Cold Winter THC Shutdown

[VillagePlank]

Good overview of risks here

(Apologies to mods but it seems sensible to start splitting the issues under Environmental Change into their own threads, now)

[Anti-Mild]

Good overview of risks here

(Apologies to mods but it seems sensible to start splitting the issues under Environmental Change into their own threads, now)

I used to subscribe to this theory but having some read some articles illustrating just how much fresh water would be required to disrupt the THC and just how much is being poured in to the N. Atlantic at present, I cannot see any disruption occurring in the next 100 years at least.

Interesting read though, even though Bill McGuire is a cold ramper extraordinaire :lol: !!

[parmenides3]

Good overview of risks here

(Apologies to mods but it seems sensible to start splitting the issues under Environmental Change into their own threads, now)

Good idea, Wilson. This is the Schlesinger paper that the article refers to: http://www.stabilisation2005.com/Schlesing...hermohaline.pdf

The site you have linked to is a very good one, but I have some issues with the presentation of the information in the article, which I will address shortly. There are also some useful links from other discussions which I will try to find & put here.

:)P

Edited October 3, 2006 by parmenides3

[noggin]

Thanks for the link, Wilson. That theory is the one to which I have adhered for many years and I am always pleased to see "professionals" mooting it!

Any more links like that will be most welcome!

[parmenides3]

Thanks for the link, Wilson. That theory is the one to which I have adhered for many years and I am always pleased to see "professionals" mooting it!

Any more links like that will be most welcome!

Don't be fooled by the rhetoric, Noggin. As Anti-mild says, Schlesinger's paper concludes only a possibility of a shutdown, and not likely in 100 years. A similar conclusion in this, totally separate piece of work (can't access the original, but the press release is detailed); http://www.whoi.edu/mr/pr.do?id=5098

There are several key paragraphs near the end, which include (paraphrasing); no observable change to date in Nordic overflow waters; collapse of THC in 200 years possible, slowdown in 100 years possible; change in near future unlikely.

There is some good news for you, though: I'll dig it out & add it.

:)P

[Dawlish]

I used to subscribe to this theory

Me too. [edit] Still do, when I put my brain in gear and engage the thinking process - I subcribe to the theory, at least.

Nothing wrong with the theory, it's just the chances of it happening in my lifetime (or anyone else's) that I'd rather concentrate on, which as P3 says, are slim.

Edited October 3, 2006 by Dawlish

[parmenides3]

This page will access the Met report cited in McGuire's article: http://www.met-office.gov.uk/research/hadl...pubs/brochures/

:)P

Oh; and this... http://www.netweather.tv/forum/index.php?s...0299&st=204 post 216. :)P

And this one, too: http://www.cicero.uio.no/fulltext.asp?id=3914〈=no

Edited October 3, 2006 by parmenides3

[VillagePlank]

The reason I thought I'd post the Benfield Grieg article is simply because they effectively 'bet' on the weather - they are an insurance company; the policies they issue for, say, nuclear power stations, have to be set correctly to account for future weather or they'd go broke (their policy income would not exceed their claim payout)

This is not the case of an organisation with a vested interest in doom and gloom and vice versa; this is an organisation that regardless of the weather simply need to get it right whichever way they turn.

And on that basis I'll nod a fair bit of credit to what they publish.

In terms of the risk, of which I'll agree with 25% published in that article, I can see no problem; consider the inverse - there is a 75% chance of it not happening. A 25% risk, though, is still of a magnitude where it should raise eyebrows and such like, methinks.

Edited October 3, 2006 by Wilson

[parmenides3]

The reason I thought I'd post the Benfield Grieg article is simply because they effectively 'bet' on the weather - they are an insurance company; the policies they issue for, say, nuclear power stations, have to be set correctly to account for future weather or they'd go broke (their policy income would not exceed their claim payout)

This is not the case of an organisation with a vested interest in doom and gloom and vice versa; this is an organisation that regardless of the weather simply need to get it right whichever way they turn.

And on that basis I'l nod a fair bit of credit to what they publish.

As I said (and meant), Wilson; I think its a good link. Whilst it may seem odd after what I have already posted, I have some new ideas about the shutdown scenario, which I am just 'putting together'. I have to say, though, that whoever they employed to do the research for them, and whatever the brief was (they may have asked for evidence of a C21 shutdown, after all), there are some problems with the article, for example: (excuse the paraphrasing)

Freshwater influx has been linked in the past with a shutdown of the THC - Wally Broecker's theory; covered in the link to the other NW page.

Schlesinger 'highlights the risk of a shutdown this century' - misleading, if not false; Schlesinger uses models to assess the risk and concludes, with BAU, a 25% possibility of a slowdown in 100 years. He highlights nothing. Semantics, but important.

'dramatic changes' have already been observed; in one paper, yes (with disputed conclusions); the Woods Hole (no observable change so far) and the Norwegian paper (warmer and slower, but no net change in heat transfer), throw light on this.

the THC is 'likely to jump to a new state'; ah! he has access to some information on this? If not, it is an assumption, at best a possibility. (but see my next post on this).

In all, then, and not assuming any intent on the part of the publishers, I just think that it is not a very good summary of the current state of knowledge vis a vis the THC and the possibility of a shutdown.

Now, before all the cold-lovers slink off, if Mr (Prof.?) McGuire had seen the Andersen paper, about which you will hear more shortly, he might have reached the conclusion that a THC shutdown was possible on slightly better (scientifically) grounds.

Next instalment due... (I'm at home atm with a brochial virus (cough, cough)).

:)P

[Dawlish]

The reason I thought I'd post the Benfield Grieg article is simply because they effectively 'bet' on the weather - they are an insurance company; the policies they issue for, say, nuclear power stations, have to be set correctly to account for future weather or they'd go broke (their policy income would not exceed their claim payout)

This is not the case of an organisation with a vested interest in doom and gloom and vice versa; this is an organisation that regardless of the weather simply need to get it right whichever way they turn.

And on that basis I'll nod a fair bit of credit to what they publish.

In terms of the risk, of which I'll agree with 25% published in that article, I can see no problem; consider the inverse - there is a 75% chance of it not happening. A 25% risk, though, is still of a magnitude where it should raise eyebrows and such like, methinks.

I'd go 99.9999% it will happen. The only difficulty for an insurance company, is deciding upon the timeframe.

Edited October 3, 2006 by Dawlish

[VillagePlank]

I downloaded and read the Schlesinger et al paper and the assessment of risk is between now (the publish date) and 2205; a little more than 100 years.

The paper is also geared towards economic risk ie risk without economic (policy intervention is the term used in the paper) manipulation.

Also, The summary states quite clearly that 'Such probabilities are worrisome. Of course they should be checked by additional modelling studies. ... if these future studies find similar results, it would seem that the risk of a THC collapse is unacceptably large . . ."

I think, as you say P3, that BG are misrepresenting this study, somewhat; for what ends, I have no idea

[parmenides3]

I downloaded and read the Schlesinger et al paper and the assessment of risk is between now (the publish date) and 2205; a little more than 100 years.

The paper is also geared towards economic risk ie risk without economic (policy intervention is the term used in the paper) manipulation.

Also, The summary states quite clearly that 'Such probabilities are worrisome. Of course they should be checked by additional modelling studies. ... if these future studies find similar results, it would seem that the risk of a THC collapse is unacceptably large . . ."

I think, as you say P3, that BG are misrepresenting this study, somewhat; for what ends, I have no idea

Thanks for the correction: it's been a while since I read it. Here are a couple of other useful links:

http://faculty.washington.edu/wcalvin/teac...Broecker99.html An influential paper on the subject. Note that he is currently reconsidering the idea that the younger Dryas was caused by a flood/thc shutdown, though.

The other is a useful document from Hadley's Richard Wood, which I found quite clear.

Wikipedia has a rather good, up-to-date entry under 'Thermohaline Circulation Shutdown', which covers the ground in a simplified form.

:)P

33_Richard_Wood.pdf

[Guest Viking141]

Last time I looked the scientific community actually had no earthly idea what the "tipping point" for a THC shutdown would be, have things changed then?

[parmenides3]

Last time I looked the scientific community actually had no earthly idea what the "tipping point" for a THC shutdown would be, have things changed then?

Yes, Viking. Read the Schlesinger paper. In the models, they could force a shutdown by simulating a 'hosing' of freshwater into the system; that was the only way they could do it. Doesn't mean it's the only way it could happen in real life, but that's the current theory.

How much freshwater? They got the 'tipping point' to 0.6 Sv: about 600,000 cubic metres per second, or 0.6 of a cubic kilometre. That's an order of magnitude more than the sum of all the freshwater inputs into the Atlantic over recent years, even allowing for recent increases, which are generally measured in thousands of cubic kilometres per year.

:)P

Just got the calculator out; 0.6 Sv = 18,921,600 Km3/year. Current best estimates for freshwater input are around 4,000 Km3/year. We've a long way to go.

:(P

Edited October 3, 2006 by parmenides3

[Shiny_Bottom_1]

Its an interesting theory, but one which I (for at least now) will not back.

Its a huge thing, where we are basically saying that the world will shut down in a self reactive reaction to the global warming.

Its possible, but also the stuff that movies are made of.

[Essan]

From the Benfield article:-

This heat plays a critical role in maintaining a relatively benign climate in the UK and NW Europe, keeping temperatures up to 8° C higher than in comparable latitudes such as northern Canada or the Kamchatka Peninsula of eastern Siberia.

Oddly enough, the climate is fairly similar to that of British Colombia. Which is likewise on the western side of a large continent. But which does not have such a beneficial effects of warm ocean currents as the Pacific equivalent of the NAD tracks further south .....

Bryden forecasts that if the slowdown persists, temperatures in the UK and Europe could be expected to fall by about 1° C over the coming decade.

Great! That means we may have a chance of having a month here and there that's below the CET 30 year average

A fall back to 'normal' temps is hardly going to be catastrophic.....

[Gray-Wolf]

Yes, Viking. Read the Schlesinger paper. In the models, they could force a shutdown by simulating a 'hosing' of freshwater into the system; that was the only way they could do it. Doesn't mean it's the only way it could happen in real life, but that's the current theory.

How much freshwater? They got the 'tipping point' to 0.6 Sv: about 600,000 cubic metres per second, or 0.6 of a cubic kilometre. That's an order of magnitude more than the sum of all the freshwater inputs into the Atlantic over recent years, even allowing for recent increases, which are generally measured in thousands of cubic kilometres per year.

P

Just got the calculator out; 0.6 Sv = 18,921,600 Km3/year. Current best estimates for freshwater input are around 4,000 Km3/year. We've a long way to go.

P

A few 'lazy man' questions on those figures If I may.

Did the Schlesinger papers make it clear whether the 'hosing' was localised or basin wide? I mean was it freshwater flow just in the areas where there currently is sinking or freshwater flow across the whole of the area?

The other thing which I'm not quite clear on is time scales. Obviously a continual flow over a number of years is a sneck of a lot of water but a short term (days or weeks) outflow over a localised area (the major sinking zones) is a more concievable scenario.

We don't have the kind'a Glacial Lakes left at the end of the last ice age but we do have one very large remnant ice sheet that could produce the necessary 'hosing' under the right set of circumstances I think.

Edited October 3, 2006 by Gray-Wolf

[senior ridge]

The reason I thought I'd post the Benfield Grieg article is simply because they effectively 'bet' on the weather - they are an insurance company; the policies they issue for, say, nuclear power stations, have to be set correctly to account for future weather or they'd go broke (their policy income would not exceed their claim payout)

This is not the case of an organisation with a vested interest in doom and gloom and vice versa; this is an organisation that regardless of the weather simply need to get it right whichever way they turn.

And on that basis I'll nod a fair bit of credit to what they publish.

In terms of the risk, of which I'll agree with 25% published in that article, I can see no problem; consider the inverse - there is a 75% chance of it not happening. A 25% risk, though, is still of a magnitude where it should raise eyebrows and such like, methinks.

Thank you Wilson for posting the article. Without stating the obvious, one of the challenges for the insurance and re-insurance industry is to properly set insurance premiums to cover weather related claim risks. To date, most insurers and re-insurers have failed badly so far and only rely on their investors to bail them out e.g last year's hurricanes.

[parmenides3]

A few 'lazy man' questions on those figures If I may.

Did the Schlesinger papers make it clear whether the 'hosing' was localised or basin wide? I mean was it freshwater flow just in the areas where there currently is sinking or freshwater flow across the whole of the area?

The other thing which I'm not quite clear on is time scales. Obviously a continual flow over a number of years is a sneck of a lot of water but a short term (days or weeks) outflow over a localised area (the major sinking zones) is a more concievable scenario.

We don't have the kind'a Glacial Lakes left at the end of the last ice age but we do have one very large remnant ice sheet that could produce the necessary 'hosing' under the right set of circumstances I think.

This is not as simple as it sounds, G-W (sorry). I think the 'hosing' was an artefact of the way they ran the models; they couldn't generate a shutdown with the usual variables, so they 'forced' the model to produce a shutdown by inputting one, very large variable into the run. The argument is that this kind of 'hosing' could be equated to the sort of ice-sheet collapse which might have caused a rapid cooldown in the Younger Dryas (several thousand years ago).

As for geography: this, too, is problematic. The Younger Dryas and Holocene cooling events seem to be related to large inputs of freshwater into the Labrador Sea from the Davis Strait, principally. Today, this is no longer possible, because the outflow area's configuration has changed, and you can't get that much Arctic water through the Davis Strait any more. Most freshwater enters the North Atlantic through the Fram Strait (North of Iceland) nowadays.

Curry (2005), suggests that the critical area to watch for large scale freshwater dumping into the Atlantic is now the Greenland-Iceland-Norwegian Seas, specifically, the area to the North of the 'lip' which runs from Greenland to Shetland. There is evidence that freshwater is building up in this area, but so far, not at a rate that might cause a THC slowdown in less than about 100 years.

On the timescales, as far as I know, the model's synthetic 'hosing' was more or less instantaneous (relative to the scale it was using). This is less likely in the real world, where we would be looking for evidence of a build up over a period of, at least, years.

But all of this does not necessarily mean that we can't reach a 'tipping point' in the near future (though I am going against the science in saying this). I'll explain my reasoning in another post; this one is too long already.

:)P

[Guest Viking141]

This is not as simple as it sounds, G-W (sorry). I think the 'hosing' was an artefact of the way they ran the models; they couldn't generate a shutdown with the usual variables, so they 'forced' the model to produce a shutdown by inputting one, very large variable into the run. The argument is that this kind of 'hosing' could be equated to the sort of ice-sheet collapse which might have caused a rapid cooldown in the Younger Dryas (several thousand years ago).

As for geography: this, too, is problematic. The Younger Dryas and Holocene cooling events seem to be related to large inputs of freshwater into the Labrador Sea from the Davis Strait, principally. Today, this is no longer possible, because the outflow area's configuration has changed, and you can't get that much Arctic water through the Davis Strait any more. Most freshwater enters the North Atlantic through the Fram Strait (North of Iceland) nowadays.

Curry (2005), suggests that the critical area to watch for large scale freshwater dumping into the Atlantic is now the Greenland-Iceland-Norwegian Seas, specifically, the area to the North of the 'lip' which runs from Greenland to Shetland. There is evidence that freshwater is building up in this area, but so far, not at a rate that might cause a THC slowdown in less than about 100 years.

On the timescales, as far as I know, the model's synthetic 'hosing' was more or less instantaneous (relative to the scale it was using). This is less likely in the real world, where we would be looking for evidence of a build up over a period of, at least, years.

But all of this does not necessarily mean that we can't reach a 'tipping point' in the near future (though I am going against the science in saying this). I'll explain my reasoning in another post; this one is too long already.

:)P

What about the increasing fresh water input from Siberian rivers does this not add a huge amount of fresh water to the equation? Combined with that from the sources you quoted above that has to be a humungous amount of fresh water entering the North Atlantic on a regular basis?

Edited October 3, 2006 by Viking141

[VillagePlank]

What about the increasing fresh water input from Siberian rivers does this not add a huge amount of fresh water to the equation? Combined with that from the sources you quoted above that has to be a humungous amount of fresh water entering the North Atlantic on a regular basis?

It is, as you say, certainly a large amount of water; I think what P3 is saying is that in order to trigger a shutdown we need even more

Precipitation, and evaporation rates increase with warmth but the difference between the two also increases ((Manabe 1994) What is not well specified is whether the rate of increase between the two (P-E) is linear, exponential or whatever; clearly the Schlesinger report seems to discount it rather quickly out of hand. It may indeed be the case the P, and E increase, but I think the question is where does P, and E actually happen; if the E rate is higher say over N America, and the P rate is higher over the N Atlantic and the weather is, overall, W to E in this neck of the woods, then (P-E) seems to be less than what is needed for such a dismissive stance (N America evaporates and tips that evaporation into the Atlantic)

I'll try and dig out the Manabe paper to see if we can get our freshwater from rain

Edited October 3, 2006 by Wilson

[parmenides3]

What about the increasing fresh water input from Siberian rivers does this not add a huge amount of fresh water to the equation? Combined with that from the sources you quoted above that has to be a humungous amount of fresh water entering the North Atlantic on a regular basis?

Sorry for the delay; had to walk the dog, which ain't easy with a bronchial virus, I can tell you!

Stats on Arctic freshwater discharge here (Maurer paper). There a lot, but it doesn't get directly into the Atlantic; it has to work around the Arctic for a bit, shift up & down in the water column, then hustle around, freezing and thawing. It works out at 5,249 Km3 per year, estimated increase +1.1%/an. into the Arctic Ocean; less into the Atlantic freshwater influx.

Try Permafrost melting... see what you can find for the figures in this; I have'nt looked.

Wilson; I think the P-E equation for the Arctic is negative ATM. Have a look at a couple of pieces of research found;

Maurer_Discharge_Arctic_Ocean_ACSYS_Book_2004.pdf

CRR275.pdf

[Guest Viking141]

Sorry for the delay; had to walk the dog, which ain't easy with a bronchial virus, I can tell you!

Stats on Arctic freshwater discharge here (Maurer paper). There a lot, but it doesn't get directly into the Atlantic; it has to work around the Arctic for a bit, shift up & down in the water column, then hustle around, freezing and thawing. It works out at 5,249 Km3 per year, estimated increase +1.1%/an. into the Arctic Ocean; less into the Atlantic freshwater influx.

Try Permafrost melting... see what you can find for the figures in this; I have'nt looked.

Wilson; I think the P-E equation for the Arctic is negative ATM. Have a look at a couple of pieces of research found;

Sorry if it seems like Im asking daft questions at the mo but I dont have a lot of time to wade through scientific papers just now. Got my hands full studying for my all important final exams in just 4 weeks time (eek) so you'll forgive me for the lack of effort on my part at the moment!

[parmenides3]

Sorry if it seems like Im asking daft questions at the mo but I dont have a lot of time to wade through scientific papers just now. Got my hands full studying for my all important final exams in just 4 weeks time (eek) so you'll forgive me for the lack of effort on my part at the moment!

No need to apologise; you're giving the rest of us a chance to show how erudite and articulate we are. And the questions aren't daft; the central to the discussion.

Now P*** *(f & do some revision. P (Don't do sympathy...)

[Guest Viking141]