Aerosols & Clouds

Programme overview

The overarching aim of the Aerosols & Clouds programme was:

To reduce the uncertainty in estimates of radiative forcing and climate feedbacks relating to aerosol and cloud processes through focused laboratory and theoretical studies.

Of particular interest was improving knowledge of the following key core physical and chemical processes:

  • Quantification of indirect effects of aerosols on the radiative forcing due to their interaction with clouds and the underlying cloud/aerosol processes.
  • Ice particle processes in deep frontal, convective clouds and cirrus clouds.

This programme was strategically important, as some of the largest uncertainties in future climate prediction centre on the radiative impacts of aerosols and clouds and the feedback processes involved through cloud formation and albedo.

Background & objectives

Clouds have a very large effect on the Earth's radiation budget, which can be perturbed through the addition of aerosol particles into the atmosphere from anthropogenic and natural processes. Particles act as sites for cloud droplet and ice formation. This influences cloud microphysical properties, and subsequently affects cloud dynamics and thermodynamics, and the way the cloud interacts with radiation.

Human-induced changes to the particle loading affecting these processes, known as indirect effects, are large and highly uncertain. The fourth IPCC Assessment Report rates scientific understanding of the aerosol-cloud interactions and cloud albedo radiative forcing as "low".

The influence of pollution on warm clouds, that is clouds containing only liquid water, are the largest source of attributable uncertainty in radiative forcing estimates in global models at the present time. However, the uncertainties surrounding ice and mixed phase clouds are deemed to be so large that no estimates of the uncertainty in their radiative forcing have been made.

A major contributor to this uncertainty stemmed from a rather poor knowledge of the fundamental aerosol and cloud properties and processes that leads to their poor representation in models. Significant fundamental research in these areas is necessary in order to reduce systematic errors in future climate models.

The UK has a very strong community in the aerosol cloud and climate area and is well positioned to lead internationally. The NERC APPRAISE research programme has initiated the development of a range of model and laboratory tools that can be used to make substantial contributions to fundamental understanding in the area of aerosols and clouds.

In order to build on APPRAISE and other recent investments in field programmes, NERC invested in this Aerosols and Clouds programme.

Reports & key findings

This programme achieved impact by improving process understanding, that will narrow the uncertainty in climate prediction models. Further outputs from the programme - external link can be found on the University of Manchester website.