CET Winter Trends

By Paul Homewood

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https://www.metoffice.gov.uk/hadobs/hadcet/data/download.html

As promised, I have now some detailed analysis of the Central England Temperature Series, specifically winter trends.

As can be seen above, there has been an underlying trend increase since the start of the record in 1660. However, certain things stand out:

1) There have been other winters back in the past which have been just as warm as anything recently.

The warmest winter was actually 1868/9, with 1833/4 in third place behind 2016/7.

2) The 10-year average has been dropping away since it peaked in 2008, and is now  back where it was in the 1970s, and indeed in 1739.

3) There is huge year to year variability throughout the series.

All of this tends to begs the question  – how much of this trend is due to “weather”, as opposed to “climate”?

If we look at daily numbers, we get more clues:

image

 image

image

https://www.metoffice.gov.uk/hadobs/hadcet/cetdl1772on.dat

I have shown each month separately and limited the analysis to the period since 1901 for clarity.

Two things become immediately apparent:

1) Throughout the three months, extremely cold days have become much rarer in the last couple of decades. This is despite the exceptionally cold weather in January and December 2010.

2) There is, however, no indication that temperatures are rising at the top of the bands.

 

We can see the changing pattern in extremely cold days, in the graph below:

image

 

Fascinatingly though, we find that the relative absence of cold days is not something new. There was a very similar situation in the 1930s, when there were just 17 days below –2.0C, and this despite the fact that 15 of these occurred in 1940.

The 1920s also saw few such days.

This all points strongly to the likelihood that what we have experienced recently is weather and not climate. It is also a warning that cold winters may not be a thing of the past.

 

Does any of this matter? I would argue it does, for two reasons:

1) If winters have become milder on average because of a shift in weather patterns, it does not support the assumption that winters will carry on becoming milder.

Indeed the figures suggest that we have already hit the ceiling, and that temperatures won’t go any higher.

2) Weather being weather, we cannot rule out a return to previous climatic regimes.

 

I have, by the way, looked at trends in min and max temperatures, but they also come up with similar conclusions.

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March 9, 2018 at 07:45AM

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