A sleeping giant is stirring

Monitoring the world’s biggest sheet of ice is mostly a humdrum affair for Jan Lieser. Every day since 2006 the University of Tasmania glaciologist has been checking satellite images of the East Antarctic coast that are almost always pretty much the same as the day before. 

In the daily satellite picture of the coast 3000 km south-west of Hobart he got used to the familiar outline of a 1200 sq km ice shelf abutting Bowman Island, fed by the Conger glacier. Then suddenly, a year ago this week, it wasn’t there. Where the ice shelf should have been were small bits of floating ice and, 50-odd kilometres to the west, a couple of large icebergs.

The Conger breakup did not initially attract the attention it deserved. This was not the first ice shelf break-up in Antarctica, nor the largest. The Larsen ice shelf decreased in size by nearly 20,000 sq km between 1995 and 2002 – most spectacularly in February 2022 when over 3000 sq km disappeared. 

But Larsen is off the Antarctic Peninsula in West Antarctica, south of South America, in a recognised global warming hotspot. Sitting atop an archipelago of islands, the West Antarctic ice sheet is exceptionally vulnerable to decay and eventual collapse due to the influx of warming ocean waters.

Conger, by contrast, is in a part of Antarctica that until fairly recently was considered unlikely to show much sign of warming for many decades. The East Antarctic ice sheet contains four-fifths of the planet’s ice, enough to raise global sea levels by over 50 metres. Signs of coastal melting in this part of the world are no small matter.

An early indication that change was afoot came in 2016, when an international team including Tasmanians Jason Roberts and Tas van Ommen found that the massive Totten Glacier, about 600 km east of Conger, was losing ice as a result of warmer ocean water penetrating underneath it.

In 2019 a University of California project to map Antarctic bedrock identified the world’s deepest land canyon about 200 km west of Conger, below Denman glacier, another huge ice river which feeds the Shackleton ice shelf. A few months later a second paper associated with the project concluded that Denman had “potential for rapid and irreversible retreat”.

Coinciding with the Conger collapse last year was a heatwave in which warm air lifted the temperature in parts of East Antarctica by more than 30C. But while that may have marginally affected ice shelf melting, the main cause lay to the north, in the Southern Ocean.

For many years the Antarctic Circumpolar Current was assumed to shield Antarctica from the worst effects of global warming, but a study published in Nature Communications two years ago found that subsurface waters between Tasmania and Antarctica are experiencing “radical” warming, enough to threaten the stability of ice shelves. 

Another indication of a warming Antarctic is sea ice. Unlike in the Arctic, the extent of Antarctic sea ice had changed little this century, but last year it was the lowest in all 42 years of satellite records. The February 2023 summer minimum continued that record-breaking trend.

Anyone who has crossed the Southern Ocean by ship knows the difference sea ice makes to surface waters. When you enter the sea ice, suddenly you’re no longer rolling everywhere and sick to the stomach. Sea ice means gentler swells, even complete calm, and sea ice next to the coast means much less wave damage to ice shelves and glacier tongues. 

The absence of coastal sea ice around the Conger ice shelf over a couple of summers undoubtedly contributed to its breakup, which is in turn another indication, if we needed it, that East Antarctica is not immune from global warming.

Jan Lieser warns that stretched research resources put strict limits on our understanding of  Antarctic processes involving the hugely complex interplay between atmosphere, ocean, ice, bedrock and biological systems. But be warned: the sleeping giant that is the East Antarctic icecap, 20 million years in the making, is waking up. Prepare to be surprised.

• NEXT WEEKEND marks a big birthday for Sustainable Living Tasmania, which for 50 years has championed living within planetary means.

To celebrate, SLT is at Brighton Civic Centre (Green Point Road, Bridgewater) for a “Big Weekend” of ideas for low-impact living, including workshops on cycling (Bicycle Network), vegie gardening (Hannah Moloney from Gardening Australia), Aboriginal bush tucker (Kitana Mansell) and affordable cooking (Matthew Evans from Fat Pig Farm).

Metro Tasmania is putting on free shuttle buses from Hobart and Glenorchy bus malls. For details go to www.slt.org.au/events.

This entry was posted in Uncategorized. Bookmark the permalink.