The Gulf stream....

[disco-barry]

If for example the amount of fresh water far outweighed the amount of salt water and this stopped the Gulf-stream, what would we expect?

Should we expect weather like Norway ??? And would we get fewer westerlies?!

Thanks, DB

[Supercell 89]

Thats what i've been debating to myself the last year or so, i reckon it would but then i'm no professional but the rate that fresh water is going into the sea's i think its quite possible, and might do enough to give us a different climate e.g. I think if it did we would still get quite warm summers but winters would be very cold.

[summer blizzard]

I also believe that it is very possible and upto 2004, the strength of the return flow was dropping at something like 3% per year i believe, which is quite worrying personally, it it were to happen, the result would be a much more southerly tracking Jet Stream, causing colder and dryer winters, and cooler and wetter summers.]

The main problem is, as the effect would be most pronounced in winter, we may not even know what was happening, we would just get gradually colder and longer winter spells, until one year, summer never really arrived at all.

Within a few years of this event happening, we would see glaciers forming in the Scotish, Welsh and English peaks, gradually encrouching to lower levels, however the most scary thing is, that natural cycles indicate that we are heading back towards the next Ice Age, in around 1000 years, we are supposed to be seeing a net cooling anyway assuming global warming does not affect this, so paradoxically, we could affectively just beat the rest of the world into the next Ice Age by a millenia.

[John Cox]

If this were to happen our temps would drop by up to 5C. Our climate would be like Canada.

The more Global warming occurs the more likely is the shutdown of the NAD.

Patience is called for and I have lots of it.

If the shutrdown does happen it could happen quite quickly

[disco-barry]

John it would be a Major shock to us and alot of Europe.

[Supercell 89]

How long do you think it'll be before we start to see any effects, that is if it actaully is changing

[PersianPaladin]

I think that the speed of melting and obviously the geographic location of the ice-shelf will be important as to what impact dense fresh water will likely have on the highly variable temp gradient in the north Atlantic. The way these oceanic circulation gyres work is a tad complicated and relative to several feedback mechanisms which may moderate (or even reverse) the effect of large-scale melting or increase in sea-level to our north. It really depends on the scenario and the scale....imo.

Edited April 4, 2007 by PersianPaladin

[Roger J Smith]

I am not sure what confidence anyone in active research might have about the projections for a complete "shutdown" of the North Atlantic drift, probably slight though.

However, let's say for the sake of argument that such a thing takes place and the North Atlantic cools off by several degrees. It may make less difference to the climate of the UK than some are speculating.

The Pacific west of British Columbia is generally 2-3 degrees cooler at given latitudes than the North Atlantic. For example, right now 7-8 C is a fairly common reading out in the open Pacific west of here. But this is not the main reason why Canada is colder at various latitudes than the UK. Actually, sea level locations in British Columbia are not colder, but about the same. We do tend to get more variation in winter here, but differences in climatological terms are slight.

The reasons why most other parts of Canada are colder have to do with the blocking effects of the Rockies and other western mountain ranges, and the location of a mean trough in the upper atmosphere near 85 W, which steers the very cold arctic air across the continent and makes all latitudes north of about Atlanta GA colder relatively speaking than in Europe, but only from November to April, the rest of the year is relatively warmer in North America.

If the Atlantic cooled down, winters in the UK would no doubt return to something more similar to the early 20th or 19th centuries, but I doubt that the jet stream would take a huge hike to the south, because other factors are in play determining where the jet stream will set up shop. As for more dire projections of a near ice age sort of climatic turn, that would depend more on long-term astronomical cycles that are not currently moving in that direction.

All of the above ignores possible effects of AGW which would further modify any cooling influences of this shutdown effect.

The other factor to be considered is that said shutdown may not be complete, or permanent, but more of a tendency thing, in which case its effects would be further reduced relative to recent averages.

As I say, I am not really sure if anyone active in research thinks this is imminent or large-scale, or if it's more of a factor among many that could introduce a slight change. But as far as I know the predictability of this is very much of a question, so really it is more in the realm of speculation with a very large margin of error. Sort of like tomorrow's forecast.

[acbrixton]

If this were to happen our temps would drop by up to 5C. Our climate would be like Canada.

The more Global warming occurs the more likely is the shutdown of the NAD.

Patience is called for and I have lots of it.

If the shutrdown does happen it could happen quite quickly

John apart from the points made by PP:

1. Not at all sure that even a 5c drop would leave us with a climate "like Canada". First Canada has a considerable range of climates; secondly with the exception of Vancouver/the southern parts of the Pacific coast of British Columbia even a 5c drop in winter temperatures (assuming all seasons were equally affected post-shutdown) would not bring us to the current winter temperature averages experienced say in St Johns or Halifax [According to data from the BBC St. Johns experiences maxima over winter in the range +1 to -2c and minima of -4 to -9c whilst Halifax experiences maxima of +2 to -1c and minima of -6 to -9c];the mainly continental climates of most of Canada are due in part to the fact that it is part of a large landmass stretching from the high Arctic to the Gulf of Mexico: even if the NAD were to shut down substantially we would still be a group of islands off the north west of Europe subject to maritime influences; thirdly even allowing for an increase in anticyclonic blocking to our north and east we would still be subject to mild damp westerlies (albeit cooler than now) whilst westerlies in Canada away from the Pacific coast of BC are modified by the north/south Rocky Mountains range.

2. Not all sure that the implied linear relationship between GW and a NAD shut down is right...might it not be the case that GW above a particular level could start to reverse the cooling effects of a shut down? [i am not sure of this btw!]

3. I have to say that I am baffled by your apparent strong desire for a sudden drop in average temperatures of 5c: this is not the same as hoping for some decently cold/snowy winters or even a return to the conditions of the Little Ice Age; such a change (especially if sudden)would be economically and socially catastrophic with conditions similar to those at the end of the last Ice Age.

Regards

ACB

[Gray-Wolf]

Firstly lets not forget that this is a 'warming world' and that the largest body receiving this 'extra' heat is the oceans. Past Ocean current shutdowns have been against the backdrop of a stable planet (probably the ablation of a glacial episode) and so any 'lessons' gleaned from those times will not provide an adequate framework of what we are to expect.

Sure, the Atlantic (north) would cool off but there would be plenty of warmer waters wishing to balance this out. The Plankton blooms show the seasonal movement of warmer waters each spring so the mechanisms for a straight south to north migration of warmer waters exists already and would probably just strengthen. In turn this would mean a more widespread warming of the Atlantic over summer (as against 'rivers' of warmer waters) leading to more rapid ablation of northern pack ice leading to more 'dark water' to warm up further.

All along we will be raising CO2 levels (extra warming) and cleaning out more and more particulate pollution (less 'dimming' so more 'warming').

If we were looking for a worrying northern hemisphere trend then we should be focusing of ice sheets and sea ice ablation!

[parmenides3]

Current thinking is that a complete shut down of the THC is 'unlikely'. Most AOGCMs model a slow down of the Atlantic current, but no shut down.

The amount of freshwater input required, (if this is the meachanism which cause a 'trip') is vastly larger than the currently very large amounts flowing out of the Arctic.

It is also important to remember that, even if there was a slowing of the current, the temperatures of thwe water would be higher, so the net transport of heat would stay more or less in balance. This phenomenon was noted last year in a paper about ten years of analysis of the Norwegian Atlantic Current (NwAC); the data showed a slowing, but an increase of temps; the two balanced out fairly closely, so the net heat transport stayed relatively constant in this period.

The Hadley model estimates, under a BAU scenario, that the THC will slow a bit, but the reduction in the heat from this will be, on the century timescale, more than offset by the rise in global temperatures.

If you really want to believe that the THC will have an adverse effect on UK weather (a reasonable belief), the science suggests (it is still at the stage of 'likelihood' rather than certainty), that we will get a shortish period (10-20 years) of somewhat cooler weather - in the order of 1-2C on average - followed by a return to the long-term warming, which will eventually overtake the cooling effect.

Hope this helps.

:)P

[summer blizzard]

1C-2C cooling is fine with me, makes the winter 0f 1979 around average.

[parmenides3]

1C-2C cooling is fine with me, makes the winter 0f 1979 around average.

Side note; that'll be a 1-2C cooling in comparison to the immediately preceding climate, so what the Winters will be like would depend on when, if at all, such a slowdown kicks in; if it were to happen in the next thirty years, you might be in with a chance of some decently cold winters, after that, it may resemble the last couple, instead. Too many uncertainties to call this one, really. Sorry to spoil some people's hopes...

:)P

[The Penguin]

Firstly lets not forget that this is a 'warming world' and that the largest body receiving this 'extra' heat is the oceans. Past Ocean current shutdowns have been against the backdrop of a stable planet (probably the ablation of a glacial episode) and so any 'lessons' gleaned from those times will not provide an adequate framework of what we are to expect.

But that is simply not true G-W. The planet has never been stable or shutdowns and reactivations would never have happened. Our entire climate history and function is founded in instability - is that not what makes it so hard to model?

[parmenides3]

But that is simply not true G-W. The planet has never been stable or shutdowns and reactivations would never have happened. Our entire climate history and function is founded in instability - is that not what makes it so hard to model?

Whilst G-W's comment may not be exactly correct (in the sense that you point out), his general idea probably is: we do not know enough about previous climates or the causes and effects of various changes to be able to directly compare the current situation with any in the distant past in a meaningful way. An example might be Wally Broecker, who established the 'Laurentide hosing' hypothesis in the 90's, but now is less sure that this is an explanation of why the THC might have shut down at that time. I agree with you, though, that a sense of the planet having a 'stable climate state' is not right. In this sense, the last 2000-odd years are exceptional, in the unusually consistent patterns which dominate up to the 20th century (not forgetting the MWP and the LIA, of course).

:)P

Edited April 4, 2007 by parmenides3

[Gray-Wolf]

But that is simply not true G-W. The planet has never been stable or shutdowns and reactivations would never have happened. Our entire climate history and function is founded in instability - is that not what makes it so hard to model?

Behave Pengers!

We happen to be talking about Human induced instabilities/forcings within our climate system and how that could/might affect ocean currents.

That being so the 'Stable' phase of Earth climate is prior to our inputs/upsets that we now see are starting to impact our climate over and beyond the planets own 'Stable' suite of influences.

I don't mean to be rude but pedantry and 'point scoring' adds nothing to our understanding.

[Guest Daniel]

If for example the amount of fresh water far outweighed the amount of salt water and this stopped the Gulf-stream, what would we expect?

Should we expect weather like Norway ??? And would we get fewer westerlies?!

Thanks, DB

I have gone of the gulf stream theroy because the theroy does not add up. We have been told now for more than 10 years the currents has weakened and that we would freeze. Yet there is no sign of that occuring at all. If they are right we should be now be seeing very sever winters and cooler summers. but we are not. Also its just does not add up at all. We cant have a warm ice free Arctic while we freeze. In order to understand what made us colder in the last little ice age of the 17th century we need to look at the weather patterns. Back then the weather patterns were very dffernet than now. the great winters of that period were caused by east winds and powerful blocking highs to the north of us. Also arctic sea ice was much greater then with the ice sheet comming far south of Iceland. something that does not occur now. The reason why we are warm today is down to the simple fact that get get strong west winds from a warm atlantic with lows to the north. In other words pressure patterns are differnent now to what they were. Also I wish to point out the average temps of the little ice age in the U.K were no more than 2 degrees colder than now. that may not seem much but it was enough to freeze over our rivers and coasts and cause long lying deep snows in England. so a full 6 degree drop would be very bad for us in deed. As for the future just because its warm now it will not be warm for ever. In fact we could enter another little ice around the middle of the century starting any were from 2010 to 2015. this will be cause by the changes in the sun not the gulf stream. Also if we have any major volcanic eruptions that two can cool us enouigh to freeze us in winter. This is because when we get a quiter sun or large dust in the skie the wind patterns for some reason change over the Atlantic bringing us cold in winter.

[Admiral_Bobski]

Behave Pengers!

We happen to be talking about Human induced instabilities/forcings within our climate system and how that could/might affect ocean currents.

That being so the 'Stable' phase of Earth climate is prior to our inputs/upsets that we now see are starting to impact our climate over and beyond the planets own 'Stable' suite of influences.

I don't mean to be rude but pedantry and 'point scoring' adds nothing to our understanding.

I don't think it's pedantic to make Penguin's point. Our incomplete understanding of the causes of past climate changes is precisely the reason why we should be wary about placing the blame firmly in the lap of human activity.

Let me try a dreaded analogy...

Imagine a time before there was any concept that the world was spherical - it was thought to be flat, and the cause of the sunrise and sunset was unknown. Nobody could figure out what it was that made the sun rise and set. Then one chap comes along and says, "Every time I wake up in the morning and open my curtains it's light outside. So, opening my curtains in the morning must make the sun rise."

Now, this says nothing as to what the cause of sunrises might have been prior to the advent of curtains, but the theory can be tested every morning with a pretty good success rate.

Okay, so you can invoke the argument that this analogy ignores any scientific principles (except that of observation!), but the basis is pretty similar to the current view of human-influenced global warming - "past events are beside the point, we've found a theory that fits observation."

CB

[Gray-Wolf]

C-Bob , our understanding may be 'incomplete' but we have some of the major pieces of the puzzle in place (sun/earth relationship, albedo, continental jet stream influence, oceanic current blocking etc.) to explain past climate 'lurches' and we know none of those 'forcing's' are present, and at work here today yet change continues apace.

I know most of these threads are for the sake of argument but maybe our time would be better invested in theorising the more extreme scenarios of continued change than the extreme scenarios as to why change isn't happening as we predict it to.

Most authorities now accept climate change as a given and are scampering to better understand it's potentials on humanity and humanities continuance so maybe we should follow their lead?.

The 'curtains ' analogy would only take the man walking outside whilst his curtains were shut to bring the 'theory' into question and most of the arguments demoting human influence are as easily debunked.

[The Penguin]

Behave Pengers!

We happen to be talking about Human induced instabilities/forcings within our climate system and how that could/might affect ocean currents.

That being so the 'Stable' phase of Earth climate is prior to our inputs/upsets that we now see are starting to impact our climate over and beyond the planets own 'Stable' suite of influences.

I don't mean to be rude but pedantry and 'point scoring' adds nothing to our understanding.

G-W, I really wasn't trying to score points, and I am aware of the context here, however my point was that against a history of natural instability it is kind of difficult to overlay human induced instability and say "there, told you so".

To use another dreadful analogy, simple in this case, it's easy to see ripples resulting from a stone thrown into a calm pond, but it is not so easy to see ripples in a stormy sea.

Unless and until we can understand the origin of the waves in the stormy sea we will certainly not be able to judge the true cause and effect of possible human induced ripples.

[Admiral_Bobski]

C-Bob , our understanding may be 'incomplete' but we have some of the major pieces of the puzzle in place (sun/earth relationship, albedo, continental jet stream influence, oceanic current blocking etc.) to explain past climate 'lurches' and we know none of those 'forcing's' are present, and at work here today yet change continues apace.

I know most of these threads are for the sake of argument but maybe our time would be better invested in theorising the more extreme scenarios of continued change than the extreme scenarios as to why change isn't happening as we predict it to.

Most authorities now accept climate change as a given and are scampering to better understand it's potentials on humanity and humanities continuance so maybe we should follow their lead?.

The 'curtains ' analogy would only take the man walking outside whilst his curtains were shut to bring the 'theory' into question and most of the arguments demoting human influence are as easily debunked.

I don't want to take this thread off-topic, so I shall reply to this on the "CO₂ levels" thread.

CB

[Stratos Ferric]

G-W, I really wasn't trying to score points, and I am aware of the context here, however my point was that against a history of natural instability it is kind of difficult to overlay human induced instability and say "there, told you so".

To use another dreadful analogy, simple in this case, it's easy to see ripples resulting from a stone thrown into a calm pond, but it is not so easy to see ripples in a stormy sea.

Unless and until we can understand the origin of the waves in the stormy sea we will certainly not be able to judge the true cause and effect of possible human induced ripples.

It's a weak argument against G-W. There are illnesses, such as Parkinsons, the precise cause and nature of which are not known, but the outcome of which is certain. When I was at school a kid from a younger age group died in the space of 24hrs: his heart just kept beating slower and slower until it stopped. Medicine will try to treat symptoms when causes are unclear. In the case of our climate it is perfectly easy to understand the basics of the whole system. For the world to be getting warmer (which it is, let's just accept that fact) there must be a change in net flux. Most known and obvious drivers have been measured for long enough for their impact to be measured against earlier baselines, and excluded. The one reasonable variable is the nature of the atmosphere itself, which is quite demonstrably changing, and, what's more, is doing so in precisely the fashion that would suggest warming. The argument has face validity AND is backed up by science. It's highly unlikely that there's any hitherto undiscovered forcing factor at work. The flux required would be just too great to not have been spotted by now by some monitoring process or another.

[noggin]

It's highly unlikely that there's any hitherto undiscovered forcing factor at work. The flux required would be just too great to not have been spotted by now by some monitoring process or another.

But this assumes that we know everything, does it not? That's a scary assumption.

I maintain it's the Sun wot's doin' it.

[Devonian]

But this assumes that we know everything, does it not? That's a scary assumption.

I maintain it's the Sun wot's doin' it.

Now, THAT, is a scary assumption. Scientists have been studying the climate, the weather and the sun in ever greater detail for a long time - as time goes by the evidence they are right gets stronger and greater. Yet, you assume they've missed an effect of great magnitude?? Well, then, publish your findings

[The Penguin]

It's a weak argument against G-W. There are illnesses, such as Parkinsons, the precise cause and nature of which are not known, but the outcome of which is certain. When I was at school a kid from a younger age group died in the space of 24hrs: his heart just kept beating slower and slower until it stopped. Medicine will try to treat symptoms when causes are unclear. In the case of our climate it is perfectly easy to understand the basics of the whole system. For the world to be getting warmer (which it is, let's just accept that fact) there must be a change in net flux. Most known and obvious drivers have been measured for long enough for their impact to be measured against earlier baselines, and excluded. The one reasonable variable is the nature of the atmosphere itself, which is quite demonstrably changing, and, what's more, is doing so in precisely the fashion that would suggest warming. The argument has face validity AND is backed up by science. It's highly unlikely that there's any hitherto undiscovered forcing factor at work. The flux required would be just too great to not have been spotted by now by some monitoring process or another.

No, I take issue with that. Firstly, it was not an argument against G-W if you refer to Global Warming and was I think a pertinent one against Grey Wolf if it is to his original proposition that you refer. The crux is whether in the absence of a specific formula tying together inputs and outputs before human induced CO2, you can somehow ascertain through extrapolation the effects of human activity. Secondly, unlike Parkinson’s where we only know the outcome because we've seen it before, we cannot project anything from where we stand because we've never been here before. We are, if we must use analogies, examining a patient whose symptoms give us concern but whose exact condition baffles us (except that it is certainly not Parkinson’s) and their prognosis is therefore beyond our skill to predict. Third, and last, there could be an as yet unidentified factor involved in the forcing you refer to, and it is just as likely to be very small as very big. Either way it remains outside our capacity to isolate and explain.