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1. CCIRG91

The first 'official' UK climate change scenarios were produced in 1991 as part of the work of the Climate Change Impacts Review Group (CCIRG). The work was primarily a literature review – informed by the then recently published First Assessment Report of the IPCC – and the CCIRG scenarios were based on the results of five global climate models. These were analysed to construct scenarios of temperature and precipitation change for the UK. The results generally suggested a warmer wetter UK, with the exception of summer precipitation where the five models used did not unanimously agree about the direction of change. 

2. CCIRG96

The second set of UK climate change scenarios was published in 1996 by CCIRG. They were based on the results of the first Met Office Hadley Centre coupled ocean-atmosphere model (HadCM1). The CCIRG96 scenarios provided greater detail, including some analysis of daily model output and estimates of additional climate variables to temperature and precipitation change. As with CCIRG91, the CCIRG scenarios suggested warmer wetter winters for the whole UK, but with dryer summers in the South and wetter summers in the North. However, the pattern of warming across the UK (greatest warming in the South East and least warming in the North West) was different to that described in CCIRG91. 

3. UKCIP98

The third set of UK climate change scenarios – UKCIP98 – were one of the first major publications of UKCIP (which was formed in 1997). They were based on the results from the second Met Office Hadley Centre global climate model (HadCM2). For the first time, future climate changes were associated with scenarios of future emissions of greenhouse gases, labelled Low, Medium-Low, Medium-High and High. Changes to a wider range of climate variables were reported, with many mapped to show the six ~250 km resolution grid squares that cover the UK. The results were similar to those presented in CCIRG96. UKCIP98 presented results from three other global climate models in map form to illustrate differences and similarities between different climate models. 

4. UKCIP02

UKCIP02 had a relatively extended period of consultation, with users involved to some extent throughout most of the two-year design and development period. This included the establishment of a UKCIP02 stakeholder panel and a number of dedicated consultation exercises. These consultations revealed the broadening user community and its evolving range of needs. Based on their experience of using UKCIP98, users asked for greater regional and temporal detail, estimates of changes to extremes and better guidance on how to handle uncertainties.

Consequently, UKCIP02 made use of downscaling, whereby results from the third Met Office Hadley Centre global climate model (HadCM3) were used to drive their new regional climate model (HadRM3). Model output at monthly and daily resolution with 50km spatial resolution for 104 grid squares across the UK allowed for the provision of more detailed regional changes and analysis of extremes. The trade-off of these enhancements is the increased computational resources they require. This meant a package of statistical procedures (e.g. pattern-scaling techniques) were used in order to provide estimates of changes for four emissions scenarios and three future time-slices. UKCIP02 uses results from other global climate models to derive estimates of uncertainty margins to account for differences between different climate models.

The UKCIP02 scenarios described a slightly larger rate of warming compared to UKCIP98, in part due to the inclusion of suplhate aerosols for the first time. The UKCIP02 scenarios also projected that summers will become dryer across the whole of the UK – not just in England and Wales – and by a larger amount than the UKCIP98 scenarios. The UKCIP02 scenarios also included a more comprehensive analysis of projected changes in some aspects of extreme weather and extreme water levels.