In the early years of the 20th century, several teams of explorers were racing to reach a new frontier: the South Pole. During what's known as the Heroic Age of Antarctic Exploration, many explorers perished and the expeditions were fraught with failure, but their efforts were not in vain. Now, over a century later, their logbooks and journals have helped piece together a new discovery: Antarctic sea ice coverage may not be on a steady downward trend, but fluctuating over cycles lasting decades.

Much of the bad news concerning melting ice is centered around the Arctic region, which is taking a solid beating. At the other end of the world, Antarctic ice shelves are also shrinking by as much as 159 billion tonnes each year, but a new study from the University of Reading suggests this may be part of a longer-term cycle.

Using logbooks from early 20th century explorers, like Robert F. Scott and Sir Ernest Shackleton, the Reading research compared where the edges of the ice were observed then, to where they are now, and found that sea ice levels in the Antarctic summer has only dropped by around 14 percent.

"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," says Jonathan Day, lead researcher on the study. "We know that sea ice in the Antarctic has increased slightly over the past 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."

With the exception of the Weddell Sea, which has declined significantly, the team estimates that in the early 1900s Antarctic ice spanned between 5.3 and 7.4 million km2 (2 and 2.9 million mi2) – figures comparable to today's levels. That means ice coverage may have increased from then up to a peak level during the 1950s, before declining once again to our current figures.

"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," says Day.

The study is the first to examine what southern sea ice levels were like before the 1930s, suggesting that Antarctica is much less sensitive to the effects of climate change that are ravaging the Arctic. Instead, the South Pole may undergo regular fluctuations between high and low ice cover, on a scale of decades. Studying more texts from explorers of that time may help paint a clearer picture of these long-term trends.

"The Southern Ocean is largely a 'black hole' as far as historical climate change data 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," says Day.

The research was published in the journal The Cryosphere.

Dr. Jonny Day from the University of reading discusses the findings in the following video.