ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-715-2005 Global indirect aerosol effects: a review Lohmann U. 1 Feichter J. 2 ETH Institute of Atmospheric and Climate Science, Schafmattstr. 30, CH-8093 Zurich, Switzerland Max Planck Institute for Meteorology, Bundesstr. 53, D-20146 Hamburg, Germany 03 03 2005 5 3 715 737 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/5/715/2005/acp-5-715-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/715/2005/acp-5-715-2005.pdf

Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei, they may inhibit freezing and they could have an influence on the hydrological cycle. While the cloud albedo enhancement (Twomey effect) of warm clouds received most attention so far and traditionally is the only indirect aerosol forcing considered in transient climate simulations, here we discuss the multitude of effects. Different approaches how the climatic implications of these aerosol effects can be estimated globally as well as improvements that are needed in global climate models in order to better represent indirect aerosol effects are discussed in this paper.