Ice Loss? Maybe

  • Date: 15/06/18
  • Dr David Whitehouse, GWPF Science Editor

The headlines say “Antarctica loses three trillion tonnes of ice in 25 years.” They add that it’s shedding ice at an accelerating rate. Sounds a lot, perhaps it will be gone soon? Actually it amounts to only 0.011 percent of total Antarctic ice. If that is, anything is being lost at all.

 

An analysis published in the journal Nature looks at satellite observations of the continent. They began in the early 90s and measure the height of the ice and its motion. Some satellites can measure the change in gravity as they pass over the ice and infer its mass.

The papers abstract reads:

The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modeling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992–2017 (5 ± 46 billion tonnes per year) being the least certain.

The main loss of ice is from west Antarctica which is the largest and densest volcanic region on Earth with over 100 volcanoes under the ice.

The first worrying thing about the paper are the error bars. In scientific literature it is normal to use errors of two standard deviations and not one. Even two sigma errors are in my opinion not enough but one certainly isn’t. It’s often used in cases where to quote two sigma errors would make the measurement look unconvincing. The paper states that 2720 +/- 1390 billion tonnes of ice were lost between 1992 -2017. Using two sigma errors changes that to a loss of 2720 +/- 2780 billion tonnes, which gives an entirely different impression. In fact the hypothesis that there has been any ice loss at all is not warranted by such errors.

If you accept the figures then the ice loss has been contributing 0.3 mm per year to sea level rise, or just over ten percent of the observed rise since the 19th century.

Another talking point about these observations is that they contradict other studies. In particular a NASA study of a few years ago which indicates Antarctica is gaining ice.

With only 25 years of observations it is not possible to tell if this is part of cyclic behaviour. As the authors of the paper admit the ice loss in west Antarctica is due to the intrusion of warmer water, and nothing at all to do with global warming. It is likely that such changes have happened before.

Feedback: david.whitehouse@thegwpf.com

 

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