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On 30/9/2002, Zero Sum wrote:

Anybody have any idea what will happen o the southern hemisphere (particularly Aust.) when the atlanic conveyor stops and North America and Europe freeze?
 

On Tuesday 01 October 2002 16:14, Ray wrote:
> I don't know Zero, but the trade consequences on top of European and
> North American farming consequences would be the food for open civil
> rebellion.

I was actually concerned with the climatic changes.  Since the north and south hemisphere don't mix much, what would happen?
 

Stephen Berry responded:

Apparently acording to the currant models the halting of the Atlantic conveyor would actually cause North America to become warmer and wetter while Europe freezes.One of the effects for Australia could be a permenant El Nin'o that would render much of the country uninhabitable.Another possibility is an icrease in rainfall in some areas mainly the wet tropics with an increased wet seaon and a shorter dry season.

My understanding is that the computer models indicate a drier windier climate.  Also I think that during much, but not all, of the last ice age Aust was drier than at present.  It should be remembered that the ice age was not a static time but fluctuated widely.

There would presumably be some effect on the ocean.  The Atlantic deep water would not be bring O2 to the deep ocean.  However the Antarctic Deep Water would still be formed I guess?? and may be enough to stop the oceans becoming stagnant again.
 

Peter Macinnis replied:

I get paid to write worrying stories.  Yup.

Here is what I wrote in November 1997 -- I haven't seen anything much that is new since then . . . there was an article in "New Scientist" February 8, 1997, page 26 (UK edition, may be different in Oz)

A quick check there reveals a diagram showing that one part of the current passes northwest Australia -- probably helps feed the monsoon clouds, at a ROUGH guess.

Try Web searches on "Stefan Rahmstorf"

****************

A great cost of global warming might come about if we lost a giant ocean current called the conveyor. This system, which among other things drives the Gulf Stream, is all that prevents Ireland from having a climate like Spitsbergen (Svalbard), 600 miles north of the Arctic Circle.

This Doomsday scenario is no mere piece of science fiction. Worked out by Wallace S. Broecker, Newberry Professor of Earth and Environmental Sciences at Columbia University's Lamont-Doherty Earth Observatory, it was published in the journal "Science" at the end of November. In something of an understatement, Broecker describes the results as devastating, saying that Dublin could encounter a fall of 20°F (about 11°C) in just ten years, even as the rest of the world was heating up.

The Conveyor is delicately balanced and vulnerable, and it has shut down or changed direction many times in Earth's history, according to Broecker. Each change has produced massive climatic variation in a matter of decades, causing large-scale wind shifts, fluctuations in atmospheric dust levels, glacial advances or retreats, and other changes as the Conveyor jumps from one stable mode to another.

So while the current warming from the enhanced greenhouse effect may be a slow one, it may well be all that is required to take us "over the hump", and into a new climatic regime. Right now, the system is driven by cold salty water sinking to the bottom of the North Atlantic Ocean. This then pushes waters through the world's oceans, a flow 16 times greater than the flow of all the world's rivers combined.

The waters of the equatorial Indian Ocean are too warm to sink, while the north Pacific is too diluted by the snow and rains of the western United States and Canada. If the north Atlantic warms by just a few degrees, or if it gets a bit more rain, the whole flow could stop, and once stopped, who can say if it will start again?

Ice core evidence tells us that when a climatic change comes, it happens over a short period, geologically speaking, with just a few decades of transition. Broecker believes that the Conveyor is the key factor that we need to watch and worry about. And who is Broecker? Just one of the world's leading authorities on global climate change. He has won nearly every major geological award, including the Vetlesen Prize, considered by many to be the equivalent of the Nobel Prize in Earth sciences. Last year he was awarded the National Medal of Science and the Blue planet Prize, for achievements in global environmental research. When people like Broecker are worried, it is time to be worried too.

Coincidentally, evidence appeared in nature, just two weeks before that, giving us the same message. A 53-meter-long sediment core, retrieved from the Bermuda Rise in the western North Atlantic, now gives us the most detailed picture yet of events during the previous interglacial. The key feature: "its termination seems to have been marked by a sudden reduction in the ocean 'conveyor' circulation which today carries ocean heat north from the tropics and warms much of Europe." In this case, the blip took less than four hundred years to throw the world back into a severe Ice Age.

PS -- I should have pointed out that the name is a misnomer -- the current goes all over the place in all the world's oceans.
 

> G'Day Zero,Apparently acording to the currant models the halting of
> the Atlantic conveyor would actually cause North America to become
> warmer and wetter while Europe freezes.

Errmm...  The East coast of the USA would freeze, I think.  The West
coast would be fine.
 

> One of the effects for Australia could be a permenant El Nin'o that
> would render much of the country uninhabitable.  Another possibility
> is an icrease in rainfall in some areas mainly the wet tropics with
> an increased wet seaon and a shorter dry season.

It is the former I was afraid of.
 

On Tuesday 01 October 2002 18:21, WM wrote:
> And is there any possibility of this happening? Do I have something
> else to worry about now?

Pretty close to a certainty.  We may live to see this one.

The conveyor lost something like 20% of it's power in the years 1970 to 1990.  I don't know what happened since.  The problem is the dilution of seawater from melting ice.  The dilute seawater does not sink as readily.

Jim Edwards added:

>At 18:21 1/10/02 +1000, Bill wrote:
> >And is there any possibility of this happening? Do I have something else
>to
> >worry about now?
>
>I get paid to write worrying stories.  Yup.
>
>Here is what I wrote in November 1997 -- I haven't seen anything much that
>is new since then . . . there was an article in "New Scientist" February 8,
>1997, page 26 (UK edition, may be different in Oz)
>
<snip>>
>Ice core evidence tells us that when a climatic change comes, it happens
>over a short period, geologically speaking, with just a few decades of
>transition.

<snip>

>The key
>feature: "its termination seems to have been marked by a sudden reduction
>in the ocean 'conveyor' circulation which today carries ocean heat north
>from the tropics and warms much of Europe." In this case, the blip took
>less than four hundred years to throw the world back into a severe Ice Age.
>

This suggests that the change may have been even more sudden than Peter's article says.  What sort of event could cause the conveyor to stop so suddenly?
 

Perter Macinnis responded:
At a rough guess, a winter blizzard in autumn.  I suspect that the term "temperate grasses" may have been used loosely.

> The sis-in-law recently sent us a mag article "Have we built our
> last snowman?". It seems that winters are, of late, getting warmer
> and wetter in the UK at least.
>
Temporarily.

It is a negative feedback situation.  I won't say this makes it temporary though...

Recent warmth has caused glaciers (and ice) to melt faster.  This will have a big impact on polar bears who can no longer spend long periods on ice catching seals because the ice is disappearing.

This melting ice has cause a dilution of the seawater.  The diluted seawater is not as heavy and cannot drive the conveyor with the same degree of force.  This (if it continues - and it will) is going to shut off the conveyor and the world's oceans will have to find a new stable state.

Without the conveyor, those areas which have provided much of the melted ice should then cool and freeze (make sea ice) returning the salinity to normal.  Whether this will re-establish the conveyor is unknown.  We may have a different climate entirely.

Gary Ruben added:

I think some list members may have been confused by my confusing question because I somehow failed to mention that Plimer seems to disagree with humans being the cause of global warming. I think he thinks it's due to resonances/changes in the earth's orbit (not sure about this as I haven't read the book).

Perhaps I will ask one of my maths lecturers what his opinion is - he is also one of Australia's scientists who used to be seen as on the outer by the scientific community but who seems to have mostly forced them to eat
their words.

It'd be interesting to know who all the seriously rebellious scientists in Australia are; not the ones who have made discoveries which were immediately accepted but the ones who have and are battling in the face of
overwhelming opposition to their ideas. It's interesting because it often gives you an idea of the holes in mainstream models.