Introduction

Uncertainty is at the heart of the climate change debate. We face it in many forms. We do not know how serious will be the impacts of increased greenhouse gas (GHG) concentrations, nor how much will these impacts decline as a result of measures that we undertake. Such measures also have uncertain effects on the amount of reduction in GHG concentrations, both because technological developments have a significant random component and because economic and social systems are prone to shocks and surprises. In spite of the hundreds of papers that have been written in this area many open questions remain.