Shipping and aviation are the only industrial sectors not regulated under the Kyoto Protocol, which sets targets for greenhouse gas emissions by rich countries for the period 2008-12.
Shipping accounts for nearly 3% of global carbon dioxide (CO2) emissions and pressure has grown for cuts ahead of a crucial climate change summit in Copenhagen in December. Delegates from around 90 countries approved non-compulsory technical and operational measures to reduce greenhouse emissions from ships.
These included an energy efficiency design index for new ships to ensure that new vessel designs are environmentally friendly, as well as guidelines for existing vessels' development index.
The measures will be trialled until March 2010, when they will be addressed again by the IMO's marine environment protection committee.
Peter Lockley, head of transport policy at environmental group WWF UK, said the measures should have been mandatory with set targets.
"This does not meet our demands or what is necessary to protect the climate, and we are going to call on the UNFCCC to set targets and timelines and guiding principles," Lockley said, referring to the UN Framework Convention on Climate Change (UNFCCC).
Peter Hinchliffe, marine director with the International Chamber of Shipping (ICS), which represents 75% of the global industry, said the proposals were an important step, adding that shippers wanted them to be mandatory as soon as possible.
"I think the IMO is quite right to express just a little bit of caution about making sure what is actually eventually adopted in a mandatory sense will work," he told Reuters.
"I think therefore the trial period that has been agreed to is a very sensible way to take it forward."
France called last month for a decision in Copenhagen on curbs to ship emissions, but stopped short of stating figures.
Some analysts argue that the IMO has been slow to come up with a mechanism to curb CO2 due to differences between member nations, especially ahead of Copenhagen (EurActiv 19/05/09).
Christian Breinholt, director of the Danish Maritime Authority and part of the Danish delegation, said the design index was an important step forward.
"For some delegations it is very, very delicate to apply legal effects in advance of COP 15 (Copenhagen)," he said.
IMO Secretary-General Efthimios Mitropoulos told delegates earlier this week they should avoid the temptation to seek "overly ambitious results we cannot deliver".
Shipping industry officials have accepted some kind of market-based mechanism is needed, with the purpose of offsetting growing emissions in other sectors and providing incentives for the industry to invest in more fuel-efficient technologies. They argue that given shipping's global nature any solution must be directed by the IMO.
The session of the IMO's marine environment protection committee discussed for the first time the issue of market-based measures and agreed on a work plan. It "could be in a position" to report progress made on the issue in 2011.
"The IMO has got the technical expertise," WWF UK's Lockley said. "But this is a bigger political issue and we need to see some movement in Copenhagen if it's going to progress."
(EurActiv with Reuters.)