ABSTRACT
Uncertainties in climate change science are inevitably large. They arise from questions of data quality, inadequate understanding of the climate system and its representation in climate models, and uncertainties about future emissions of greenhouse gases resulting from socio-economic and technical developments. Policies therefore must be based on risk management; that is, on consideration of the probability times the magnitude of any deleterious outcomes for different scenarios of human behavior (Schneider, 2001; Jones, 2004; Kerr, 2005a; Pittock, 2005). We do not insure our house for the coming year because we are certain it will burn down, but because there is a small chance that it might, with serious consequences for our finances. Better flood protection for New Orleans should have been built before 2005 (Fischetti, 2001), not because it was certain New Orleans wouldbe flooded in 2005, but because it mighthave been.
