We covered this extensively at WUWT last summer, including the “unprecedented claim” where a researcher said it was a recurring 150 year event that was ‘right on time‘. It turns out jet stream changes and thin cloud cover was the driver. Also “the analysis shows that ocean temperatures and Arctic sea-ice cover were relatively unimportant factors in causing the extra Greenland melt.”.
From the University of Sheffield
Jet stream changes cause climatically exceptional Greenland Ice Sheet melt
Research from the University of Sheffield has shown that unusual changes in atmospheric jet stream circulation caused the exceptional surface melt of the Greenland Ice Sheet (GrIS) in summer 2012.
An international team led by Professor Edward Hanna from the University of Sheffield’s Department of Geography used a computer model simulation (called SnowModel) and satellite data to confirm a record surface melting of the GrIS for at least the last 50 years – when on 11 July 2012, more than 90 percent of the ice-sheet surface melted. This far exceeded the previous surface melt extent record of 52 percent in 2010.
The team also analysed weather station data from on top of and around the GrIS, largely collected by the Danish Meteorological Institute but also by US programmes, which showed that several new high Greenland temperature records were set in summer 2012.
The research, published today in the International Journal of Climatology, clearly demonstrates that the record surface melting of the GrIS was mainly caused by highly unusual atmospheric circulation and jet stream changes, which were also responsible for last summer’s unusually wet weather in England.
The analysis shows that ocean temperatures and Arctic sea-ice cover were relatively unimportant factors in causing the extra Greenland melt.
Professor Hanna said: “The GrIS is a highly sensitive indicator of regional and global climate change, and has been undergoing rapid warming and mass loss during the last 5-20 years. Much attention has been given to the NASA announcement of record surface melting of the GrIS in mid-July 2012. This event was unprecedented in the satellite record of observations dating back to the 1970s and probably unlikely to have occurred previously for well over a century.
“Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting. These jet stream changes over Greenland do not seem to be well captured in the latest Intergovernmental Panel on Climate Change (IPCC) computer model predictions of climate change, and this may indicate a deficiency in these models. According to our current understanding, the unusual atmospheric circulation and consequent warm conditions of summer 2012 do not appear to be climatically representative of future ‘average’ summers predicted later this century.
“Taken together, our present results strongly suggest that the main forcing of the extreme GrIS surface melt in July 2012 was atmospheric, linked with changes in the summer North Atlantic Oscillation (NAO), Greenland Blocking Index (GBI, a high pressure system centred over Greenland) and polar jet stream which favoured southerly warm air advection along the western coast.
“The next five-10 years will reveal whether or not 2012 was a rare event resulting from the natural variability of the NAO or part of an emerging pattern of new extreme high melt years. Because such atmospheric, and resulting GrIS surface climate, changes are not well projected by the current generation of global climate models, it is currently very hard to predict future changes in Greenland climate. Yet it is crucial to understand such changes much better if we are to have any hope of reliably predicting future changes in GrIS mass balance, which is likely to be a dominant contributor to global sea-level change over the next 100-1000 years.”
###
In a story at RedOrbit the scientists report:
Scientists have been trying to determine what led to the 50-year-record ice melt in Greenland. In April a team of scientists wrote in the journal Nature that they determined that the ice melt could be due to thin cloud cover.
h/t to junkscience.com
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“Remember that ‘unprecedented’ Greenland ice sheet surface melt that was allegedly caused by global warming? Never mind”
How could I forget I still can’t move for tripping over sandbags !!!!
Stephen Wilde will agree with this one – it all comes back to the jet streams, Rossby waves, and the Ferrel and Hadley cells. They are influenced by the ocean heating due to short wave and ultra-violet and the modulation of the SST due to cloud cover and albedo changes.
Sigh. Yet another case of “we have no idea why it happened, we didn’t predict it, we cannot predict it, it had profound consequences, the models that should have predicted it didn’t” that still manages to avoid concluding that a) the GCMs were wrong yet again and hence cannot be trusted and b) that this wasn’t actual evidence of CAGW after all. Because even though we could not predict the diversion in the jet stream, even though we do not know exactly what caused it or what caused the causes of it or what caused the causes that caused the causes of it (iterate back to the big bang) we can of course be certain that we humans caused it with our carbon dioxide.
Is there actually any such thing as science any more. Can’t anybody say the magic words “we don’t know what caused it”, perhaps in association with “models that should have predicted it failed. Again.
I’m curious as to what the UAH or RSS LTT are going to be doing this month. Temperatures outside in Beaufort have remained (or so it seems to me) cooler than they have been for the last four years for the time of year with only a few days of hot and muggy and quite a few days of almost chilly. The water temperature is also still quite cool, and it has negatively affected the fishing quite extraordinarily compared to the last two years, at least. Even my next door neighbors, who have lived here forever and who almost never fail to catch all the fish they want have come home empty handed for pretty much the second half of May and entire month of June so far. Yes, I know, this is semi-anecdotal except that the temperatures are usually regulated by the Gulf Stream flowing up the coast only 20 miles offshore, and so when inshore temperatures remain cooler than usual one wonders what the Gulf Stream is doing. The North Atlantic SST map on the weather underground shows the coastal water still in the 70s and a lot of the Atlantic still in the 70s with only a comparatively thin plume of 80s offshore, but I can’t mentally compare this with the map on similar dates over the last few years and don’t trust my memory.
I do hope that the fishing, at least, heats up soon though. The weather can stay as cool as it likes, for summer;-).
rgb
Another Emily Latella moment.
No matter what is debunked they will continue to play the man-made global warming blame game. Next.
New paper finds Greenland surface melt was due to natural variability
http://hockeyschtick.blogspot.com/2013/02/new-paper-finds-brief-greenland-surface.html
Last summer, the mainstream media breathlessly reported that a brief 4-day surface melt over the Greenland ice sheet represented evidence of man-made global warming. However, a paper published today in The Cryosphere finds that “the recent warmer summers over [the Greenland ice sheet] cannot be considered as a long-term climate warming but are more a consequence of [the natural North Atlantic Oscillation] variability affecting atmospheric heat transport.” In other words, the brief Greenland surface melt was related to natural variability rather than alleged man-made global warming.
And it never stopped melting in the minds of the 97% consensus, or least the contrivers of the 97% claim.
lt looks like at long last that climate science is waking up to just how important the jet stream is to the climate in the NH. l think underplaying its importance has been one of climate science’s biggest mistakes. My own interest in the weather and later the jet stream is leading me to think it was changes to the jet stream that set up the ice age.
unprecedented, exceptional, catastrophic……
Has anyone else noticed you have to be a drama queen to report the weather?
” and probably unlikely to have occurred previously for well over a century.”
““The next five-10 years will reveal whether or not 2012 was a rare event”
….we have our feet firmly planted on the ground
“The analysis shows that ocean temperatures and Arctic sea-ice cover were relatively unimportant factors in causing the extra Greenland melt.”
“that the record surface melting of the GrIS was mainly caused by highly unusual atmospheric circulation and jet stream changes,”
..well thank goodness it was contained in the GrlS…and didn’t affect Arctic sea ice
Please excuse my ignorance. Could the change in the circumpolar vortex from zonal flow to meridional flow have contributed?
Dr. Tim Ball talked about this change in June of 2012.
http://drtimball.com/2012/current-global-weather-patterns-normal-despite-government-and-media-distortions/
A similar weather pattern to the one last summer also happen in Nov/Dec of 2010.
Where a Greenland set up in the north Atlantic and drew the jet stream northwards over Greenland bringing warm air and high temps for the western side of Greenland. But for the UK on the other side of the Atlantic it brought down a Arctic blast.
Sorry meant to write “Where a Greenland high set up in the north Atlantic”.
rgbatduke says (June 17, 2013 at 1:56 pm): “Can’t anybody say the magic words “we don’t know what caused it”, perhaps in association with “models that should have predicted it failed. Again.”
A lot has been written on WUWT lately about GCM shortcomings, much of it by RGB. So when I was reading this article the sentence
“These jet stream changes over Greenland do not seem to be well captured in the latest Intergovernmental Panel on Climate Change (IPCC) computer model predictions of climate change, and this may indicate a deficiency in these models.”
really jumped out at me. We might as well predict the state of the climate system in 2100 this way. It’s cheaper and might actually (by chance) give the correct answer.
‘has shown that unusual changes in atmospheric jet stream circulation
caused the exceptional surface melt of the Greenland Ice Sheet’ and what causes ‘unusual….jet stream’? Well that would be AGW of course! Heads I win, tails you lose!
Hey! They forgot to use the word “unequivocal” !!!
“…probably unlikely to have occurred previously for well over a century”
Pure supposition.
That’s not science, it’s just b*llsh*t
Myron Mesecke
Yes, that is basically what they are saying. A blocking pattern left a dome of high pressure over Greenland causing unprecedented melt. In the summary of the article it says, ”
“Taken together, our present results strongly suggest that the main forcing of the extreme GrIS surface melt in July 2012 was atmospheric, linked with changes in the summer North Atlantic Oscillation (NAO), Greenland Blocking Index (GBI, a high pressure system centred over Greenland) and polar jet stream which favoured southerly warm air advection along the western coast
We know from the studies of Jennifer Francis that arctic amplification has weakened the polar jet stream this year, this has severely increased meridional flow to the rossby waves of the jet stream.
Here is her short explanation.
The jet stream causes high pressure systems to stay… sure… have another glass.
“””””…..An international team led by Professor Edward Hanna from the University of Sheffield’s Department of Geography used a computer model simulation (called SnowModel) and satellite data to confirm a record surface melting of the GrIS for at least the last 50 years – when on 11 July 2012, more than 90 percent of the ice-sheet surface melted. This far exceeded the previous surface melt extent record of 52 percent in 2010…….”””””””
I thought if the Greenland Ice Sheet melted, that the sea level would rise 200 feet, or 60.96 meters, whichever comes first.
So 90% melt would only be 55 meters or 180 feet.
And back in 2010, when 52% melted, the sea level rise was just 104 feet or so. Can’t say it had much effect on San Francisco Bay. Well it might have been the cause of a couple of catastrophic Americas cup, catamaran pitch pole capsize calamities, in the bay; one fatal.
Oh! I see they say “surface” melted, not “ice sheet melted”. Well that would be just the one molecular layer on the top side of the ice sheet I suppose.
And they say all of this happened right before their eyes on a computer screen outputting a model simulation.
Whew! had me worried for a bit, that it might have been real.
Well they do say that a satellite confirmed it by watching for the last 50 years, back to 1962; just 5 years after Sputnik.
I didn’t even know they has a satellite in 1962 that could observe, let alone measure the top molecular layer of Greenland ice sheet.
And this jewel:- “””””….. – when on 11 July 2012, more than 90 percent of the ice-sheet surface melted. This far exceeded the previous surface melt extent record of 52 percent in 2010……”””””
Now by my calculation, 90% is an increase over 50 %, of just 73.1 %, or 1.73 x if you prefer.
Now you see we just don’t know the value of the climate sensitivity, to within a factor of 1.73, so if that is all that the change was, why all the hyping about “””…far exceeding….”””
They really should have said: “we don’t know if the simulated change is statistically significant or not, as climate data goes.
They need to tone down their use of superlatives. 90% does not “far exceed” 52% in climate terms.
Does anybody know if the top molecular layer of Greenland ice gives you enough ice water to cool down rgbatduke, who is having a fit over the lousy Carolina fishing. Well ProfBob, If I had Carolina fishing off California, instead of an explosion of furbags, I’d be pretty steamed about the situation too.
[Snip. Off topic. — mod.]
here’s the headline over at ThinkClimate. “Exceptional 2012 Greenland Ice Melt Caused By Jet Stream Changes That May Be Driven By Global Warming”
“The next five-10 years will reveal whether or not 2012 was a rare event resulting from the natural variability of the NAO or part of an emerging pattern of new extreme high melt years.”
This year is shaping up similarly so it will be interesting to see how it plays out.
Reich.Eschhaus says:
June 17, 2013 at 4:35 pm
(Note: “Plain Richard” is a sock puppet for Reich.Eschhaus. This is in violation of site Policy. Comments snipped. Further infractions will result in a permanent ban. ~mod.)”
No worries. My housemate known here as Richard is not going to comment here anymore (for obvious reasons). Neither will I comment here anymore (solidarity with a friend I live with). Actually there are 7 persons here who share the same internet connection. I am sure you won’t mind. So Bye Bye!
____________________________________________________________________________
*wipes away a tear*
I was looking at the sea ice page after seeing this, curious why it still uses 2007/2013 comparisons when last year was the low point, wasn’t it?
Sure wish that “global warming” would happen. We have a frost warning on for much of the Upper Peninsula (Michigan) tonight.