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Aerosols are a collection of airborne solid or liquid particles arising from both natural and human sources. Examples include salt particles, desert dust, soot and charcoal (black carbon) and sulphate particles that reside in the atmosphere and range in size between 0.01 and 10 micrometres (one micrometre is 1/1000000 of a metre).

Aerosols have both a direct and an indirect effect on climate processes. The direct effect is to scatter and absorb solar radiation. The indirect effect is that they affect a number of cloud processes. Different types of aerosol affect climate processes in different ways, but the overall net effect of aerosols is that they cool the atmosphere.

In detail

In developing the UKCP09 probabilistic projections, the effect of sulphate aerosols was considered through the use of a sulphate aerosol Perturbed Physics Ensemble (PPE).

The UKCP09 projections therefore include direct and some indirect effects of sulphate aerosols, and uncertainties in these. Other sources of aerosols are not explicitly included in UKCP09.

Find out more

  • More details about the treatment of sulphate aerosols in UKCP09 are given in Box 2.1 of the UKCP09 Climate change projections report. This provides a list of the constituents included, and not included, in the UKCP09 probabilistic projections.
  • A discussion of sources of uncertainty in the UKCP09 probabilistic projections is available in Annex 2.4 of the Climate change projections report.
  • IPCC Fifth Assessment Report, Working Group 1 report The Physical Science Basis, Chapter 7.