FIXING GLOBAL CARBON EMISSIONS - CHOOSING THE BEST TARGET YEAR

Confronted with issues fraught with the enormous complexity, policy ma kers have shown a proclivity towards considering and enacting simple a nd apparently equitable structures that can be easily explained to and understood by their constituents, In the global change arena, this te ndency seems to lead to consideration of global emissions targets defi ned by levels achieved in some specific year along a previously unregu lated trajectory, The question raised then is one of determining which year's emissions would, if set as a global limit, maximize the discou nted net benefit of the policy? In addition, how sensitive is that yea r to changes in the damages associated with a doubling of atmospheric concentrations of greenhouse gases anchor the pace of near-term, unreg ulated emissions of those gases? Results produced here support two qua litative results that speak to the answers to these questions. Support for limiting emission below levels that would be achieved along almos t any reasonable unregulated trajectory prior to the year 2020 require s, first of all, accepting the notion that doubling damages will be at least 5% of world GDP, Secondly, discovering that the globe is moving along an emissions trajectory that is higher than otherwise expected need not imply that the target year for fixing emissions should be mov ed forward; indeed, higher emissions sometimes mean that the discounte d net benefit of fixing emissions climbs as the target year is pushed further into the future. (C) 1998 Elsevier Science Ltd. All rights res erved.