Gulf Stream disruption?

[12345]

On another forum, I saw a link to this discussion re: a possible disruption of the Gulf Stream. They include many NOAA sea surface temperature maps that seem to demonstrate a possible disruption. Many Europeans wrote in with anecdotes about the effects on the weather in Europe.

http://www.climatepatrol.com/forum/10/2484/pg1/index.php

There was also a link to a 2006 Guardian article re: a previous disruption in the Gulf stream that occurred in 2004 http://environment.guardian.co.uk/climatechange/story/0,,1932761,00.html.

The current anomaly apparently began mid-April. I thought it was interesting given some maps I've seen posted on this forum that show significant Antarctic warming, but below-normal temperatures in Greenland...It's also interesting to see the effects of a short term disruption in the Gulf Stream on weather in Europe.

[Warpy]

1. The prediction has always been that the melting of the

ice caps will push enough cold, fresh water into the Gulf Stream to first slow it and then divert it southward, toward the coast of Africa.

It's slowing.

[xchrom]

2. yup -- and indeed it is slowing --

it could not only move but stop.

england would be the hardest hit.

some predict that temps have gotten warm enough for it to happen at any time.

we'll see.

[Dogmudgeon]

3. First seen in 2004 from 2002 data

The thermohaline convection system does seem to be in trouble. An increasing number of "data points" indicate that the slowdown is well under way.

On the other hand, recent evidence has softened the expected nightmare scenario that a THC shutdown would trigger a new Ice Age. While it is still a troubling development, this seems to be less critical than it was thought even as recently as a year ago. But we would still be well-advised to fear a "climate flip-flop", in William Calvin's terms. (Calvin was the first scientist to write about this for a lay audience, in a 1998 issue of The Atlantic Monthly.)

But this is understandable. Human activity has interfered with natural processes, damping some of them and strengthening others. Now we not only have the task of figuring out Nature's ways, but also the contribution of our own folly.

--p!

[HooptieWagon]

4. The Gulf Stream is created by the easterly trade winds.

Its very unlikely the Gulf Stream can move south enough that it bucks against the trades. It may move south some , affecting France more than Britain, but probably can't get as far south as Africa. Also, the Gulf Stream will not die out, unless the trades quit altogether. IMO, that is very unlikely. If anything, they are apt to increase with global warming. Also, the volume of water comprising the Gulf Stream is huge, it would take a sudden, instantaneous melting of all the Artic ice to significantly cool the Gulf Stream, which may only negate the additional warmth it got from increased temps in the tropics. The Gulf Stream is a moderating influence on global temperatures; it is more likely to affect (by moderating) warming temperatures than it is to be influenced by rising temperatures. IOW, the causal relationship works opposite that postulated in the OP.

BTW, my expertise is from 42 years experience as a recreational sailor and navigator in Florida, the Carribbean, and the East Coast, and discussions I've had about the Gulf Stream with a friend who's a US Navy Oceanographer who specializes in the Gulf Stream (especially at it's deeper levels).

[Nihil]

5. Err ...

> Also, the volume of water comprising the Gulf Stream is huge,
> it would take a sudden, instantaneous melting of all the Artic ice to
> significantly cool the Gulf Stream, which may only negate the additional
> warmth it got from increased temps in the tropics.

The THC shutdown is not about cooling the water, it is about the problems
with freshwater density interfering with the thermal process.

:hi:

[HooptieWagon]

7. The desities are very close

62.4 lbs/ft^3 vs. 64 lbs/ft^3, as I recall. Plus, the volume of melted ice (or even all the ice) is very small compared to the total amount of salt water in the Arctic... picture dropping a single ice cube into a 55 gal barrell of salt water that is a degree or two above freezing - it's just not going to have a significant effect on either density or temperature. Global warming IS a problem, but it should be discussed factually and soberly, not like a bunch of melodramatic Chicken Littles making all sorts of wild claims - and claiming the Gulf Stream is going to stop (or move to Africa) falls into that latter category, IMO.

[OKIsItJustMe]

6. Yes, well... sorta

Yes, the Gulf Stream is wind driven, but... The North Atlantic Current is water driven.
http://oceancurrents.rsmas.miami.edu/atlantic/north-atlantic.html

...

The North Atlantic Current represents the bulk of the Gulf Stream continuation past its branch point. Mann (1967) shows the The North Atlantic Current as comprised of waters from the Slope Water Current and from the Gulf Stream. In his representation approximately 15 Sv are derived from the Slope Water Current with the remaining 20 Sv contributed by the Gulf Stream. The remaining 30 Sv head off to the north east. The NAC is strengthened by mixing interactions of the Gulf Stream and Labrador Current as well. Worthington had shown the NAC as part of a separate Northern gyre, however subsequent work later revealed that this hypothesis was incorrect and that the North Atlantic Current was indeed derived from the Gulf Stream. The North Atlantic Current is generally thought of as the end of the Gulf Stream, however it goes on to feed some of the major subarctic currents completing the poleward transport of tropical waters.

...

http://svs.gsfc.nasa.gov/vis/a010000/a010000/a010031/index.html

As part of the ocean conveyor belt, warm water from the tropical Atlantic moves poleward near the surface where it gives up some of its heat to the atmosphere. This process partially moderates the cold temperatures at higher latitudes. As the warm water gives up its heat it becomes more dense and sinks. This circulation loop is closed as the cooled water makes its way slowly back toward the tropics at lower depths in the ocean.

If the poles warm, it is possible that melt water from glaciers and the polar ice cap can shut off this circulation and interrupt this circulation system. The melt water is fresher and hence less dense than the ocean water it melts into, and thus the melt water will tend to accumulate near the surface. This layer of fresh water acts as an insulating barrier between the atmosphere and the normal ocean water. The water from the tropics can not release its heat to the atmosphere, and the circulation loop is interrupted. The mechanism has a positive feedback potential in that if the ocean circulation slows, then even less heat will make it to the higher latitudes re-enforcing an effect that will cool the climate at these higher latitudes.

(Follow the link for an illustrative animation.)


http://ipcc-wg1.ucar.edu/wg1/wg1-report.html

...

• Based on current model simulations, it is very likely that the meridional overturning circulation (MOC) of the Atlantic Ocean will slow down during the 21st century. The multi-model average reduction by 2100 is 25% (range from zero to about 50%) for SRES emission scenario A1B. Temperatures in the Atlantic region are projected to increase despite such changes due to the much larger warming associated with projected increases in greenhouse gases. It is very unlikely that the MOC will undergo a large abrupt transition during the 21st century. Longer-term changes in the MOC cannot be assessed with confidence.

...

[nebenaube]

8. wait a minute...

a "layer of fresh water lying on the ocean surface"? This is not physically possible since diffusion is a fairly rapid process and in this case; facilitated by the movement of the currents.

I have no qualifications to second guess the scientists but I did take chem 101.

[OKIsItJustMe]

9. Try an experiment

https://pao.cnmoc.navy.mil/educate/neptune/lesson/science/DENSITY.HTM

[phantom power]

10. Actually, haloclines are very common in the oceans.

Bodies of water with differing salinity (or other properties) do not mix nearly as well as "common sense" suggests.

[OKIsItJustMe]

13. A practical example...

During WWII, the Nazis figured out how to get past Gibraltar using no power.

The Mediterranean loses more water through evaporation than it gains from rivers. So, water from the Atlantic flows in to make up the deficit. In addition, When the surface water evaporates it becomes more saline and sinks. This fills up the lower part of the basin, until it flows out through the straight.

The result is that near the surface, there is a flow into the Mediterranean of lighter, less salty water, and deeper there is a flow out of heavier, saltier water. So, a U-Boat, with the right level of buoyancy could get a free ride into or out of the Mediterranean, while maintaining silence.

[nebenaube]

17. thank you that helps my understanding....

replying to myself in order to post a thank you to those who responded.

[12345]

11. A few questions for those more knowledgeable than I,

Do you think that the series of maps referenced demonstrate a disruption? If they do, what are the long term implications? Is this an unusual occurance? Most of articles that I've read recently about global warming seem to talk about Europe warming, not cooling. How do you think a permanent disruption in the Gulf Stream affect those predictions? Thanks.

[phantom power]

12. I can speak to warming and cooling in Europe.

Currently, Europe is definitely warming, along with the rest of the planet. The classic theory of a THC shutdown is that the north atlantic current we know and love moves an enormous amount of heat energy from the equator towards the arctic. I once read that the energy is transferred at the rate of one petawatt. The trade winds pick up that heat energy and move it over Europe. So, if the current stalls out, Europe's average temperature would drop several degrees, possibly quite fast. The effects might be felt in 1-3 years, although people debate the actual time frame.

So, Europe would continue to warm, until it suddenly got a lot colder, very fast. If the THC shuts down. That's the baseline theory. As Pigwidgeon pointed out, the basic theory is subject to continual debate.

[12345]

14. Thanks. I think I know the gist of the theory. What about

a cool down in Europe. How would that affect warming elsewhere, and would the arctic cool down as well?

Thanks again.

[phantom power]

15. I don't really know, but I'll riff on it anyway:

The arctic would cool down, unless that heat energy found some other way to get there. One thing I'm fond of speculating about is what might happen to the atmospheric heat flow. The heat at the equator "wants" to flow to the cooler arctic (or antarctic). If it can't get there via the ocean, it's going to "try" getting there via the air. I think we should expect new and interesting weather.

It's all complicated by the fact that there are entirely new circumstances in the mix. We've boosted the atmospheric GHG concentrations to levels not seen in a long, long time. To my knowledge, no THC shutdown has ever happened with atmosphereic GHG concentrations so high. The arctic is experiencing positive feedbacks in terms of it's albedo decreasing. So, that will work to lessen the heat gradient between it and the equator. On the other hand, a stalled current will cause heat to build up around the equator. Warmer oceans and nastier hurricanes?

I have a feeling that modeling the outcome of all this is beyond our state of the art. Climate scientists are learning fast, and computing power is growing fast. But ultimately, I think that events are going to proceed faster than our ability to learn how to simulate them in advance. But that question, too, is beyond our ability so model :evilgrin:

[12345]

16. Once again, thanks for the response. You hit on two issues

I've been trying to grapple with. Which would dominate, the ghg effect or the ocean current? Also, one thing that I noticed in the discusion on the other site was the correlation between the disruption in the Gulf Stream, the cool spell in Europe, and the hot, dry weather in the southeastern US.