Surprise: Defying Models, Antarctic Sea Ice Extent 100 Years Ago Similar To Today

By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt

German text edited/translated by P Gosselin)

Satellite measurements of Antarctic sea ice do not go back even 40 years. That’s not very much, especially when we consider that many natural climate cycles have periods of 60 years and more.

Luckily we have the field of climate reconstruction. Using historical documents and sediment cores, the development of ice cover can be estimated. In November, 2016, Tom Edinburg and Jonathan Day examined shipping log books from the time of Antarctic explorers and published on ice extent in The Cryosphere:

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

The surprising result: with respect to sea ice extent 100 years ago things looked similar to what we have today, with the exception of the Weddell Sea. A study by Hobbs et al. 2016 also looked back at the last century, here using geoscientific sea ice reconstructions. Once again the strong discrepancies between the real ice development and model simulations were criticized:

Century-scale perspectives on observed and simulated Southern Ocean sea ice trends from proxy reconstructions
Since 1979 when continuous satellite observations began, Southern Ocean sea ice cover has increased, whilst global coupled climate models simulate a decrease over the same period. It is uncertain whether the observed trends are anthropogenically forced or due to internal variability, or whether the apparent discrepancy between models and observations can be explained by internal variability. The shortness of the satellite record is one source of this uncertainty, and a possible solution is to use proxy reconstructions, which extend the analysis period but at the expense of higher observational uncertainty. In this work, we evaluate the utility for change detection of 20th century Southern Ocean sea ice proxies. We find that there are reliable proxies for the East Antarctic, Amundsen, Bellingshausen and Weddell sectors in late winter, and for the Weddell Sea in late autumn. Models and reconstructions agree that sea ice extent in the East Antarctic, Amundsen and Bellingshausen Seas has decreased since the early 1970s, consistent with an anthropogenic response. However, the decrease is small compared to internal variability, and the change is not robustly detectable. We also find that optimal fingerprinting filters out much of the uncertainty in proxy reconstructions. The Ross Sea is a confounding factor, with a significant increase in sea ice since 1979 that is not captured by climate models; however, existing proxy reconstructions of this region are not yet sufficiently reliable for formal change detection.”

A paper published by Ellen & Abrams 2016 even looked back 300 years ago and showed that the increase in sea ice from 1979-2016 has been part of a long-term growth trend of the 20th century:

Ice core reconstruction of sea ice change in the Amundsen-Ross Seas since 1702 A.D.
Antarctic sea ice has been increasing in recent decades, but with strong regional differences in the expression of sea ice change. Declining sea ice in the Bellingshausen Sea since 1979 (the satellite era) has been linked to the observed warming on the Antarctic Peninsula, while the Ross Sea sector has seen a marked increase in sea ice during this period. Here we present a 308 year record of methansulphonic acid from coastal West Antarctica, representing sea ice conditions in the Amundsen-Ross Sea. We demonstrate that the recent increase in sea ice in this region is part of a longer trend, with an estimated ~1° northward expansion in winter sea ice extent (SIE) during the twentieth century and a total expansion of ~1.3° since 1702. The greatest reconstructed SIE occurred during the mid-1990s, with five of the past 30 years considered exceptional in the context of the past three centuries.”

3 responses to “Surprise: Defying Models, Antarctic Sea Ice Extent 100 Years Ago Similar To Today”

  1. Curious George

    The Ship of Fools, an Antarctic expedition led by Chris Turney, a Professor of Climate Change of UNSW, was trapped by thick ice in 2013 in Commonwealth Bay for two weeks. Expedition members were evacuated by a helicopter while chanting slogans about global warming. Mawson expedition sailed there one hundred years earlier with no problems.

    The name of Professor Turney can not be found in a Wikipedia article on the expedition vessel,

  2. JerryMaype

    China will have to launch more ambitious renewable energy and non-fossil fuel targets and ramp up efforts to enforce them to avoid missing global climate accord requirements, two government think tanks said on Monday.

    China’s capacity for renewable energy, including hydro, wind and solar, will significantly exceed Beijing’s own target set in the five-year plan to 2020, according to the report jointly issued by China National Renewable Energy Centre (CNREC) and the Energy Research Institute of Academy of Macroeconomic Research.

    The world’s top energy consumer pledged to install 340 gigawatts (GW) of hydropower capacity, 210 GW of wind and 110 GW solar by 2020 in the five-year plan.

    But to meet commitments agreed to in 2015 in the Paris global pact to fight climate change, China should raise its target for non-fossil fuel to 26 percent of its total energy mix from a current target of 15 percent by 2020, the report said.

    “The Paris agreement of reducing the global temperature by two degrees puts pressure on the short-term energy transition from coal and oil to non-fossil fuels,” said Wang Zhongying, deputy director general at CNREC.

    China, the world’s second-largest economy, overtook the United States as the world’s biggest emitter of greenhouse gases in 2007.

    China pledged to bring its carbon emissions to a peak by 2030 or earlier as part of a joint pledge made with the United States ahead of the 2015 Paris talks.

    If current government policy is enforced properly, non-fossil fuels should account for 60 percent of energy supply by 2050, higher than an official government target of reducing coal alone to just half, the report said.

    Still, getting stranded clean power in the west to urban users has been a major headache for the government as Beijing seeks wean the nation off coal, the nation’s favorite fuel.

    An official at the National Energy Administration said at the conference on Monday he reckons the country will solve the problem of wasted energy by 2020.

    Chinese authorities have been striving to improve energy efficiency and upgrade energy infrastructure by introducing measures including national carbon trade, green certificates and promoting energy storage systems.

    “(But) to ensure compliance with the Paris agreement, strong support to renewable energy deployment is needed on both the national and local levels,” said Wang.

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  3. Cjones1

    One large volcanic eruption combined with the downward trend of the Solar sunspot cycle may well accelerate a cooling trend and increased ice formation.