Talk:Shutdown of thermohaline circulation

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I rolled back [1] Abe Froman; apologies for not doing it via normal means. Anyway - I thought that Europe is not cooling is pretty well known and barely needs support from a ref. But [2] would do if you want one William M. Connolley 21:46, 13 October 2006 (UTC)

Contents

[edit] Bryden measurements reported late 2005

I'm not sure if some of 71.123.23.59's changes ([3]) make too much use of text from the Guardian article Sea change: why global warming could leave Britain feeling the cold. Does someone who's familiar with Fair Use and Copyright have a view on this? --Leigh 06:33, 30 October 2006 (UTC)

Update - not completely sure I agree with William_M._Connolley's recent edit [4], but I suspect he knows rather more about this than I do. Just making note of what was on page here, and will revisit in a while once press has settled down.

On 27 October 2006, The Guardian reported that Bryden, presenting findings to a conference in Birmingham on rapid climate change, had uncovered evidence that part of the current came to a 10-day halt in November 2004.
Oceanographers were not previously aware that a 10-day halt in the deep flow of cold-water southwards in the western Atlantic was possible. Lloyd Keigwin at the Woods Hole Oceanographic Institution, in Massachusetts, described the temporary shutdown as 'the most abrupt change in the whole [climate] record'.
Prof. Bryden's group stunned climate researchers last year with data suggesting that the flow rate of the Atlantic circulation had dropped by about 6m tonnes of water a second from 1957 to 1998. The study prompted the UK's Natural Environment Research Council to set up an array of 16 submerged stations spread across the Atlantic, from Florida to north Africa, to measure flow rate and other variables at different depths. Data from these stations 'confirmed the slowdown in 1998 was not a "freak observation"'- although the current does seem to have picked up slightly since.[5][6][7][8]

--Leigh 13:04, 31 October 2006 (UTC)

Having talked to people who were there, this was just one minor issue out of a large conference. It isn't published; it isn't interpreted. Its probably just a natural fluctuation. It isn't what is sounds like (the entire circulation halting for 10 days, which would be impossible anyway). The RAPID array *wasn't* set up in response to Brydens paper, either William M. Connolley 13:40, 31 October 2006 (UTC)

[edit] Bias

This article says that the shutdown of thermohaline circulation would not affect the climate in Europe greatly, yet the majority of the references state otherwise. That was my general impression of the article; and the view of general unimportance of THC is not a commonly held one. -Iopq 12:01, 28 November 2006 (UTC)

The article doesn't say that. It does say that shutdown of the THC is considered unlikely. I'm not sure what you mean by "maj of refs" William M. Connolley 13:20, 28 November 2006 (UTC)
The article keeps changing pretty quickly. My comment is no longer valid as of this revision. -Iopq 12:07, 13 December 2006 (UTC)

Could this article be Euro-centric? If it happened, how is it going to affect Asia? __earth (Talk) 02:04, 21 January 2007 (UTC)

The theory is for the major changes to affect N Europe mostly William M. Connolley 13:01, 21 January 2007 (UTC)

"The chances of this occurring are unclear; there is some evidence for the stability of the Gulf Stream but a possible weakening of the North Atlantic drift; and there is evidence of warming in northern Europe and nearby seas, rather than the reverse." This sentence doesn't make much sense; obviously the Gulf Stream hasn't stopped *yet*, so whatever cooling process would occur were it to shut down wouldn't be in effect yet. The warming in northern Europe would clearly be a more direct consequence of global warming. -Meganomics 02:55, 10 July 2007 (UTC)

If it were on the way to slowing down you would expect to see soomething William M. Connolley 08:25, 10 July 2007 (UTC)

[edit] Nature, vol. 448, pp844

Just thought I'd answer the question in the edit history, in the forementioned article it talks that shutdown of the THC is unlikely to have been a result of Global Warming and that the Bryden measurements picked up a short term variability. If that is what 198.151.13.8 was on about. AlexD 17:56, 11 September 2007 (UTC)

[edit] Inaccuracy

The first sentence of this article shouldn't be "Shutdown or slowdown of the thermohaline circulation is a possible effect of global warming," but "Shutdown or slowdown of the thermohaline circulation is a highly unlikely effect of global warming." Both Wunsch (2004) and Jungclaus et al. (2006) need to be mentioned in this article. ––Bender235 (talk) 11:15, 9 June 2008 (UTC)

I'm not very well versed on this topic (so I apologize in advance if I'm wrong), but I thought there wasn't any consensus as to whether or not it is likely? · AndonicO Engage. 11:24, 9 June 2008 (UTC)
Well, besides Wunsch (2004) and Jungclaus (2006) there is also Kerr (2006), who acknowledges that Bryden's results were wrong. Also, the IPCC answers the question 10.2: “How Likely are Major or Abrupt Climate Changes, such as Loss of Ice Sheets or Changes in Global Ocean Circulation?” with “Abrupt climate changes … are not considered likely to occur in the 21st century, based on currently available model results.” ––Bender235 (talk) 11:41, 9 June 2008 (UTC)
If i'm not mistaken, a shutdown is impossible, while at least some slowdown is likely. (Faq 10.2 in the IPCC report seems to confirm this). --Kim D. Petersen (talk) 14:49, 9 June 2008 (UTC)
At the moment, the article seems to suggest it's already slowing; I also remember seeing a couple of BBC programs on the Science Channel saying the same. Maybe the article should be moved to "Slowdown of the thermohaline circulation"? · AndonicO Engage. 15:25, 9 June 2008 (UTC)
Yes but iirc the BBC reports where based on preliminary results, that have been shown as wrong. (see Kerr(2006)). The IPCC WGI report states ([9] Chapter 5: "Observations: Oceanic Climate Change and Sea Level" - Executive Summary - page 386 ):
Key oceanic water masses are changing; however, there is no clear evidence for ocean circulation changes. Southern Ocean mode waters and Upper Circumpolar Deep Waters have warmed from the 1960s to about 2000. A similar but weaker pattern of warming in the Gulf Stream and Kuroshio mode waters in the North Atlantic and North Pacific has been observed. Long-term cooling is observed in the North Atlantic subpolar gyre and in the central North Pacific. Since 1995, the upper North Atlantic subpolar gyre has been warming and becoming more saline. It is very likely that up to the end of the 20th century, the Atlantic meridional overturning circulation has been changing significantly at interannual to decadal time scales. Over the last 50 years, no coherent evidence for a trend in the strength of the meridional overturning circulation has been found.
So it would be wrong to state it as ongoing. As for changing the name of the article... Slowdown could be good, but we need a redirect, because the concept is well-known and talked about. (per WP:COMMONNAME). --Kim D. Petersen (talk) 15:54, 9 June 2008 (UTC)

I removed that tag; its an overreaction at this stage. Lets at least try to find a wording we can all be happy with. I agree that shutdown is unlikely. I've changed "possible" to "postulated", which I think is weaker. Note, though, that the next para is There is some speculation that global warming could, via a shutdown or slowdown of the thermohaline circulation, trigger localized cooling in the North Atlantic and lead to cooling, or lesser warming, in that region. This would affect in particular areas like Iceland, Ireland, the Nordic countries, and Britain that are warmed by the North Atlantic drift. The chances of this occurring are unclear; there is some evidence for the stability of the Gulf Stream but a possible weakening of the North Atlantic drift; and there is evidence of warming in northern Europe and nearby seas, rather than the reverse. To me, that indicatess quite clearly that the effect is not well understood. In fact, the entire article is fairly skeptical (I think because I added those bits). Para 3 ends with It is by no means clear that sufficient freshwater could be provided to interrupt thermohaline circulation — climate models indicate not, but research continues. and para 4 with Also, in coupled Atmosphere-Ocean General Circulation Models the THC tends to weaken somewhat rather than stop, and the warming effects outweigh the cooling, even locally: the IPCC Third Annual Report notes that "even in models where the THC weakens, there is still a warming over Europe".[4] Model runs in which the THC is forced to shut down do show cooling — locally up to 8 degrees Celsius [5]— although the largest anomalies occur over the North Atlantic, not over land. I'm really not sure how much more you could want.

As to your refs: Wunsch is just pointing out that the GS is wind-driven. Its not really relevant to shutdown of the THC. Junclaus is just repeating the IPCC, so I can't see why you're so keen to mention it William M. Connolley (talk) 21:38, 9 June 2008 (UTC)

I wouldn't say this is a dispute, either. As for the changing of "possible" to "postulated," I like that quite a bit; are you alright with the new wording, Bender? · AndonicO Engage. 21:47, 9 June 2008 (UTC)