Search site

How can I deal with changes in UK since the 1961-1990 baseline period?

An indication of how the climate of the UK has changed since the baseline period (1961–1990) is provided by the Observed Trends report. This provides a series of tables showing the change in several climate variables from 1961 to 2006, based on the assumption that there is a linear trend.

Another source of information is the 5 km gridded daily observed data that is being supplied by the Met Office Hadley Centre. There will be daily data for temperature and metrics of precipitation. Annual, seasonal and monthly series are provided for some other variables.

In detail

Knowledge of observed changes in climate allows an average annual rate of change to be estimated by dividing the total change by the number of years. The estimated average annual rate of change can be used to adjust the UKCP09 , which give changes relative to the 1961–1990 baseline period.

However, users should note that (i) changes may not be linear and (ii) that natural climatic variability means that actual climate change over the last few decades may be different to that simulated by climate models. 

As an example, an observed change of 1.72°C between 1961 and 2006 is reported for daily mean temperature in South West England in the UKCP09 Observed Trends report (Table 2.3). This is a 45 year period, giving an average annual rate of change of 0.038°C per year (1.72 ÷ 45), assuming a linear trend. The year 2008 is 33 years after the mid-point of the 1961–1990 baseline period (1975). This suggests that since 1975, South West England has experienced an increase in daily temperature of 1.25°C (0.038 x 33), assuming a linear trend. This implies that 1.25°C can be subtracted from the UKCP09 projections of change for South West England, as that amount of change is assumed to have already occurred since the 1961–1990 baseline period.