Antarctic Ice Shelf Melt Accelerating

March 26, 2015

Fig. 1. Eighteen years of change in thickness and volume of Antarctic ice shelves. Rates of thickness change (m/decade) are color-coded from -25 (thinning) to +10 (thickening). Circles represent percentage of thickness lost (red) or gained (blue) in 18 years. Only significant values at the 95% confidence level are plotted (see Table S1). Lower left corner shows time series and polynomial fit of average volume change (km 3) from 1994 to 2012 for the West (in red) and East (in blue) Antarctic ice shelves. Black curve is polynomial fit for All Antarctic ice shelves. We divided Antarctica into eight regions (Fig. 3), which are labeled and delimited by line segments in black. Ice-shelf perimeters are shown as a thin black line. The central circle demarcates the area not surveyed by the satellites (south of 81.5°S). Original data were interpolated for mapping purposes (see Table S1 for percentage area surveyed of each ice shelf). Background is the Landsat Image Mosaic of Antarctica (LIMA)

There will be a new video, out next week, I hope, that will add a little to this. Yet another indicator that Antarctica, which scientists hoped would be static this century – is on the move.

Greg Laden’s Blog:

Antarctica is pretty much covered with glaciers. Glaciers are dynamic entities that, unless they are in full melt, tend to grow near their thickest parts (that’s why those are the thickest parts) and mush outwards towards the edges, where the liminal areas either melt (usually seasonally) in situ or drop off into the sea.

Antarctic’s glaciers are surrounded by a number of floating ice shelves. The ice shelves are really the distal reaches of the moving glaciers floating over the ocean. This is one of the places, probably the place at present, where melting accelerated by human caused greenhouse gas pollution occurs. The ice shelves are fixed in place along their margins (they typically cover linear fjord like valleys) and at a grounding point underneath the shelf some distance form the ice margin but under sea level.

The collapse or disintegration of an ice shelf is thought to lead to the more rapid movement of the corresponding glacial mass towards the sea, and increased melting. This is the big problem right now with estimating the rate of glacial melting in the Antarctic. This is not a steady and regular process, as rapid disintegration of an ice shelf is possible. Most likely, Antarctic glacial melting over the coming decades will involve occasional catastrophic of an ice shelf followed by more rapid glacial melting at that point.

Unfortunately, the ice shelves are generally becoming more vulnerable to this sort of process, a new study just out in Science shows. From the abstract:

The floating ice shelves surrounding the Antarctic Ice Sheet restrain the grounded ice-sheet flow. Thinning of an ice shelf reduces this effect, leading to an increase in ice discharge to the ocean. Using eighteen years of continuous satellite radar altimeter observations we have computed decadal-scale changes in ice-shelf thickness around the Antarctic continent. Overall, average ice-shelf volume change accelerated from negligible loss at 25 ± 64 km3 per year for 1994-2003 to rapid loss of 310 ± 74 km3 per year for 2003-2012. West Antarctic losses increased by 70% in the last decade, and earlier volume gain by East Antarctic ice shelves ceased. In the Amundsen and Bellingshausen regions, some ice shelves have lost up to 18% of their thickness in less than two decades.

This is one of many reasons that even the most extreme of the IPCC estimates of ice loss (generally) and its contribution to sea level rise have to be seen as a lower limit. This is a substantial change, and it is very recent. It isn’t just that the ice sheets have gotten thinner, but also, that the rate of melting at these margins is increasing.

Scripps Institute of Oceanography:

A new study led by Scripps Institution of Oceanography at UC San Diego researchers has revealed that the thickness of Antarctica’s floating ice shelves has recently decreased by as much as 18 percent in certain areas over nearly two decades, providing new insights on how the Antarctic ice sheet is responding to climate change.

Data from nearly two decades of satellite missions have shown that the ice volume decline is accelerating, according to a study published on March 26, 2015, in the journal Science and supported by NASA. Scripps graduate student Fernando Paolo, Scripps glaciologist Helen Amanda Fricker, and oceanographer Laurie Padman of Earth & Space Research (a non-profit institute specializing in oceanography research) constructed a new high-resolution record of ice shelf thickness based on satellite radar altimetry missions of the European Space Agency from 1994 to 2012.

Merging data from three overlapping missions, the researchers identified changes in ice thickness that took place over more than a decade, an advancement over studying data from single missions that only provide snapshots of trends.

Total ice shelf volume (mean thickness multiplied by ice shelf area) across Antarctica changed very little from 1994 to 2003, then declined rapidly, the study shows. West Antarctic ice shelves lost ice throughout the entire observation period, with accelerated loss in the most recent decade. Earlier gains in East Antarctic ice shelf volume ceased after about 2003, the study showed.  Some ice shelves lost up to 18 percent of their volume from 1994 to 2012.

“Eighteen percent over the course of 18 years is really a substantial change,” said Paolo. “Overall, we show not only the total ice shelf volume is decreasing, but we see an acceleration in the last decade.”

While melting ice shelves do not contribute directly to sea-level rise, the researchers indicate that there is an important indirect effect.

“The ice shelves buttress the flow from grounded ice into the ocean, and that flow impacts sea-level rise, so that’s a key concern from our new study,” said Fricker.

Under current rates of thinning, the researchers estimate the ice shelves restraining the unstable sector of West Antarctica could lose half their volume within the next 200 years.

7 Responses to “Antarctic Ice Shelf Melt Accelerating”

  1. dumboldguy Says:

    Great graphic, great source quotes.

    Can you say “tipping point”, children? Or “likely to be irreversible”? Or “cascading effects and feedbacks”?

    Can you bend over and kiss your butt goodbye? You have some time to practice that move, or at least it appears that way today. Stay tuned, things may change rapidly.

  2. Richard Says:

    I doubt there’s any cause for humans to worry about what Earth will be like in 200 years. I think it’s highly unlikely the species will last that much longer.

    • dumboldguy Says:

      200 years? Don’t be so quite so pessimistic. Estimates I have seen range widely, but BAU may take as long as 1 or 2 thousand years before the really bad SHTF and begins to impact human populations heavily, and anywhere from 1/2 billion to 2-3 billion humans may survive.

      It all depends on when we hit the tipping points, how powerful the positive feedbacks may be, and whether we will be able to reverse or mitigate any of it. Read Gilding’s “The Great Disruption”.

  3. redskylite Says:

    The Scripps Institution of Oceanography at UC San Diego researchers are using the emotive words rapidly and acceleration, and please note Mr. A.Watts that they are esteemed scientists and certainly not alarmist/warmists.

    They are basing their observation (that some Antarctic ice shelves have thinned by nearly 20% over nearly 2 decades) and language in their report on empirical scientific monitoring instruments, not palaeontology proxies or computer modelling, which some are very mistrustful of. I have to agree with DOG that NASA should divert it’s capital to the study of our own terrestrial sphere, we no longer have the time and luxury to explore the wonders outside.

    This is not caused or explainable by decadal cycles such as AMO cycles (note to Ms. Curry), this is irreversible (at least until the next glaciation period in the next Milankovitch Cycle), and recently there has been some questions on that.

    This week has been very significant and makes the case for an Abrupt Climate Change early warning system even stronger.

    Wikipedia – “Early warning is a major element of disaster risk reduction. It prevents loss of life and reduces the economic and material impact of disasters. To be effective, early warning systems need to actively involve the communities at risk, facilitate public education and awareness of risks, effectively disseminate messages and warnings and ensure there is constant state of preparedness. A complete and effective early warning system is more than about supporting the prediction of catastrophic environment events, it supports four main functions, spanning a knowledge of the risks faced through to preparedness to act on early warning.”

    “Study Raises Questions About the Cause of Global Ice Ages”

    • redskylite Says:

      Whether you are a denier, contrarian or respect the consensus of Earth Scientists, this must make sense to all visions, sensibilities and beliefs. It is just plain common sense.

      “Must abrupt changes always be surprises? Certainly not. As knowledge of the tipping points in natural and human systems improves, an early warning system can be developed.
      Careful and vigilant monitoring, combined with a constantly improving scientific understanding of the climate system, can help society to anticipate major changes before they occur.”

      “This report, sponsored by the US intelligence community, the National Oceanic and Atmospheric Administration, the National Science Foundation, and the National Academies, examines current
      knowledge about the likelihood and timing of potential abrupt changes, discusses the
      need for developing an abrupt change early warning system to help anticipate major
      changes before they occur, and identifies the gaps in the scientific understanding and
      monitoring capabilities.”

      “To address these needs the Committee recommends development of an Abrupt
      Change Early Warning System (ACEWS). Surprises in the climate system are inevitable:
      an early warning system could allow for the prediction and possible mitigation of such
      changes before their societal impacts are severe.”

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