EXTERNALITY ESTIMATION OF GREENHOUSE WARMING IMPACTS

The impacts of greenhouse warming have been described by Working Group 2 of the 1995 IPCC assessment. They include the impacts of changing v egetation zones on agriculture and silviculture, changes in the occurr ence of crop pests and disease-carrying insects, as well as estimates of the effects of increased frequencies of extreme events such as heat waves, dry spells and floods. The present study attempts to quantify and valuate each of these impacts, integrated over the 21st century, u nder the assumption of continued injection of greenhouse gases into th e atmosphere, leading to a doubling of atmospheric content around the middle of the 21st century. The result is a greenhouse warming externa lity constituting a sizable fraction of the global gross national prod uct, provided that impacts are valued in the way normally done in exte rnality studies for the industrialized world. As the greenhouse gas em issions are chiefly from industrialized countries, while the largest i mpacts are in those regions of the world least likely to reach stages of high development during the 21st century, the results pose a diffic ult geo-political problem The implications for estimating externalitie s of particular energy conversion activities are briefly discussed. (C ) 1997 Elsevier Science Ltd.