Patterns of climate change across Scotland

Patterns of climate change across Scotland
CC03
March 2006

EXECUTIVE SUMMARY

Project funders/partners: Scotland and Northern Ireland Forum for Environmental Research (SNIFFER), Scottish Executive, Scottish Environment Protection Agency (SEPA), Scottish Natural Heritage (SNH) and the Forestry Commission.

Background to research

The Scottish mainland and Scottish Isles warmed by 0.69°C and 0.64°C respectively, over the period 1861-2000 (Jones and Lister, 2004). Precipitation patterns have also altered, generally producing drier summer and wetter winters but there has also been an increased frequency of heavy rain events (Mayes, 1996; Smith, 1995). Generalised annual values at a national level can mask significant regional and seasonal variations. In order to plan for adaptation to climate change there is a need to know the degree of change in specific locations across the seasons. Only then can potential future trends for that locality be considered in the context of the latest UK Climate Impacts Programme (UKCIP) climate change scenarios.

Objectives of research

The aim of this study is to collate records of observed data in order to provide an up to date assessment of how the climate of Scotland has changed, not just giving a nationally averaged result but identifying regional patterns of change. This study provides a benchmark against which future change can be measured. The analysis of trends shows how far Scotland’s climate has altered. It also places the predicted future climate of Scotland within the context of changes already observed. It thereby provides information essential to those considering the need to adapt to the impacts of climate change in Scotland. A stakeholder survey was conducted in order to ensure the capture of key variables. The findings of the study are presented in summary form as a Handbook, with the full details of the analysis being given in this technical handbook.

When descriptions of our changing climate are presented in terms of nationally averaged annual mean statistics, significant regional and seasonal variations can be masked. This technical report describes the analysis of a number of high-resolution datasets. These are based upon data from a dense network of observing stations that has been gridded using some of the latest data regression and interpolation techniques. The datasets include temperature and precipitation from 1914 to 2004, sunshine from 1929 to 2004, and a range of other variables, such as mean sea level and snow cover, from 1961. A number of quantities based upon either temperature or rainfall, such as growing season length and rainfall intensity, have also been derived. These datasets have been analysed in order to identify patterns of change in the Scottish climate over time and space.

Key findings

Since 1914 average temperatures in Scotland have risen by 0.5°C. Northern Scotland has warmed at a slower rate than the rest of the country, with average increases in temperature only being significant in spring. In northern Scotland, there has been little change in winter temperatures since 1914.
Temperatures have increased in every season and in all parts of Scotland since 1961. This has been the fastest period of warming observed over the 1914 to 2004 period analysed in this study. Since 1961 average spring, summer and winter temperatures have risen by more than 1°C.
Since 1961 average daily maximum temperatures have been increasing at a faster rate than average minimum, or night time, temperatures in Scotland. Globally, over approximately the same period, it is minimum temperatures that have increased at the faster rate. It is interesting to note that conversely the trend in Scotland over the 1914 to 2004 period also has the minimum temperatures increasing at the faster rate.
Scotland has become wetter since 1961, with an average increase of almost sixty percent in winter months in northern and western Scotland. For the majority of the country there has not been a large-scale significant change in average summer rainfall although some parts of north west Scotland have become up to forty five percent drier in summer. Contrary to the Scottish national trend, Aberdeenshire has seen little change in precipitation in winter months although this is compensated for in this region by a significant increase in precipitation in autumn (September-November).
Heavy rainfall events have increased significantly in winter, particularly in northern and western regions.
The snow season has shortened across the country since 1961, with the season starting later and finishing earlier in the year. The greatest reductions have occurred in northern and western Scotland.
Since 1961 there has been more than a twenty-five percent reduction in the number of days of frost (both air and ground frost) across the country. At the same time, the growing season length has increased significantly, with the greatest change occurring at the beginning of the season.
Inconsistent methods for observing cloud data and the challenges of analysing wind observations have meant that identification of any trends or patterns of change in these quantities has not been possible in this study. Further, more complex, data analysis techniques would be required for such an undertaking.
The majority of the analysis presented here is based upon data for 1961 to 2004. Longer data records for temperature and precipitation have allowed trends over this time to be put into the context of a long period. The study highlights the fact that since 1961 both annual mean temperature and precipitation have increased at a faster rate than at any other time in the ninety years considered.
The trends identified since 1961 are not always consistent with those that might be expected based upon the future climate of Scotland projected by climate models, although evidence of such trends often exists in the longer record, i.e. the 1914 to 2004 dataset. This underlines the fact that caution is required when drawing conclusions about trends and climate change based upon a relatively short data period.

This study is focused upon the identification of trends in Scottish climate and providing the regional and spatial detail that national averages mask. The study does not seek to explain, or attribute a cause, for identified trends. Although some of the trends identified are consistent with projected future climate for Scotland, it is not possible to say that the trends are evidence of man-made, i.e. anthropogenic, climate change. However, many of the trends identified are significant and therefore beyond the range expected from natural variability. Whether or not the changes are due to anthropogenic climate change it is clear that these observed trends are often comparable with those predicted for the future. This means that Scotland already has experience of the impact of such changes and is therefore well placed to plan the necessary adaptation measures for the future.

Key words: Scotland, climate change, observed trends

N.B. The report is available for download from the SNIFFER Website

The Technical Report and Handbook are each available separately in electronic format at £20.00 + VAT
Hard copy available at the following prices:
Technical Report £35.00
A Handbook of Climate trends across Scotland £25.00

All prices less 20% to FWR members.