Emission scenarios and global climate protection

This paper evaluates the effectiveness of a wide range of emission scenarios in protecting climate (where 'protecting climate' is used here to mean minimizing 'dangerous anthropogenic interference with the climate system' which results in impacts to society and the natural environment). Under baseline (no action) conditions there is a significant increase in emissions, temperature and climate impacts. Controlling only CO2 emissions (ie freezing emissions in year 2000 at 1990 levels, and decreasing them afterwards at 1%/yr) and only in Annex I countries, does not significantly reduce the impacts observed under the baseline scenario. However, impacts are substantially reduced when emissions are controlled in both Annex I and non-Annex I countries, and when both CO2 and non-CO2 emissions are controlled. It was also found that stabilizing CO2 in the atmosphere below 450 ppm substantially reduces climate impacts. But in order to follow the pathway to stabilization at 450ppm specified by the IPCC, global emissions can only slightly increase in the coming decades, and then must be sharply reduced. On the other hand, stabilizing CO2 in the atmosphere above 450ppm can have significant impacts, which indicates that stabilization of greenhouse gases in the atmosphere will not necessarily provide a high level of climate protection. Results from these and other scenarios are synthesized and related to climate protection goals through a new concept-'safe emission corridors'. These corridors indicate the allowable range of near-term global emissions (equivalent CO2) which complies with specified short- and long-term climate goals. For an illustrative set of climate goals, the allowable anthropogenic global emissions in 2010 are computed to range from 7.3 to 14.5 Gt C/yr equivalent CO2 (1990 level = approximately 9.6 Gt C/yr); when these limits are set twice as strict (ie divided by two), the allowable range becomes 7.6 to 9.3 Gt C/yr. To fall within this lower corridor, global emissions must be lower in 2010 than in 1990. Copyright (C) 1996 Elsevier Science Ltd