How we're waking climate change's sleeping giant

The remnants of the Larsen B Ice Shelf in the Weddell Sea Antarctica. Photo / NASA/Ted Scambos/NSIDC

A world-leading glaciologist visiting New Zealand says scientists are fast running out of time to fully understand dramatic changes under way in climate change's sleeping giant: Antarctica.

Professor Eric Rignot, based at the University of California, Irvine and NASA's Jet Propulsion Laboratory, will this week give a free talk in Wellington, outlining growing concerns scientists have about the frozen continent and pressing the urgent case for action on climate change today.

Rignot has studied the world's largest glaciers in Greenland and Antarctica since the early 1990s, when NASA and other international space agencies first started collecting satellite data on them.

He is best known for ground-breaking research in 2014 which revealed the rapidly melting section of the West Antarctic Ice Sheet appeared to be in an irreversible state of decline, with nothing to stop the glaciers in this area from melting into the sea.

In an interview with the Herald, Rignot said while historical measurements stretched back a century, some of the most worrying discoveries in Antarctica had come only in recent decades.

The first evidence of warmer water causing melting at Pine Island Glacier, now known to be responsible for a quarter of Antarctica's ice loss, was made in 1996.

The glacier is part of the 25 million square kilometre West Antarctic Ice Sheet, which satellite measurements estimate is losing more than 150 cubic km of ice each year.

Rignot further noted the first physical measurements of warmer water affecting the much larger East Antarctic Ice Sheet, at Totten Glacier, were recorded only in 2015.

If all of it melted, the giant ice sheet, which forms most of Antarctica, would contribute an equivalent of around 50 metres of sea level rise, the vast majority of the total 58m that could come from the continent.

The Larsen ice shelf. Photo /NASA/Jesse Allen/U.S. Geological Survey

The new evidence meant the wider ice sheet's contribution to future sea level rise could be much greater than realised.

Rignot has also been tracking an expanding crack in the Larsen C ice shelf in the Antarctic Peninsula, which has dramatically accelerated its spread, increasing 18km in length in the space of a month.

It potentially meant the floating ice shelf, which is nearly as big as Scotland and the fourth largest of its kind in Antarctica, was poised to break off a piece nearly 5180sq km in size, or more than 10 per cent of its total area.

An ice island the size of a small US state would then be afloat in the Southern Ocean.

An edge of the Thwaites Ice Shelf. The Thwaites Glacier is already contributing 10 per cent of all global sea level rise. Photo / NASA

But Rignot said the crack merely pointed to a much larger, more disturbing situation.

"The crack in itself is not the most important factor. What's important is that this crack is happening further upstream than ever before, at least since the 1980s, and that shows that the front of this ice shelf is receding.

"We know that the ice shelves can not survive very long in such a climate, so the crack is just one part of a very, very slow trend of warming in the peninsula that has been going on for decades."

Scientists now believe that across the continent, more water was coming in contact with glaciers than in the past, triggering some of the biggest changes around Antarctica.

"And these changes in the presence of warm water are controlled by the wind patterns.

"That's the story that's unfolding here, and we have this tiny window of opportunity, and of observations, which didn't start so long ago but are getting finer and more detailed with time."

Scientists could now compare data captured by early Antarctic explorers, and with aerial surveys carried out as early as the 1930s and 1940s, with modern analysis drawing on such approaches as satellite monitoring and ice core samples.

"But regardless, we are also looking at the changes on the ice sheet and there are simple things that can be inferred from that.

The evolution of a large tabular iceberg, which broke off Pine Island Glacier, West Antarctica sometime between November 4 and 12, 2001. Photo / NASA

"So if you see some glaciers thinning at metres per year, in some places you can quickly realise that this could not have been going on forever and that this is something we can trace back to the 1970s and there is no way that this has been going for 1000 years at the same rate."

The growing realisation that Antarctica was changing on a much shorter time-scale than previously expected was making it more urgent for numerical models to be more accurate and representative of the wider climate system around the continent.

"What I hope we can do as scientists is gather enough evidence and run models that are a little bit more advanced to put some risk level on what's going to happen to the Antarctic in the coming centuries, but with smaller error bars than what we have at present so the public and policy makers can look at it with more scrutiny.

"As scientists, we don't have 30 years to do that and we need to make progress on this much faster.

"I'm hopeful that's it going the right way, but whether it's coming fast enough, I don't know."

The widening crack in the Larsen C ice shelf. Photo / NASA/John Sonntag

While changes in ice sheets could now be observed from year to year, and even from week to week, big picture patterns tended to play out on decadal time-scales.

"Some of what's going on now and what's going to happen in the next 20 or 30 years is probably already written in stone.

"There is no red button to stop the process right away.

"So, for instance, if we were to control our carbon emissions and even change the composition of the atmosphere in a significant way, we know it would it take, 20 or 30 years for the climate system to go back to something and the ice sheets might take 100 years to go back to something else.

Professor Eric Rignot. Photo / Supplied

"Another element of importance is we are starting to see something in the Antarctic that is without inertia. There is no red button to stop it tomorrow.

"That also puts more urgency into understanding in detail as much as we can, and because if we take some action tomorrow to change it, it will bear fruit in decades.

"It's much longer than a political term."

Rignot's Wellington lecture will be held from 5.30pm on Tuesday in Lecture Theatre 1 in Rutherford House, at the Victoria University's Pipitea Campus.</i>