An overview of non-CO2greenhouse gases

Non-CO2 greenhouse gases, included in the Kyoto Protocol, are methane (CH4), nitrous oxide (N2O), hexafluorocarbons (HFC), perfluorinated compounds (PFC) and sulphur hexafluoride (SF6). Together they account for about 25% of the present global greenhouse gas emissions. Reductions in emissions of these gases have occurred in the industrialised countries, and they contribute to the efforts to reach the target of 5% greenhouse gas emission reduction as agreed in the Kyoto Protocol for these countries. Globally however, greenhouse gas emissions continue to increase as do the concentrations of these gases in the atmosphere. The relation between emissions and concentrations is not clear for all non-CO2 greenhouse gases. This especially holds for methane. This article discusses the contribution of non-CO2 greenhouse gases to global climate forcing within the causal chain approach of the DPSIR schema (Drivers, Pressures, State, Impact and Response) as a background for the studies presented in this special issue. Although considerable reductions in non-CO2 greenhouse gas emissions are expected in the first commitment period under the Climate Convention (Kyoto Protocol), it is argued that further substantial emission reductions in subsequent commitment periods for the most important non-CO2 greenhouse gases (CH4 and N2O) are difficult to achieve.