but conclusive findings from modelling prove elusive.

A group of 23 scientists from around the world have concluded that climate change increased both the likelihood and severity of the rainfall unleashed by Cyclone Gabrielle, but have been unable to put a definitive number on that impact.

The rapid study by a team from the World Weather Attribution initiative, including several New Zealand scientists, produced a “mixed bag of results”, said Sam Dean, principal climate scientist at Niwa. While observational data indicated that climate change had exacerbated the downpours in the areas focused on, Tairāwhiti and Hawke’s Bay, modelling was not conclusive.

“Based on the analysis of the observation records, we undertook a statistical analysis which showed that the rainfall due to Cyclone Gabrielle was increased by 20% to 30% and was made three to four times more likely as a result of the human emissions of greenhouse gasses into the atmosphere which has caused the planet to warm,” explained Dean at a media briefing.

As well as analysing historical weather station data, Dean and his collaborators around the world ran thousands of simulations on supercomputers to compare the weather event in the climate as it is today with the climate before the impacts of warming. That modelling proved unable to quantify the influence of climate change on the rainfall produced by the cyclone, which ripped across the north and east of the North Island a month ago, wreaking massive destruction and 11 deaths.

Rapid analysis of severe weather and climate attribution is a burgeoning branch of climate science. The World Weather Attribution group looks at specific events with a view to urgently assessing the extent to which climate change is more likely and more extreme, with the ambition of putting that information into the public domain while the impacts are fresh in people’s minds.

‘If you regularly enjoy The Spinoff, and want it to continue, become a member today.’

Toby Manhire
— Editor-at-large

“The [Gabrielle] event is challenging us as climate scientists,” said Dean, who had in recent weeks endured “a lot of sleepless nights trying to work on this”. Gabrielle was “a gargantuan event, and I have no doubt whatsoever in my mind, based on my experience as a climate scientist, that climate change has influenced that event. But do we know it’s exactly 30%? No, we don’t,” he said.

“We would never say that climate change caused this event,” Dean stressed. “This event could have happened without climate change. It would have been quite rare in a world without climate change. It is now not quite so rare. It is still an unusually extreme event.”

Sam Dean, principle climate scientist at Niwa.

Researchers focused on the impact of climate change on rainfall. The study did not assess the role of wind, nor did it seek to measure how climate change might have exacerbated the damage. “Even small changes in intensity can play through to a much bigger depth of impact,” said Dean. “It might be that the last bit of water that breaches your stopbanks was what climate change added. That’s doing a lot of the damage. So if you did [assess] damages, then you might well find a much larger impact from climate change. It depends on the situation.”

Another of the scientists involved in the project, Luke Harrington, a senior lecturer in climate change at the University of Waikato, said that the observations showed clearly that extreme rainfall was occurring with greater regularity in the region studied, and even when La Niña and the marine heatwave were factored in, “we don’t have a clear alternative explanation for [the increase] other than climate change, particularly over this long period of time”.

He said: “I appreciate that there’s always a desire to come up with a singular answer as to what the impact [of climate change] in an event is, but in this situation we’d be much more comfortable providing a range, and acknowledging there is uncertainty there.”

When evaluating the modelling results, said Harrington, “we have quite a range of uncertainty as to what the real world is in nature, in terms of the statistics of extreme rainfalls in this part of the country. So our ability to discard models on the basis of them not performing well was limited. We need to spend a bit more time looking at the reasons why these different models show different answers.”

He noted that they were still awaiting rainfall data from stations which remained difficult to access as a result of the storm, and that some of those had longer records which would help to draw conclusions.

Friederike Otto, a climate scientist at Imperial College and a key figure in the “rapid reaction force” of severe event weather attribution studies, said interest in and understanding of the branch of climate science continued to grow, accelerated by the IPCC Working Group 1 report “which put a huge emphasis on the advances made in event attribution”. The collaborative energy had similarly increased. “Finding scientists to work with in all countries has become a lot easier,” she said.

Another of the New Zealand scientists involved in the study released today, Dave Frame of the University of Canterbury, told The Spinoff that a commitment to “the integrity of the scientific process” meant that those involved were determined not to overstate the conclusions. “We know there are plenty of events where we can quantify the climate change contribution fairly well. We’re confident here that the obs are showing a trend. These models don’t really give much of a signal but this is the first step, the first piece of the puzzle.”

He said: “If we’d pulled that process because we didn’t like the answer, well, that would be shabby.” It might be a hackneyed phrase, he said, but “sometimes further work really is needed”.