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there are better explanations than the legendary Gulf Stream breakdown for the current coolish autumn.

My first stop on climate questions is always the excellent RealClimate, collective blog of the "hockey team" (i.e. the Hansen crowd)

That pointed me here, to a much more plausible mechanism for global warming causing the cold weather : a combination of the North Atlantic Oscillation and an exceptionally low level of sea ice in the eastern Arctic :

Typically cold weather in northern Europe is associated with the NAO which consists of a high pressure system over the Azores and a low pressure system over Iceland. The so-called negative phase of the NAO was particularly strong during the second half of November, according to Petoukhov. The NAO is the dominant mode of atmospheric variability in the north Atlantic throughout the year and particularly prominent in the winter. The pressure difference drives the winds and the weather fronts.
[...]
"We had a strong negative phase of the NAO in the second half of November. The pressure gradient between the Azores high and the Icelandic low was very small. This is the favourite situation for cold winters

So, we have the NAO which is an apparently random/cyclical type thingy, giving us a bit of a chill this year... But there's more!

Warming oceans, thought by many to be associated with climate change, are contributing to reductions in sea ice in the Arctic area. Computer models suggest that a reduction in sea ice in the eastern Arctic leads to a loss of ocean heat and a consequent warming of the lower atmosphere which can trigger atmospheric circulation anomalies that can in turn lead to an overall cooling of northern continents, according to Petoukhov's research which was published in the Journal of Geophysical Research in November. This can result in a continental-scale winter cooling reaching, on average, −1.5C colder than it would otherwise have been.
[...]
"Just yesterday I checked the sea ice in the Barents-Kara and it was very low. Nearly as low as it was between 2005 and 2006," Petoukhov told Reporting Climate Science .Com on 2 December 2010.

The strong diminishing trend in Arctic sea ice, particularly when it is accentuated in the Barents sea, gives us colder winters. This year it looks like we get the Quinella.

This correlation between the sea ice reduction and the continental cooling is strong, according to the research. Other explanations linking cold winters and global warming include reduced solar activity and changes in the Gulf Stream are less strongly correlated. However, the NAO could interact with sea-ice decrease, the study concludes and one could amplify the other. This is what may be happening at the moment, suggested Petoukhov.

If the Gulf Stream gets messed up as well, that would be the Trifecta. But even without it, I think we'll have a very cold winter.

Footnote : I was hoping to do a bit of early skiing this weekend with the kids... but it's a tepid 15° today, and it's all turned to mush. The joys of a semi-continental climate.

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Wed Dec 8th, 2010 at 10:18:05 AM EST
More cold winters ahead

Petoukhov believes that we may already be seeing evidence of an increase in the frequency of cold winters compared with the more random, or stochastic, distribution of cold winters in previous decades that were associated with the NAO. "We have already had two chilly winters in Europe in the last decade, and this November situation, as it developed, also forces us to be on the alert. This makes it questionable that only a purely stochastic mechanism of the European cold winter extremes is at work, and this deserves an exhaustive investigation," he commented.

The possibility suggested by Petoukhov that the Barents-Kara Sea effect could triple the probability of cold winter extremes in Europe,will almost certainly be of interest to policy makers and planners in north European states such as the UK where there is an ongoing debate about the level of investment required to deal with "occasional" cold weather events.

Policy implications of colder European winters :

  • Insulation, insulation, insulation
  • Reinforced, weatherproof public transport : a reshag of infrastructure specs (what about the Dublin metro?)
  • Energy security :  oh bugger, Ireland is in the poo on that one. Your home heating problem on a national scale.


It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II
by eurogreen on Wed Dec 8th, 2010 at 10:42:47 AM EST
[ Parent ]
I don't think it is a case of either/or.  There are numerous factors at work and I chose to highlight one.  What I found interesting, as a non climate scientist, is the quite drastic effect relatively small changes in average global temperatures can have in particularly regions, and the degree to which even non-anthropogenic climate change has, in the past, led to quite sudden and dramatic changes in Europe in particular.

Petoukhov talks of other correlations being stronger, but the excerpts you quote don't really provide a theory of causation which explains why low ice in the East Arctic should result in colder winters in NW Europe and doesn't exclude the possibility of global warming ->low Arctic sea ice -> reduced thermohaline circulation -> weaker NAD -> colder winters.

In any case, I'm not qualified to debate the finer points of the available evidence and theories. My purpose was to demonstrate that whilst you cannot prove that exceptionally cold winters in NW Europe are caused by global warming, you cannot exclude that possibility either, and there is no reason why slow and gradual global trends cannot lead the sudden and dramatic localised fluctuations.

Index of Frank's Diaries

by Frank Schnittger (mail Frankschnittger at hot male dotty communists) on Wed Dec 8th, 2010 at 11:15:25 AM EST
[ Parent ]
I find the evidence fairly compelling that there is a causal link between global warming and colder European winters. For the rest, I agree with you completely.

Thanks for the excuse to update my understanding of this subject...

Anyway, if you won't believe me (and who could blame you), perhaps you'll believe...

the UK Met Office?

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Wed Dec 8th, 2010 at 12:01:44 PM EST
[ Parent ]
Meteorological office for anything.  

Just not relevant.  

I don't mean to pick on the UK--I wouldn't believe the US either.  

From your link

according to Vicky Pope, Head of Climate Change for Government at the UK Meteorological Office
 

Not to be rude, but lying is their job.  

The Fates are kind.

by Gaianne on Thu Dec 9th, 2010 at 02:56:52 AM EST
[ Parent ]
Gaianne:
Not to be rude, but lying is their job.  

I'm not sure I understand why this has to be the case.  What are the institutional/class interests which are served by falsifying climate science?

Index of Frank's Diaries

by Frank Schnittger (mail Frankschnittger at hot male dotty communists) on Thu Dec 9th, 2010 at 04:34:03 AM EST
[ Parent ]
One that has popped up here in Sweden:

* Water security

Water supplies, purification and distribution is adapted to current conditions. Adaptation is needed.

Sweden's finest (and perhaps only) collaborative, leftist e-newspaper Synapze.se

by A swedish kind of death on Wed Dec 8th, 2010 at 04:25:13 PM EST
[ Parent ]

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