The UN maritime agency is holding a weeklong meeting aimed at curbing emissions from ships.
Proposals at the International Maritime Organization meeting that began Monday in London include keeping emissions below 2008 levels, but some shipping nations oppose such a cap.
European Union members and other countries want a 70 per cent to 100 per cent reduction in greenhouse emissions by 2050.
They cite a study which found that alternative fuels, wind-assisted ships and electric engines could replace shipping fuels without endangering global trade.
Proposals to cut sulfur oxide emissions and to extend to the Arctic a ban on heavy fuel oil that already covers the Antarctic also will be considered.