Commentaire invité par David Vaughan
Le recul récent des plate-formes glaciaires de la Péninsule Antarctique a été largement attribué au réchauffement des témpératures atmosphériques. Cependant, peu de travaux se sont intéressés a la réponse des positions de la large des glaciers a ce changement climatique régional. Dans l’article Retreating Glacier Fronts on the Antarctic Peninsula over the Past Half-Century publié cette semaine dans Science, nous avons présenté de nouvelles données qui décrivent les tendances de 244 fronts de glaciers marins de la Péninsule Antarctique au cours des 50 dernieres années. Les données proviennent de plus 2000 photographies aériennes et images satellites de la Péninsule Antarctique, et représentent plus de trois années de travail par Alison Cook. Ce travail a été effectué au British Antarctic Survey, mais a été financé par l’US Geological Survey, dans le cadre plus général d’un programme de cartographie des changements de la cote Antarctique.
L’analyse de ces données montre que 87% des glaciers ont reculé (cliquer sur l’image pour plus de détails) et que ce changement de l’avance au recul s’est produit progressivement en corrélation avec la latitude. Dans les années 1950, seuls les glaciers les plus septentrionaux apparaissaient en recul, mais une transition de l’avance des glaciers a un recul a progressivement migré vers le Sud de la Peninsule Antarctique au cours d’une période d’environ 10 a 20 ans, en accord avec l’hypothese que ces mesures refletent le réchauffement mesuré dans cette zone. Néanmoins, certaines caractéristiques des changements sont difficilement attribuables au seul réchauffement atmosphérique. En particulier, au cours de la période allant de la fin des années 1980 au début des années 1990, le recul s’est généralement ralenti, sans qu’il n’y ait de changement associé dans les enregistrements de température – observation impliquant que d’autres facteurs sont également en jeu comme peut etre la température de l’océan.
Le recul de ces glaciers aura un effet négligeable sur le niveau marin global, comme la plus grande partie de la glace qui a reculé était déja dans l’eau. Cependant, si en réponse au raccourcissement des glaciers ceux-ci accélerent leur vitesse de progression, alors ceci impliquerait une (petite) hausse du niveau marin. Cette suggestion est ce que nous étudions actuellement, et nous la documenterons prochainement.
Référence: Retreating Glacier Fronts on the Antarctic Peninsula over the Past Half-Century A. J. Cook, A. J. Fox, D. G. Vaughan, J. G. Ferrigno, Science, Vol 308, Issue 5721, 541-544 , 22 April 2005 [DOI: 10.1126/science.1104235]
Voir également RealClimate post on Antarctic temperature change.
Note: Cet article (et”RealClimate.org”) ont été discutés “Climate Change Update” sur NPR’s “Science Friday” (en anglais: audio ici).
Le Monde présente également un article sur ce travail : ici, ainsi que Le Nouvel Observateur : ici.
15 Responses to "Recul du Front des Glaciers de la Péninsule Antarctique au cours des 50 dernières années"
Tom easley says
Given the one percent rise of temperature over the last century is an “average”, and the Arctic and Antarctic regions are now warming faster, purportedly by up to eleven degrees, there must be areas that are now cooler. Where are the areas of the earth that are cooler? Why are they cooler?
[Response: I’m not quite sure where the 11 degrees comes from. The Peninsula is warming very fast, especially in winter, up to 1oC/decade – here. But that pic also shows the smaller (or -ve) trends elsewhere in Antarctica. Globally, look at http://www.cru.uea.ac.uk/cru/climon/data/tgrid/2004/7.gif and other pics from there. A strong positive in one region doesn’t need to be balanced by -ve’s elsewhere, just by weaker positives. And what causes some regions to show cooler? Natural variability: we expect (given a global warming trend) local/regional random variations year-to-year – William
Presumably this commentor’s statement about 11 degrees comes from the media hype surrounding some climate model results, which we discussed earlier — here. He/she should also look at the earlier post on Antarctic temperature variability, here. — eric
Stephen Berg says
“Where are the areas of the earth that are cooler? Why are they cooler?”
I would guess that marine areas adjacent to higher glacial melt would be these “cooler” areas, due to waters in the area being newly melted from glaciers. This cool new meltwater would then take in some of the heat from the air above, leaving this air cooler and the water just slightly warmer than before. (This is sensible heat transfer, am I right? Heat transfer from a warm body to a cool body by conduction?)
Although I heard the audio from Science Friday, I am hampered in that I cannot access the article in Science is based on, so take this with a grain of salt.
When Vaughn says that the West Antarctic glaciers are in retreat, does he mean that the fronting ice shelves are in retreat? or the glaciers themselves? If the former, then that would mean that the land-based glaciers would eventually no longer be buttressed by the ice shelves and their flow would empty right into the sea, increasing GSLR. This happens as the ocean undermines the land-sitting glaciers right at the waterline causing the glaciers to detach from the bedrock on which they are sitting. In addition, it is my understanding that much of the peninsula itself is actually below sea-level. Also, there is some evidence that what happens at the front of such glaciers can affect the “back” (inland) parts of the glaciers increasing glacial flow toward the ocean. This has been observed in the glaciers fronting the Amundsen Sea (Pine Island, etc.).
As to causes, natural variability is not ruled out but Vaughn states that there is evidence that some of the disappearing ice (shelves) have been there for thousands of years – this would appear to undermine arguments for a short-term natural cycle. If the peninsula is heating up at 1C/decade (cited by William), I wonder when we can expect this glacial ablation to affect sea-level rise. More dramatic events like detachment of the Larsen B ice shelf seem to plausibly lie in the future.
I found an article via Google’s news service which referenced this study. If you could, I would like to hear some informed commentary on it. I noted that the author works for the CATO Institute, and thus I immediately came here to ask about it.
[Response:The TCS peice isn’t very good. Citing MC, as someone else pointed out, is a poor start. Claiming that Antarctic-as-a-whole temperatures have declined isn’t a great continuation either: see http://www.nerc-bas.ac.uk/public/icd/gjma/trends2004.col.pdf for a piccy from station data. The total picture is complex – see the prev RC post – but yes, the Peninsula is the place with by far the strongest trends, and they are for warming. The figure in the TCS piece, from Doran et al, is… not very good. But: it is fair to say that the vital disctinction – that the paper was about the Peninsula glaciers – was lost on some of the worlds press – W]
Michael Jankowski says
The author at TCS is not contesting the paper published in Science. What he’s complaining about is a headline that took the study results and implied something greater (such as glaciers melting across the entire continent). And as he pointed-out, much of the rest of Antarctica hasn’t seen the warming that this penninsula has.
He also complains that the authors/Science made no mention of the studies concerning the rest of Antarctica, and I see his point. Personally, I would’ve included (or required) wording as such in the background info and possibly the conclusions to put the results of the study in the proper context.
Stephen Berg says
Authors Cook and Dr. Vaughan were on the CBC’s “Quirks and Quarks” radio show this past Saturday. Here is an excerpt of their segment:
A description of the show can be found here:
Steve Bloom says
Re #5: To understand this issue, you need to read the prior RC article (the second linked reference at the end of this article) *and* all of its linked references. There is no substitute for a little homework, and in any case it’s unfair to the RC authors to ask them to simply repeat or restate information that’s already been provided.
Re #6: I don’t believe Michaels is taken seriously in the scientific community. His favorable reference to “State of Fear” is a dead giveaway, as is his broad-brush scathing dismissal of the scientific consensus on human-caused climate disruption.
In any case, why should the Science article’s references be limited to just the purported cooling in the main part of Antarctica? What about all the melting ice *everywhere else on the planet*?
John Booth says
Very interesting piece. I look forward to reading it in Science. A couple of questions immediately came to mind that perhaps someone can answer.
Is the determination of glacier recession based solely on interpolation of aerial and satelite images?
If so, does the report detail how scaling, viewing angle, and sea level were accounted for?
alex kahl says
Has anyone else been following Elizabeth Kolbert’s series in the New Yorker? Although she is a political correspondent, her work usually includes the interaction of science and politics. She was the New Yorker reviewer of Crichton’s book back in December. Anyways, I have found the first two parts of her series to be enjoyable even though I was highly skeptical at the outset (as I am with any mainstream presentation of the climate change science). The first two parts of her series seem to be the type of writing that we really need to bring the mounting evidence of anthropogenically induced climate change into the public arena… without contention. I am curious what other folks think about the series thus far. The first part is available here at the New Yorker magazine’s website. As a grduate student studying the export flux of biogenic particles from the ocean’s surface, I have been pleasantly surprised with the breadth of scientific evidence she has brought together. Plus, she seems to have given the appropriate credit where it is due by citing Manabe (among others) for early climate modelling and Broecker for his conceptualization of the conveyor belt (as two of many examples).
Brad Westervelt says
“…In particular, there was a period in the late-1980s and early-1990s when retreat slowed down along most of the coast, and we don’t see any cause for this in the temperature records – so there may be some other factors at work, perhaps ocean temperature.”
Perhaps the elsewhere discussed “global dimming” phenomena: airborne particulate from volcanoes, unusual storms or other factors during said period reducing the cumulative light energy worldwide.
[Response: Global dimming is mostly associated with anthropogenic aerosols, and in the southern hemisphere these are in pretty short supply… -gavin]
stephan harrison says
Response to Number 11: Could this slowing of glacier recession be related to changes in precipitation? In Patagonia we noticed a short readvance within a general recession phase of the outlet glaciers around the early 1990s. The glaciers were probably responding to a marked increase in precipitation in the region in the 1970s and 1980s and I think a similar situation has occurred in parts of New Zealand.
Joseph O'Sullivan says
Michaels on the TCS website is referring to an AP article. The article is at:
RealClimate has mentioned Patrick Michaels on the Jan 20 post Peer Review: A Necessary but not Sufficient Condition and TCS on the Feb 8 post Strange Bedfellows.
Bringing up Michaels employment with Cato is important. Cato and TCS are political advocacy groups as are many of these think-tanks. They advance conservative and corporate political agendas. That is why conservative foundations and industry fund them. For examples see:
Being politically active for conservatives, industry, environmentalists or any other group is not a bad thing. Any political advocacy group has an agenda and when evaluating their messages about climate change science it is important to examine how they advance this agenda. Every political group uses spin to try to persuade the public, but Cato and TCS are some of the groups that use what can be called extreme tactics in the climate change science debate.
Cato and TCS are hostile to environmental regulation. Current environmental regulations were passed after environmental groups ran political campaigns that reflected the public’s call for action addressing environmental problems. Conservatives and industry were stung by these political defeats. Noting the success of environmentalists, conservatives and industry founded their own political advocacy groups like Cato and TCS to oppose environmental regulation.
Cato, TCS and other groups are waging a public relations campaign against environmental regulation. For example:
http://www.cato.org/pub_display.php?pub_id=3030 (Michaels makes a dubious claim that environmental regulations will cause human suffering and even deaths)
Because science, when objectively examined, often supports environmental regulation science and scientific institutions have also been subject to criticism. For example:
http://www.cato.org/pub_display.php?pub_id=2620 (Michaels claims the Journal Nature is “deceptive”, “outlandish” and publishes “junk science” about climate change)
http://www.cato.org/pub_display.php?pub_id=3358 (Michaels calls the AAAS a “lobbying organization”, claims the Journal Science “only accepts one side of the global warming story” and “they go a little overboard in their one-sided zeal”)
The goal of Cato and other similar groups is to publicly cast doubt on the science so the public will not support climate change legislation. Without public support it is unlikely any climate change regulation will be enacted. Even conservative politicians who support climate change legislation have been targeted. For example:
http://www.cato.org/pub_display.php?pub_id=2879 (Michaels criticizes Senator McCain’s proposed climate change regulations as a political ploy)
The claims about climate change science on the Cato and TCS websites have questionable scientific value. Most of these claims are political attacks that promote a partisan agenda and are not objective information about climate change science.
Michaels is openly in the political arena and his statements on the Cato and TCS websites show this. He is interested in political actions that are based on climate change science. Concern about policies based on science is understandable and can be used to create better policies, but in Michaels case it has affected his objectivity.
Michael Jankowski says
Global context would certainly be welcomed in background and/or conclusion sections, but regional context is important, IMHO (and absolutely necessary if global references are included), especially on a topic like climate change.
Michaels may get attacked a lot from the AGW crowd, but if that blinds people from looking objectively at the points of his commentary, then they have a serious prejudices to overcome.
I don’t see Michaels’ reference to “State of Fear” as damning, and I’m assuming Crichton had thorough references to support it based on what I’ve heard of the book. If anything, it’s a stretch in that same statement for Michaels to say that “every scientist” knows that the average temp across Antarctica has been declining for decades. Michaels’ then summarizes a 2002 Nature article as supporting information (I guess for those TCS readers who either aren’t scientists or who haven’t read Crichton’s book).
I think Michaels’ points are valid about (1) hysterical media headlines and (2) lack of regional context in the Science article. I don’t quite like the summary Michaels provides of the 2002 Nature article because it is a simple beginning-to-end trend. Way too often I’ve seen cherry-picked bookends, and even legitimate bookends can conceal important trends within. But maybe that’s all Michaels’ had to work with from the Nature article and/or TCS space limitations and not his fault.
Just for the record, I’m not associated with Cato, TCS, or any other politically-related group.
Hank Roberts says
Useful debunking here, from a pointer I found at the public health weblog
The Real Junk Science
George Monbiot, AlterNet
Posted on May 14, 2005, Printed on May 16, 2005
QUOTE (my excerpts)
… For the past three weeks, a set of figures has been working a hole in my mind. On April 16, New Scientist published a letter from the famous botanist David Bellamy. Many of the world’s glaciers, he claimed, “are not shrinking but in fact are growing. … 555 of all the 625 glaciers under observation by the World Glacier Monitoring Service in Zurich, Switzerland, have been growing since 1980.”
His letter was instantly taken up by climate change deniers. And it began to worry me. What if Bellamy was right? ….
for the same data can be found all over the internet. They were first published online by Professor Fred Singer …. They are constantly quoted as evidence …. Singer cites half a source: “a paper published in Science in 1989.” ….
I went through every edition of Science published in 1989, both manually and electronically. Not only did it contain nothing resembling those figures; throughout that year there was no paper published in this journal about glacial advance or retreat…..
END QUOTE, see original for full content