The Wilkins Ice Shelf Breakup: Natural Processes or Climate Alarmism?

Ian Read is a researcher, author and geographer with a special interest in climatology and vegetation. He has written over twelve books including The Bush: A Guide to the Vegetated Landscapes of Australia, and Australia: The Continent of Extremes – Our Geographical Records. Thank you, Ian, for offering your article to Webdiary.

The Wilkins Ice Shelf Breakup: Natural Processes or Climate Alarmism?
by Ian Read

In July 2009 Senate Foreign Relations Committee convenor Senator John F Kerry of Massachusetts stated:

We are here today to discuss a grave and growing threat to global stability, human security, and America’s national security. As you will hear from all of today’s witnesses, the threat of catastrophic climate change is not an academic concern for the future.
It is already upon us, and its effects are being felt worldwide, right now. Earlier this year, a 25-mile wide ice bridge connecting the Wilkins Shelf to the Antarctic landmass shattered, disconnecting the Shelf from the Antarctic continent. In four years, the Arctic is projected to experience its first ice-free summer – not in 2030, but in 2013. The threat is real and fast approaching.¹

In March 2008 a joint press release from the United States National Snow and Ice Data Center (NSIDC), the British Antarctic Survey (BAS) and the Earth Dynamic System Research Center EDSR) in Taiwan stated:

Satellite imagery from the National Snow and Ice Data Center at the University of Colorado at Boulder reveals that a 13,680 square kilometer (5,282 square mile) ice shelf has begun to collapse because of rapid climate change in a fast-warming region of Antarctica²[author’s emphasis].

The Wilkins Ice Shelf is a broad plate of floating ice, possibly grounded on its continental margin, covering an area of 13,680sqkm. On 28 February 2008 satellite images showed that a large iceberg 41km long and 2.5km wide became detached from the ice shelf on its exposed south western side, triggering a disintegration of 406sqkm (2.97%) of the shelf behind the detached iceberg, as indicated by the sky-blue patterns of upturned glacial ice. Associate Professor Cheng-Chien Liu, of Taiwan’s National Cheng-Kung University, described the iceberg calving as, “if something is slicing the ice shelf piece by piece on an incredible scale, kilometers long but only a few hundred meters in width.”³

The spectacular photographic footage of this event showed the hundreds of metres-deep ice cleaved with perpendicular sides, the sign of a structural breakage or sheer failure. NSIDC Lead Scientist Ted Scambos, at the time was reported to have said that, “we believe the Wilkins has been in place for at least a few hundred years. But warm air and exposure to ocean waves are causing a break-up”, to which he added, “The Wilkins is an example of an event we don’t see very often. But it’s a key process in being able to predict how sea level will change in the future.”⁴

This statement is telling: the press release at the time described the shelf as permanent while the quoted lead scientist qualifies that to a “few hundred years”, which is wrong as we shall see; at the same time he suggests that warm air and ocean wave action were the cause of the break up – only the ocean wave action can be substantiated; that the partial break-up is predictive in assessing sea level change – also wrong – ice shelves float, adding nothing to sea levels on disintegration or melting.

If warm air was involved then the calved berg would not display the precise structural cleavage as shown in the footage but rather the signs of melting: an uneven surface of wet hollows and cupola formations with visible pools of meltwater. Furthermore, warm air can only melt the upper and other exposed surfaces with a slow downwards melting as the upper melted surfaces drain away – it is inconceivable that warm air played any part given the ice shelf’s location, the shortness of the summer thawing season, and the fact that the above freezing temperatures required for melting would be of insufficient duration to affect ice of this thickness.

Ice shelves calve icebergs, a well-known and observed physical phenomenon. In part, this is due to the continuous movement of mainland ice sheet glaciers towards and over the coast (where it forms ice shelves) whereupon meeting the surrounding ocean, especially in the short summer season when sea ice is at its minimum or non-existent, they are subjected to ocean currents, and wind and wave action. As the icebergs calve they initially exhibit the clear structural cleavage of ice before drifting upon the currents, melting as they enter warmer waters and air.

Additional to this calving process is the effect that precipitation has upon an ice shelf attached or grounded to land on its continental side, its oceanic side floating upon the sea. With an estimated 200mm per annum precipitation, mainly falling as snow, in coastal Antarctica (equivalent to 20m per century) there is an additional 18 million tonnes per square kilometre weight added to the ice shelf every century, sufficient to cause a floating mass of ice to sink 18m per century as the ice adjusts itself to its equilibrium with the water.

A grounded ice shelf on its continental margin is unable to readily adjust its equilibrium with water, the effect of leverage over time resulting in a structural breakage or cracks – this influence is likely to be exacerbated by additional pressures exerted during the expansion in the surrounding sea ice over the winter season. Such a structural breakage can occur at any time of the year but during the short summer season, when the surrounding sea ice pack at its lowest extent, the ice shelf itself is likely to be exposed to the impact of wave action, especially on the exposed side of the Antarctic Peninsula that protrudes northwards into the Antarctic Circumpolar Current. Due to this exposure the western Antarctic Peninsula is prone to regular ice shelf break-up, especially as the circumpolar current brings with it warmer seawater originating in the sub-tropical western Pacific Ocean (STWP) lying east of the Queensland coast of Australia and north of New Zealand.

Given the exposure of the western Antarctica Peninsula, the dynamics of ice shelf break-up, the paucity of direct observations, and the short period of satellite imagery (around 30 years), the observation record is too short to assume that the partial Wilkins Ice Shelf break-up is anything but a natural process – there is no direct evidence that AGW was involved.

Rather than issuing a press release that seeks to attribute a natural process to AGW, thereby causing alarm when the joint NSIDC-BAS-EDSR press release is filtered by the media without full explanation, the press release would have been more honest if it had said that they did not know what caused the Wilkins Ice Shelf disintegration but from a study of the physical geographical processes involved then it is likely that increased pressure from an expansion in sea ice during the 2007 winter, combined with additional precipitation accumulating as ice on the ice shelf’s surface, thereby increasing its weight and altering its equilibrium, caused a structural crack in the ice bridge that was holding back that part of the ice shelf that had suffered partial disintegration the previous autumn. By March of 2008, when the sea ice was at it lowest extent (the western side of the Antarctic Peninsula is normally sea ice free during the short summer and may remain relatively free during the colder months due to the warming influence of the Antarctic Circumpolar Current), the exposed and cracked ice bridge was subjected massive oceanic swells as well as other tidal and wind influences, acting in concert with the warmed partially STWP-derived circumpolar current as it passed the western Antarctic Peninsula, an area well-known for ice shelf disintegration.

Satellite images have shown that the Wilkins and other ice shelves of the western Antarctic Peninsula are subjected to these natural processes on an almost annual basis, suggesting that NSIDC Lead Scientist Ted Scambos’ quoted statement above is incorrect in regard to the Wilkins Ice Shelf being permanent and that such an event is something not often seen.

To its credit the joint NSIDC-BAS-EDSR press release did state that there is no threat that the ice shelf disintegration will in any way allow the Western Antarctic ice sheet outlet glaciers (or ice streams) to enter the ocean (unlike the mass media-filtered versions that hinted that this was a possibility), thereby raising sea levels. This is due to the relatively small size of the shelf affected (around 3%), the fact that the Wilkins Ice Shelf lies between two offshore islands off the west coast of the Antarctic Peninsula, and is some hundreds of kilometres north of the outlet glaciers of the West Antarctic ice sheet.

It is therefore alarming, and dishonest, that in March 2009, similar reportage once again cited the disintegration of the Wilkins Ice Shelf using the same information and imagery, as was used in the 2008 coverage, with no explanation as to why the same information from the year before was used.⁵

On 26 March 2008, MSNBC’s website had the headline, “Vast Antarctic ice shelf on verge of collapse”, with the byline, “Latest sign of global warming’s impact shock scientists”. The article by Andrea Thompson stated that, “a vast ice shelf hanging on by a thin strip looks to be the next chunk to break off from the Antarctic Peninsula, the latest sign of global warming’s impact on Earth’s southernmost continent” [author’s italics]. On 5 April, 2009, the guardian.co.uk website headlined a story by Paul Harris in New York with, “Antarctic ice shelf half the size of Scotland on verge of collapse” that followed with the statement that, “a huge ice shelf in the Antarctic is in the last stages of collapse and could break up within days in the latest sign of global warming’s impact on Earth’s southernmost continent” [author’s italics]. These are just two examples of the hundreds of stories in the mass media that simply reiterated the same exaggerated news from the year before, putting pay to the lie of the independence of the media.

Both articles, more than 12 months apart used the identical British Antarctic Survey’s (BAS’s) Jim Elliot’s dramatic photograph of the cleaving of the Wilkins iceberg mentioned above. On 25 March, 2008, National Geographic News reported the same story with a quote from NSIDC’s Ted Scambos, mentioned above, being reported as saying, “[It’s] an event we don’t get to see very often.” This is disingenuous. A Google search of ‘Ted Scambos and Wilkins Ice Shelf’ comes up with nearly 5,000 results, one of which is this quote, attributed to Ted Scambos, dated 1999, saying, “On the southwest side of the peninsula, the Wilkins ice shelf retreated nearly 1,100 square kilometers in early March of last year [1998] . . . Within a few years, much of the Wilkins ice shelf will likely be gone”.⁶ A comparison of satellite photographs between January 1996 and March 2008 shows very little variation in the extent of the Wilkins ice shelf with historical satellite images of the ice shelf showing that, “the disintegration/re-growth is an annual event (winter ice re-growth season; summer melt season)”.⁷

Assumptions regarding the Wilkins ice shelf disintegration due to increasing atmospheric temperatures or global warming are also not substaniated by reference to the historic temperature data at Rothera Point, the nearest weather station to the Wilkins Ice Shelf, with a record going back to the 1940s. Average January temperatures hover between 0ºC and 2ºC with no increase in averages over that time, just a relatively cooler period in the 1960s and 70s, and a relatively warmer period in the 1980s and 90s that closely matches temperature variability over similar time frames measured elsewhere, presumably in response to changes in the Pacific Decadal Oscillation alternating between its ‘cool’ and ‘warm’ modes.

With the recent scoping studies for the proposed 5^th Intergovernmental Panel on Climate Change report due out in 2014 suggesting a downplaying of the role of anthropogenic carbon dioxide as a significant driver of (catastrophic) climate change it is time that scientists can speak and publish freely without suffering ad hominem attacks (or threats to funding) and that the media (and blog sites) report their findings honestly and accurately. This is very important for the citizenry is not always able to differentiate between science and advocacy, the implications of which, as regards policy development in term of climate change mitigation, are likely to have a profound effect on society.

References

1. http://www.boston.com/news/politics/politicalintelligence/2009/07/kerry_panel_loo.html

2. Antarctic Ice Shelf Disintegration Underscores a Warming World http://nsidc.org/news/press/20080325_Wilkins.html

3. ibid.

4. ibid.

5. http://wattsupwiththat.com/2009/04/17/the-antarctic-wilkins-ice-shelf-collapse-media-recycles-photos-and-storylines-from-previous-years/

6. http://www.heatisonline.org/contentserver/objecthandlers/index.cfm?ID=3209&Method=Full&PageCall=&Title=Antarctic%20Ice%20Shelf%20Break-Up%20Accelerates&Cache=False

7. http://www.appinsys.com/GlobalWarming/AntarcticWilkinsIceShelf.htm