Abstract
This article compares the cases of ozone layer protection and climate change. In both cases, scientific expertise has played a comparatively important role in the policy process. The author argues that against conventional assumptions, scientific consensus is not necessary to achieve ambitious political goals. However, the architects of the Intergovernmental Panel on Climate Change operated under such assumptions. The author argues that this is problematic both from a theoretical viewpoint and from empirical evidence. Contrary to conventional assumptions, ambitious political regulations in the ozone case were agreed under scientific uncertainty, whereas the negotiations on climate change were much more modest albeit based on a large scientific consensus. On the basis of a media analysis, the author shows that the creation of a climate of expectation plus pressure from leader countries is crucial for success.