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Melting at the bottom of the Earth
by -- February 9th, 2016

There is no factoid that doubters of human-induced climate change like to throw around more than the idea that the ice in Antarctica is not melting, perhaps even expanding. I’ve heard it stated emphatically at a hearing in the North Carolina legislature,[1] and I’ve seen it in the Wall Street Journal.[2]

Trouble is:  it just ain’t so.

Summer is winding down in Antarctica. The penguins have finished nesting and now head out to sea for the winter. Soon the continent will bask in 24 hours of darkness for the next six months. The end of summer is a good time to assess the status of the Antarctic ice pack. How much remains this year?

First we must remember the difference between sea ice and ground ice. Sea ice is frozen from sea water and floats on the surface of the ocean waters around Antarctica. It forms and melts every year and hasn’t shown much change in recent years.  Ground ice is the ice that forms on land.  It forms from snowfall, which hardens to form glacial ice.  Some of it melts or moves to the sea in glaciers each year. You can tell the difference between a piece of sea ice and a piece of ground ice by its salt content.  Forming from snowfall, ground ice contains very little sodium chloride.

If you visit Antarctica, you’ll see a lot of ice melting.   This should not cause immediate worry; much of it will reform during the winter.  What really matters is the net, long-term trend in the amount of ice on the Antarctic continent, and the end of summer is a good time to look.

We’ve known for about 10 years from a variety of studies that the ice pack on Antarctica is getting smaller. Now, a new study by Alba Martin-Español and a team of coworkers uses a variety of methods to estimate the total mass loss of 84 billion metric tons per year in the past decade. The greatest loss is seen in the Antarctic Peninsula (28 billion metric tons annually). The West Antarctic ice sheet is also thinning. These losses are partially balanced by a gain of ice in East Antarctica.  The net balance for the Antarctic continent is negative and consistent with independent observations that show lower salinity in the Ross Sea from melting ground ice.  The loss of ice on Antarctica is also consistent with the rise in sea-level seen globally.

Some of the ice sheets lost in Antarctica have been stable for up to 10,000 years; their loss is indicative of a new set of conditions, likely due to human activity. The overall loss of ice from Antarctica portends long-term changes at the South Pole. Should the West Antarctic ice sheet collapse, we would see sea levels rise 5 meters (~15 feet) globally.  Along with the rapid melting of ice on Greenland, that’s enough to cause serious havoc in Miami and Houston, yet U.S. Senators from both Florida and Texas have expressed doubt about the reality of human-induced climate change.

When some folks don’t like the science, they substitute belief.   Let’s hope voters know the difference.

References

Cavalieri, D.J. and C.L. Parkinson. 2008. Antarctic sea ice variability and trends.  Journal of Geophysical Research—Oceans 113: 1979-2006.

Jacobs, S.S., C.F. Giulivi, and P.A. Mele. 2002. Freshening of the Ross Sea during the late 20th century. Science 297: 386-389.

Martin-Español, M. et al. 2016. Spatial and temporal Antarctic ice sheet mass trends, glacio-isostatic adjustment and surface processes from a joint inversion of satellite altimeter, gravity and GPS data. Journal of Geophysical Research—Earth Surface  120:  doi: 10.1002/2015JF003550

Rietbroeck, R. et al. 2016. Revisiting the contemporary sea-level budget on global and regional scales.  Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1519133113

Rignot, E., I. Velicogna, M.R. van den Broeke, A. Monaghan and J. Lenaerts. 2011. Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise.  Geophysical Research Letters 38:

Shepherd, A., et al. 2012. A reconciled estimate of ice-sheet mass balance.  Science 338: 1183-1189.

Zwally, H.J. and B.M. Glovinetto. 2011. Overview and assement of Antarctic  ice-sheet mass balance estimates, 1992-2009.  Surveys in Geophysics 32: 351-376.

Zwally, H. J., J. Li, J.W. Robbins, J.L. Saba, D. Yi, A.C. Brenner, 2015. Mass gains of the Antarctic ice sheet exceed losses.  . Journal of Glaciology doi:10.3189/2015JoG15.Jo71

 

[1] Legislative Commission on Global Climate Change, North Carolina General Assembly, 3 February 2006

[2] Matt Ridley and Benny Peiser. 2015. Your complete guide to the climate debate. Wall Street Journal, November 27.  These writers refer to a recent publication by Zwally et al. (2015), which is based on data from 1992 to 2001. The paper seems “cherry-picked” to justify Ridley’s well-known skepticism about global warming.  Meanwhile, a variety of recent and longer term analyses with better instrumentation show significant losses, not gains, of ice mass from Antarctica, including an earlier analysis by Zwally and Glovinetto. 2011.

 

 

3 Comments

  1. Bets
    Feb 10, 2016

    Your blog on Antarctica was timely and well done. We just watched the movie “Antarctica: A Year on Ice.” What beautiful photography! As I watched it, I kept wondering how it is going to change as the ice melts. Arghh!!

    How does one remain at all optimistic in the face of these changes? You are doing your part by documenting them. Thank you.

    • Harold W Borns Jr, PhD
      Feb 18, 2016

      The same warming ocean and atmosphere controlling Antarctic sea ice volume also causes increased top and bottom melting of the floating margin of the intrinsically unstable West Antarctic Ice Sheet.
      While I was Program Manager of Polar Glaciology at NSF, the potential sea level rise danger of the West Antarctic Ice Sheet, grounded 2000 m below sea level, became clear. Consequently, we set in motion the long term West Antarctic Ice Sheet Program (WAIS), about 1989, to determine it’s stability with an eye to prediction. Because of its vast size, research is proceeding slowly by US, UK and other scientists.
      Because it is grounded in deep water and has a floating margin it has the potential to self destruct due to on going sea level rise forcing its grounding line “up-stream” into ever deepening water, causing a faster rate of production of large icebergs from the floating shelf.
      This scenario, for all practical purposes, guarantees self destruction with a possible 20 foot eustatic sea level rise. Apparently this is in progress in Pine Island Bay of the Amundsen Sea., where Pine Island Glacier’s floating margin has recently bouyed up by an on-going sea level rise, lifting the grounding line off of its pinning point’ beyond which the water deepens continuously.
      Consider this … If we reverse global warming will Earth return to its cooling trend towards the next glaciation?

  2. Linda Zall
    Feb 27, 2016

    This well written article clearly explains to the general public the Antarctica situation. Thank you for writing this for “the rest of us”, who are trying to make sense of the confusing articles that are out there in the media world.
    Linda Zall

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