Maps of probability for a given threshold

Maps for the UK can now be produced to show the projected probability, across the UK, of a relative user-defined threshold. They are available for download from the UKCP09 User interface. 

Each map depicts for the UK:

• Projected probability of change across the UK based on a user-defined threshold (greater than or less than the defined threshold)
• For one variable
• For the marine regions or 25 km land grid squares or aggregated regions across the UK
• For one temporal average (month, season or annual)
• For one time period
• For one of the three emission scenarios

• What should I use them for?

• To show the nature and extent of probability of a projected change associated with a user-defined threshold.

• To inform nationwide or region-wide assessments that have the same climate thresholds

• What should I be aware of?

• 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 because the projections are not spatially consistent across adjacent grid squares. This characteristic should be taken into account when interpreting all UKCP09 maps (see the background to the SCPs for more information) <link to SCP tech note>. 

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

It is important to recognise that 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.

• A single map does not represent changes through time

A single map shows the projected climate change associated with a single, user-defined, future 30-year time period. As such, they provide no information about the evolution of changes through time. UKCP09 as a whole, delivers future climate information for static 30-year time periods, yet 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 (i.e. for a series of 30-year time periods).

• Use the extremes of the probability level range with caution

Normally we advise to use projections from the 10 to 90% probability levels as a robust range of the projections and to treat the probability levels outside this range with caution. In production of these maps it is necessary to show the full 100 probability levels so that changes within the range of uncertainty can be captured. This means that specified thresholds falling outside the range of uncertainty of the projections are classified as 0 or 100% probability.  However, even though probability levels outside the 10–90% are shown on the map we encourage users to use these projections with caution.

• The probabilities are based on the strength of evidence that supports the projections

The maps do not show a probability of actual occurrence of a particular outcome, they show the probabilities as reflected by the projections (see probability in UKCP09 for more information).