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Huge Cavity In Antarctic Glacier

posted by cmn32480 on Friday February 01 2019, @11:36PM   Printer-friendly
from the get-the-dentist dept.

An Anonymous Coward writes:

A gigantic cavity — two-thirds the area of Manhattan and almost 1,000 feet (300 meters) tall — growing at the bottom of Thwaites Glacier in West Antarctica is one of several disturbing discoveries reported in a new NASA-led study of the disintegrating glacier. The findings highlight the need for detailed observations of Antarctic glaciers' undersides in calculating how fast global sea levels will rise in response to climate change.

Researchers expected to find some gaps between ice and bedrock at Thwaites' bottom where ocean water could flow in and melt the glacier from below. The size and explosive growth rate of the newfound hole, however, surprised them. It's big enough to have contained 14 billion tons of ice, and most of that ice melted over the last three years.

https://www.nasa.gov/feature/jpl/huge-cavity-in-antarctic-glacier-signals-rapid-decay

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  • (Score: 0) by Anonymous Coward on Friday February 01 2019, @11:53PM (6 children)

    by Anonymous Coward on Friday February 01 2019, @11:53PM (#795249)

    The findings highlight the need for detailed observations of Antarctic glaciers' undersides in calculating how fast global sea levels will rise in response to climate change.

    [...]

    It's big enough to have contained 14 billion tons of ice, and most of that ice melted over the last three years.

    Apparently sea level rise (in m) for a glacier is 0.41 meters per km^3 of melted ice: http://www.antarcticglaciers.org/glaciers-and-climate/estimating-glacier-contribution-to-sea-level-rise/ [antarcticglaciers.org]

    And there is 1 Gigaton per 1.091 km^3 of ice: https://www.sealevel.info/conversion_factors.html [sealevel.info]

    So 14 Gt -> 15.274 km^3 -> 6.26234 meters of sea level rise. Has the sea level risen 6 meters in the last three years?

    Where is my error?

  • (Score: 4, Informative) by bob_super on Saturday February 02 2019, @12:10AM (1 child)

    by bob_super (1357) on Saturday February 02 2019, @12:10AM (#795255)

    From your link.
    > Fretwell et al. 2013 estimated that the Antarctic Ice Sheet comprised 27 million km3 of ice, with a sea level equivalent of ~58 m

    Also
    >If we took our 458.30 Gt of ice (as calculated above), then we could calculate the global sea level equivalent by: SLE = 1.27 mm

    Your error is in the 410mm per km3. That's quite a few orders of magnitude off

  • (Score: 0) by Anonymous Coward on Saturday February 02 2019, @12:12AM (2 children)

    by Anonymous Coward on Saturday February 02 2019, @12:12AM (#795256)

    The only place 0.41 is found is near the top in the table "Table 1. Sea level equivalent (SLE) from various land ice sources. From IPCC AR5 (Vaughan et al, 2013)." which looks like .41m of sea level rise from glaciers and ice caps but not any ice sheets.

    At the bottom you'll find their math for estimating the sea level rise.

    We can calculate the volume of water required to raise global sea levels by 1 mm:

    Volume = area x height

    Area = 3.618 x 108 km2

    Height = 10-6 km (1 mm)

    Volume (km3) = (3.618 x 108 km2 ) x (10-6 km) = 3.618 x 102 km3 = 361.8 km3 water.

    We can convert km3 of water to Gt of water as we did above; 1 km3 water = 1 Gt water. In the same way, 1 Gt of ice = 1 km3 water. So, 361.8 Gt of ice will raise global sea levels by 1 mm. 361.8 Gt of ice is equivalent to 394.67 km3 ice.

    .....

    So, 361.8 Gt of ice will raise global sea levels by 1 mm. 361.8 Gt of ice is equivalent to 394.67 km3 ice.

    I have no idea how you decided the 0.41 was m/km^3. If 361.8 Gt = 1mm then 14 gt is .038 mm rise

    • (Score: 0) by Anonymous Coward on Saturday February 02 2019, @08:42PM (1 child)

      by Anonymous Coward on Saturday February 02 2019, @08:42PM (#795466)

      Here it defines sea level equivalent

      such volume of ice (km3) is equivalent to so many millimetres of sea level rise (sea level equivalent (SLE); the amount of sea level rise on full melting of the ice).

      Here is the header of the column in the table (appears to use units of meters):

      Sea level equivalent (m)

      • (Score: 0) by Anonymous Coward on Sunday February 03 2019, @05:51PM

        by Anonymous Coward on Sunday February 03 2019, @05:51PM (#795730)

        Yes but that is full meltimg of all the ice specified on the left. Not meters per volume, meters per geologic features.

  • (Score: 2) by HiThere on Saturday February 02 2019, @05:12AM

    by HiThere (866) Subscriber Badge on Saturday February 02 2019, @05:12AM (#795323) Journal

    Maybe. How much of that glacier was floating before it melted? If it's already floating, melting doesn't raise the sea level, and lots of glaciers are partially on land, and partially floating shelves.

    The implication was that it was all on land, and it may have been. But that's a "perhaps".

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