The implications of switching fuels on global CO2 levels has had a lot of traction in recent debates on INTERTANKO's proposal and other scenarios.
Sustainable shipping looked at one angle after speaking with Dr James Corbett.
http://www.sustainableshipping.com/news/2007/08/68719
The current industry poll is also looking at this issue and, so far, around two-thirds of respondents have said that increased CO2 is not a reason to delay a switch to cleaner fuels.
Has CO2 become less salient in the debate?