The finding settles some questions and raises others. Even though, on balance, the Antarctic sea ice seems stable, it is under attack.

An alarming rate of melting has been observed in West Antarctica − and scientists now think they know when that melting started.

Antarctic sea ice

The Antarctic sea ice protects the largest body of ice on the planet − the glaciation, sometimes kilometres deep, that covers almost all of the bedrock of the enormous empty continent.

Satellite studies began only 30 or so years ago, so researchers have had no historical baseline from which to measure change – until now.

Two British scientists remembered that Captain Robert Falcon Scott, who reached the South Pole in January 1912, wrote in his journal: “Great God! This is an awful place.”

He had hoped to be the first, but he found instead a Norwegian flag planted by his rival, Roald Amundsen, Scott continued: “Now for the run home and a desperate struggle. I wonder if we can do it.”

Scott and his four comrades perished before they could reach their base camp, and their ship, Discovery.

But Tom Edinburgh and Jonathan Day, research scientists in the University of Reading’s Department of Meteorology, report in the European Geosciences Union journal The Cryosphere that the logbooks of Scott’s three expeditions − and those of Sir Ernest Shackleton, who lost his ship Endurance when it was trapped in sea ice, and of other explorers − preserved a precise measure of the latitudes reached by the summer ice between 1897 and 1917.

“The missions of Scott and Shackleton are remembered in history as heroic failures, yet the data collected by these and other explorers could profoundly change the way we view the ebb and flow of Antarctic sea ice,” Dr Day says.

“We know that sea ice in the Antarctic has increased slightly over the last 30 years, since satellite observations began. Scientists have been grappling to understand this trend in the context of global warming, but these new findings suggest it may not be anything new.

“If ice levels were as low a century ago as estimated in this research, then a similar increase may have occurred between then and the middle of the century, when previous studies suggest ice levels were far higher.”

The research continues. Whaling ships’ log books are already beginning to provide answers about the historic extent of the north polar ice. And maritime museums and naval archives may hold more detailed answers about the Antarctic.

Dr Day says: “The Southern Ocean is largely a black hole as far as historical climate change is concerned, but future activities planned to recover data from naval and whaling ships will help us to understand past climate variations and what to expect in the future.”

Gigantic glacier

Meanwhile, British, US, Danish German and Swiss scientists report in Nature journal that they analysed sediment cores far beneath West Antarctica’s Pine Island glacier shelf ice to confirm that the gigantic glacier began its alarming retreat around 1945.

“Ice loss from this part of West Antarctica is already making a very significant contribution to global sea level rise, and is actually one of the largest uncertainties in global sea-level predictions,” says David Vaughan, director of science for the British Antarctic Survey.

“Understanding what initiated the current changes is one major piece of the jigsaw, and now we are already looking for the next − how long will these changes continue and how much ice will Pine Island Glacier and its neighbours lose in the coming century?” – Climate News Network

• This report was first published in Climate News Network