Ports authorities from around the world gathered in Rotterdam Wednesday to adopt a plan to cut CO2 emissions from the activities of some 100,000 large ships sailing global waters.

Alongside scientists, lawmakers and businessmen, officials from more than 50 ports in 35 countries started a three-day meeting at the home of Europe's largest harbour. They are looking at regulatory and technological ways of shrinking their contribution to global warming.

But the setting of measurable common targets appeared to be a long way off as speakers differed on the maritime transport industry's contribution to global greenhouse gas emission -- put at anything from 1.4 percent to 4.5 percent.

Delegates did agree, though, that the shipping sector would grow by leaps and bounds, and that alternatives had to be found in order to save the planet.

"The climate is changing every minute, even as we sit here," said Ogunlade Davidson, co-chairman of the United Nations' Inter-governmental Panel on Climate Change.

"Human beings have to solve it (global warming), because we created it. The marine environment has to take its own responsibility, as do all of us."

Davidson told the gathering that technical alterations, including the use of hydrodynamics in propellers, could reduce CO2 emissions by up to 30 percent on new ships and 20 percent on older ones.

Renewable fuels, speed reduction and fleet maintenance also had a role to play.

The potential existed to reduce the global fleet's CO2 emissions by 17.6 percent by 2010 and 28.2 percent by 2020, "but this will not be enough to offset the projected fleet growth," he said.

Efthimios Mitropoulos, secretary-general of the International Maritime Organisation, told delegates his organisation was working hard on setting greenhouse gas emission targets for the shipping industry to come into effect by February 2010.

But this could never work if developing countries were excluded from obligation, he argued. The developed world accounted for only 25 percent of the world's merchant fleet, he said.

"In my view, if reductions in CO2 emissions from ships are to benefit the environment as a whole, they must apply globally to all ships in the world fleet, regardless of their flag.

"It seems completely incongruous that two ships, carrying similar cargo, loaded in the same port, sailing at the same speed and having the same destination, should be treated differently because they are registered under two different flags."

China, a developing nation with one of the world's largest ports in Shanghai, did not attend the conference, having sent an apology and explaining that its recent killer earthquake and hosting of the Olympic games required all hands on deck back home.

Rotterdam mayor Ivo Opstelten told the gathering that port cities had a unique responsibility to combat climate change.

The port of Rotterdam planned to reduce its CO2 output by half of 1990 levels by 2025.

Dutch scientists were examining better ways of capturing and storing CO2 emissions, developing a new ship coating with lower algae growth to reduce drag, and testing new collapsable containers enabling ships to transport more empty containers to cut trips.

"For a long time, it (CO2 emissions) was something we did not pay much attention to," said Opstelten. "Now is the time for action."

About 80 ports have been invited to sign the World Ports Climate Declaration once completed.

A draft document circulated Wednesday supported CO2 reduction measures, but mentioned no caps.