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 Post subject: Re: Brrrrrr: Melting Ice Caps Altering The Gulf Stream ??.
PostPosted: Thu Mar 01, 2012 6:03 pm 
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Joined: Wed Dec 31, 2008 3:22 pm
Location: Plymouth
The Doctor wrote:
oggyale wrote:
Were the three colder Winters before this one ('11/'12) just ''one offs'' and are we back to the normal mild conditions we usually get. Or is this mild Winter just a ''one off'',and that next Winter it will be back to the cold again,with all the problems that will bring..


I have a project student looking at a topic related very closely to this at the moment using data from Plymouth (not the coldest spot in the UK obviously) stretching back to the 1870s. The recent cold winters are not particularly exceptional when considered with reference to the full record. There is a general cycle between colder/drier and warmer/wetter winters with a timescale of around 50 years (not exactly). This is linked to a cycle of variations in atmospheric pressure that occurs in the North Atlantic (called the North Atlantic Oscillation). Basically, we seem to be moving into a phase of more negative NAO index values which are historically linked to an increased tendency for cold/dry winter conditions in the UK. This has come after an extended period of more positive NAO index values stretching back to the 1980s and linked to warmer and wetter UK winters. Before that was a more negative NAO index period running from the late 1950s to the late 1970s again linked to colder/drier conditions (including the very famous cold winter of 1963). So, the colder/drier winters we have recently experience are not really extreme and quite normal within this cycle - it is just that we are not used to them. For anybody aged up to about 30 these will be the coldest winters they have experienced but anyone aged over about 55 will delight in telling you about the cold winter of 1963. I think it is interesting to consider how natural changes that occur on this kind of timescale are perceived by humans (given our typical lifespans). A typical human will experience one period of increased tendency for warmer/wetter winters and one of colder/drier winters. If you were born within the last 10 years or so then it is likely (who can be sure about the future?) that when you are 30-40 years old you will be commenting on how warm and wet the winters have suddenly become...

Bear in mind though that this is just one cycle which is superimposed on other variations and any long-term trends (for example, Plymouth winters have possibly become a little bit warmer and a little bit wetter over the last 140 years - I say possibly because the trend is not statistically significant at the 95% confidence level). It is also best to think of these things as tendencies, by which I mean that we are entering a phase where the NAO index will have a tendency to be more negative (but could still be positive in a particular year) and that a negative NAO index tends to be linked to cold/dry conditions in the UK (but warm/wet conditions are still possible). Think probabilities/tendencies and not hard and fast rules.



Thanks for that. Interesting to read.

I remember part of the 1978 Winter being cold [not sure now if it was the ' 77-' 78,or the ' 78-' 79 Winter],my family and i were living in Shortlanesend,Cornwall and the village was cut off for a few days. The roads were like skating rinks and plenty of snow too..

Parts of the 1984/1985 Winter were cold,not much snow,but biting frosts that lasted an age it seemed. I was living in Bristol at the time and the day time temperatures were in the minus area. The night time temperatures went down to minus 10 and more.

The coldest night time temperature i can recall was also in Bristol,minus 15. That was back in the 90s. The reason i remember that is because the Evening Post temperature display board was on my route to work back then. I was working nights.

Last Winter '10/'11,one of the Met Office chaps on the BBC said after his weather forecast that the recent cold Winters were a thing we would now see more of. Was he being over dramatic.

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 Post subject: Re: Brrrrrr: Melting Ice Caps Altering The Gulf Stream ??.
PostPosted: Thu Mar 01, 2012 8:08 pm 
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oggyale wrote:
Last Winter '10/'11,one of the Met Office chaps on the BBC said after his weather forecast that the recent cold Winters were a thing we would now see more of. Was he being over dramatic.


Probably not. After all, his statement was consistent with the idea I outlined in my post (we're moving into a negative NAO phase which is generally linked to cold winters) and it is also consistent with the research findings reported in the story you linked to in your original post (which makes complete sense to me).

But having colder winters in the UK isn't at all incompatible with the fact that, overall, global temperatures are rising.


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 Post subject: Re: Brrrrrr: Melting Ice Caps Altering The Gulf Stream ??.
PostPosted: Sat Mar 03, 2012 12:59 pm 
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Location: Plymouth
This was informative...

http://www.bbc.co.uk/weather/feeds/17199313

The 2011/2012 Winter review was a good watch and listen too.

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