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CCNet 25/03/15

Study: Observations Refute Claims That Climate Change Is Slowing Pace Of Gulf Stream

20 Years Of Data Demonstrates Gulf Stream Is Stable


In contrast to recent claims of a Gulf Stream slowdown, two decades of directly measured velocity across the current show no evidence of a decrease. --T. Rossby et al., Geophysical Research Letters, Volume 41Issue 1pages 114–12016 January 2014


New NASA measurements of the Atlantic Meridional Overturning Circulation, part of the global ocean conveyor belt that helps regulate climate around the North Atlantic, show no significant slowing over the past 15 years. The data suggest the circulation may have even sped up slightly in the recent past. --NASA News, 25 March 2010





The Gulf Stream that helps to keep Britain from freezing over in winter is slowing down faster now than at any time in the past millennium according to a study suggesting that major changes are taking place to the ocean currents of the North Atlantic. --Steve Connor, The Independent, 24 March 2015


A few times a year the British media of all stripes goes into a tizzy of panic when one climate scientist or another states that there is a possibility that the North Atlantic ocean circulation, of which the Gulf Stream is a major part, will slow down in coming years or even stop. Whether the scientists statements are measured or inflammatory the media invariably warns that this will plunge Britain and Europe into a new ice age, pictures of the icy shores of Labrador are shown, created film of English Channel ferries making their way through sea ice are broadcast... And so the circus continues year after year. --Richard Seager, Lamont-Doherty Earth Observatory of Columbia University
 
 


1) Observations Refute Claims That Climate Change Is Slowing Pace Of Gulf Stream - University of Rhode Island, 3 March 2014
 
2) On The Long-Term Stability Of Gulf Stream Transport Based On 20 Years Of Direct Measurements - Geophysical Research Letters, Volume 41Issue 1pages 114–12016 January 2014
 
3) Reminder: NASA Study Finds Atlantic ‘Conveyor Belt’ Not Slowing - NASA News, 25 March 2010
 
4) German Researchers Pour Cold Water Over Rahmstorf/Mann Proxy Paper
NoTricksZone, 24 March 2015
 
5) Michael Mann & Stefan Rahmstorf Claim The Gulf Stream Is Slowing Due To Greenland Ice Melt, Except Reality Says Otherwise - Watts Up With That, 24 March 2015
 
6) Climate Mythology: The Gulf Stream, European Climate And Abrupt Change - Lamont-Doherty Earth Observatory of Columbia University
 
 
 
Several recent studies have generated a great deal of publicity for their claims that the warming climate is slowing the pace of the Gulf Stream. They say that the Gulf Stream is decreasing in strength as a result of rising sea levels along the East Coast. However, none of the studies include any direct measurements of the current over an extended period to prove their point. But this is exactly what has been underway at the University of Rhode Island and Stony Brook University for the last 20 years: measurement of the strength of the Gulf Stream. And according to a paper published in Geophysical Research Letters, the researchers find no evidence that the Gulf Stream is slowing down. These new results reinforce earlier findings about the stability of Gulf Stream transport based on observations from as far back as the 1930s. --University of Rhode Island, 3 March 2014
 
 
The ADCP measures currents at very high accuracy, and so through the repeat measurements we take year after year, we have a very powerful tool by which to monitor the strength of the current. There are variations of the current over time that are natural -- and yes, we need to understand these better -- but we find absolutely no evidence that suggests that the Gulf Stream is slowing down. – Prof H. Thomas Rossby, University of Rhose Island, 3 March 2014

 
 
From your “Day after Tomorrow” department (where a slowing Gulf Stream turned NYC into an icebox) comes the claim [that the Gulf Stream is slowing due to Greenland ice melt], from the bowels of Mannian Science. Unfortunately, it looks to be of the caliber of Mann’s Hockey Schtick science. --Anthony Watts, Watts Up With That, 24 March 2015
 
 
Overall the latest paper by Rahmstorf and Mann did not even survive birth. --Pierre Gosselin, NoTricksZone, 24 March 2015
  
 
 
1) Observations Refute Claims That Climate Change Is Slowing Pace Of Gulf Stream
University of Rhode Island, 3 March 2014
 
Media Contact: Todd McLeish, 401-874-7892
 
20 years of data demonstrates it remains stable

NARRAGANSETT, R.I. – March 3, 2014 – Several recent studies have generated a great deal of publicity for their claims that the warming climate is slowing the pace of the Gulf Stream. They say that the Gulf Stream is decreasing in strength as a result of rising sea levels along the East Coast. However, none of the studies include any direct measurements of the current over an extended period to prove their point. 

But this is exactly what has been underway at the University of Rhode Island and Stony Brook University for the last 20 years: measurement of the strength of the Gulf Stream. And according to a paper published in Geophysical Research Letters, the researchers find no evidence that the Gulf Stream is slowing down. These new results reinforce earlier findings about the stability of Gulf Stream transport based on observations from as far back as the 1930s. 

H. Thomas Rossby, a professor at the URI Graduate School of Oceanography, has spent much of his long career studying ocean circulation – especially the Gulf Stream – and how it makes its way across the Atlantic towards Europe and as far north as northern Norway. For the last 20 years he and his colleagues have measured the Gulf Stream using an acoustic Doppler current profiler (ADCP) attached to a ship, the freighter Oleander, which makes weekly trips across the Gulf Stream from New Jersey to Bermuda. The instrument, which measures the velocity of water moving beneath the ship down to more than 600 meters, has collected some 1,000 measurements of the Gulf Stream since it was installed in late 1992.

“The ADCP measures currents at very high accuracy, and so through the repeat measurements we take year after year, we have a very powerful tool by which to monitor the strength of the current,” said Rossby. “There are variations of the current over time that are natural -- and yes, we need to understand these better -- but we find absolutely no evidence that suggests that the Gulf Stream is slowing down.”

The rapidly flowing Gulf Stream plays a major role in the global heat balance through its transport of very warm water from the Caribbean toward Europe. 

For this reason alone, Rossby says, there is good reason to be concerned about the long-term stability of the Gulf Stream, since if the Gulf Stream were slowing, a decrease in the flow of warm water to the northern North Atlantic could cause significant cooling in parts of Europe. But the data tell him that there is no evidence that this is happening, contrary to recent claims in the literature. 

Although he officially retired in 2011, Rossby is continuing his Gulf Stream research and hopes to install a new instrument on the Oleander in the coming years that will be able to profile currents to even greater depths. 

“Once we do that, all of the water going north will be well within our reach,” he said.
 
 
 
2) On The Long-Term Stability Of Gulf Stream Transport Based On 20 Years Of Direct Measurements
Geophysical Research Letters, Volume 41Issue 1pages 114–12016 January 2014
 
T. Rossby1,*,  C. N. Flagg2,  K. Donohue1, A. Sanchez-Franks2 and J. Lillibridge3
Article first published online: 13 JAN 2014
DOI: 10.1002/2013GL058636
 
Abstract
In contrast to recent claims of a Gulf Stream slowdown, two decades of directly measured velocity across the current show no evidence of a decrease. Using a well-constrained definition of Gulf Stream width, the linear least square fit yields a mean surface layer transport of 1.35 × 105 m2 s−1 with a 0.13% negative trend per year. Assuming geostrophy, this corresponds to a mean cross-stream sea level difference of 1.17 m, with sea level decreasing 0.03 m over the 20 year period. This is not significant at the 95% confidence level, and it is a factor of 2–4 less than that alleged from accelerated sea level rise along the U.S. Coast north of Cape Hatteras. Part of the disparity can be traced to the spatial complexity of altimetric sea level trends over the same period.
 
©2013. American Geophysical Union. All Rights Reserved.
 
Full paper
 
 
 
3) NASA Study Finds Atlantic ‘Conveyor Belt’ Not Slowing
NASA News, 25 March 2010
 
PASADENA, Calif.: New NASA measurements of the Atlantic Meridional Overturning Circulation, part of the global ocean conveyor belt that helps regulate climate around the North Atlantic, show no significant slowing over the past 15 years. The data suggest the circulation may have even sped up slightly in the recent past. 
 
The findings are the result of a new monitoring technique, developed by oceanographer Josh Willis of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., using measurements from ocean-observing satellites and profiling floats. The findings are reported in the March 25 issue of Geophysical Research Letters. 

The Atlantic overturning circulation is a system of currents, including the Gulf Stream, that bring warm surface waters from the tropics northward into the North Atlantic. There, in the seas surrounding Greenland, the water cools, sinks to great depths and changes direction. What was once warm surface water heading north turns into cold deep water going south. This overturning is one part of the vast conveyor belt of ocean currents that move heat around the globe. 

Without the heat carried by this circulation system, the climate around the North Atlantic — in Europe, North America and North Africa — would likely be much colder. Scientists hypothesize that rapid cooling 12,000 years ago at the end of the last ice age was triggered when freshwater from melting glaciers altered the ocean’s salinity and slowed the overturning rate. That reduced the amount of heat carried northward as a result. 

Until recently, the only direct measurements of the circulation’s strength have been from ship-based surveys and a set of moorings anchored to the ocean floor in the mid-latitudes. Willis’ new technique is based on data from NASA satellite altimeters, which measure changes in the height of the sea surface, as well as data from Argo profiling floats. The international Argo array, supported in part by the National Oceanic and Atmospheric Administration, includes approximately 3,000 robotic floats that measure temperature, salinity and velocity across the world’s ocean. 

With this new technique, Willis was able to calculate changes in the northward-flowing part of the circulation at about 41 degrees latitude, roughly between New York and northern Portugal. Combining satellite and float measurements, he found no change in the strength of the circulation overturning from 2002 to 2009. Looking further back with satellite altimeter data alone before the float data were available, Willis found evidence that the circulation had sped up about 20 percent from 1993 to 2009. This is the longest direct record of variability in the Atlantic overturning to date and the only one at high latitudes. 

The latest climate models predict the overturning circulation will slow down as greenhouse gases warm the planet and melting ice adds freshwater to the ocean. “Warm, freshwater is lighter and sinks less readily than cold, salty water,” Willis explained. 

For now, however, there are no signs of a slowdown in the circulation. “The changes we’re seeing in overturning strength are probably part of a natural cycle,” said Willis. “The slight increase in overturning since 1993 coincides with a decades-long natural pattern of Atlantic heating and cooling.”
 
Full post
 
 
 
4) German Researchers Pour Cold Water Over Rahmstorf/Mann Proxy Paper
NoTricksZone, 24 March 2015
 
Pierre Gosselin
 
The Potsdam Institute for Climate Impact Research has been loudly trumpeting its latest paper on Atlantic ocean overturning circulation today, claiming there’s been an “exceptional twentieth-century slowdown“. The authors, who include Stefan Rahmstorf and Michael E. Mann, even suggest that the “possible cause of the weakening is climate change“.
 
Some sites, like Climate Central here, have been unable to contain their glee over the news of the potential climate-change induced oceanic shifts being served up by the PIK. For example the site called the findings “dramatic” and writes (my emphasis):
 
If the climate relationships identified by the researchers, led by the Potsdam Institute for Climate Impact Research in Germany, hold true, growing melt rates in Greenland ‘might lead to further weakening of the AMOC within a decade or two, and possibly even more permanent shutdown’ of key components of it, the scientists warn in their paper.”
The “new” weakening Atlantic meridional overturning circulation. Credit: Nature Climate Change.
 
Spiegel and the FAZ pour cold water on paper
 
Fortunately other media sources have been somewhat more critical and report that there’s skepticism on the paper – coming from warmist circles, no less.
 
Germany’s Frankfurter Allgemeine Zeitung (FAZ) here for example writes that Rahmstorf is puzzled that a part of the north Atlantic has cooled over the last 100 years: “The cooling was stronger than what most computer models calculated it would be,” the FAZ reports. Models wrong again!
 
The FAZ then writes that, “An independent expert assesses the estimation skeptically”, adding:
 
Climate scientist Martin Visbeck of the GEOMAR Helmholtz Centre for Ocean Research in Kiel sees Rahmstorf’s assertion of the results critically: ‘The study’s focus on the sub-polar part of the Atlantic and the spectral analysis are interesting,’ he says. But there are other AMOC assessments that point to a completely other development. The paper does not offer any strong indication of the development of the AMOC during the past fifty years.”
 
When a warmist dismisses another warmists’s science, then you know it’s likely pretty slipshod.
 
Der Spiegel reports that the study is lacking
 
German flagship online news weekly Der Spiegel echoed the FAZ, quoting Michael Hofstätter of the Austrian national weather service: the Zentralanstalt für Meteorologie und Geodynamik (ZAMG) in Vienna. Spiegel writes that Hofstätter also “rates the Rahmstorf study with skepticism“.
 
Spiegel reminds its readers: “Most studies are assuming that the current is in fact stronger.” Spiegel continues:
 
The temperature fluctuations could also be a ‘temporary natural variation,’ Hofstätter told the online service of the ORF. The measurements covered a time period that was too short to allow concrete forecasts.”
 
Full post
 
 
 
5) Michael Mann & Stefan Rahmstorf Claim The Gulf Stream Is Slowing Due To Greenland Ice Melt, Except Reality Says Otherwise
Watts Up With That, 24 March 2015
 
Anthony Watts 
 
From your “Day after Tomorrow” department (where a slowing Gulf Stream turned NYC into an icebox) comes this claim from the bowels of Mannian Science. Unfortunately, it looks to be of the caliber of Mann’s Hockey Schtick science.

 
day-after-tomorrow
 
As WUWT reported on a peer reviewed paper last year, H. Thomas Rossby says: URI oceanographer refutes claims that climate change is slowing pace of Gulf Stream saying in a paper published in Geophysical Research Letters:
 
“The ADCP measures currents at very high accuracy, and so through the repeat measurements we take year after year, we have a very powerful tool by which to monitor the strength of the current,” said Rossby. “There are variations of the current over time that are natural — and yes, we need to understand these better — but we find absolutely no evidence that suggests that the Gulf Stream is slowing down.
 
Of course, Rahmstorf and Mann don’t list Rossby’s study in their references, nor seem to use the “highly accurate” ADCP data. Instead they use a model along with [proxies, reconstructions, and] the highly interpolated GISS data to come to the conclusions they want. So, it isn’t surprising they are chasing phantoms in their study. [...]
 
When actual Gulf Stream measurement data (the ADCP data cited by Rossby 2014) is available, why would Mann and Rahmstorf use proxies? And why try to say that temperature is the indicator, when you have actual speed data? The obtuseness boggles the mind. [...]
 
Duke University physicist Robert G. Brown, in comments noted:
 
Seriously — they found “good evidence” that such a slowing is occurring, only the actual evidence, consisting of the measured speed of the Gulf Stream itself, shows no such thing? The cognitive dissonance involved is stupifying.
 
Full post
 
 
 
 
6) Climate Mythology: The Gulf Stream, European Climate And Abrupt Change
Lamont-Doherty Earth Observatory of Columbia University
 
Richard Seager, Lamont-Doherty Earth Observatory of Columbia University
 
A few times a year the British media of all stripes goes into a tizzy of panic when one climate scientist or another states that there is a possibility that the North Atlantic ocean circulation, of which the Gulf Stream is a major part, will slow down in coming years or even stop. Whether the scientists statements are measured or inflammatory the media invariably warns that this will plunge Britain and Europe into a new ice age, pictures of the icy shores of Labrador are shown, created film of English Channel ferries making their way through sea ice are broadcast... And so the circus continues year after year. Here is one example.
 
The Gulf Stream-European climate myth
The panic is based on a long held belief of the British, other Europeans, Americans and, indeed, much of the world's population that the northward heat transport by the Gulf Stream is the reason why western Europe enjoys a mild climate, much milder than, say, that of eastern North America. This idea was actually originated by an American military man, Matthew Fontaine Maury, in the mid nineteenth century and has stuck since despite the absence of proof.
 
We now know this is a myth, the climatological equivalent of an urban legend. In a detailed study published in the Quarterly Journal of the Royal Meteorological Society in 2002, we demonstrated the limited role that ocean heat transport plays in determining regional climates around the Atlantic Ocean. Popular versions of this story can be found herehere and, in French, here.
 
The determinants of North Atlantic regional climates
We showed that there are three processes that need to be evaluated: 
  1. The ocean absorbs heat in summer and releases it in winter. Regions that are downwind of oceans in winter will have mild climates. This process does not require ocean currents or ocean heat transport.
  2. The atmosphere moves heat poleward and warm climates where the heat converges. In additions, the waviness in the atmospheric flow creates warm climates where the air flows poleward and cold climates where it flows equatorward.
  3. The ocean moves heat poleward and will warm climates where it releases heat and the atmosphere picks it up and moves it onto land.
 
Using observations and climate models we found that, at the latitudes of Europe, the atmospheric heat transport exceeds that of the ocean by several fold. In winter it may even by an order of magnitude greater. Thus it is the atmosphere, not the ocean, that does the lion's share of the work ameliorating winter climates in the extratropics. We also found that the seasonal absorption and release of heat by the ocean has a much larger impact on regional climates than does the movement of heat by ocean currents.
 
Seasonal storage and release accounts for half the winter temperature difference across the North Atlantic Ocean. But the 500 pound gorilla in how regional climates are determined around the Atlantic turned out to be the Rocky Mountains. Because of the need to conserve angular momentum, as air flows from the west across the mountains it is forced to first turn south and then to turn north further downstream. As such the mountains force cold air south into eastern North America and warm air north into western Europe. This waviness in the flow is responsible for the other half of the temperature difference across the North Atlantic Ocean.
 
Hence:
  1. Fifty percent of the winter temperature difference across the North Atlantic is caused by the eastward atmospheric transport of heat released by the ocean that was absorbed and stored in the summer.
  2. Fifty percent is caused by the stationary waves of the atmospheric flow.
  3. The ocean heat transport contributes a small warming across the basin.
 
The seasonal ocean heat storage and pattern of atmospheric heat transport add up to make winters in western Europe 15 to 20 degrees C warmer than those in eastern North America. A very similar process occurs across the Pacific Ocean. The ocean heat transport warms the North Atlantic Ocean and the land on both sides by a modest few degrees C. The only place where the ocean heat transport fundamentally alters climate is along the coast of northern Norway which would be sea ice-covered were it not for the warm northward flowing Norwegian Current.
 
The Gulf Stream and future climate change
A slowdown of the Gulf Stream and ocean circulation in the future, induced by freshening of the waters caused by anthropogenic climate change (via melting glaciers and increased water vapor transport into high latitudes) or simply by warming, would thus introduce a modest cooling tendency. This would leave the temperature contrast across the Atlantic unchanged and not plunge Europe back into the ice age or anything like it. In fact the cooling tendency would probably be overwhelmed by the direct radiatively-driven warming by rising greenhouse gases.
 
North Atlantic Ocean circulation and abrupt climate change
The conflation of the Gulf Stream, ocean heat transport and Europe's climate has led to changes in ocean circulation being the reigning theory of the cause of glacial era abrupt climate change. These abrupt changes - the Dansgaard-Oeschger events of the last ice age and the Younger Dryas cold reversal of the last deglaciation - are well recorded in the Greenland ice core and Europe and involved changes in winter temperature of as much as thirty degrees C! For the Younger Dryas it has been proposed that the sudden release of glacial meltwater from ice dammed Lake Agassiz freshened the North Atlantic and shut down the overturning circulation causing dramatic regional coooling.
 
Only through an inflated view of the impact of ocean circulation could it be thought that the enormous glacial era abrupt changes were caused by changes in ocean circulation. Instead, as we have argued, changes in atmospheric circulation regimes had to be the driver, see (Seager and Battisti,2007). Determining how this could happen has become more of a priority now that the geological evidence for the Lake Agassiz flood has not been found, see (Broecker,2006).
 
Moving beyond the myth
It is long time that the Gulf Stream-European climate myth was resigned to the graveyard of defunct misconceptions along with the Earth being flat and the sun going around the Earth. In its place we need serious assessments of how changes in ocean circulation will impact climate change and a new look at the problem of abrupt climate change that gives the tropical climate system and the atmosphere their due as the primary drivers of regional climates around the world.
 
Full paper & references
 
See also: Richard Seager's presentation to the New York Academy of Sciences: The Gulf Stream, European Climate and Abrupt Climate Change
 
 
 

 
 

 
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