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• 1 Introduction
• 1.2 What information is provided?

• Reports & guidance
• About the UK climate change projections
• Online Climate change projections report
• Summary
• 1 Introduction & overview
• 1.1 Why are climate change projections needed?
• 1.2 What information does UKCP09 provide?
• 1.2.1 Climate change over land areas
• 1.2.2 Climate change over marine regions
• Box 1.2: Further information on climate variables
• Table 1.1: Climate variables
• Figure 1.3: Time periods
• 1.3 Uncertainty
• 1.4 Projections at a daily resolution over land
• 2 Why do we need probabilistic information?
• 3 The construction of probabilistic climate change projections  
• 4 Probabilistic projections of seasonal climate changes
• 5 Projections from the ensemble of regional climate models
• Annexes
• Download & ordering page

It is useful at this stage to define some of the terms that we will be using extensively in this report, using definitions broadly in line with those given in IPCC AR4, but adapted to be relevant to UKCP09. The term climate is usually defined as the statistical description in terms of the mean and variability of relevant weather variables over a period of time, which in this report is taken as 30 years (the period adopted by the World Meteorological Organisation).

A climate change projection is a projection of the response of the climate system to a given emissions or atmospheric concentration scenario, expressed as a change relative to a baseline climate (taken as 1961–1990 in UKCP09). Both the projection and baseline climate are simulations by a climate model.

A climate projection is a projection of the response of the climate system to a given emissions or atmospheric concentration scenario. In UKCP09 climate projections are generated from model climate change projections added to a baseline observational climate.

Climate models are often used to make a single projection of climate change, for a given emissions scenario, which reveals nothing about uncertainty. Using an ensemble of a large number of model projections, probabilistic projections can be generated, allowing the uncertainty in projections to be quantified by giving the relative probability of different climate change outcomes.

A variable is a climate-related quantity such as mean temperature or precipitation.

A time period is a 30-year period over which changes in variables are averaged.

Changes are spatially averaged over four areas: a 25 km grid square, an administrative region, a river basin or a marine region. Changes are temporally averaged over a month, a season or a year. So, as an example, projections of change in mean daily maximum temperature for the summer season (temporal average) might also be averaged over Wales (spatial average) and for the 2080s (time period).

An emission scenario is a plausible future pathway of emissions of greenhouse gases and other pollutants which can affect climate.

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