Atmospheric aerosols affect climate change in two ways: they reflect sunlight back to space and they participate in cloud formation. Aerosols and the clouds formed from them slow down the warming of climate but the strength of this cooling effect is yet not known precisely. In addition, aerosols reduce air quality and cause approximately 4 million premature deaths per year. Both climate change and air quality have significant impacts on our lives and therefore the modelling group's emphasis is on aerosols, their effects on clouds and consequently on climate. The group members use models such as ECHAM and UCLALES to investigate aerosol-cloud-interactions and the effects of aerosols on the climate.
Current research topics include:
the role of natural aerosol in climate change
better representation of natural aerosols in atmospheric models
better representation of clouds at both LES and GCM resolutions
Research highlight: RECON
Refining climate effects of anthropogenic and natural aerosol
Both biogenic carbon and anthropogenic pollutants produce a layer of cooling haze in the atmosphere. They can also increase the amount of sunlight which is reflected back to space by clouds. This means that they can diminsh the warming effect of greenhouse gases. Recent laboratory studies indicate that the cooling effect of biogenic carbon can be stronger than previously anticipated. In this study, by using a comprehensive aerosol-chemistry-climate model, we will test if these finding from laboratory studies can be extrapolated to the global atmosphere. We will also evaluate, how much of the cooling comes from natural biogenic carbon compared to anthropogenic pollutants.
Research highlight: COLDCLOUD
Supercooled Water in Mid-level Mixed-Phase Clouds: Microphysics, Dynamics and Global Radiation Balance
Mid-level clouds in the atmosphere are composed of supercooled liquid drops and ice particles. It has been observed, that clouds are not homogeneous, but quite often a layer of liquid water is found at the top of mixed-phase or ice particle cloud. This layer can be optically relatively thick compared to rest of the cloud as it contains a high number concentration of small droplets. Due to a low vertical resolution used in atmospheric models, the separation of cloud layers is not possible, and thus modeled clouds freeze too easily and their effect on atmospheric radiation is underestimated. In this project we develop new methods to parameterize the vertical structure of clouds into a global atmospheric model, and use the new model to estimate the radiative forcing of mid-level clouds and how it is expected to change in the warming atmosphere. Beyond that, we will explore the potential aerosol particles has in modifying the properties of these clouds.