Aerosols

Human-induced increases in greenhouse gases in the atmosphere are thought to exert a significant positive radiative forcing of climate leading to a warming of the Earth/atmosphere system. However, human activities are also responsible for increasing the atmospheric concentrations of microscopic particles, such as sulphate from industrial sulphur dioxide emissions; smoke from burning of agricultural waste, and pollution particles from traffic emissions.

These atmospheric particles scatter and absorb sunlight and terrestrial radiation and also act as cloud condensation nuclei and modify the microphysical and optical properties of clouds.

The net effect of the impacts on radiation and cloud properties is to induce a net cooling of the climate system which acts to oppose the warming due to increases in greenhouse gases. Aerosols are also implicitly linked to climate change via climate feedback mechanisms. For example, some regions of the Tropics are expected to be subject to water stress in future climate projections, leading to desertification and the subsequent emission of more mineral dust. Biogenic aerosols emitted from plants may also be significantly affected by the health of vegetation, which is forecast to change under future emission projections.

Recently, there have been suggestions that the cooling effect of aerosols could be harnessed to counteract the impact of global warming. Such 'geoengineering' options include the deployment of a fleet of sea-salt producing ships to brighten stratocumulus cloud decks or deliberate injection of sulphur dioxide into the stratosphere to reflect sunlight back to space. The aerosol group develops the aerosols emission, transport, and deposition schemes, and the interaction of aerosols with radiation and clouds within the Met Office Hadley Centre global models (e.g. Met Office climate prediction model: HadGEM2 family) to address the scientific questions summarised above. Satellite remote sensing methods have also been developed and used for model validation purposes.

Key aims

• To maintain and develop aerosol schemes within the global models.

• To develop and study the impact of aerosols upon solar and terrestrial radiation (direct effect).

• To develop and study the impact of aerosols upon cloud microphysical and optical properties (indirect effect).

• To investigate the impact of aerosol direct and indirect effects upon climate.

• To investigate the impact of climate change scenarios upon aerosols.

• To investigate the impacts of potential mitigation and geoengineering solutions to global warming.

Current activities

• Development of the United Kingdom Chemistry and Aerosols (UKCA) Model model aerosol scheme.

• Participation in AEROCOM intercomparison exercises.

• Development and implementation of the IPCC 4AR aerosol emission scenarios.

• Investigation of the impacts of solar radiation management geoengineering scheme.

• Investigation of the Sarychev and Kasatochi volcanic eruptions.

• Investigation of the impacts of aerosols upon the diffuse/direct solar radiation at the surface and the impacts on vegetation productivity and CO₂ drawdown.