Scientists Say Slower Atlantic Currents Could Mean a Colder Europe

NY Times ^ | December 1, 2005 | ANDREW C. REVKIN

[neverdem]

Scientists say they have measured a significant slowing in the Atlantic currents that carry warm water toward Northern Europe. If the trend persists, they say, the weather there could cool considerably in coming decades.

Some climate experts have said the potential cooling of Europe was paradoxically consistent with global warming caused by the accumulation of heat-trapping "greenhouse" emissions. But several experts said it was premature to conclude that the new measurements, to be described today in the journal Nature, meant that such a change was already under way.

The currents, branching off from the Gulf Stream, are part of an oceanic system that disperses tropical heat toward the poles and makes Northern Europe far warmer than its latitude would suggest.

Warming, in theory, could stall the salty, sun-heated, north-flowing currents by causing fresh water to build up in high-latitude seas as ice melts and more precipitation falls.

The scientists, from the National Oceanography Center in Britain, measured sea temperature, currents and other conditions across the Atlantic from the Bahamas to Africa last year and found a 30 percent drop in the flow of warming waters since a similar set of measurements were taken in 1957.

The team, led by Harry L. Bryden, wrote that even though they had measurements from only 5 years out of the past 50, the pattern of change seen at various depths supported the idea that the shift was a significant trend and not random variability.

They also cited independent measurements of a long-term decline in the flow of water between some Arctic seas and the North Atlantic as evidence that a slowing of the overall Atlantic circulation was under way.

In an accompanying commentary in Nature, Detlef Quadfasel of the University of Hamburg

[neverdem]

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Published online: 30 November 2005; | doi:10.1038/news051128-9

Atlantic currents show signs of weakening

Research cruise reveals evidence of half-century of wane.

Quirin Schiermeier

The Atlantic Ocean circulation system. Click here to see enlarged view.© Nature

The North Atlantic's natural heating system, which brings clement weather to western Europe, is showing signs of decline. Scientists report that warm Atlantic Ocean currents, which carry heat from the tropics to high latitudes, have substantially weakened over the past 50 years.

Oceanographers surveying the 'Atlantic meridional overturning circulation', the current system that includes the warm Gulf Stream current, report that it seems to be 30% weaker than half a century ago.

Failures of the Atlantic Ocean's circulation system are thought to have been responsible for abrupt and extreme climate changes during the ice age that lasted from 110,000 to 23,000 years ago. More recently, a fictional shutdown of the Gulf Stream inspired the 2004 Hollywood blockbuster The Day after Tomorrow.

The climate shifts depicted in the movie, in which New York is engulfed by an instant ice age, are mere fancy. But scientists are worried about the real changes measured in the North Atlantic. Both salinity and water density, which influence the transport of warm waters, have previously been found to be decreasing.

Stuck in a loop

The likely cause is more fresh water flowing into the ocean from rivers, rain and melting ice, and this is thought to be linked to global warming. But climate modellers are worried that the resulting weakening of ocean currents could ultimately lead to substantial cooling of the North Atlantic.

This is quite sensational information. It is also an important message to politicians: We do change our climate.  Detlef Quadfasel University of Hamburg

The team behind the new study are the first to spot these signs of decline in Atlantic currents. Harry Bryden of the National Oceanography Centre in Southampton, UK, and his team report their results in this week's Nature¹.

During a cruise in spring 2004 from the Bahamas to the Canary Islands, on board the British research vessel RRS Discovery, the team measured water temperature and salinity along a latitude of 25º North, taking samples roughly every 50 kilometres. They then calculated from the density and pressure differences between each sample, the volume and velocity of the circulation at various depths, assuming that from coast to coast the balance of water flowing north and south must be zero.

Similar measurements along the same latitude were previously made in 1957, 1981, 1992 and 1998. But until now, the data never showed any significant decline in circulation. "In 1998 we saw only very small changes," says Bryden. "I was about to give up on the problem."

However, this time things were very different. The near-surface, and mostly wind-driven, Gulf Stream has remained almost constant since 1957. But the deep-ocean return flow of cooler water has decreased dramatically. This cycle usually returns water to more southerly latitudes from as far north as Greenland and Scandinavia.

But much of this water now seems to be trapped in a loop in the subtropical Atlantic, instead of cycling all the way to the ocean's northern extremity. Bryden and his colleagues estimate that, overall, the circulation has slowed by about 30% since 1957.

"This is quite sensational information in itself," says Detlef Quadfasel, an oceanographer at the University of Hamburg in Germany. "But it is also an important message to politicians who negotiate the future of the Kyoto agreements: we do change our climate."

A direct impact of the weakening circulation on air temperatures in western Europe has so far not been observed. Average temperatures have increased by around 0.6 ºC since 1900. Whether or not the true warming is partly eclipsed by an opposite oceanic cooling trend is not clear, says Quadfasel.

A long-term trend?

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Other oceanographers warn that this is not proof of a long-term trend. Possible disturbances such as ocean eddies, and natural fluctuations in the strength of the circulation system, must be considered, they say.

"Something is clearly going on," says Jochem Marotzke, an oceanographer at the Max Planck Institute for Meteorology in Hamburg. "But we still have only a series of snapshots. The crux is to determine how representative they really are." He adds that the chances of imminent collapse of the circulation system is small.

Sensor-equipped moorings installed at 25 locations across the subtropical Atlantic have now begun to monitor continuously the circulation at all depths. The next four years or so should tell us whether the Atlantic heating system is still working well, says Marotzke.

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References

1. BrydenH., LongwortH. & CunninghamS. Nature, 438. 665 - 657 (2005).

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Story from news@nature.com:
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[highlander_UW]

guess that solves the global warming problem.

[aft_lizard]

Frankly if that shuts the Euroweenies up about globalwarming then I am all for it. Its for the children after all.

[metmom]

Perhaps I don't recall my oceanography right, (it was one course 20 years ago) but wouldn't greater temperature differences in the water mean greater differences in the density of the water which would cause the currents to become STRONGER instead of weaker? Anyone out there know fluid flow?

[InABunkerUnderSF]

Just another good reason to let the SUV idle in the driveway over night.

[fortunecookie]

Interestingly, I thought I read somewhere that during the Dark Ages, Europe had a cold spell kind of like they are predicting. Maybe not Ice Age worthy, but colder than usual for the area. And now, Europe is declining, except for it's growing immigrant Muslim population who are reluctant to assimiliate and many of whom live as though they are still in the Dark Ages. Just a thought...

[ClearCase_guy]

Some climate experts have said the potential cooling of Europe was paradoxically consistent with global warming

Uh huh.

[JustAnotherOkie]

If the french loose their wine crops who do you think they will turn to for financial aid?

[metmom]

If the whole globe isn't getting warmer, than how can they call it *global* warming? IMO, it should be referred to as *globull* warming.

[taxesareforever]

You must remember, these are climate EXPERTS. I know, they don't want us to know their names because we just might not be able to stop laughing.

[IronChefSakai]

This is obviously due to racism and homophobia. Dont let anyone else tell you different.

[spokeshave]

Perhaps I don't recall my oceanography right, (it was one course 20 years ago) but wouldn't greater temperature differences in the water mean greater differences in the density of the water which would cause the currents to become STRONGER instead of weaker? Anyone out there know fluid flow?

The fresh (but colder) water stays on top...the more dense salty hot water is pushed down.

The mass of fresh water acts as a "plug" shutting off the warm water flow.

In any case the imminent switch in the earth's magnetic poles N to S and South pole to North will cause even more problems.....

enjoy

[kvanbrunt2]

In any case the imminent switch in the earth's magnetic poles N to S and South pole to North will cause even more problems.....

i heard about that how's that going.

[neverdem]

Abortion pill 'may be linked to infection'

CDC: Deadly bacterial illness may be spreading

FReepmail me if you want on or off my health and science ping list. How's that for a hat trick, side by side threads on two species of Clostridia.

[Brad from Tennessee]

The Little Ice Age was not just in Europe but also North America. It lasted into the 19th Century--the beginning of modern air temperature records. This may be why when it seems the earth is warming it is actually just returning to the norm. Temperatures were warmer in the 1400's than they are today.

[Grizzled Bear]

And when I boil water on my stove top it freezes!

[adam_az]

"The Little Ice Age was not just in Europe but also North America. It lasted into the 19th Century--the beginning of modern air temperature records. This may be why when it seems the earth is warming it is actually just returning to the norm. Temperatures were warmer in the 1400's than they are today."

Yep, global warming theory is BS because it assumes that the earths temperature would stay the same if it weren't for us.

[demlosers]

This movie lives on...

[Ursus arctos horribilis]

HC had a 2 hour special on it. Started early 1300's & lasted up through the 1700's.

[MilleniumBug]

The figure shows two kinds of ocean currents: red and green. In the west we have the green-house gases which tend to overheat the politicians. In Europe they have the red-light-house gases which cool them off.