Second IMO Greenhouse Gas Study 2009

The main conclusions reached by the Second IMO Greenhouse Study 2009:

  • Shipping was estimated to have emitted 1046 million tonnes of CO2 in 2007, which corresponded to 3.3% of the global emissions during 2007. International shipping was estimated to have emitted 870 million tonnes, or about 2.7% of the global emissions of CO2 in 2007. 

  • Exhaust gases were the primary source of emissions from ships. Carbon dioxide was the most important GHG emitted by ships. Both in terms of quantity and of global warming potential, other GHG emissions from ships were less important.

  • Mid-range emissions scenarios showed that, by year 2050, in the absence of policies, ship emissions could grow by 200% to 300% (compared to the emissions in 2007) as a result of the growth in world trade.

  • A significant potential for reduction of GHG emissions through technical and operational measures had been identified. Together, if implemented, these measures could increase efficiency and reduce the emissions rate by 25% to 75% below the current levels. Many of these measures appeared to be cost-effective, although non-financial barriers may discourage their implementation.

  • A number of policies to reduce GHG emissions from ships were conceivable. The report analysed options relevant to the current IMO debate. The report found that market-based measures were cost-effective policy instruments with a high environmental effectiveness. Such instruments captured the largest amount of emissions under the scope, allowed both technical and operational measures in the shipping sector to be used, and could offset emissions in other sectors. A mandatory limit on the Energy Efficiency Design Index for new ships was a cost-effective solution that could provide an incentive to improve the design efficiency of new ships. However, its environmental effect was limited because it only applied to new ships and because it only incentivized design improvements and not improvements in operations.

  • Shipping had been shown, in general, to be an energy-efficient means of transportation compared to other modes.

  • The emissions of CO2 from shipping lead to positive “radiative forcing” (a metric of climate change) and to long-lasting global warming. In the shorter term, the global mean radiative forcing from shipping was negative and implied cooling; however, regional temperature responses and other manifestations of climate change may nevertheless occur. In the longer term, emissions from shipping would result in a warming response as the long-lasting effect of CO2 would overwhelm any shorter-term cooling effects.

  • If the climate was to be stabilized at no more than 2°C warming over pre industrial levels by 2100 and emissions from shipping continue as projected in the scenarios that were given in the report, then they would constitute between 12% and 18% of the global total CO2 emissions in 2050 that would be required to achieve stabilization (by 2100) with a 50% probability of success.