GHG emissions from international shipping and aviation

International shipping accounts for about 2 percent of annual global CO2 emissions. Aviation annually contributes to approximately 3.5 percent of the total human climate change effects, taking into account that several emissions from planes contribute. The emissions occur outside national control, and need broad international cooperation to be curbed. Voluntary agreements and technical standards are the most promising policy instruments towards these emissions in the short and medium term. Emission reductions beyond the standard could in the longer run form a basis for emissions credits that could be sold to land-based emission sources. Carbon taxes would not be a viable option due to huge evasion possibilities. Emissions trading would for the same reason not be viable for shipping, but should be considered for aviation as part of an international emission trading system for land-based sources.