Global warming is no longer a theory. Since the 1970s, the world has warmed by about 0.15 °C per decade, and 1998 was the warmest year on record. In England, four of the five warmest years in the 340-year record occurred in the last decade. These are startling statistics. The clear message from the scientific community is that this warming is due, at least in part, to the increasing concentrations of greenhouse gases in the atmosphere.

The United Kingdom signed the Framework Convention on Climate Change at Rio in 1992, and, following the meeting of parties to the Convention in Kyoto in 1997, has set itself the challenging target to reduce greenhouse gas emissions by 20% below 1990 levels by 2008-2012. However, even if all nations fulfill their Kyoto commitments, warming is likely to continue. We must, therefore, remain alert and be prepared for change.

This report is the first step in identifying a set of indicators which could be used to monitor how the climate of the United Kingdom is changing and how it may be affecting aspects of our lives and natural environment. In the long term, climate change may have large impacts on our economy and daily lives, but within the next decade or so, the first things to change may be subtle aspects of the behaviour of plants, animals and people where we already know them to be sensitive to climate from past records. These are the sort of indicators listed here.

This set of indicators may be seen in the context of broader initiatives. The Organization for Economic Cooperation and Development (OECD) produces a twice-yearly set of 33 environmental indicators for its 23 member states in Western Europe, North America and Asia. Similar work is ongoing within Europe, led by Eurostat (the Statistical Office of the European Union) and the European Environment Agency. In the UK, the Department for Environment, Food and Rural Affairs (DEFRA) and the Government Statistical Service have published a consultative document listing over 120 Indicators of Sustainable Development for the United Kingdom (DETR, 1996) including climate change.

This report takes account of previous studies on climate change impacts in the UK. The UK Climate Change Impacts Review Group, established by DEFRA, has published two reports which detail likely changes in climate and the responses of 12 sectors ranging from Agriculture and the Water Industry to Transport and Manufacturing (CCIRG, 1991, 1996). In addition, DEFRA commissioned studies on the environmental impacts in the UK of the unusually mild winter in 1988/89 and hot summers in 1989 and 1990 (Cannell and Pitcairn, 1993). Later, a report was commissioned on the economic impacts of the hot summer and unusually warm year of 1995 (Palutikof et al., 1997).

It should be stressed at the outset that the indicators given in this report is a preliminary set which has been chosen with the following constraints:

• Indicators are included only where long-term datasets are available and the historic record shows that the indicators are sensitive to climate. Consequently, these indicators do not give a comprehensive coverage of all sectors and do not represent a balanced picture of the likely impacts of climate change in the UK. Rather, these indicators show where climate change impacts can be detected.
  
• Climate change is defined here as change in temperature, rainfall and associated meteorological variables. This report does not consider the impacts of increased UVB radiation or the effects of changes in pollutant gases, acid and nitrogen deposition.
  
• This report is primarily concerned with how the climate of the UK is changing and the effects of that climate change. It does not cover all the factors which may be causing climate change, including increased concentrations of greenhouse gases in the atmosphere, or measures that may be taken to reduce emissions. Furthermore, it cannot be assumed that any climatic change that may be detected can be attributed to increasing concentrations of greenhouse gases in the atmosphere. Indicators have been chosen to detect change - whether this change is due to an enhanced greenhouse effect is another question.

The following criteria were used to select indicators of climate change from among a large number of candidates.

1. The state variables (see Appendix I) covering climate, sea level rise and hydrology could not cover the whole UK in detail (eg all hydrological regions). However, regions of the UK will probably experience different shifts in rainfall and temperature (Hulme and Jenkins, 1998) which presented a problem in identifying single indicators for the UK as a whole and made site-specific data of limited general value. The compromise solution was to select indicators which covered regions that represented extremes or gradients (eg rainfall in SE and NW Britain) or areas particularly sensitive to climate change (eg sea level in S England and groundwater depth in chalk). More comprehensive data on hydrological trends can be found at http://www.nwl.ac.uk/ih/
   
2. The response variables which were selected had to be sensitive to climate and this sensitivity had to be demonstrated by close correlations with climatic variables using long-term historic time series. Stated conversely, the variables had to be relatively insensitive to non-climatic factors. Furthermore, each indicator should respond to climate such that it might be expected to produce a long-term trend in response to future trends in temperature and/or precipitation. The indicator should not simply respond to seasonal changes in weather with no possible long-term consequences and there should not be a long term trend due to other factors which would obscure any effect of climatic change. These considerations meant that some variables were described as percentages rather than as absolute variables (eg percentage of gas consumed in winter rather than absolute consumption, which shows a strong long-term increase as gas-fired central heating has become more widespread).
   
3. The indicators should have long and accurate historic time series, which could be used to establish the historic climate sensitivity of the indicator and also to establish a baseline against which future perturbations due to climate change or variability could be measured.
   
4. The indicator data must be available from sources which will provide a reliable record promptly and at low cost at present and in the future, with consistent methods of data collection over time. Ideally, the data should be published annually and be available at no cost, but it was found that many useful datasets are collected by individual organizations, are calculated intermittently and are provided only at a charge.
   
5. The indicators must be readily understandable by the intelligent layman and generally have public resonance and/or be closely related to policy concerns.
   
6. Where possible, the chosen indicators related to the natural environment should be part of the suite of variables being measured within the UK Interdepartmental Environmental Change Network.

Many potential indicators were considered and rejected because they did not meet the criteria (Appendix II) and not all indicators met all criteria. However, taken together, the package of 34 indicators a good starting point to observe change. These indicators will be watched to see whether signs of change already emerging develop into important trends which affects our daily lives.

MGR Cannell
JP Palutikof
TH Sparks

February 1999. Updated October 2003

Comments and suggestion should be sent to:

Professor MGR Cannell
Centre for Ecology and Hydrology
Edinburgh Research Station
Bush Estate
Penicuik
Midlothian EH26 0QB
E-mail: mgrc@ceh.ac.uk