Costs of a Ceiling on Kyoto FlexibilityD.GusbinauthorG.KlaassenauthorN.KouvaritakisauthorThis paper examines the potential costs of a ceiling on the use of flexibility mechanisms in the Kyoto Protocol using POLES, a partial equilibrium model of the world energy systems. The results suggest that if emission trading were restricted to Annex I countries, halving the traded volume would increase costs by US$11 billion per year. If emission trading were to operate at a global level, reducing the trade to half the perfect market volume would increase annual costs by US$12 billion per year. Global carbon emission might, however, be 1% lower. The sensitivity of the results is discussed.1999RR-00-011. Reprinted from Energy Policy, 27:833-844 [1999].Monograph