Global Warming

[parmenides3]

Freshwater wise there are many contributory factors. Meltwater from glaciers, ice cover, snowcover melt, river deposit, very high precipitation levels. One quote from the horizon programme was that there would be Armadas of icebergs flowing into the North Atlantic due to the Greenland 'meltdown'. Someone forgot to mention that up til recently Greenland had been cooling for wee while I found that report posted by Permanides3 very intriguing but do not see that as an option in our lifetimes...but of course is possible.

Re the change in ocean patterns I believe solar variance can cause/affect that so a shutdown is not necessary for this to occur.

BFTP

You are right, of course, that there are lots of things adding to the freshwater budget, but the contribution of the other factors compared to the Arctic-Atlantic flux is quite small.

The Horizon programme may have been referring to the past (Laurentide) event, which resulted in the last THC shutdown. Other than that, I can't see where they would get the idea of 'armies of icebergs'.

Greenland is more complicated: colder in the high interior, with increased precipitation, but a rapid acceleration of glacier movement in the past 10-15 years (I think about 40%). The NSIDC graphics shows continuing coastal deglaciation and a retreat of the ice sheet compared to the past 100 years, even though the continent as a whole has been cold. Current research into this suggests a possible link between the two phenomena.

Do you think it's time to consider merging strands? Mods?

P

Edit: Greenland ice sheet loss 2000 (NASA):

Edited August 11, 2006 by parmenides3

[parmenides3]

[Essan]

The last shut-down of the THC was probably the 8,200kya Event - which I don't think gets the same publicity as the Younger Dryas 'cos it doesn't have such a catchy name

It caused a 200 year long cold/wet spell across much of Europe - and possibly started human migrations which eventually led to the rise of the Sumerian civilisation...

However, like the YD, it was caused by a sudden and catastrophic influx of fresh water into the N Atlantic. Not a slow and gradual process as is happening today. So neither the 82,00kya Event nor the Younger Dryas can be used as a precedent on which to predict possible future climatic changes.

The best precedent for a future shut-down of the THC may in fact be the Little Ice Age - although it's not known for sure that that was what caused it (though logically, it was preceeded by several hundred years of warmer conditions in the arctic - hence the Viking colonies - and, we must therefore presume, a long period when there was a steady increase in glacial meltwater flowing into the N Atlantic).

[BLAST FROM THE PAST]

Essan

The little ice age is connected to the Maunder Minimum. However, interesting points raised

BFTP

[parmenides3]

However, like the YD, it was caused by a sudden and catastrophic influx of fresh water into the N Atlantic. Not a slow and gradual process as is happening today. So neither the 82,00kya Event nor the Younger Dryas can be used as a precedent on which to predict possible future climatic changes.

How sudden? Generally speaking, when a palaeographer says 'sudden' it can cover timescales of thousands of years.

Because many of the current figures are frequently compared with the proxy record for similar past events, there are ways of estimating the current rates, and they are relatively rapid - certainly comparable with the rates preceeding the YD in the earlier stages.

It has been suggested that the 'Little ice age' was an example of a weakened Dansgaard-Oeshger event (Bond, et.al.), and a case might be made for suggesting that we are entering a D-O-type scenario, but these were generally preceded by a Heinrich event - something like what the BBC were referring to, and we haven't had one - yet.

Also, courtesy of the Beeb, another cat to throw in... http://news.bbc.co.uk/1/hi/sci/tech/4783199.stm

What this all seems to be boiling down to, Essan et. al. (correct me if I'm wrong), is a discussion of the possible timescale and subsequent impact of a 'cooling event'. But as things stand, we are still warming...

P

[Terminal Moraine]

If we're talking about the THC shutting down, (I think we are), the thing to watch out for (the necessary condition) is the amount of 'freshwater' getting into the Atlantic from the Arctic. There are other elements to consider, but the evidence is fairly strong that this is what caused the rapid cooling in the Younger Dryas (about 11,500 years ago). Thing is, the amount of freshwater influx needed to cross the 'threshhold' is hugely mega-ginormous; about 0.6 Sv is the estimate based on recent modelling. (1 Sv = 10,000,000 m3/sec). The average freshwater contribution from the Arctic to the Atlantic is about 5000 km3/year. Glaciers have contributed about 600 km3/year on average.

Some very interesting statistics there, Parmenides. I hadn't realised the required amount of fresh water influx was quite so vast.

If my maths is correct this means that, during the required influx of fresh water to initiate a shut down, the current entire annual discharge from the Arctic to the Atlantic would be realised in about 167 seconds. The current dischage from the Arctic amounts to 31.7m3 per second, averaged over the year, as opposed to the required, 6,000,000 m3 per second required to initiate a shut down, quite mind boggling

amounts.

Even allowing for the fact that we may be some way further down the road to shut down than is suspected it seems very unlikely that such an event will occur during what remains of my lifetime, unless of course I am a future entry in the Guinness Book of Records under the longevity section.

T.M

[parmenides3]

Even allowing for the fact that we may be some way further down the road to shut down than is suspected it seems very unlikely that such an event will occur during what remains of my lifetime, unless of course I am a future entry in the Guinness Book of Records under the longevity section.

Thanks, TM; this is just the point I was trying to make. All is not lost for the 'sooner rather than later' camp, though; another piece of research concluded that what you need to kick-start a shutdown is about 9000km3 of extra freshwater hanging around the Nordic Seas outflow area. This report suggested that between 1965-1995 there was a net gain in the region of 2500km3, mainly related to the 'great salinity anomaly' and similar events during the period. That works out as an average excess of 62.5km3. Now, if you assume that the freshwater levels are still increasing (plenty of evidence for this), and therefore an average increase in excess of +0.09% (figure from the report), compounded, you end up with a date of...

(it'll be more fun if you do the sum ).

A caveat, however; as well as forcings, there are also inhibitors, such as Caribbean salinity increases due to reduced precipitation, so the report concludes that 200 years (once again) is a plausible 'soonest'. I've enailed to ask if it could be sooner, circumstances permitting. Am awaiting reply.

This is truly an intriguing 'puzzle', and one of considerable significance in terms of the climate, so it pays for us all to keep an open mind. I don't know which report, if either, offers the more realistic scenario, though I will say that the first was highly dependent on modelling from palaeo. records, and the second was driven by analysis of recent data.

P

edit: I'm not sure what a enail is, but it sounds quite exciting.

Edited August 11, 2006 by parmenides3

[BLAST FROM THE PAST]

P3

Just thinking out loud here, the increased salinity in the caribbean may be of little consequence. If the THC is slowing [about 30% is that the figure] then the amount of saltwater transfer would have decreased too/or take much longer to transfer?

BFTP

[parmenides3]

P3

Just thinking out loud here, the increased salinity in the caribbean may be of little consequence. If the THC is slowing [about 30% is that the figure] then the amount of saltwater transfer would have decreased too/or take much longer to transfer?

BFTP

That would be jumping the gun, BFTP. The extra-saline Caribbean water isn't my idea; it came from the report. I try to offer up such matters as they do have an impact, but I haven't found anything yet for the salinity levels of the water arriving at the top of the gyre; it's out there, so I'll look. If you look at the diagrams of the circulation patterns, you have to include the Caribbean waters, as they are 'on' the 'conveyor belt'.

Oh, my head hurts...

P

[BLAST FROM THE PAST]

That would be jumping the gun, BFTP. The extra-saline Caribbean water isn't my idea; it came from the report. I try to offer up such matters as they do have an impact, but I haven't found anything yet for the salinity levels of the water arriving at the top of the gyre; it's out there, so I'll look. If you look at the diagrams of the circulation patterns, you have to include the Caribbean waters, as they are 'on' the 'conveyor belt'.

Oh, my head hurts...

P

P

Cheers mate, I think aloud sometimes as to entice responses to questions and thoughts I don't know the answer to. I enjoy these threads and I enjoy reading other members thoughts and findings. Re Caribbean yes of course it has to be included just throwing one in about its increased salinity level and its effects positive/negative.

BFTP

[parmenides3]

Fun. isn't it?

Here's another, I think excellent, website to give us all headaches: (sorry if you already know about it)

The Discovery of Global Warming, by Spencer Weart, on http://www.aip.org/history/climate/index.html

It's actually a long history of Climate Science, from the beginnings to the present (it's very up-to-date), and covers a hell of a lot of what we've been discussing on these threads. Two especially good essays (the second is quite long);

'Ice sheets and sea level rise' and 'Ocean currents and climate', (as above, follow the links).

Like you, I find the challenges/ questions posed by others an incentive to find out more and share the findings; your speculations, along with those of other posters, are an excellent way to get all of us to think about what we know (see my signature). Thanks for the input, like I said, it's fun.

P

Edited August 12, 2006 by parmenides3

[Essan]

Essan

The little ice age is connected to the Maunder Minimum. However, interesting points raised

BFTP

Partly yes. But the Maunder Minimum lasted only about 70 years (1645 - 1715). Some of the coldest weather of the LIA occured long after the MM was over.

How sudden? Generally speaking, when a palaeographer says 'sudden' it can cover timescales of thousands of years.

A matter of years at most. Probably weeks. It was caused by the collapse of an ice dam, allowing Lake Agassiz to drain into the Labrador Sea.

http://www.eos.ubc.ca/research/glaciology/...akeAgassiz.html

http://www.geo.vu.nl/~renh/8200yrBP-event.html

Also, not sure if this has been posted yet, but a good read:

http://www.whoi.edu/institutes/occi/viewArticle.do?id=9986

[parmenides3]

I think it is important to consider that, whilst Solar Irradiance definitely does influence climate, we can't pin either historic or current changes on one dominant forcing agent; the situation at the moment is far more complicated than that (as I am rapidly coming to realise). If there is an eefect of the forthcoming Gleissberg minimum, it is most likely to be as an enhancement, or repressant, of existing trends, rather than a causal agent.

[Essan]

Spot on

IMO people have spent too long trying to pin climatic change on this, that or the other - when in reality it's most likely an incredibly complex and virtually unpredicable combination of factors and associated feedbacks - some enhancing some reducing the overall effects.

What effect the forthcoming Gleissberg Minimum has on climate under AGW and also a potential THC slowdown is anyone's guess!

[parmenides3]

Spot on

IMO people have spent too long trying to pin climatic change on this, that or the other - when in reality it's most likely an incredibly complex and virtually unpredicable combination of factors and associated feedbacks - some enhancing some reducing the overall effects.

What effect the forthcoming Gleissberg Minimum has on climate under AGW and also a potential THC slowdown is anyone's guess!

Agreed. Good read, Andy, thanks. Thing is, if you look carefully at what all of these papers and reports are saying, then ask the question 'So, when are we going to see this happen?', the most common response seems to be 'Er..'

Which takes us (on NW) back to where we started.

P

[parmenides3]

Having continued with my research, I though some of you might be interested by some of my latest 'findings'.

A couple of days ago on the Climate Science website http://climatesci.atmos.colostate.edu/ , a preview of a new paper discussed the discovery of a large net cooling of the mid-layers of the ocean. This has sparked a lively series of discussions on both that website, and on RealClimate http://www.realclimate.org

I had the temerity to put questions on both comment boards, and have received quite a response, including comments from the authors of the papers and from Roger A. Pielke in person. These are 'heavy players' in the current climate/GW debate, and both their responses and the comments of others were quite a revelation.

The most important 'finding', for me, was that two of the subjects we have been discussing here, the Global Conveyor and the Younger Dryas, are now problematic, scientifically.

Firstly, as pointed out in the paper by Wunsch et. al., referred by Bryan Sralla, ( a very mathematical paper, from the perspective of Oceanography), the currently popular image we have of the oceans' currents is a myth. Although this is the 'mega-pattern' used in most GCMs and AOGCMs, it is not even a close approximation to the true complexity of ocean circulation, and is thus a bit of a 'headache' as far as climate modelling goes.

Secondly, there are doubts about the causes of the Younger Dryas glaciation. Broecker et. al., and others, are now questioning the assumption that a large freshwater influx from a Laurentide 'hosing' of the Atlantic was a cause of this event. This is a 'cornerstone' of a lot of the discussions of the Paleographic record in relation to current climate conditions, so it is very important. But it seems that, as things stand, it is not a sustainable assumption.

The implications of these and other revelations for our discussion, here on NW? We have assumed that the THC, as popularly illustrated, is a reasonable model of ocean circulation; this is not the case. We have assumed that a large net influx of freshwater could, at some stage, effect the Global conveyor; but the global conveyor idea is inadequate, and the effect of an influx is unclear, but may well not involve a slowing down of currents.

That there is a lot of freshwater getting into the Atlantic from the Arctic, and getting into the Arctic itself, are both measured facts. How this might effect our climate, or the Global climate, or the models used to predict climate, is very unclear. It looks like the next ice age is going to have to wait a while. It looks like we are even less certain about the future of the climate than I, for one, tended to assume.

Please remember that my posts are only a summary of my understanding, and are therefore very imperfect. I would encourage anyone with a real interest to follow the links and look at what the proper climate scientists are saying.

I thought this strand was closing down; perhaps, for the moment, this will stimulate some more interest. Enjoy.

P

[The Penguin]

P3,

If there was a Clap Hands Smilie, I'd line them up right across the screen. Excellent work.

[parmenides3]

[VillagePlank]

Hey, mate, you are an antithesis to the norm. This IS a VERY good thing. Not only that you report your findings with sources, and admit the bias. You, my friend, deserve the utmost respect.

And NEVER be ashamed of excellence.

[parmenides3]

Hey, mate, you are an antithesis to the norm. This IS a VERY good thing. Not only that you report your findings with sources, and admit the bias. You, my friend, deserve the utmost respect.

And NEVER be ashamed of excellence.

My embarrassment, not shame, is a function of a long-standing sense of inadequacy, which causes me both to seek praise and simultaneously reject the idea that I am worthy of it. I can't help it. I'll try not to use the blush smilie too often in future.

In the meantime, I only hope that the posts on this strand are encouraging people to find out the facts for themselves; when I think of the comments I was making only a few weeks ago, I shudder at my own ignorance and the huge assumptions that some of us were making. IMO, this is too important a subject to be left to vox-pop type speculation. The information is out there. Sometimes it is hard to find, often difficult to digest, but it can be found and shared. That said, I wouldn't want any strand on NW to go beyond the scope of any of its members; interaction is, after all, the essence of the forum.

I do appreciate your respect, regardless of my neuroses, so thank you.

Now; there's a lot of 'cold' freshwater, both in the Arctic and the Atlantic; more than there used to be, and more than even the scientists anticipated only a couple of years ago. So, does anyone have any ideas on how this is going to affect the climate, excepting discussions of a THC shutdown? It's an open forum; speculate.

P

[kold weather]

I haven't got much to say at the moment, but I do think the THC rule in how warm this country and West Europe is somewhat overstated, there are other geographic features which I think are just as important on thier own, one such factor is the Sahara desert which must help to store and throw northwards huge amounts of heat. I also seem to remember an article somewhere stating other key factors for our climte but I don't have a clue where it is!

[parmenides3]

I haven't got much to say at the moment, but I do think the THC rule in how warm this country and West Europe is somewhat overstated, there are other geographic features which I think are just as important on thier own, one such factor is the Sahara desert which must help to store and throw northwards huge amounts of heat. I also seem to remember an article somewhere stating other key factors for our climte but I don't have a clue where it is!

There's a decent overview on http://www.met-office.gov.uk/education/sec.../ukclimate.html

I don't think you have to be a teacher to look at it.

P

[parmenides3]

For those with an interest in the subject, an update on last week's discussions in the Climatology literature.

Climate Science reports on two papers in the journal Boundary Layer Meteorology, which might be of interest to weather forecasters as well as climate specialists. One paper focuses on a comparison of model types in accurately modelling observed weather in relation to boundary conditions, the other looks at the issue of predicting the stable atmosphere boundary layer in the Antarctic. The broad conclusions from both of these papers were that LES models were more effective than 1D models at simulating actual changes in climate, particularly along the boundary layer, but that significant trends in overstating the strength of cyclonic vorticity and in temperature changes raised questions about the predictive capacity of both types of model. Without being a meteorologist, I would not want to discuss the implications for weather forecasting, but it is another example of how models need to be improved for climate change prediction.

RealClimate deals with two new papers on the Antarctic, asking the question 'Is the Antarctic climate changing?'

The first paper analyses snowfall patterns over the past fifty years. previously, it had been thought that increased snow accumulation in the area helped account for a decrease of about 1cm in expected sea level rise. The new finding is that snowfall has not increased significantly, in spite of model predictions that it should have. It finds a correlation between precipitation patterns and temperature changes. It concludes (but the conclusion is speculative), that there is a possibility, therefore, that current models are underestimating the likely sea level rise in the coming years from warming in the Antarctic.

The second paper, not yet published, concludes in the finding that there has been a net warming of the Antarctic over the last four decades. This is a 'hot' area of debate at the moment, and the conclusion will undoubtedly raise some discussion when the paper comes out.

As usual, both sites have their own 'agendas' in publishing these findings; one wants to point out the inadequacies of the IPCC and the current science of climate modelling, the other wants to establish that the models are broadly accurate and that the climate is changing in line with expectations.

I'll try to keep updating here as more material comes out. P

[Stratos Ferric]

I'll try to keep updating here as more material comes out. P

Just make sure to overlook IceAgeNow!

[parmenides3]

Just make sure to overlook IceAgeNow!

I promise.

P