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UP: Fachverband Umweltphysik

UP 4: Climate; jointly with Arbeitsgruppe Junge DPG (AGjDPG)

UP 4.1: Hauptvortrag

Mittwoch, 16. März 2011, 14:00–14:30, HSZ 201

The role of clouds in climate forcing and feedbacks — •Johannes Quaas — Max Planck Institute for Meteorology, Hamburg

Global climate change is forced by anthropogenic activities, and dampened and/or amplified by feedbacks within the climate system. Second to the greenhouse gases, anthropogenic aerosols are a main forcing agent, and an important pathway of this forcing is the "indirect" one, via the capability of aerosols to serve as cloud condensation nuclei. This aerosol indirect forcing, in which clouds are involved, is the most uncertain one among the most important climate forcings. The presentation demonstrates how satellite observations can be used to reduce this uncertainty. In the purely physical climate system (as opposed to the Earth system where biogeochemical feedbacks also play a role), five feedback mechanisms are known, which are the fundamental dampening "Planck feedback", the dampening "lapse rate" feedback, and the amplifying feedbacks due to water vapour, snow/ice albedo, and clouds. The presentation will explain these feedbacks, demonstrate how these can be quantified, and show how their uncertainty - especially due to the cloud feedback - leads to substantial uncertainties in projected future climate change. Approaches to improve the climate change projects are discussed.