Climate Change Study
www.dchopkins.co.uk


A Comparison of Temperature Records for Sites in the
United Kingdom with Global Temperature Trends
.

D.C. Hopkins August 2007

1. Introduction

Perceptions of weather trends can be greatly influenced by extreme weather events - analysis of historic weather records should more reliably reveal long term trends. As part of a project I wanted to compare weather data from UK sites with global data - the following is a shortened version of the results.

A comparison of weather temperature records from Durham and Oxford in the United Kingdom with the mean global temperature record was performed over the years 1887 to 2006, using data points over year and decade periods. Other aspects of climate such as sunshine amout and precipition are not included, but Appendix 1 contains a graph of yearly rainfall at the two UK sites.

[Note: links open a in new window]


2. Data Sources

UK weather data were downloaded from The Meteorological Office (Hadley Centre Historic Station Data) http://www.metoffice.gov.uk/climate/uk/stationdata/index.html . The data used were maximum and minimum temperatures .

Global weather data were downloaded from the NASA GISS (Goddard Institute for Space Studies) Surface Temperature Analysis http://data.giss.nasa.gov/gistemp/. The data used were global mean temperatures relative to a best estimate mean 1951-1980 global temperature of 14C.

Whilst it is usual to compare the same parameters in data sets I considered that comparing maximum and minimum temperatures for UK sites with global mean values was actually more useful, since extremes of temperature can have the greatest influence on life forms and the environment.


3. Data Processing

The weather at any location depends on complex temporal factors, and so it was thought that comparison at yearly time intervals alone would not give realistic results. So, in addition to yearly values, averaged temperatures over 10 year intervals were calculated and correlated. The decade average values provide a more realistic comparison of weather data, allowing for long term processes such as mixing of the atmosphere, heat transfer in ocean currents, and other global weather influences - notably the El Nino Southern Oscillation (ENSO). Linear Correlation and Spearman Rank statistical methods were used.


4. Global Temperature Trends

Figure 1 below shows a generally rising temperature trend over 1887-2006 of about 1 deg C, but with an increasing steep rise from around 1975. Short term variations (typically over 3-6 years) make it difficult to see the long term trend, which is more apparent from the decade averaged values.

Figure 1 Global Temp versus Year

5. Oxford and Durham Temperature Trends

As can be seen from Figures 2 and 3 below, the maximum and minimum temperatures averaged over 12 decades generally follow the global trend. There appears to be an increased steepness in rise of UK site temperatures since about 1975 (particularly maximum values). This is also apparent on the HadCET plot of Central England mean temperatures (1772-2007) http://www.metoffice.gov.uk/research/hadleycentre/obsdata/cet.html [Sorry, link invalid 2016]

Figure 2 Maximum Temperatures

Figure 3 Minimum Temperatures

6. Temperature Correlation Results

The Linear Correlation values shown in Table 1 column (A) below indicate little relationship between global and UK sites when yearly data points are used – this is to be expected as outlined in Section 3. The values for decade averaged temperatures in column (B) show a close relationship (since the values are near to 1). Both UK sites give near identical results, and correlation is better for minimum temperatures.

Data Set 1 Data Set 2 (A) Yearly Linear Correlation Value
(1887-2006)
(B) Decade Linear Correlation Value
(1887-2006)
Global Average Temperature Oxford Maximum Temperatures 0.52 0.86
Global Average Temperature Durham Maximum Temperatures 0.50 0.84
Global Average Temperature Oxford Minimum Temperatures 0.64 0.91
Global Average Temperature Durham Minimum Temperatures 0.66 0.91

Table 1    Linear Correlation Values (0 = none, 1 = maximum)

Correlation using the Spearman Rank method was performed only on the decade average temperatures. In all cases there was correlation between global and UK Site temperatures (with a certainty of 95%). The results showed a narrow correlation margin for maximum temperatures, but a wider margin for minimum temperatures.


7. Conclusion

For the decade averaged temperatures, there is a strong correlation between Durham and Oxford site temperatures and global temperatures. This does not prove a causal link between UK and global temperature trends, however extensive climate studies indicate that this is largely the case. The sites below provide detailed climate change information.

DEFRA (UK Department for Environment, Food & Rural Affairs) - Understanding the Causes of Climate Change
http://www.defra.gov.uk/environment/statistics/globatmos/gagccunder.htm [Sorry, link invalid 6/2016]

Intergovernmental Panel on Climate Change (IPCC)
http://www.ipcc.ch/

Within the limited resolution of the decade data points used for this report, the following trends were observed:

(i) The UK site minimum and maximum temperatures are rising at a greater rate than the global mean. It appears that Northern Hemisphere mean temperatures are rising faster than global ones – which would partly explain this observation.

(ii) The steeper rise of both global and UK site mean temperatures in 1975-2006 is apparent from Figures 1-3, and from the HadCET 1772-2007 plot. Similar warming and cooling anomalies can be seen periodically on the HadCET plot, but 1975-2006 is exceptional because the warming period started at an elevated base temperature of about 1 deg C.

(iii) The UK site maximum temperatures are rising more rapidly than minima in the period 1975-2006. This can be seen in Figures 2, 3 and is borne out by the less conclusive correlation results for maxima.


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go to Appendix 1 (Oxford and Durham Yearly Rainfall 1887-2006)

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