Inconvenient: Antarctica’s Ice Sheet May Be More Durable Than We Thought

On the same day that WaPo and other alarmist media outlets were wailing about a small loss in Antarctic ice balance, another study came out. This study found that the East Antarctic Ice Sheet has survived higher temperatures than we are experiencing now.

Mt. Erebus rising above the ice-covered continent. Credit: Ted Scambos & Rob Bauer, NSIDC

From PM:

Summary:

  • Scientists studied the Pliocene epoch, which happened a few million years ago.
  • Temperatures were a little warmer then, so the epoch could be a good preview of a warmer Earth.
  • They found Antarctic ice was more prevalent back then than we’d believed.

One of the biggest potential dangers of increasing climate change is sea level rise caused by the melting of the polar ice caps. As our planet heats up, large ice sheets in Greenland and Antarctica will melt, potentially triggering several feet of increased sea level rise. If the entire Antarctic ice sheet melts into the ocean, it could lead to dozens of feet of sea level rise, likely enough to wipe out entire cities.

Of course, it’s important to remember that ice sheets are complex and predicting how they will react is difficult—there’s a wide range of possibilities. Perhaps the best way for scientists to predict how ice sheets will behave in the future is by learning how they behaved in the past, so one group of scientists traveled to the East Antarctic Ice Sheet to learn its history.

Specifically, the researchers were interested in what happened to the ice sheet during the Pliocene epoch, the geologic period from about 5.4 million years ago to around 2.5 million. During the Pliocene, global temperatures were a few degrees warmer than they are today, which means this era is a good model for what our world might look like in a few decades, if climate change remains unchecked.

To determine just what happened to the ice sheet during this period, the researchers drilled deep into the rock beneath it. The scientists were looking for samples of certain isotopes, beryllium-10 and aluminum-26. These particular isotopes are created from the impact of cosmic rays from space. When these cosmic rays hit the atoms in the soil, they trigger atomic reactions that produce these isotopes.

The key fact here is that cosmic rays can’t penetrate ice. If there was ice over the ground during the Pliocene, the cosmic rays wouldn’t have reached the ground and these isotopes shouldn’t be present in the soil. But if the ice sheet melted significantly, the researchers would find higher levels of these isotopes.

“Based on this evidence from the Pliocene, today’s current carbon dioxide levels are not enough to destabilize the land-based ice on the Antarctic continent,” said study author Jeremy Shakun.

Full story here


The study: https://www.nature.com/articles/s41586-018-0155-6

Minimal East Antarctic Ice Sheet retreat onto land during the past eight million years

Abstract

The East Antarctic Ice Sheet (EAIS) is the largest potential contributor to sea-level rise. However, efforts to predict the future evolution of the EAIS are hindered by uncertainty in how it responded to past warm periods, for example, during the Pliocene epoch (5.3 to 2.6 million years ago), when atmospheric carbon dioxide concentrations were last higher than 400 parts per million. Geological evidence indicates that some marine-based portions of the EAIS and the West Antarctic Ice Sheet retreated during parts of the Pliocene1,2, but it remains unclear whether ice grounded above sea level also experienced retreat. This uncertainty persists because global sea-level estimates for the Pliocene have large uncertainties and cannot be used to rule out substantial terrestrial ice loss3, and also because direct geological evidence bearing on past ice retreat on land is lacking. Here we show that land-based sectors of the EAIS that drain into the Ross Sea have been stable throughout the past eight million years. We base this conclusion on the extremely low concentrations of cosmogenic 10Be and 26Al isotopes found in quartz sand extracted from a land-proximal marine sediment core. This sediment had been eroded from the continent, and its low levels of cosmogenic nuclides indicate that it experienced only minimal exposure to cosmic radiation, suggesting that the sediment source regions were covered in ice. These findings indicate that atmospheric warming during the past eight million years was insufficient to cause widespread or long-lasting meltback of the EAIS margin onto land. We suggest that variations in Antarctic ice volume in response to the range of global temperatures experienced over this period—up to 2–3 degrees Celsius above preindustrial temperatures4, corresponding to future scenarios involving carbon dioxide concentrations of between 400 and 500 parts per million—were instead driven mostly by the retreat of marine ice margins, in agreement with the latest models5,6.

via Watts Up With That?

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June 14, 2018 at 04:12PM

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