http://www.bbc.co.uk/news/science-environment-21699115quote:The glaciers of the Canadian Arctic Archipelago will undergo a dramatic retreat this century if warming projections hold true.
A new study suggests the region's ice fields could lose perhaps as much as a fifth of their volume.
Such a melt would add 3.5cm to the height of the world's oceans. Only the ice of Greenland and Antarctica is expected to contribute more.
The assessment is reported in the Geophysical Research Letters journal.
"This is a very important part of the world where there has already been a lot of change," said lead author Jan Lenearts from Utrecht University, Netherlands.
"And it is all the more important that we talk about it because it has been somewhat overshadowed by all the news of Greenland and Antarctica," he told BBC News.
The Canadian Arctic Archipelago is a vast area, comprising some 36,000 islands.
Being so far north, much of region - some 146,000 square km - is covered by glaciers and ice caps (a type of ice field where glaciers flow off in many directions).
Current data indicates all this ice is already thinning at a rapid rate. Gravity measurements from space suggest the annual loss since 2003 has been running at about 70 billion tonnes, and it is accelerating.
With snowfall reasonably constant over the period, it appears that melt as a result of the 1-2-degree rise in air temperatures has tipped the ice out of balance.
Arctic amplification
Dr Lenearts' team wanted to understand how this retreat might progress in the decades ahead if the warming continues.
They developed a climate computer model for the archipelago that was based on a mid-range temperature projection being used for a big upcoming UN global-climate report - the 5th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).
First of all, they ran the model backwards to check that it could accurately recreate conditions seen in the region since the 1960s.
They then ran it forwards to simulate the possible shrinking and growth of glaciers right up to 2100.
What they found was that the annual ice loss by this date would be running at about 145 billion tonnes, with the north of the archipelago, on and around the likes of Ellesmere Island, experiencing the greatest retreat.
Added to the general atmospheric warming in the region, the researchers also describe an amplification process whereby reduced snow cover on the surrounding tundra and less sea-ice in the Arctic Ocean push up temperatures still further.
This is a consequence of darker surfaces absorbing more heat from the Sun rather than reflecting it back out into space.
"What we find is that the processes that are currently ongoing will actually continue and be re-enforced, so the mass loss will increase in time," said Dr Lenearts.
"Our model estimates that in 2100, we have lost about 20% of the volume of Canadian Arctic Archipelago glaciers, which is a really large amount. It is equivalent to 3.5cm of global sea-level rise."
Similar systems
The Utrecht study was funded by the European Union's Ice2Sea project, which aims to tie down some of the major uncertainties that surround the possible contribution to ocean rise from melting in Earth's cryosphere.
Ice2Sea's project leader is Prof David Vaughan from the British Antarctic Survey.
He said the Canadian Arctic Archipelago was an important region for study because it was not very well mapped, was already experiencing major change and because in some places the ice had "its toes in the water", which meant it was subject to both atmospheric and ocean impacts.
"We've got similar systems in Alaska, in Svalbard, in Patagonia and the Russian high Arctic, and we really need to understand them better," he told BBC News.
Al zal d'r bij sommige media de nodige spin aan gegeven worden (ik denk daarbij aan Elsevier en Simon Roosendaal).quote:Op donderdag 7 maart 2013 18:20 schreef Norrage het volgende:
Het is straks waarschijnlijk ook in alle populaire media te lezen
Hij zit al de hele dag aan de telefoon
quote:Eind deze eeuw? Da 's nog 87 jaar. Kan een hoop in gebeuren. Een heel mensenleven bijvoorbeeld. Het gaat hier straks ook weer vriezen, terwijl het eind van de maand alweer zomertijd is.
Het is gewoon zielig dat wij verplicht zijn in deze samenleving te moeten leven, dat dit soort mensen rondlopenquote:Echt gelul in de ruimte dit soort uitspraken is alleen maar bedoeld om weer iets te verzinnen om geld uit onze zakken te plukken , 3,5 cm aan het eind van deze eeuw dan lig ik al 3 meter onderde grond heb ik nog een prive zwembad ook
quote:Conspiracist ideation has been repeatedly implicated in the rejection of scientific propositions, although empirical evidence to date has been sparse. A recent study involving visitors to climate blogs found that conspiracist ideation was associated with the rejection of climate science and the rejection of other scientific propositions such as the link between lung cancer and smoking, and between HIV and AIDS (Lewandowsky, Oberauer, & Gignac, in press; LOG12 from here on). This article analyzes the response of the climate blogosphere to the publication of LOG12. We identify and trace the hypotheses that emerged in response to LOG12 and that questioned the validity of the paper's conclusions. Using established criteria to identify conspiracist ideation, we show that many of the hypotheses exhibited conspiratorial content and counterfactual thinking. For example, whereas hypotheses were initially narrowly focused on LOG12, some ultimately grew in scope to include actors beyond the authors of LOG12, such as university executives, a media organization, and the Australian government. The overall pattern of the blogosphere's response to LOG12 illustrates the possible role of conspiracist ideation in the rejection of science, although alternative scholarly interpretations may be advanced in the future.
interessant. Maar het klinkt allemaal niet heel wetenschappelijk, met Google maps en zo Wat is de bron hier?quote:Op maandag 3 juni 2013 09:47 schreef aloa het volgende:
Is dit serieus. Iemand een idee?
Ik had zelf laatst ook het idee, dat de zon wel erg ver in het noordwesten onderging. (maar dat kan aan mij liggen )
Kwam het tegen op twitter.quote:Op maandag 3 juni 2013 09:50 schreef Norrage het volgende:
[..]
interessant. Maar het klinkt allemaal niet heel wetenschappelijk, met Google maps en zo Wat is de bron hier?
Deze heeft het over 260 km in een half jaar.quote:Op maandag 3 juni 2013 10:04 schreef Felagund het volgende:
De noordpool verplaatst zich ongeveer 60km per jaar, zie http://www.mnn.com/earth-(...)-might-signal-pole-r.
Wel een artikelen van een paar jaar oud, kan ook niet echt een wetenschappelijk artikel over vinden.
Ik heb het youtube filmpje niet gezien, maar er is ook al gespeculeerd dat er shift van de polen aan zitten komen en dat daardoor de noordpool zich sneller verplaatst.quote:Op maandag 3 juni 2013 10:06 schreef aloa het volgende:
[..]
Deze heeft het over 260 km in een half jaar.
Die video gaat over de magnetische noordpool, die staat los van de rotatieas van de aarde wat de baan van de zon door de hemel bepaald. Al zou het aardmagnetisch veld omflippen (wat niet zomaar even gebeurt, in tegenstelling tot wat sommige BNW-ers beweren) dan beweegt de zon bij ons nog steeds gewoon van oost naar west door de hemel.quote:Op maandag 3 juni 2013 09:47 schreef aloa het volgende:
Is dit serieus. Iemand een idee?
Ik had zelf laatst ook het idee, dat de zon wel erg ver in het noordwesten onderging. (maar dat kan aan mij liggen )
Het is helaas/gelukkig niet elk jaar een recordjaarquote:Op zondag 4 augustus 2013 19:57 schreef aloa het volgende:
Over iets meer dan een maand gaat de boel weer dichtvriezen. De lijn van nu zit hoger dan vorig jaar.
En vorig jaar was het ijs boven Canada al open.
Bron: NASAquote:'Like Butter': Study Explains Surprising Acceleration of Greenland's Inland Ice
July 24, 2013
Surface meltwater draining through cracks in an ice sheet can warm the sheet from the inside, softening the ice and letting it flow faster, a new NASA-funded study finds.
During the last decade, researchers have captured compelling evidence of accelerating ice flow at terminal regions, or “snouts,” of Greenland glaciers as they flow into the ocean along the western coast. Now, the new research shows that the interior regions are also flowing much faster than they were in the winter of 2000-2001, and the study authors propose a reason for the speedup.
“Through satellite observations, we determined that an inland region of the Sermeq Avannarleq Glacier, 40 to 60 miles from the coast, is flowing about 1.5 times faster than it was about a decade ago,” said Thomas Phillips, lead author of the new paper and a research associate at the time of the study with the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder.
The researchers used ice-sheet-wide velocity maps for Greenland from a NASA program called Making Earth System Data Records for Use in Research Environments. Studying the velocity maps, the researchers saw that in 2000-2001 the inland segment of the Sermeq Avannarleq Glacier was flowing at about 130 feet (40 meters) per year. In 2007-2008, that speed was closer to 200 feet (60 meters) per year.
“At first, we couldn’t explain this rapid interior acceleration,” Phillips said. “We knew it wasn’t related to what was going on at the glacier’s terminus. The speedup had to be due to changes within the ice itself.”
To shed light on the observed acceleration, Phillips and his team developed a new model to investigate the effects of meltwater on the ice sheet’s physical properties. The team found that percolating meltwater carries heat from the sun and warms the ice sheet, which then—like a warm stick of butter—softens, deforms and flows faster.
Previous studies estimated that it would take centuries to millennia for new climates to increase the temperature deep within ice sheets. But when the influence of meltwater is considered, warming can occur within decades and, thus, produce rapid accelerations. The paper has been accepted for publication in the Journal of Geophysical Research: Earth Surface, a journal of the American Geophysical Union.
The researchers were tipped off to this mechanism by the massive amount of meltwater they observed on the ice sheet’s surface during their summer field campaigns, and they wondered if it was affecting the ice sheet. During the last several decades, atmospheric warming above the Greenland Ice Sheet has caused an expanding area of the surface to melt during the summer, creating pools of water that gush down cracks in the ice. The meltwater eventually funnels to the interior and bed of the ice sheet.
“The sun melts ice into water at the surface, and that water then flows into the ice sheet carrying a tremendous amount of latent energy,” said William Colgan, a coauthor and adjunct research associate with the University of Colorado’s Cooperative Institute for Research in Environmental Sciences. “The latent energy then heats the ice.”
The new model shows that this speeds up ice flow in two major ways: One, the retained meltwater warms the bed of the ice sheet and preconditions it to accommodate a basal water layer, making it easier for the ice sheet to slide by lubrication. Two, warmer ice is also softer (less viscous), which makes it flow more readily.
“Basically, the gravitational force driving the ice sheet flow hasn’t changed over time, but with the ice sheet becoming warmer and softer, that same gravitational force now makes the ice flow faster,” Colgan said.
This transformation from stiff to soft only requires a little bit of extra heat from meltwater. “The model shows that a slight warming of the ice near the ice sheet bed—only a couple of degrees Celsius—is sufficient to explain the widespread acceleration,” Colgan said.
The findings have important ramifications for ice sheets and glaciers everywhere. “It could imply that ice sheets can discharge ice into the ocean far more rapidly than currently estimated,” Phillips said. “It also means that the glaciers are not finished accelerating and may continue to accelerate for a while. As the area experiencing melt expands inland, the acceleration may be observed farther inland.”
The study’s results suggest that to understand future sea-level rise, scientists need to account for a previously overlooked factor — meltwater’s latent energy — and its potential role in making glaciers and ice sheets flow faster into the world’s oceans. In 2007, the Intergovernmental Panel on Climate Change wrote that one of the most significant challenges in predicting sea-level rise was “limited” understanding of the processes controlling ice flow. The panel’s next assessment is due out in 2014.
“Traditionally, latent energy has been considered a relatively unimportant factor, but most glaciers are now receiving far more meltwater than they used to and are increasing in temperature faster than previously imagined,” Colgan said. “The chunk of butter known as the Greenland Ice Sheet may be softening a lot faster than we previously thought possible.”
The study was funded through a NASA ROSES grant, NASA’s Greenland Climate Network and the National Science Foundation. Other coauthors on the paper were CIRES Director Waleed Abdalati, who is also former chief scientist for NASA; former CIRES Director Konrad Steffen; and CU-Boulder engineering professor Harihar Rajaram.
Adapted by NASA/Maria-José Viñas Garcia
Based on press release by CIRES/Katy Human and AGU/Peter Weiss
quote:
Ja een groot verschil.quote:Op dinsdag 20 augustus 2013 19:52 schreef aloa het volgende:
Groot verschil met vorig jaar. Nog een week of 4 en dan gaat de winter weer beginnen op de noordpool. Alaska heeft inmiddels de eerste sneeuw alweer gehad.
[ afbeelding ]
Is daar ook een archief van..om het te vergelijken met voorgaande jaren?quote:Op dinsdag 20 augustus 2013 20:12 schreef barthol het volgende:
[..]
Ja een groot verschil.
Overigens zijn er ook gedetaileerdere kaarten dan de cryosphere today
De AMSR2 kaart van de Universiteit van Bremen
[ afbeelding ]
En die van de Universiteit van Hamburg
[ afbeelding ]
Afbeelding aanklikken want het zijn grote afbeeldingen
De service van de Universiteit van Hamburg is vrij nieuw (dit jaar begonnen)quote:Op dinsdag 20 augustus 2013 20:21 schreef aloa het volgende:
[..]
Is daar ook een archief van..om het te vergelijken met voorgaande jaren?
Bedankt voor de linkquote:Op dinsdag 20 augustus 2013 22:20 schreef barthol het volgende:
Ik kijk overigens ook veel op deze pagina van het Naval Research Laboratory.
En dan met name naar de animaties over de Sea Ice Thickness. (daar is ook een deel voorspelling bij want het loopt door tot enige dagen in de toekomst)
De gif animatie van de laatste 30 dagen ziet er zo uit:
[ afbeelding ]
De gif animatie van de afgelopen 12 maanden zo:
[ afbeelding ]
Forum Opties | |
---|---|
Forumhop: | |
Hop naar: |