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West Antarctica warming more than expected

Posted on 25 December 2012 by John Hartz

This is a reprint of a news release posted by the National Center for Atmospheric Research (NCAR) on Dec 23, 2012.

In a finding that raises further concerns about the future contribution of Antarctica to sea level rise, a new study finds that the western part of the continent’s ice sheet is experiencing nearly twice as much warming as previously thought.

Map of WAIS Temp Correlation with Byrd Station

Researchers have determined that the central region of the West Antarctic Ice Sheet (WAIS) is experiencing twice as much warming as previously thought. Their analysis focuses on the  temperature record from Byrd Station (indicated by a star), which provides the only long-term temperature observations in the region. Other permanent research stations with long-term temperature records (indicated by black circles) are scattered around the continent. On this map, the color intensity indicates the temperature correlation with the measurements at Byrd Station. (Image by Julien Nicolas, courtesy of Ohio State University.)


The temperature record from Byrd Station, a scientific outpost in the center of the West Antarctic Ice Sheet (WAIS), demonstrates a marked increase of 4.3 degrees Fahrenheit (2.4 degrees Celsius) in average annual temperature since 1958. The rate of increase is three times faster than the average temperature rise around the globe for the same period.

The study was published Sunday in the journal Nature Geoscience. It was conducted by scientists at Ohio State University (OSU), the National Center for Atmospheric Research (NCAR), and the University of Wisconsin-Madison, with funding coming from the National Science Foundation, which is NCAR’s sponsor.

"Our results indicate that temperature increases during the past half century have been almost twice what we previously thought, placing West Antarctica among the fastest warming regions on Earth,” says NCAR scientist Andrew Monaghan, a co-author. “A growing body of research shows that the West Antarctic Ice Sheet is changing at an alarming rate, with pressure coming from both a warming ocean and a warming atmosphere.”

This study reveals warming trends during the summer months of the Southern Hemisphere (December through February), notes co-author David Bromwich, professor of geography at Ohio State University and senior research scientist at the Byrd Polar Research Center.

“Our record suggests that continued summer warming in West Antarctica could upset the surface mass balance of the ice sheet, so that the region could make an even bigger contribution to sea level rise than it already does,” Bromwich says.  “Even without generating significant mass loss directly, surface melting on the WAIS could contribute to sea level indirectly by weakening the West Antarctic ice shelves that restrain the region’s natural ice flow into the ocean.”

Researchers consider the WAIS especially sensitive to climate change because the base of the ice sheet rests below sea level, making it vulnerable to direct contact with warm ocean water. Its melting currently contributes 0.3 millimeters to sea level rise each year. This is second only to Greenland, whose contribution to sea level rise has been estimated as high as 0.7 mm per year.

Filling in the data gaps

Due to its location some 700 miles from the South Pole and near the center of the WAIS, conditions at Byrd Station are an important indicator of climate change throughout the region.

In the past, researchers haven’t been able to make much use of the Byrd Station measurements because of incomplete temperature observations. Since its establishment in 1957, the station has not been occupied continuously. A year-round automated station was installed in 1980, but it has experienced frequent power outages, especially during the long polar night when its solar panels can’t recharge.

The new study fills in the data gaps with a powerful computer model of the atmosphere and a numerical analysis method

In addition to offering a more complete picture of warming in West Antarctica, the new study shows for the first time that significant melt is occurring during summer.  Monaghan says the summertime warmth is particularly troubling because that is the season in which enhanced surface melting could most affect the WAIS and potentially weaken the ice shelves that buttress it.

“We've already seen enhanced surface melting contribute to the breakup of the Antarctic’s Larsen B Ice Shelf, where glaciers at the edge discharged massive sections of ice into the ocean that contributed to sea level rise,” he says. “The stakes would be much higher if a similar event occurred to an ice shelf restraining one of the enormous WAIS glaciers."

“West Antarctica is one of the most rapidly changing regions on Earth, but it is also one of the least known,” says Bromwich. “Our study underscores the need for a reliable network of meteorological observations throughout West Antarctica, so that we can know what is happening—and why—with more certainty.”


 
Subject Paper: Central West Antarctica among most rapidly warming regions on Earth

Authors: David H. Bromwich, Julien P. Nicolas, Andrew J. Monaghan, Matthew A. Lazzara, Linda M. Keller, George A. Weidner, and Aaron B. Wilson 
 
Publication: Nature Geoscience(2012,)doi:10.1038/ngeo1671

Received 02 May 2012, Accepted 15 Nov 2012, Published online 23 Dec 2012


Note: The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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Comments

Comments 1 to 7:

  1. Speaking as someone who knows nothing about the NCAR study besides what's here, and couldn't evaluate it even if he read the whole thing, I wonder if the much-processed instrumental record of a single site can bear the weight of the reinterpretation. How can West Antarctica warm so much more than East Antarctic coastal areas that are much further north? Is it elevation?

    I also don't understand the map. Does the color show temperature (per the caption) or temperature correlation (per the legend at right), and if the latter, what are the units? And why is the Antarctic Peninsula showing up with the dark blue of least warming/least correlation?
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  2. Philip Cohen @1, the map shows only correlation to Byrd Station temperature anomalies. It does not show temperature increases at all. Indeed, when Byrd Station temperatures are falling, bright red portions of the map will also, most probably, be falling as well. In that respect, the caption attached to the map is simply wrong, and contradicts the legend provided within it.

    William Connolley discusses the BBC's use of the map at Stoat. He also presents the far more useful in his (and my) opinion figure 2 from the paper, which actually shows the reconstructed Byrd Station temperatures:



    Also of interest, from Real Climate, is this comparison of this reconstruction of Byrd Station temperatures with prior reconstructions:

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  3. As Tom Curtis @2 already noticed, the legend: "On this map, the color intensity indicates the extent of warming around Antarctica." is wrong. The figure shows the correlations of the measurements at Byrd with reanalysis data as the text at the colorbar states.

    Anyway, I would interpret this study with care. There were changes in the instrumentation and location, which may cause non-climatic temperature changes. Especially in such a hostile environment.

    The supplemental information suggests that there were only corrections for calibration problems and drift and that they did not search for inhomogeneities in the data by comparison with neighbouring stations. This may also be difficult as the figure suggests, but does not show, that the station at Byrd does not correlate well with its neighbours.

    I do not have access to the paper itself, but I would expect that there are thus likely non-climatic changes in the time series.
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  4. Here’s how Prof. Ricky Rood (University of Michigan) summarized the Bromwhcih et al paper which is the subject of the OP.

    Since this blog was first published, David Bromwich and colleagues published the paper, Central West Antarctica among the most rapidly warming regions on Earth, in Nature Geoscience. This paper is a complex study, which uses models to reconstruct and complete the temperature record in West Antarctica since the 1950s. They explain in detail their evaluation techniques and search for cause and effect of the regional warming that they find. Their ultimate conclusion is that West Antarctica is warming rapidly, especially in summer. They point to the summer of 2005, which saw significant surface ice melting, and warn that the temperature is getting to the point that melting might accelerate. This is especially significant in West Antarctica because the base of the ice sheets there are below sea level and especially vulnerable.”,

    Source: Things Going Fast, a Blog post by Dr. Ricky Rood, Weaterunderground.com, Dec 21, 2012
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  5. @Philip M Cohen #1:

    There is no discrepency between the caption under the graphic and the graphic's legend. Both use the term, "temperature correlation."

    We have invited the paper's co-author, David Bromwich, professor of geography at Ohio State University and senior research scientist at the Byrd Polar Research Center, to particpate in this discussion thread and clear-up any confusion about what the graphic portrays.
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  6. The caption did initially say it was a measure of temperature - I changed it to temperature correlation, since that's what the figure is actually showing.
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  7. I admit (and regret) that the correlation figure as it is described in the media has been a source of confusion, and the caption associated with it is sometimes downright incorrect. This was the case, in particular, for the initial version of the figure caption in the NCAR press release. Note that this caption has since been amended by NCAR to emphasize that "the color scale represents correlations, not temperatures". To clarify, in the paper we refer to the correlation map as the "footprint" of the Byrd temperature record: the orange-red areas denote where the temperature tends to vary in phase with Byrd temperature on an interannual basis (being warmer-than-normal when it's warmer-than-normal at Byrd, colder-than-normal when it's colder-than-normal at Byrd). The figure should not be interpreted - as it has often been -- as a map of the long-term temperature trends for Antarctica. Such a map is not part of our results. If it were, it would show warming in central West Antarctica, as well as in the Antarctic Peninsula.

    The fact that, in the correlation map, Byrd temperature doesn't show much of a relationship with temperature in the Antarctic Peninsula (AP) might surprise some. But it can be easily explained. For example, sea-ice conditions have a greater effect on temperatures in the AP than in the West Antarctic interior. Some seasons also show signs of anticorrelation between Byrd and the AP: some anomalies in the wind pattern over the Amundsen Sea cause more warm air advection from the north to the Byrd region, while the AP receives more cold air from the south (or vice versa). If we had temperature records that were long enough to correlate the mean decadal temperatures across Antarctica, then we expect the orange-red area in the correlation map to encompass the AP.

    David Bromwich
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    Moderator Response: [JH] Prof Bromwich: Thanks for stopping by and posting this clarification.

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