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The UKCP09 projections are some of the most advanced climate projections available anywhere in the world. They provide a number of benefits that make them more useful for decision-making than previous UK projections. These benefits include:

1 - The UKCP09 projections are designed to represent uncertainties as comprehensively as possible

One of the most significant advantages of the UKCP09 projections is that they were designed to include key known drivers of uncertainty in future climate change. In the case of the land projections, the results are presented probabilistically, based on the outputs of a range of climate models combined with a suitable statistical methodology.

The explicit treatment of uncertainties in the UKCP09 projections means that they are more useful for decision-makers. In particular, the use of probabilities in the land projections makes it possible to estimate what the likely range of outcomes is for a particular variable, such as temperature change.

For more information see Probability in UKCP09 and Chapters 2 and 3 of the climate change projections report.

2 - UKCP09 reflects modelling uncertainties

For a given pathway of future emissions, the UKCP09 probability distributions reflect uncertainties in the modelling of future climate change and the effects of natural climate variability. Whilst different climate models produce projections of large-scale changes in climate that show some consistent features, there are important local and regional differences and the magnitudes of change vary. Regarding modelling uncertainties, the UKCP09 probability distributions incorporate the effects of both structural uncertainty (different climate models) and parameter uncertainty (different parameter values for one model). These parameter effects were incorporated by basing the projections on a 'perturbed parameter ensemble' (PPE) approach using the Met Office Hadley Centre's global climate model.

Using a systematic approach based on PPEs allows the UKCP09 projections to take account of feedbacks in carbon cycle processes, as well as in physical atmosphere and ocean processes. However, not all forcing or feedback processes are accounted for by UKCP09, as some are assumed to be small or are as yet too poorly understood to be included in climate models.

Feedbacks are explained in more detail in Box 2.1 of the climate change projections report.

More information about the method is given in Chapters 2 and 3 of the climate change projections report.

3 - UKCP09 uses a wide range of climate models

The UKCP09 projections use 12 of the climate models that were included in the IPCC's 4th Assessment Report, in order to represent modelling uncertainties more comprehensively than could be achieved by using only a PPE based on the Met Office Hadley Centre model.

More information about the method is given in Chapters 2 and 3 of the climate change projections report.

4 - UKCP09 presents outputs in a range of ways

UKCP09 gives users considerable flexibility in terms of how outputs are presented. Users are able to explore and interrogate UK climate projections by using the UKCP09 User Interface . This enables users to produce customisable maps, graphs and other outputs or download the raw data.

5 - UKCP09 is at 25km resolution

The probabilistic projections are calculated for every 25km grid square over land areas of the UK. This level of resolution is designed to be more useful for decision makers, many of whose decisions need to be made at the local scale. While increased resolution accounts better for the local influences of mountains and coastlines, it does not remove the effects of errors in global climate model simulations, which affect the projections at all spatial scales.

Due to the manner in which the probabilistic projections are calculated, it is not possible to aggregate, average or 'merge' a number of 25km grid squares. However, projections have been calculated for certain, pre-defined, aggregated areas; these can be accessed through the User Interface . The eleven regional climate model simulations used to provide information at 25km scale do provide a set of About the Spatially Coherent Projections, although these do not represent uncertainties as comprehensively as the probabilistic information does.