When we consider the environmental impact of long-distance travel, we tend to think of air traffic as the big culprit. But a study issued in 2002 by the German Advisory Council on Global Change noted that ocean shipping emissions are surprisingly high:
Shipping is responsible for around 7% of the CO2 emissions from the transport sector or for around 2% of global CO2 emissions. Furthermore, around 7% of all sulphur dioxide (SO2) and 11–12% of all nitrogen oxide (NOX) emissions may be attributed to shipping.
The Kyoto Protocol does not cover international air or sea transport. The German study proposed closing this loophole with a levy on international transport related to the emissions of particular routes and technologies, although it is not clear just how this would be administered or how the level of charges would be set.
In true lobby group style, the UK Chamber of Shipping argues about the impact of ocean shipping compared with aviation, noting that ships carry 90% of all world trade, but are responsible (together with rail) for only 1.75% of all GHG emissions. (Figure attributed to the Stern Report.) Their logic is that switching traffic from air to sea would reduce total emissions. Maybe so, but that doesn't negate the need to look at emissions from all transport modes.
The German proposal is anachronistic at a time when there is growing political acceptance of the need for a global carbon mitigation system and the debate is focusing on the merits of carbon taxes versus carbon markets. It would be double counting if there were a tax on carbon-intense fuels at the same time as an international shipping levy.
The challenge is in setting up a global system, be it a tax or a cap-and-trade market. If one government slaps a carbon tax on fossil fuels, as Quebec is doing, this will reward transport modes that use less carbon - but while this will help reduce local emissions, it could in fact encourage the import of products from regions that don't apply a similar tax. The Quebec approach would not reduce the embodied energy in goods traded internationally (or even between provinces within Canada). A carbon system would only encourage low-carbon international transport if it were applied globally.
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