There are several pathways of mankind to change climate, e.g. depletion of stratospheric ozone, enhanced turbidity of air by emission of particles and/or their precursor gases, emission of long-lived greenhouse gases, change of surface properties by land use change (construction of roads, changes in crops, deforestation and afforestation, etc.). If the processes leading to cli mate change are understood and forcing history is known as well, the influence of a distinct human activity can be separated, i.e. a facet of climate change can be attributed to a certain cause. A definition of attribution following IPCC (2001a) is: Attribution of anthropogenic climate change is understood to mean a) detection (as defined above), b) demonstration that the detected change is consistent with a combination of external forcing including anthropogenic changes in the composition of the atmosphere and natural internal variability and c) that it is not consistent with alternative physically plausible explanations of recent climate change that exclude important elements of the given combination of forcings.
Examples for attribution questions are:
1. Do clouds have properties reacted to the recently reduced air pollution in Central and Eastern Europe after the collapse of the East Block and has this accelerated warming at the surface of the region?
2. Is the observed strong cooling trend of the recent decades in the lowest stratosphere caused by ozone depletion rather than by the enhanced greenhouse effect?
3. Does air pollution lead to more or new extreme precipitation events?
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