I posted on how Europe might end up cooler rather than warmer as a consequence of global warming and its affect on ocean currents, click here for the post.
Following the post, a reader of this blog, Phil Done, suggested in response to a comment from Ian Mott, that Mott really should read up on the phenomenon at Wikipedia.
Mott, who likes working things out for himself, has had a read at Wikipedia and done a bit of a general google and emailed me his findings as follows:
A check of the first pages of google sites dealing with the claimed ice age that would be produced by the collapse of the 'Atlantic Conveyor' reveals some interesting stuff. Most carry vague descriptions of how this would take place and seem to indicate that it will be caused by a change in northern salinity levels due to melt water from the Greenland Ice Sheet that will prevent this less dense water from submerging and thereby altering the flow pattern. Most carry the claim that evaporation from the gulf stream currently make this body of water very saline and more dense than the rest of the ocean. All point to the disruption of this salinity level by fresh melt water as the primary agent of disturbed flow pattern.
A good example is http:www.enviroliteracy.org/article.php/545.htm which has a curious link to a graphic called "The Atlantic Thermohaline Circulation" at www.clivar.org/publications/other_pubs/clivar_transp/pdf.files/ . Now the most curious thing about this graphic is that the Gulf Stream is shown as flowing due east from New York to Portugal before heading north past the UK. The generally accepted route up the US east coast appears to have been an inconvenient fact to be ignored for the sake of the story. Even more curious is a "cold, saline bottom current" heading north past New Zealand, through the shallows of Vanuatu into the far north pacific where it surfaces between Alaska and Kamchatka where, curiously, it is supposedly warmed in this sub-arctic clime for the journey south.
The brightest spot was at www.awitness.org/column/global_warming_ice_age.html that rightly pointed out that the mini-iceage of the 1400's was no such thing and that the other common example provided 12000 years ago was actually a slight pause in the middle of a period of glaciation with little relevance to this scenario.
But it is the actual numbers involved that reveal the truth. According to www.encyclopedia.com/html/G/GulfS1tre.asp the initial speed of the Gulf Stream is 6.4km/hour over a width of 80km. This slows further north as it widens so for the sake of this analysis we assume the Gulf Stream/North Atlantic Current has a median flow of only 3.6km/hr, is 100km wide and about 500m deep. At this speed the entire trip from Florida to Iceland will only take 70 days. And even assuming zero rainfall, the maximum evaporation is only likely to be 70/365 days x 2000mm evaporation = 383mm evaporation per cycle. And this means the 500 metre thick water column is left to absorb the salt reserves of 0.383 metres of evaporated water before it heads south again. As normal ocean salt level is 3.5% then the 499.617 remaining metres of the water column absorbs 3.5% of 0.383 metres of water, a total of 13.4 millimetres of salt that is added to the 17.5 metres of salt in the column. This is an increase of only 0.07657 of 1%.
And as for the claimed impact of fresh water on the current, we have a total of 180 km3 of water flowing past any given point in the north atlantic each hour. This amounts to 1.577 million km3 each year which disperses into the approx 160 million km3 North Atlantic (40 million km2 x average depth of 3.926km). This north atlantic data is derived from the whole of atlantic data from http://en.wikipedia.org/wiki/atlantic_ocean .
The entire ice volume of Greenland is only 2.44 million km3 so a complete melt over a highly improbable twenty years would add only 0.122 million km3 to the annual current flow of 1.577 million km3, for a total of 1.699 million km3 pa. The existing salt in the NA Current, at 3.5% of volume, will be 0.055195 million km3. And this will only reduce the salinity level of the combined current and melt water by one 14th to 3.25%.
A slightly less improbable 100 year total melt, but still very rapid in climatic terms, would involve only 0.0244 km3 per annum. This would produce a combined flow of 1.6014 million km3 with a salinity of 3.45%. This range is only half the variation normally observed within a 1000 metre ocean profile. See www.windows.ucar.edu/tour/link=/earth/water/salinity_dept
In summary:
The North Atlantic currents are horizontal cycles that flow in a clockwise direction due to the rotation of the Earth. They are doing the same thing as the water in a northern hemisphere bathtub and for the same reason. They are, in most part, not vertical cycles with surface water flowing north and sea floor water flowing south so any theory based on a disturbed flow due to lower salinity from ice sheet melt water is a theory that ignores the primary determinants of current flow, the rotation of the earth.
The theory of increased salinity in the Gulf Stream/Nth Atlantic Current due to evaporation ignores the fact that precipitation also takes place in the same regions. Ocean salinity maps indicate that highest salinity is actually in the middle of the North Atlantic (Sargasso Sea with high air pressure and low rainfall), not in the northern regions.
The volume of water in the Gulf Stream/Nth Atlantic Current is of such magnitude that a complete melt of the Greenland Ice Sheet over a period of only 100 years, contracting North at 27km/year, would dissipate the fresh water to such an extent that salinity levels would only drop from 3.5% to 3.45%. This variation is well within the normal range of ocean salinity levels. To suggest that a minor change in the chemical composition of such a large body of water could override the influence of factors of such magnitude as the rotation of the Earth, itself, is pure fantasy.
Consequently, we must conclude that the Pentagon was rather charitable in describing the Atlantic Conveyor/Ice Age scenario as an extreme scenario and very low probability event. It is, in fact, a highly improbable event that not only extrapolates known effects to improbable extremes but also excludes mitigating factors that are of thousands of orders of magnitude greater.
I am not endorsing Mott's conclusions, but posting them for general discussion.
Interesting reading on salinity levels and conveyor
http://www.realclimate.org/index.php?cat=19
Saltier or not?
Filed under: Climate Science Arctic and Antarctic Oceans— group @ 1:43 pm - ()
In a recent (of Sept. 16, 2005) publication in Science, Hatun et al. find that record-high salinities have been observed over the past decade in the region where water from the Atlantic flows into the northern oceans. They combine an analysis of observations with simulations using an ocean model, concluding that the salinity of the inflow to the northern oceans is controlled by ocean dynamics and the circulation in the sub-polar gyre. The observations by Hatun et al. may suggest that at the moment the warm and salty waters from the south are especially warm and salty.
In another publication paper in Science from June 17th 2005, on the other hand, Curry & Mauritzen conclude that as a whole the northern North Atlantic has become significantly fresher (less salty) in recent decades. The latter study was based entirely on observations (hydrographic data between Labrador and Europe in the past 50 years). The recent evidence for salinification provided by Hatun et al. has been interpreted by some as being inconsistent with the evidence for high-latitude North Atlantic freshening found in previous reports. So what is really happening? Is the salinity increasing or decreasing? And can the two recent Science studies be consistent with each other?
Ian - I am not sure that if you google google scholar with porn that you would get 1000 hits. Though you might get some because socialogical studies of pornography and society.
I searched google scholar which is a search of the scientific literature with that exact term in them. It indicates that there is a lot of research going on and you simplistic dismissal of the saline/temp gradient powering of the current is at best against most current scientific opinion. This of course does not make it wrong. However I did ask a specific question as it is a crucial, to me, test of your idea.
From a previous post I found this in an abstract "Changes in ocean circulation have been inferred from records of the deep water chemical composition derived from sedimentary nutrient proxies1"
It would seem that this current has changed in the past - how do you reconcile this with the fact that the Earths rotation has been approx constant over this same time scale?
Ian - I agree there is a lot of unknowns - so do the modellers. But what do you make of the paleo evidence on the issue.
And I would dispute that the El Nino phenomenon is "cyclical" - not just nit-picking. It can "occur" but what causes it and and no particular cycle (well so it appears from the stats /evidence thus far). Reason I am bringing this aspect into the discussion is simply to say that large scale reversals in circulations can occur and do occur.
The paleo evidence seems to indicate the Atlantic climate is more variable than we might think and that the conveyor appears to have shut off in the past from deductions made of that evidence.
Thank you Warwick Hughes and Louis Hissink for your support. Phil Done has two questions. I am outside my area of expertise here (I am a palaeo-climatologist, not an astronomer) but that has never stopped me before - why should it now?
Question 1. "Tell us some more about the solar torque cycle." The Sun and the giant outer planets orbit the centre of mass of the solar system (boring Earth just orbits the Sun). Most of the angular momentum of the system is held by those outer giants, and their combined orbits apply a variable torque to the Sun. It is rate of change of applied torque which drives the Sun's own irregular orbit, and also controls the widely-variable quantity of magnetised plasma ejected from the Sun into the solar wind.
Crucially, planetary motions, and hence solar eruptive activity, can be calculated. If the Sun keeps playing by the rules, detectable global cooling should be here by the end of this decade; and the next Little Ice Age cold period will be developed by 2030. This is within the planning horizon of responsiblle governments. How will they keep their people warm and fed during the Landscheidt Minimum? Enough! Question 2 will have to wait.
Phil, the El Nino/La Nina upwelling is part of a thermohaline cycle but it is exactly that, a cycle of changes within a range of variation. And this range of variation interacts with surface currents to produce climatic cycles. The so-called Atlantic Conveyor theory speculates on a total disruption to that cycle based on an assumption that these surface currents either do not exist or play no part climate cycles.
Ender, the awitness.org/ url mentioned in my post above points out that the younger Dryas was in the middle of a period of glaciation. It cannot be used as an example of triggering a new or mini ice age.
Gosh 8000 google sites. Does that mean that if there are 10,000 porn sites then porn must be a greater "truth" than thermohaline circulation. My post poses a few simple questions that need to be answered. They are;
Is the total supply of fresh water from Greenland ice melt sufficient to significantly alter the salinity (and hence density) of the total volume of sea water circulating through the area claimed to drive the cycle? No.
Is there even the very early traces of freshening of sea water in the North Atlantic? No.
Are there other places where freshening of sea water is more significant? Yes.
Does the model calculate the volume of circulating water or does it assume a fixed, static volume?
If a partial melt of the ice sheet reduces the speed of the cycle and thereby cools the Northern Atlantic climate then why would the ice melt continue to the point where it stops altogether?
Someone familiar with all these models should provide me with the assumed reduced salinity threshhold at which this combined sea and fresh water stops descending and thereby supposedly stops the cycle. And they can explain why they chose that number. And with that information we can then calculate exactly how fast the ice sheet would need to melt to produce that outcome.
My suspicion is that they have assumed the cycle has stopped before the actual cause takes effect.
Any other response is obfuscation or political spin. Does this particular scientific emperor have clothes or not?
Ian - "The North Atlantic currents are horizontal cycles that flow in a clockwise direction due to the rotation of the Earth. They are doing the same thing as the water in a northern hemisphere bathtub and for the same reason."
I have not seen a response to my question that if the above statment is true then how does the current change in flow if the rotation of the Earth is constant.
Warwick - we should not forget for the people that do not read you blog that Steve Bloom posted this comment. I have grave problems with one data point being used to prove a point.
This is what Steve Bloom said:
"Loius, the reference is to two separate problems in the Coolwire 13 article, a) the temp data and b) the sea ice data. Sorry if I didn’t make that clear.
John A., I don’t understand how your first response relates to the point I was making, but as long as we’re on the subject I have read the methodology used by GISS to come up with their temp numbers, and it appears to deal nicely with any potential urban/suburban issues. Do you have any specific problems with it? Before you ask, I’m not in a position to have the same discussion about the other data sets since I frankly don’t have the time to look at everything in the field. Regarding the critique of Coolwire 13, William’s analysis of the temp data issue stands for itself. You really should read it.
To expand briefly about my point on the sea ice extent, there are two data sets maintained, one by NSIDC and the other by UIUC. While based on the same raw satellite data, they use very different metrics for deciding whether a given satellite pixel has sea ice or not. NSIDC states their metric on their site and UIUC does not, but a quick comparison of contemporaneous sea ice extent graphics on the two sites makes it apparent that the metrics are quite different. This is fair enough as far as it goes, since there’s nothing intrinsically more valid about using, e.g., 10% versus 15% coverage to determine whether a given pixel has sea ice or not. Of course these different metrics result in similar but not identical anomalies, the graphs of which are also available on each site.
Another consequence is that the two methodologies will sometimes show different record years, which is what happened this year when NSIDC showed a record and UIUC did not. In any event, the media coverage in September was about the new record set by the NSIDC data, but Willis used the UIUC data to refute it. It was only by a very unlikely coincidence that I happened to know about the difference in metrics. There was obviously some sort of discussion to be had contrasting and comparing the two data sets and talking about the overall trend, but that wouldn’t have been nearly as exciting as accusing the NSIDC scientists of being alarmists or (by implication) liars."
Gidday Jennifer,
Your readers will find some of FosBobs online papers at;
http://www.warwickhughes.com/foster/
I suggest "Climate-change science: duel of the hypotheses", 31, December, 2000., as one place to start.
I see that some of my bottom of page return links do not work so just use your "Back" button. I need to do a bit of editing of pages that date from a server now gone to that network in the sky.
On my 19C icebergs page I have the length of day graphic from the Sharp / Goodridge LOD data going back over 300 years.
http://www.warwickhughes.com/climate/Iceberg.htm
My Blog has two entries relating historical facts from polar explorations which both suggest recent polar sea ice extents may not be so different from conditions a century ago.
http://www.warwickhughes.com/blog/
4 December, "Antarctic sea ice extent, South Sandwich Islands",
and
11 December, "Little net change in Arctic sea ice extent in 110 years ?"
Best wishes,
Warwick Hughes