The Danish IMO submission, which said it was trying to initiate debate, admitted that the idea would need broad international consensus.
It did not set a level for the levy, but suggested it should apply to each metric tonne of marine fuel, taking into account emission factors.
The money raised would be used to buy carbon trading credits to counter-balance shippings' CO2 emissions.
That in turn would push up the price of emission credits in the world market, encouraging global reductions of GHG.
Denmark did not specify which 'ship efficiency improvements' might be encouraged, but a number of technologies are being developed to help ships cut bunker consumption. They include towing kites and the incorporation of 'air cushions' beneath ships' hulls.
Providers of fuel efficiency mechanisms have claimed that collectively they could provided fuel savings of up to 40