Cap melt can chill Europe

[Martin]

this is not news, I've seen the idea discussed for 10 years or so.

It comes up from time to time.

Now there is one more bit of evidence, from a sample of oceanic mud, that it is right.

The report is in technical language in SCIENCE of 30 June 2006, and also in a popular account by staff writer, interpreting the jargon.

 

here is a summary of the popular account

http://www.sciencemag.org/cgi/content/summary/312/5782/1860a

===quote===

PALEOCLIMATOLOGY:

Atlantic Mud Shows How Melting Ice Triggered an Ancient Chill

Richard A. Kerr

Paleoceanographers report on page 1929 of this issue of Science that they have found a single ocean sediment core that preserves the sought-for link between a gush of freshwater far out into the North Atlantic and the chill that swept around the Northern Hemisphere 8200 years ago. (Read more.)

===endquote===

 

Now the summary of the technical article:

http://www.sciencemag.org/cgi/content/abstract/312/5782/1929

Surface and Deep Ocean Interactions During the Cold Climate Event 8200 Years Ago

Christopher R. W. Ellison,1 Mark R. Chapman,1* Ian R. Hall2*

Evidence from a North Atlantic deep-sea sediment core reveals that the largest climatic perturbation in our present interglacial, the 8200-year event, is marked by two distinct cooling events in the subpolar North Atlantic at 8490 and 8290 years ago. An associated reduction in deep flow speed provides evidence of a significant change to a major downwelling limb of the Atlantic meridional overturning circulation. The existence of a distinct surface freshening signal during these events strongly suggests that the sequenced surface and deep ocean changes were forced by pulsed meltwater outbursts from a multistep final drainage of the proglacial lakes associated with the decaying Laurentide Ice Sheet margin.

 

1 School of Environmental Sciences, University of East Anglia (UEA), Norwich, NR4 7TJ, UK.

2 School of Earth, Ocean, and Planetary Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3YE, UK.

* To whom correspondence should be addressed. E-mail: Mark.Chapman@uea.ac.uk (M.R.C.); Hall@cardiff.ac.uk (I.R.H.)

 

http://www.sciencemag.org/cgi/content/short/312/5782/1929

[Martin]

remember this is a MODEL (it is not fact)

what we are talking about is bits of EVIDENCE that the model might actually be right.

First off one needs to understand the mechanism.

the mechanism is simple

maybe some or all the SFN regulars know how it goes but I will summarize anyway

 

CAP MELT CAN KILL THE GULFSTREAM WARMING OF THE N ATLANTIC

 

circulation in the N Atlantic brings a lot of heat up north

the way it works is warm water off shore of Europe evaporates

which makes the water SALTIER and colder

 

then the cold salty water because it is extra dense with its concentrated salt SINKS down into deep ocean and slides back to equator

 

meanwhile at the equator surface water warms and slides up north in currents like Gulfstream. it is a standard CONVECTION picture.

==============

 

BUT FRESH WATER IS LESS DENSE and if you suddenly melt a bunch of the "Laurentide" ice sheet (the East Canadian ice sheet) and dump the fresh into the N Atlantic it can form a COLD FRESH LAYER THAT WON'T SINK.

 

So the regular convective turnover that was bringing the warmth northwards from the equator STOPS. And you get a chill in Europe.

 

BTW I read some other evidence lately----people were measuring the speed of currents in the N Atlantic and found that they had SLOWED DOWN noticeably over some period of time like 100 years.

 

All these little bits of evidence. Can't ever be 100 percent sure. But anyway now they have the MUD CORE.

 

The mud core gives evidence of sudden freshening of the water at a time when they already know there was a chill. Two things happening simultaneously.

=================

 

I cant offer any authoritative word on it. You have to interpret the signals for yourself. All I know is there is this model around where global WARMING can melt the icecaps to an extent that it has this paradoxical (counterintuitive) result of actually choking the Gulfstream and making Europe COLDER. That is all it is, a MODEL. So details have to be worked out and it has to be checked against climate history etc etc.

 

Anybody have any more about this?

 

sorry but the SCIENCE articles are PAY PER VIEW which is too bad, all we can get for free are the summaries, like what i copied here. maybe somebody else has some free online articles?

 

IMHO the model is worth knowing about, since if it happens to be correct it predicts some counterintuitive local effects on certain places, like e.g. Europe.

[herpguy]

For weeks now I have been trying to understand how this works. Thanks a lot for posting this, Martin.

 

I rated this thread five starts. Everyone needs to read this thread. I would be very happy if a mod stickied this.

 

I don't have anything else on the subject, but still thanks for posting.

[DrCloud]

There's an interesting article in the new issue of American Scientist that makes an intriguing case for this: the warming of Europe (relative to, say, Labrador) by the Gulf Stream and its extension (the N. Atlantic Drift) is the climatological equivalent of an urban myth. (American Scientist is a general-scientific-audience publication, rather like Scientific American, and the article is a summary of work reported in several technical journals.)

 

This conclusion is based on computer simulations with and without a Gulf Stream, which show that the main reason that Europe (and NW N. America) are warmer than regions at the same latitudes on the west sides of the respective oceans is simply because of the maritime climate -- the greater thermal inertia of the oceans keeps the air coming off them from varying as much as the continental air that governs the climate of north-eastern N. American and north-eastern Asia. Winters are warmer in London and Seattle, and summers are cooler, than in Tornonto and Vladivostock.

 

Further, in the case of Europe, the downstream effects of standing waves in the Jet Stream set up by the Rocky Mountains enhances the effect of the maritime climate by nudging the prevailing winds to come from the southwest a bit, making the European climate all the more equitable.

 

This is relevant in the current context because it ameliorates concerns about the effects of turning off the thermohaline circulation, as might have happened with the draining of this glacial lake and could happen with global warming. (Generally speaking, Martin's reasoning is just fine -- except it, and the Science article, rely on this urban myth.)

 

Now, this doesn't speak to how Europe might warm or cool. Model simulations of warmer climates have suggested increased snowfall over Europe (it's warmer, but still below freezing, and it snows more); and this could well result in a cooler Europe simply because the increased snow cover would increase the surface reflectivity and prevent the sun from doing its job. But this has little to do with the Gulf Stream or the "conveyer belt" overturning.

 

All this is to say that the jury is still out on some of these second-order effects of global warming as well as on certain paleoclimatological connections. HPH

[Martin]

There's an interesting article in the new issue of American Scientist that makes an intriguing case for this: the warming of Europe (relative to, say, Labrador) by the Gulf Stream and its extension (the N. Atlantic Drift) is the climatological equivalent of an urban myth. ...

 

It is very interesting to hear contrary arguments! I used to read the American Scientist fairly often and remember it as a good magazine (articles as authoritative as those in Science mag, but written more for nonspecialist, less technical style).

 

I would be pleased if you could give the author's name and the title of the article so I could hunt for it----there may be a copy on the web somewhere. Or even better, do you know if Am Sci has it online?

 

I am, as you would expect, skeptical. Everything I've seen indicates that the ocean convection currents do carry a LOT of heat north from the tropics and that the circulation rate and heat transport have been quantified. So it would be especially interesting to see an article that argues this is a "myth".

 

I have no reason to argue, myself, one way or another----basically would like to understand the models and the reasoning used on either side of the issue. Please give us a link if you can, DrCloud

[DrCloud]

Here is the link to the article, but, like most new publications, getting the full article requires either a subscription or a purchase. (The technical article on which this is based is in the Quarterly Journal of the Royal Meteorological Society, 128:2563-2586 -- and this is a top tier technical journal.) American Scientist is the bi-monthly publication for Sigma Xi members, but some libraries probably have it.

 

At that link is a figure that tells part of the story;another part is this picture, which I lifted from Am. Sci. (forgive me, oh Sigma Xi gods...):

 

 

This shows results from two different climate models (the orange and the green) that have been calibrated to observations, showing how they transport heat northward. Heating is the gradient of these heat transport curves, so the maximum heating associated with the oceanic transport is south of 40 degrees. By contrast 45N is southern France, and 60N runs through the Shetland Islands, just off northern Scotland -- it's the atmospheric transport that's doing the heating in the latitudes of Europe.

 

I don't want to suggest that this new paper is the last word on the issue, and it's certainly the case that "the Gulf Stream keeps Europe warm" is not a concept that's going to die easily. But it's interesting, and the arguments, both from models and observations, hold together. If it's proven out, it'll cause any number of textbooks to be re-written. HPH

[Martin]

Thanks!

It appears that free reprints are available---so one does not have to be a subscriber after all:

 

For the Royal Meteorological Society article (2002) try this

http://www.ldeo.columbia.edu/res/div/ocp/gs/pubs/Seager_etal_QJ_2002.pdf'>http://www.ldeo.columbia.edu/res/div/ocp/gs/pubs/Seager_etal_QJ_2002.pdf

 

For a free reprint of the Am Sci article (2006) try this

http://www.ldeo.columbia.edu/res/div/ocp/gs/pubs/Seager_AmSci_2006.pdf'>http://www.ldeo.columbia.edu/res/div/ocp/gs/pubs/Seager_AmSci_2006.pdf

 

 

Your link provided me with the author's name, Richard Seager, which was all it took to find a free article of his that has some of the same message as the one published in American Scientist

 

http://www.ldeo.columbia.edu/res/div/ocp/gs/

===exerpt===

 

Climate mythology:

The Gulf Stream, European climate and Abrupt Change

Richard Seager

Lamont-Doherty Earth Observatory of Columbia University

 

...

...

belief of the British, other Europeans, Americans and, indeed, much of the world's population that the northward heat transport by the Gulf Stream is the reason why western Europe enjoys a mild climate, much milder than, say, that of eastern North America....

 

We now know this is a myth, the climatological equivalent of an urban legend. In a detailed study published in the Quarterly Journal of the Royal Meteorological Society in 2002, we demonstrated the limited role that ocean heat transport plays in determining regional climates around the Atlantic Ocean. A popular version of this story can be found here.

 

The determinants of North Atlantic regional climates

We showed that there are three processes that need to be evaluated:

The ocean absorbs heat in summer and releases it in winter. Regions that are downwind of oceans in winter will have mild climates. This process does not require ocean currents or ocean heat transport.

The atmosphere moves heat poleward and warm climates where the heat converges. In additions, the waviness in the atmospheric flow creates warm climates where the air flows poleward and cold climates where it flows equatorward.

The ocean moves heat poleward and will warm climates where it releases heat and the atmosphere picks it up and moves it onto land.

Using observations and climate models we found that, at the latitudes of Europe, the atmospheric heat transport exceeds that of the ocean by several fold. In winter it may even by an order of magnitude greater. Thus it is the atmosphere, not the ocean, that does the lion's share of the work ameliorating winter climates in the extratropics. We also found that the seasonal absorption and release of heat by the ocean has a much larger impact on regional climates than does the movement of heat by ocean currents.

...

...

===endquote===

 

HEY EVERYBODY. take note that the assumption that Europe's mild climate depends to a substantial extent on the Gulf Stream has been challenged and is CONTROVERSIAL

 

I personally don't want to take sides about how important or unimportant the Gulf Stream and the water convection system it belongs to is. I expect scientists to differ on this issue and I just want to listen to the arguments.

Seager's computer model is evidence on one side.

 

The mud core might be evidence on the other side.

[DrCloud]

Well, c'mon, now, Martin -- you're working awfully hard to tout a controversy that's unlikely to be all that controversial.

 

First, the sediment core really says nothing at all about European climate, just the composition and conditions of the ocean over time (temperature, salinity and so on). Inferences about what happened when (and to whom) are based on time reconstructions of these sediment cores, and there are pretty large uncertainties in what's synchronous with what. Further, correlations do not cause and effect make (that's the reason these guys used model simulations -- you can do actual experiments that way).

 

Second, the "urban myth" part of this can easily be overwritten with a solid explanation such as the one in the articles, but the nomenclature can still hang on. Use of the term "greenhouse effect" is an example of this: greenhouses really don't behave the way the atmosphere does, because they have (glass) lids that keep convection from carrying away the heat in them. (Yes, the glass lets sunlight in and tends to prevent IR from escaping, just like atmospheric greenhouse gases do, but it's been shown that suppressing the convection is how they really work.) But despite this lack of precision in naming the phenomenon, the terminology is in common use. I would anticipate that "the Gulf Stream keeps Europe warm" will hang around long after most people in the climate community understand that it's really the maritime climate that does it. It's no big deal, really.

 

Compared to big physics and chemistry, not to mention medicine, the climate research community is a small group of folks, most of whom know each other pretty well. They get a lot of amusement out of little studies such as this, and I doubt there will be anything resembling real controversy.

 

Now, I hijacked the thread a bit by introducing this new article, and I'm sorry for that -- I thought the new information might be of interest. But it does illustrate how people who go ballistic at the prospect of climate change because they construct a tenuous chain of events leading to a "Day after Tomorrow" like catastrophe are often only looking for self-promoting publicity. To get all hot (sorry, bad pun) about it is just to fall into their trap and give them what they're asking for. HPH

[Martin]

I dont have a horse in this race and at this point what makes the best sense for me is to wait and see.

I want to be able to understand the arguments on both sides.

 

From your viewpoint there may no difference of opinion in the climate science community about the main determinants of European climate.

You may have spent a lot more time reading about this.

 

From my perspective, I've only seen a small amount about this and it looks to me like there is a difference of opinion. So I call it controversial and take a wait and see attitude.

 

controversial is not pejorative, I'm sure you understand. differences of opinion and having evidence and supporting arguments on both sides just makes it interesting.

 

I'm happy for you to declare it NOT controversial, as you see it.

As I see it the jury is still out.

[DrCloud]

Controversy, in the sense of "a dispute, especially a public one, between sides holding opposing views" is generally limited in our community to issues in which the opposing sides have a stake. Until recently, that was the case with whether or not global warming is happening, because the skeptical side, many supported by grants and/or outright salaries by big energy, had a job to do. In recent years, they've come across to those of us who understand the science like the apologists for the tobacco companies did for so long, those who denied the lung-cancer / smoking links.

 

In the case of interest here, "controversy" is just too strong a term. And a wait-and-see attitude is fully appropriate. That attitude is appropriate for other issues in meteorology and oceanography as well, such as whether hurricanes are going to be more numerous or stronger as the climate warms. Evidence is coming in, but it's still too soon to make a final judgement. HPH

[mr d]

hello

 

just a starting point, but look into the north atlantic conveyer, and undersea river (current).

 

http://www.firstscience.com/site/articles/gribbin.asp

 

mentioned this before dealing with global warming, but most people seemed to think i was trying to use it as a ways to dismiss warming, but research the subject and you'll find it deals more with a cyclic system that deals with warming and cooling. and how global warming now may later trigger a large temperature drop in europe.

 

mr d

[DrCloud]

The "North Atlantic conveyer" is part of a global circulation also known as the meridional overturning and the thermohaline circulation. The last of these terms gives a clue to what drives it: temperature and salinity differences between the tropics and the polar regions set up density differences, and, because heavy water sinks and pushes lighter water up, a circulation gets going.

 

This circulation is a strong contributor to the oceans' thermal inertia, their slow response to changes in forcing; because of the huge volume of water involved, there is also significant mechanical inertia involved.

 

There are hints in the climatological record (mostly from proxy data derived from ocean-sediment cores) that the meridional overturning has slowed and perhaps stopped altogether in the past (we're talking thousands of years for a time scale here, though). And ocean circulation models show its sensitivity to changes in surface forcing -- modeled meridional overturnings are pretty easy to stop, all things considered. There have been several climate simulations in which they stop.

 

However, in the ocean component of the climate models, key processes in the meridional overturning are not particularly well represented, so it's not clear how faithfully they represent the real oceans. Nonetheless, it's captured the attention of the research community and, by extension, the media. HPH

[mr d]

hello

 

agree with dr quark. but it does i believe it may show that there may be some form of temperture regulation system already inplace on planet earth. involving wind currents, weather patterns, ocean currents, volcanic activity ...

one part of the equation can effect the others, and the earth's temperature system can suffer from human activity.

and it would be in our interest to modify our actiivties until that system can be better understood.

 

mankind is not above extinction

 

mr d

[SmallIsPower]

The map on page 2 of http://www.ldeo.columbia.edu/res/div/ocp/gs/pubs/Seager_etal_QJ_2002.pdf says the temperature of the Pacific Northwest is 12 degreesC above what we can expect and Western Europe is 24 degrees above what could be expected in January.

 

First could those nubers be right, or are they missing a decimal point? Second if they are OK, the heating of Europe is twice the heating of the Northwest, I doubt it's the geography of the Rockies causing this cange.

[DrCloud]

No doubt you know far more about this than the climate scientists who reviewed this manuscript, two of whom apparently had their criticisms incorporated into a pre-publication revision.

 

Perhaps you should consider writing a rebuttal to the QJRMS. They just love such things. HPH

[mr d]

hello

notice you mention the sea cores a few times. what's the latest on the artic ice cores, believe they were reporting that from their samples it tended to indicate that climate temperatures for their record period (granted a few 100,000 years) that the earth normally goes through temperature swings that are rather dramatic, occuring in 15-20,000 year cycles. and that the 10,000 year stable condictions we have enjoyed are more of an aboration than the norm.

also they were saying there before a shift from hot to cold is proceeded by a period of increased volcanic activity, hich results in largers amounts of particulate matter in the atmosphere, and an increase of sulfur dioxide gas in the atmosphere whose reflective properties help reflect sunlight away from the earth and back into space. and that while direct effect of the activity drops temperature worldwide ofr a short period of years, but serve to act as a trigger that leads to futher cooling.

 

mr d

[DrCloud]

Earth's climate, in terms of the planetary-averaged temperature [averaged also over at least a year, to eliminate summer-winter differences], has had its ups and downs over the time scale for which we have records from which temperatures can be inferred. It's important to keep in mind that regional variations (for example, Europe's "little ice age") aren't necessarily reflected in global temperatures. What this means is that reconstructions need to assemble as many datasets as they can, from all over, before they make inferences about global variations. The Michael Mann study, for example, did that, as has been discussed in the recent National Academy study and in other publications.

 

At the same time, individual records can be valuable, because they provide more detail about the (inherently noisier) global changes.

 

In the current configuration of the continents, our climatic era, the Holocene, has been rather warm compared to much of the rest of the recent several 100Ks of years of record in various cores. Ice ages happened at several times, and some of the cyclicity has been related to astronomical parameters related to Earth's orbit around the Sun (the Milankovic cycles). In the late 1960s and early 1970s, a great deal of attention was given to these cycles and how, given the past few 10ks of years, Earth would seem to be headed for another ice age. Because, however, the forcing associated with the Milankovic cycles is so small, stronger forcings associated with increasing atmospheric greenhouse gases garnered more attention, and interest in the scientific community in global warming has dominated for the past several decades.

 

Volcanos and other climate forcing mechanisms play a role in short-term variations as well. The Krakatoa explosion, for example, produced "the year without summer" by injecting so much gunk into the atmosphere that sunlight to the surface was attenuated sufficiently to keep the planet cool for a year. With new observational techniques, just about any volcano of any significance can now be shown to have some effect on the climate, for a while at least.

 

Another climate forcing that refuses to die quietly has to do with sunspots. Many climate parameters have been shown to correlate with the 22-year sunspot cycle. But correlations aren't enough: you also need a mechanism with which to explain the relationship before it becomes part of what we think of as our "understanding" of climate's behavior. The best candidate for a sunspot mechanism is their effect on the solar wind and, in turn, its effect on upper atmospheric clouds. But the link is tenuous and has never been shown to be solid.

 

The notion of triggers in the system is one that also has received a lot of attention, because there are various positive feedback mechanisms that could amplify small forcings into big responses. The snow/ice feedback (snow is white, reflects sunlight, cools things, makes more snow, reflects more sunlight...) was what piqued interest in the 1970s in another ice age: very simple (overly simplified, in fact) models suggested that a small change could "jump" the climate into an ice age.

 

In the middle of all this, it's useful to remember that climate variations have been relatively small for a long, long time. There's no really credible evidence that there was ever a "snowball Earth" (despite assertions by some to the contrary). There does seem to have been a time, when the continents were configured differently, when there was no permanent ice at the poles, however. But even then, global temperatures were such that life flourished.

 

Not, however, life in any way that's similar to our highly tuned society. That's the real concern about global warming: our world is now sufficiently sensitive to relatively small changes that we could be making trouble for ourselves. HPH

[RichF]

I'm going to be an arrogant ass now, but I told ya' so... study the European environment prior to the little ice age. I do admit that I could be wrong as I am not any sort of expert but history provides some valuable clues.

[WillTheNewf]

Well, lord knows the weather hasn't changed here in Newfoundland. Its still the pits : /

 

Just my two cents

[Genecks]

I'm going to play Surfin' USA a lot more. I need a surf board.