Implications of recent CO2 emission-limitation proposals for stabilization of atmospheric concentrations

The stabilization of atmospheric greenhouse-gas concentrations is the ultimate objective of the United Nations Framework Convention on Climate Change. To investigate the gas emissions required to achieve this goal for CO2 over the next few hundred years, the Intergovernmental Panel on Climate Change (IPCC)1,2 has used two sets of concentration pathways (‘profiles’). One set is based solely on smooth changes in emission towards concentration stabilization3, and the other goes further by incorporating economic considerations4. Here I devise new profiles that take into account emissions-limitation proposals restricted to ‘Annex I’ (developed) countries, as well as the constraints imposed by more recent emissions data (now available until the end of 1995; ref. 5). The Annex I scenarios considered are two that span proposals recently considered by the IPCC6, and a less restrictive case. Using the new CO2-concentration profiles and a carbon-cycle model7 to determine global CO2 emissions, and taking into account the prescribed Annex I country emissions, I determine the CO2-emission requirements for non-Annex I (developing) countries to achieve the stabilization of atmospheric concentration at about twice preindustrial values. I show that action by Annex I countries within the bounds of the scenarios considered can mean that non-Annex I countries have several decades before their emissions need to depart significantly from a ‘business as usual’ (no intervention) trajectory. Alternatively, if international trade in carbon emissions is permitted, non-Annex I countries can choose to emit below their ‘business as usual’ baseline and benefit from the trading of emission rights.