SUMMARY

The averaged minimum temperature in Weymouth has been rising since about 1985 and is now higher than at any time since records started in 1927. Average maximum temperatures have also risen but are still lower than temperatures experienced in the 1940s.

The rates of rise seen in Weymouth's temperature curves in the 1990s was about 1.0 degree Centigrade compared with a global rate of rise of about 0.2 degree Centigrade. 

This suggests that any rises seen in Weymouth's temperature records are not directly linked to changes in global temperature. If the rises are due to climate change then something is greatly amplifying the global heating on a local basis.

Looking at the changes in average temperatures over seasons of the year, minimum temperatures have steadily been rising in the first half of the year and falling in the second half. Spring average temperatures have risen by an incredible five degrees since 1927.

Average maximum temperatures have risen in the first half of the year but fallen in the second half of the year. Indeed, average maximum summer temperatures are now, on average, four degrees lower than in the 1930s.

In brief, Winter and Spring are getting warmer and Summer and Autumn are getting cooler - contrary to the predictions of climate modellers.

There has been a slight rise in the number of frosty days each year.

ANALYSIS

Daily maximum and minimum temperature records have been collected in Weymouth since 1927. 

Figure 1

Figure 1 shows the annual average minimum and maximum temperatures as well as the annual daily average. The black curves are five-year running means.

Note the big dip due to the severe and long winter of 1962/3.

It can be seen that, until about 1985, the temperature was fairly constant. However, since 1985, all three temperature records have shown a rise of about 0.1^o C per year.

However, annual average maximum daily temperatures have only climbed back to value last experienced in the pre-1960 decades so temperatures are not yet exceptional in Weymouth. For the annual average minimum temperature, the 1995 value exceeded any previous values back to 1927.

Figure 2

Figure 2 shows the average minimum temperature in the first quarter of each year with a five-year average plotted in red. It can be seen that temperatures were fairly constant until around 1986 after which there has been a rise of about 0.2⁰C per year.

Figure 3

Figure 3 shows the average minimum temperature in the second quarter of each year with a five-year average plotted in red. It can be seen that temperatures have risen by about 5⁰ C since 1927 and that there has been a rise of about 0.3⁰ C per year since about 1980.

Figure 4

Figure 4 shows the average minimum temperature in the third quarter of each year with a five-year average plotted in red. It can be seen that temperatures have fallen steadily by about 2⁰ C per year since records started in 1927.

Figure 5

Figure 5 shows the average minimum temperature in the fourth quarter of each year with a five-year average plotted in red. It can be seen that temperatures have fallen fairly steadily by about 2⁰ C since 1927 with little change from 1975 to the present.

Figure 6

Figure 6 shows the average maximum temperature in the first quarter of each year with a five-year average plotted in red. It can be seen that temperatures were largely constant until about 1985 after which there has been a rise of about 0.2⁰ C per year.

Notice the very distinctive dip in the above curve corresponding to the 'Great Freeze' of 1962.

Figure 7

Figure 7 shows the average maximum temperature in the second quarter of each year with a five-year average plotted in red. It can be seen that temperatures rose by about 2⁰ C from 1927 until 1950 and thereafter remained fairly steady until a rise of about 0.2⁰ C per year set in around 2000. However, this latter rise may be a short-term fluctuation.

Figure 8

Figure 8 shows the average maximum temperature in the third quarter of each year with a five-year average plotted in red. It can be seen that temperatures steadily fell at about 0.3⁰ C per year.

Figure 9

Figure 9 shows the average maximum temperature in the fourth quarter of each year with a five-year average plotted in red. It can be seen that temperatures steadily fell at about 0.2⁰ C per year until 1965 after which they have remained stead at about 4⁰ C cooler that in the 1920s.

These quite different variations might be due to the relocation of the weather recording equipment over the years. Over the period covered by the records, major moves were made in 1969 and in 1993. However, the above charts show no 'jumps' in the records that would indicate a bias imposed by different sites.

It is concluded that the changes shown above are very likely to be genuine.

Figure 10

Figure 10 shows the changes in the average Global Mean Surface Temperature (GMST). It can be seen that it started to rise around 1910 at about 0.013⁰ C per year. Then, in the 1940s, the GMST fell for nearly four decades before rising again from the mid-1970s at the same rate as previously, namely at about 0.013⁰ C per year.

What is important to note is that the rates of rise seen in Weymouth's temperature curves in the past two decades is more than ten times faster than the global temperature rise rate. 

Figure 11

Figure 11 shows the changes in the Global, Central England and Weymouth average annual temperatures. The data have been scaled relative to 1980 in all three cases. Again it can be seen that Weymouth's annual mean temperature is rising faster than even the Central England rate of rise which is about double the Global rate of rise.

Thus, any rises seen in Weymouth's temperature records appear not to be directly related to changes in global temperature. If the rises are due to climate change then something is greatly amplifying the global heating on a local basis.

It is my opinion that the above charts illustrate changes unrelated to global warming as shown in figure 10. Not only are recent temperature rises far more rapid than GMST but the overall shape of the curves do not show the same characteristic shape of the GMST curve on figure 10.

It is also my opinion that changes in Weymouth's weather are more likely to be due to long-term and short-term natural changes than to any overall effect of global warming.

Finally, Figure 12 shows the number of days each year upon which a frost was recorded expressed as a running five-year mean.

Figure 12

It can be seen that there has been no large change in the number of frosty days although there has been a slight rise since 1990.

This is probably due to the average mean minimum temperature in the fourth quarter of the year falling (figure 5) whereas the figures for the first quarter of the year has been rising (figure 2). This has balanced out the number of frosty days.

However, it has to be remembered that the weather recording equipment has been moved and this may make the measurements of frost somewhat unreliable when looking for long-term trends.