Global Warming Science - www.appinsys.com/GlobalWarming

 

Climatic Events – North Atlantic Circulation / Gulf Stream

 

[last update: 2010/09/14]

 

While the global warming scare got rolling, other climatic events have also garnered much alarmist attention.

Animals are the focus of this document.

 

Other documents in Climatic Events include:

 

 

 

 

 

 

North Atlantic Thermohaline Circulation Shutdown Scare

 

Some global warming alarmists suggest that the North Atlantic Thermohaline Circulation (NATC) or (Atlantic Meridional Overturning Circulation) will be disrupted by the melting of the Arctic ice cap, causing an ice age.

 

Although this is known by scientists to be a bogus scenario – it has often been used as a scare story in the popular media. This has mainly come about due to a general misunderstanding of the NATC and the Gulf Stream.

 

An alarmist example: The Times: “Britain Faces Big Freeze As Gulf Stream Loses Steam” [http://www.timesonline.co.uk/tol/news/uk/article598464.ece]

“The Atlantic Ocean “conveyor belt” that carries warm water north from the tropics has weakened by 30 per cent in 12 years … Scientists have long predicted that melting ice caps could disrupt the currents that keep Britain at least 5C (40F) warmer than it should be, but the new research suggests that this is already under way. It points to a cooling of 1C over the next decade or two, and an even deeper freeze could follow if the Gulf Stream system were to shut down altogether. … The Gulf Stream begins in the Gulf of Mexico and carries warm water north and east, through the straits of Florida and across the North Atlantic. Halfway across the ocean, it branches into two, with one current flowing south towards Africa and another drifting towards northern Europe. By the time the northern current reaches the Arctic, its waters have become colder and more saline, causing them to sink. A vast undersea river of cold water then flows back towards the Gulf. Global warming is predicted to disrupt this process” (Their description of the Gulf Stream and its effects are incorrect as will be described below.)

 

 

 

The North Atlantic Thermohaline Circulation

 

The simplistic view is illustrated in the following figure, which shows the Gulf Stream as a laminar flow and recirculating as a deeper stream as part of the NATC. The actual Gulf Stream and its relation to the NATC are more complex – the Gulf Stream is examined in the next section.

 [http://www.meteo.mcgill.ca/~tremblay/Courses/ATOC530/EuropeClimate.ppt]:

 

 

 

A 2006 article by Richard Seager [http://www.americanscientist.org/issues/pub/2006/4/the-source-of-europes-mild-climate/1] debunks the myth about the shutdown of the Atlantic conveyor and provides the following explanation:

 

“the still-tentative connections investigators have made between thermohaline circulation and abrupt climate change during glacial times have combined with the popular perception that it is the Gulf Stream that keeps European climate mild to create a doomsday scenario: Global warming might shut down the Gulf Stream, which could "plunge western Europe into a mini ice age," making winters "as harsh as those in Newfoundland," or so claims, for example, a recent article in New Scientist. This general idea been rehashed in hundreds of sensational news stories.”

 

“The germ of truth on which such hype is based is that most atmosphere-ocean models show a slowdown of thermohaline circulation in simulations of the 21st century with the expected rise in greenhouse gases. The conveyer slows because the surface waters of the subpolar North Atlantic warm and because the increased transport of water vapor from the subtropics to the subpolar regions (where it falls as rain and snow) freshens the subpolar North Atlantic and reduces the density of surface waters, which makes it harder for them to sink. These processes could be augmented by the melting of freshwater reserves (glaciers, permafrost and sea ice) around the North Atlantic and Arctic.”

 

“The temperature difference between Europe and Labrador should remain. Temperatures will not drop to ice-age levels, not even to the levels of the Little Ice Age, the relatively cold period that Europe suffered a few centuries ago. The North Atlantic will not freeze over, and English Channel ferries will not have to plow their way through sea ice. A slowdown in thermohaline circulation should bring on a cooling tendency of at most a few degrees across the North Atlantic—one that would most likely be overwhelmed by the warming caused by rising concentrations of greenhouse gases. This moderating influence is indeed what the climate models show for the 21st century and what has been stated in reports of the Intergovernmental Panel on Climate Change. Instead of creating catastrophe in the North Atlantic region, a slowdown in thermohaline circulation would serve to mitigate the expected anthropogenic warming!”

 

“The play that the doomsday scenario has gotten in the media—even from seemingly reputable outlets such as the British Broadcasting Corporation—could be dismissed as attention-grabbing sensationalism. But at root, it is the ignorance of how regional climates are determined that allows this misinformation to gain such traction. ... The blame lies with modern-day climate scientists who either continue to promulgate the Gulf Stream-climate myth or who decline to clarify the relative roles of atmosphere and ocean in determining European climate. This abdication of responsibility leaves decades of folk wisdom unchallenged, still dominating the front pages, airwaves and Internet, ensuring that a well-worn piece of climatological nonsense will be passed down to yet another generation.”

 

Seager provides further documentation here: http://www.ldeo.columbia.edu/res/div/ocp/gs/

 

 

 

[update 2010/03/26]: NASA Study Finds Atlantic 'Conveyor Belt' Not Slowing

[http://www.jpl.nasa.gov/news/news.cfm?release=2010-101&rn=news.xml&rst=2534]

 

 

The NASA news release states:

 

  • “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. … Willis found evidence that the circulation had sped up about 20 percent from 1993 to 2009.”

 

  • “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. … however, there are no signs of a slowdown in the circulation … No one is predicting another ice age as a result of changes in the Atlantic overturning," said Willis”

 

(Oops – models and alarmists are wrong again.)

 

 

 

[update 2010/09/14]: Analysis of temperature and salinity shakes view of global water flow

[http://www.nature.com/news/2010/100912/full/news.2010.461.html]

 

Nature reports on a new study of the “oceanic conveyor”:

 

  • “The simplified picture of what is known as meridional overturning circulation (MOC) has been brought into question by a paper suggesting that, in the past 50 years, ocean circulation closer to the Equator has grown weaker, whereas the northern waters have flowed more strongly. "The more we look, the more complicated the ocean is," says Susan Lozier, an oceanographer at Duke University in Durham, North Carolina, and lead author of the study.”

 

  • “When the conveyor-belt model was conceptualized in the 1980s, researchers understood only a rough outline of overall marine currents, she says. Because it is difficult to take measurements in the depths of the ocean, MOC models couldn't reflect the intricacy of all the factors involved. … Other measurements from recent years highlight the lack of detailed knowledge about ocean overturning.”

 

  • “The idea of the seas moving as a smooth belt is being changed by the accessibility of satellite data, says oceanographer Joël Hirschi, also at the National Oceanography Centre … Modelling the MOC is like knowing the average state of the atmosphere, he says. It can provide an overall description of the climate, but the detailed, local differences will still be hard to predict.”

 

 

 

The Gulf Stream

 

The Gulf Stream breaks up into various currents once it passes the Grand Banks. The following figures show the subsequent currents and gyres that result [http://kingfish.coastal.edu/gulfstream/p2.htm]  “Along the east coast of Florida the current is fed by the Antilles Current, and the flow, now called the Gulf Stream, runs parallel to the coast until reaching Cape Hatteras where it leaves the coast and enters deeper water. While flowing in deep water the Stream often forms large meanders or fluctuations in its path. At approximately 50°W, the Gulf Stream splits into several currents the largest being the North Atlantic Current. The North Atlantic Current then feeds both the Norwegian Current which transports water northward along the west coast of Europe and the Canary Current which flows equator-ward on the eastern side of the Atlantic. These currents are labeled in red in the figure below: Gulf Stream (GS), North Atlantic Current (NAC), Norwegian Current (NOR), Canary Current (CC).”

 

 

 

 

“The Gulf Stream begins upstream of Cape Hatteras, where the Florida Current ceases to follow the continental shelf. The position of the Stream as it leaves the coast changes throughout the year. In the fall, it shifts north, while in the winter and early spring it shifts south. The current transports a maximum amount of water in the fall and a minimum in the spring, in phase with the north-south shifts of its position. Once it reaches the Grand Banks, the structure of the Gulf Stream changes from a single, meandering front to multiple, branching fronts.” This is illustrated in the following figure, showing the surface geostrophic oceanic current speed. [http://www.jamstec.go.jp/e/about/press_release/20080313/]

 

 

 

The Gulf Stream causes various localized sea level anomalies to occur. A study called “Seasonal Fluctuations in Sea Level on the South Carolina Shelf and Their Relationship to the Gulf Stream” by Noble, M. A., and G. R. Gelfenbaum (1992) (Journal of Geophysical Research 97 [http://www.agu.org/pubs/crossref/1992/92JC00811.shtml]) states: “outer continental shelf off South Carolina document that sea level rose 35 to 50 cm between July and October. Records of coastal sea level showed a similar rise. The changes in residual sea level were seasonal and  associated with seasonal changes in the transport of the Gulf Stream. The 3 years of residual sea level records examined here indicate that the amplitude of a typical decrease in transport of the Gulf Stream off South Carolina between July and October has a strong interannual variability.”

 

NOAA maintains an assembly of drifter buoys. The following figure shows direction (heading/bearing) of the buoys in degrees relative to North (0/360°) which is dark blue. Due south (180°) is red, while due west (270°) is yellow and due east (90°) is cyan. [http://oceancurrents.rsmas.miami.edu/atlantic/spaghetti-speed/gulf-stream.jpg]

 

 

 

 

Even the science publications which typically are pro-alarmist have recently backed off on this scare scenario:

 

  • Science: “False Alarm: Atlantic Conveyor Belt Hasn't Slowed Down After All” [http://www.sciencemag.org/cgi/content/summary/314/5802/1064a]: “A closer look at the Atlantic Ocean's currents has confirmed what many oceanographers suspected all along: There's no sign that the ocean's heat-laden "conveyor" is slowing”

 

  • New Scientist: “No New Ice Age for Western Europe” [http://www.newscientist.com/article/mg19225763.900]: “New measurements have failed to show clear evidence that the current is weakening, and models of the North Atlantic show that a shutdown would not occur in the way oceanographers had expected.”

 

 

 

Gulf Stream Does Not Significantly Heat Europe

 

Another part of the misunderstanding is the myth that the Gulf Stream heats Europe. A 2006 article by Richard Seager (senior research scientist at Columbia University's Lamont-Doherty Earth Observatory) in American Scientist (“The Source of Europe's Mild Climate” subtitle “The notion that the Gulf Stream is responsible for keeping Europe anomalously warm turns out to be a myth”) [http://www.americanscientist.org/issues/pub/2006/4/the-source-of-europes-mild-climate/1] provides a good explanation of how the oceans warm the land on the eastern side of the ocean.

“The Gulf Stream indeed contributes to Europe's warmth, but it is wrong to conflate the climate difference across the North Atlantic with the northward flow of warm water in the Gulf Stream. This erroneous logic leads to such statements as (from The Times of London): "The British Isles lie on the same latitude as Labrador on the East Coast of Canada, and are protected from a similarly icy climate by the Atlantic conveyor belt." Such claims are absolutely wrong.”

 

Figure 2. Average January air temperatures...

“Average January air temperatures are warmer over oceans than they are over land, because the sea retains more summer heat, which can then be released to the overlying air in winter. Sites located close to the coasts thus tend to enjoy mild "maritime" climates. And because prevailing winds over the midlatitudes blow from west to east, coastal areas on the eastern side of ocean basins experience especially mild temperatures. Conversely, the coasts bordering the western side of ocean basins experience winters that are intermediate between typical maritime conditions and the frigid "continental" climates found in interior regions. The difference in January temperatures across the North Atlantic at the latitude of London, for example, amounts to between 15 and 20 degrees Celsius.”

 

 

 

Gulf Stream Sea Surface Temperatures

 

 

The following images show sea surface temperatures for summer (left) and winter (right) showing the extent of the turbulence and dissipation in the middle of the Atlantic ocean. (Images from http://www.psc.edu/science/OKeefe/OKeefe-movie.mpg)

 

 

 

 

 

The following graphs show sea surface temperature (SST) anomaly graphs for five Gulf Stream areas as shown on the map below [http://bobtisdale.blogspot.com/2009/03/gulf-stream-sea-surface-temperature-sst.html]. Recent SST warming is well below the warming of the 1930’s-1940’s.

 

 

 

 

 

History

 

According to the New York Times – October 22, 1907

[http://query.nytimes.com/mem/archive-free/pdf?_r=2&res=9903E2DF173EE233A25751C2A9669D946697D6CF]