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Maps of probability for a given threshold detail

This page gives more information about how to use maps of probability for a given threshold, some things to be aware of when using them and some technical information about the methodology used to create them.

What should I use them for?

These maps can be used to show the probability of a projected change associated with a user-defined threshold. This may be useful to inform nationwide or regional climate assessments that are based on a particular threshold.

Things to be aware of

When using these maps there are a few things that you need to bear in mind:

1 - The projections are not spatially consistent across grid squares

UKCP09 maps do not present a snapshot of the spatial distribution of the projected climate at a particular 30-year time period. This is because the projections are not spatially coherent across adjacent grid squares. This means that it is not possible to aggregate the findings of several grid squares.

2 - A single map is of limited value because it does not represent uncertainty across the emission scenarios

Maps produced with different emissions scenarios will provide different projections of future changes. If a single map (and therefore a single emissions scenario) is used, it should be clearly stated which has been used and why, and recognised that this choice will constrain the range of future climate outcomes that are considered.

3 - A single map does not show changes through time

A single map shows the projected climate change associated with a single, user-defined, future 30-year time period. It does not provide information about the evolution of changes through time. UKCP09 delivers future climate information for static 30-year time periods. However, information about transient changes is sometimes required for impacts and adaptation assessment. An estimate of transient changes can be obtained through comparison of multiple maps across a series of 30-year time periods.

4 - Use the extremes of the probability level range with caution

Ordinarily users should use projections that fall within 10% to 90% probability levels, as they are more robust than those that fall outside of this range. However, these maps show the full 100 probability levels so that changes within the range of uncertainty can be captured. Thresholds falling outside the range of uncertainty of the projections are classified as 0 or 100% probability. Despite the fact that probability levels outside the 10% to 90% range are shown on the map we advise users to use these projections with caution.

5 - Probabilities are based on the strength of evidence that supports the projections

Probabilities in UKCP09 are based on the weight of the evidence. These maps show the probabilities as reflected by the projections. For more information about probability see the Probability in UKCP09 page.

Technical details

This section explains the process for creating maps of probability for a given threshold.

Using the UKCP09 User Interface , select a Cumulative Distribution Function (CDF) by choosing the data source, climate change type, variable, emissions scenario, time period, temporal average and spatial average.

Then define a threshold value (such as 3˚C) and whether you want to see probabilities for values that are 'greater than' or 'less than' that threshold.

The User Interface  selects the entire CDF - defined as location versus probability level - and for each location (grid box or aggregated area) finds the two probability levels between which the user-defined condition lies. The final probability level (for each location) is derived by a linear interpolation between the two probability levels.

You can display the results as a map or download the outputs as a data file. As the maps are formatted to show probability levels as whole integers, the raw data will provide a higher level of precision.