Already one of the world's biggest polluters, campaigners want to stop the global shipping industry from generating even more greenhouse as it grows in the future.

More than 100 countries have gathered at the International Maritime Organisation (IMO) meeting in London to try to agree on a new policy regarding emissions.  Shipping accounts for more than two percent of the world's CO2 pollution, and that is poised to get worse.  If "shipping" were a country, it would jump to number six on a list of the world's biggest polluters - even ahead of industrial Germany.

A draft proposal calls for cutting greenhouse gas emissions by 50 percent by 2050.

David Paul, environment minister of the Marshall Islands, acknowledged that shipping was a major source of income for his country because of the vast number of ships flagged out of the Marshall Islands.  But the CO2 output was contributing to global warming, which causes rising sea levels, which threaten the country's very existence.  He said that failing to invest in cleaner technologies now will cost more down the road.

"There will be nothing more devastating to global trade than the cost of having to try to adapt to a world that is on average two, three or four degrees warmer," said Mr. Paul.

But other countries - particularly those run by free marketeers, such as Brazil, Panama, and Argentina - are resisting mandates for cutting shipping emissions for fear of endangering important sectors of their economies.

"We are very mindful of the fact that no measure should discriminate against exporting countries and no measure should eventually favor other exporting countries because they are close to their markets and their destinations," said Brazil's Hermano Telles Ribeiro.  Brazil claims strict limits on shipping emissions are unfair because it is so far away from most major markets and therefore 90 percent of its international trade is carried by shipping.

The Paris Climate Accord does not deal with shipping because it is an international activity, and the agreement was written to deal with national targets to lower greenhouse gas emissions.