Posted by: mynaturaldiary | January 18, 2017

First Song 2017

Song Thrush heard on 18th January. This makes it 28 days from the winter solstice. and well within the normal range of dates recorded by me since 2008.

days-from-solstice-for-first-bird-song-2017-data

days-from-solstice-for-first-bird-song-2017

This year is at the 40%, close to the average at 50% (33 days after the winter solstice). Looking at the trend of these dates, no discernible pattern emerges.

trend-of-days-from-solstice-for-first-bird-song-2017

The birds aren’t singing any earlier, year on year.

The annual Central England Temperature record (CET), running back to 1659 now has the 2016 data. The average temperature for 2016 (10.31° C) was almost the same as 2015 (10.27° C).

The yearly values (shown by points connected by a dotted line) are shown in the graphs below, together with a time series analysis of the data, using exponentially weighted moving averages (EWMA)  for the 10 year (red line) and 30 year (blue line). The 10 year (red line) is the decadal behaviour; the 30 year (blue line) is the multidecadal behaviour.   Given the length of the time series, we can look back and identify when the trends changed, by taking the turning points in the blue trend data. Clear warming or cooling trends can be identified when the red trend data rises above the blue trend data (heating), or falls below the blue trend data (cooling). Periods of time when the temperature is stable is highlighted by both the red and blue lines being similar. The blue trend multidecadal behaviour, is perhaps of more interest in understanding climate, rather than the yearly values, which are dependent upon each years weather pattern.  {Click on each image to see it enlarged}.

cet-yearly-2016

Looking at the data since 1850 (when the blue 30 and red 10 year trends were the same, so the temperature was stable) shows the current patterns more clearly. From this period of time onwards, we can be certain that robust thermometry has been used to measure the data.

average-1850

 

Currently the red line trend is above the blue line trend, which indicates a rising temperature, and has been so since 1988. For an overall falling trend, the red line trend must be beneath the blue line trend (as it did from 1880 to 1900). A stable trend in temperature would have both lines moving along together (as it did from 1900 to 1911, and 1964 to 1989). Looking at past behaviour shows it is unwise to believe that any current behaviour will persist indefinitely, and that forecasting on the basis of linear extrapolation of the current trend has limited value as a forecasting method. EWMA only allows forecasting one time step ahead, and this is shown in the graphs (next year’s prediction, based on all the data).

The year to year temperature difference from 1850 until 2016 shows evidence of a stochastic process, as shown below, with a mean value of 0.01° C, and a standard deviation of 0.70° C.

cet-yearly-difference-in-temperature-1850-to-2016

Thus if the yearly difference in temperature is greater than ± 1.4° C, we know an unusual year has occurred. (±2 standard deviations  or ±95% confidence limits). That has only happened a few times since 1850; the last time in 2011.

Looking at the monthly temperatures is instructive, as it is the basis of the yearly data. Have the trends in temperature in the yearly record above occurred across all months, or are their differences between the months and the seasons?

January

cet-january-1850-2016

A complex pattern of gradual increase (1850 until 1940; blue trend = 2.65° C to 4.05° C), followed by a decline (1940 to 1967; blue trend 4.05° C to 3.63° C), followed by the current rise (1967 to 2016; blue trend 3.63° C to 4.27° C). The red trends line reached a peak in 2009, and has declined since then.

February

cet-february-1850-2016

 

Essentially unchanged from 1850 until 1988, when a rapid increase occurred (1988 until 2016; blue trend = 3.61° C to 4.38° C). You can see the red trend line stopped increasing in 2004, and is currently slowly moving back towards the blue trend line.

March

cet-march-1850-2016

The trend has been gently up (1893; blue trend = 4.99° C to 1962 = 5.71° C), stationary (1962 to 1987), then an increase (1987; blue trend = 5.71° C to 2013 = 6.32° C). The 30 year trend has declined since then to 6.24° C in 2016. Concomitant to this, the red trend has reversed direction, and is heading towards the blue trend line. This is somewhat similar to the pattern of February. If the red line crosses beneath the blue line, we will know the current warming phase has ended. If both the red and blue lines move along together, a stable trend in temperature will be occurring. Only more time will tell.

April

cet-april-1850-2016

A complex pattern of gradual increase and decrease, with a clear rapid increase starting in 1941, peaking in 1950, then declining until 1987. Since then a gradual increase (1987; blue trend = 7.96° C to 2016 = 8.51° C). As in the earlier months above, the past few years suggest the rate of increase has slowed, having peaked in 2012.

May

cet-may-1850-2016

Essentially unchanged since 1850. (1850; blue trend = 11.50° C to 2016 = 11.55° C). The current warming phase began in 1988. The red trend recently reached a peak in 2010 (11.95° C), and has now declined in 2016 (11.75° C).

June

cet-june-1850-2016

Essentially unchanged; if anything a slight decline since 1850. (1850; blue trend = 14.52° C to 2016 = 14.40° C). The red trend recently reached a peak in 2008 (14.76° C), and has now declined; 2016 (14.47° C).

July

cet-july-1850-2016

Essentially unchanged from 1850 to 1982. (1850; blue trend = 15.75° C to 1982 = 15.92° C). Thereafter a slight warming trend, indicated by the red trend rising above the blue trend (1982; blue trend = 15.92° C to 2016 = 16.44° C). The red line reached a peak in 2007.

August

cet-august-1850-2016

Essentially unchanged from 1850 to 1975, when the red trend rose above the blue trend in the most recent period (1850; blue trend = 15.38° C to 1975 = 15.60° C). Thereafter a slight warming trend, which plateaued in 2005. (1975; blue trend = 15.60° C to 2005 = 16.21° C) . Since 2005, the blue trend has remained essentially stable (2016 = 16.13° C), and the red trend clearly shows signs of falling back to the blue trend, having peaked in 2006.

September

cet-september-1850-2016

Essentially unchanged from 1850 to 1933 (1850; blue trend = 13.08° C to 1975 = 13.08° C). A gentle increase up to 1962 (1933; blue trend = 13.08° C to 1962 = 13.57° C), then unchanged until 1998 (blue trend = 13.58° C). Thereafter a rise until 2007 (blue trend = 13.92° C), followed by a pause until now 2016 (blue trend = 13.92° C). The red trend shows signs of returning towards the blue trend, having peaked in 2008.

October

cet-october-1850-2016

A gentle rising and falling pattern from 1850 until 1921 (1850; blue trend = 9.53° C to 1921 = 9.42° C). Thereafter a slow steady increase until 1981, with the red trend consistently above the blue trend (1921; blue trend = 9.42° C to 1981 = 10.28° C). A short pause, lasting until 1995 (1981; blue trend = 10.28° C to 1995 = 10.24° C). More recently, another warming phase, currently unbroken (1995; blue trend = 10.24° C to 2016 = 10.76° C). The red line had a recent peak value in 2015.

November

cet-november-1850-2016

A gentle rising and falling pattern from 1850 until 1931, when the red 10 year trend rose above the blue 30 year trend (1850; blue trend = 5.93° C to 1931 = 5.93° C). From 1931, a steady rise in temperature, indicated by the red trend being greater than the blue trend (1931; blue trend = 5.93° C to 1965 =6.50° C), whereafter a short period of stable temperature occurred lasting until 1978 (1965; blue trend = 6.50° C to 1978 =6.38° C), indicted by the red trend and blue trend lines being similar in value. From 1978 until 2016, a period of warming has occurred (1978; blue trend = 6.38° C to 1978 = 7.10° C). The red line currently indicates 2016 as the peak value.

December

cet-december-1850-2016

A rising and falling pattern at the beginning 1850 until 1910 (1850; blue trend = 3.99° C to 1910 =3.95° C), followed by gentle rise until 1925. (1910 blue trend = 3.95° C to 1925 = 4.43° C). Thereafter a holding pattern until 1971 (1925 blue trend = 4.43° C to 1973 = 4.33° C), when the red trend rose above the 30 year blue trend.  Thereafter a warming trend continues until the present notwithstanding the exceptionally cold year of 2010, and warm year of 2015 (1973 blue trend = 4.33° C to 2016 = 4.84° C). The red line indicates 1989 as the peak value.

All the above analysis, month by month suggests recent warming in late autumn and early winter (October & November). Summer seems unchanged over the longer time period. There is clear evidence in recent years of a warming phase which has peaked and is declining. This may presage a period of stable temperatures, or further decline into a cooling period. Only time will tell.

The monthly temperatures going back to 1850 are below, shown on a probability plot.

monthly-averages-1850-2016

You can see the data is all ‘Gaussian/normal’, since they show up as a series of straight lines when plotted on a normal probability graph.

Tabulating the monthly average temperatures for 2016 showed we had one exceptional month (i.e. outside the +/- 95% confidence limits), which was September, the rest being ‘normal’ (i.e. inside the +/- 95% confidence limits).

2016-temps

Behind all these trends in British weather lies the Jetstream. The following offers a guide to what the Jetstream does to British weather.

      • The position of the jet stream over the UK determines the type of weather we experience.
      • If the polar front jet is situated significantly to the south of the UK we will experience colder than average weather, driven by the polar cell.
      • If the polar front jet is situated to the north of the UK we will experience warmer than average weather, driven by the Ferrel cell.
      • If the polar front jet is situated over the UK we will experience wetter and windier than average weather.
      • If the polar front jet has a large amplification then cold air will travel further south than average and warm air will travel further north than average.
      • The direction and angle of the jet stream arriving at the UK will determine what source of air (i.e. cold, dry, warm, wet, from maritime or continental sources) the UK experiences.

CRHQCB4W8AAyCJI.png:large

The weather in Britain is ‘difficult’ to predict over the course of a few months, which is why the Brits talk about it all the time.


Responses

  1. It appears that the CET record has been adjusted from the 1970’s, due to urban heating and land change.

    https://wattsupwiththat.com/2017/01/29/what-do-three-cet-reference-weather-stations-used-by-the-met-office-have-in-common/

    “The Met Office relies upon just three weather stations to record the Central England Temperature: Stonyhurst (Lancashire), Pershore (Worcestershire) and Rothamsted (Hertfordshire).

    http://www.metoffice.gov.uk/climate/uk/about/archives

    The Met Office averages these three temperatures and makes a 0.2 degrees C negative adjustment to compensate for the UHI effect.

    http://hadobs.metoffice.com/hadcet/

    The Met Office has made this adjustment since 1974. Bizarrely, they don’t seem to know exactly why 1974 was chosen other than being able to speculate that “It was probably around then that the effects of urbanisation began to be noticed, although this date as chosen may be slightly arbitrary” ”


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