Antarctic Sea Ice Has Not Shrunk In 100 Years, Scott And Shackleton Logbooks Prove

  • Date: 24/11/16
  • Sarah Knapton, The Daily Telegraph

Antarctic sea ice had barely changed from where it was 100 years ago, scientists have discovered, after pouring over the logbooks of great polar explorers such as Robert Falcon Scott and Ernest Shackleton.

Experts were concerned that ice at the South Pole had declined significantly since the 1950s, which they feared was driven by man-made climate change.

But new analysis suggests that conditions are now virtually identical to when the Terra Nova and Endurance sailed to the continent in the early 1900s, indicating that declines are part of a natural cycle and not the result of global warming.

Scott's ship the Terra Nova 
Scott’s ship the Terra Nova 

It also explains why sea ice levels in the South Pole have begun to rise again in recent years, a trend which has left climate scientists scratching their heads.

“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,” said Dr Jonathan Day, who led the study, which was published in the journal The Cryosphere.

“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.

“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.”

Captain Scott and team 
Captain Scott and team 

The study was based on the ice observations recorded in the logbooks from 11 voyages between 1897 and 1917, including three expeditions led by Captain Scott, two by Shackleton, as well as sea-ice records from Belgian, German and French missions.

Captain Scott died along with his team in 1912 after losing to Norwegian Roald Amundsen in the race to the South Pole, while Shackleton’s ship sank after becoming trapped in ice in 1915 as he and his crew attempted the first land crossing of Antarctica.

The study is the first to calculate sea ice in the period prior to the 1930s, and suggests the levels in the early 1900s were between 3.3 and 4.3 million square miles (5.3 and 7.4 million square kilometres)

Estimates suggest Antarctic sea ice extent was significantly higher during the 1950s, before a steep decline returned it to around 3.7 million miles (6 million square kilometres) in recent decades which is just 14 per cent smaller than at the highest point of the 1900s and 12 per cent bigger than than the lowest point.

One of the first aerial photographs of the Antarctic obtained from a balloon in 1901, showing Erich Von Drygalski's ship The Gauss 
One of the first aerial photographs of the Antarctic obtained from a balloon in 1901, showing Erich Von Drygalski’s ship The Gauss 

The findings demonstrate that the climate of Antarctica fluctuated significantly throughout the 20th century and  indicates that sea ice in the Antarctic is much less sensitive to the effects of climate change than that of the Arctic, which has experienced a dramatic decline during the 20th century.

In future the team plans to use data from naval and whaling ships as well as the logs from Amundsen’s expeditions to complete the picture.

Separate research by the British Antarctic Survey also showed that the present day loss of the Pine Island Glacier on the West Antarctic Ice Sheet has been happening since the mid 20th century and was probably caused by El Nino activity rather than global warming.

Pine Island Glacier, which drains into the Amundsen Sea in West Antarctica, is retreating and thinning rapidly, but the initial triggering mechanism was unclear. The team looked a sediment cores in the area which showed that an ocean cavity under the ice shelf began to form around 1945, following a pulse of warmth associated with El Niño events in the tropical Pacific Ocean.

Full story

see also full paper

Estimating the extent of Antarctic summer sea ice during the Heroic Age of Antarctic Exploration

The Cryosphere, 10, 2721-2730, 2016 — 21 November 2016

Tom Edinburgh and Jonathan J. Day
Abstract. In stark contrast to the sharp decline in Arctic sea ice, there has been a steady increase in ice extent around Antarctica during the last three decades, especially in the Weddell and Ross seas. In general, climate models do not to capture this trend and a lack of information about sea ice coverage in the pre-satellite period limits our ability to quantify the sensitivity of sea ice to climate change and robustly validate climate models. However, evidence of the presence and nature of sea ice was often recorded during early Antarctic exploration, though these sources have not previously been explored or exploited until now. We have analysed observations of the summer sea ice edge from the ship logbooks of explorers such as Robert Falcon Scott, Ernest Shackleton and their contemporaries during the Heroic Age of Antarctic Exploration(1897–1917), and in this study we compare these to satellite observations from the period 1989–2014, offering insight into the ice conditions of this period, from direct observations, for the first time. This comparison shows that the summer sea ice edge was between 1.0 and 1.7° further north in the Weddell Sea during this period but that ice conditions were surprisingly comparable to the present day in other sectors.
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