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A 'percentile' is the value below which a specified percentage falls. The 10th percentile for instance describes the value at which 10% of the model runs fall (in UKCP09 this is described as the probability level).

In detail

UKCP09 projects changes in climate in several ways, and some outputs involve percentiles or probability levels. The UKCP09 probabilistic projections make use of probability levels to express the likelihood of changes being greater than or less than a certain amount. See the page on probabilities in UKCP09 for how to interpret these probability levels.

For sea level and storm surge height projections, the use of percentiles represents only the percentage of model simulations that give values less than or equal to that percentile. They contain no information on the probability or frequency of exceedance of that value. For example, the sea level rise 90th percentile value is one that exceeds the sea level rise projected by 90% of climate models.

Find out more

  • An overview of how probabilistic projections are created and presented in UKCP09 is described in Box 3 of the UKCP09 Briefing Report.
  • More details are provided in Chapter 3 of the UKCP09 Climate Change Projections report, including an overview of the methodology and a discussion about the interpretation of UKCP09 probabilistic projections.