The International Maritime Organization, overseer of the highly-polluting shipping industry, sealed a landmark deal Friday to improve its target to cut carbon emissions but green campaigners said it fell far short.

Compared with 2008 levels, the United Nations' global shipping regulator agreed to cut total annual emissions of greenhouse gases "by at least 20 percent, striving for 30 percent, by 2030" and "by at least 70 percent, striving for 80 percent, by 2040" according to the agreement.

That compared with the prior target for a 50-percent reduction by mid-century from 2008.

The International Maritime Organization described the deal as "historic", adding that it "remains committed to reducing greenhouse gas emissions from international shipping and, as a matter of urgency, aims to phase them out as soon as possible".

The IMO said the "carbon intensity" of ships was expected to decline over time with "further improvement of energy efficiency" of new vessels.

Shipping emits roughly the same level of greenhouse gases as aviation, which is aiming for net zero by 2050.

The deal came at the end of a five-day meeting at the IMO's headquarters in London, attended by representatives from 100 countries.

The gathering of its Marine Environment Protection Commission pitted climate-vulnerable nations -- particularly islands in the Pacific -- and richer countries against big exporters like China.

The vast majority of the world's 100,000 cargo ships -- which carry 90 percent of the world's goods -- are powered by highly-polluting diesel.

Shipping is responsible for around three percent of global greenhouse gas emissions according to the UN.

- 'Vague' deal -

Non-governmental organisations with a focus on climate slammed the agreement, arguing it was insufficient under the framework of the landmark Paris climate accord.

The NGOs instead want the shipping sector to implement a 50-percent reduction by 2030 and deliver carbon neutrality by 2040.

"There is no excuse for this wish and a prayer agreement," said John Maggs, president of the Clean Shipping Coalition.

"They knew what the science required, and that a 50 percent cut in emissions by 2030 was both possible and affordable.

"Instead the level of ambition agreed is far short of what is needed to be sure of keeping global heating below 1.5 Celsius, and the language seemingly contrived to be vague and non-committal," he said.

Under the 2015 Paris agreement, nations have pledged to reach net-zero carbon emissions by the middle of the century with the aim of limiting the increase in global temperatures to 1.5 degrees Celsius above pre-industrial levels.

Argentina, Brazil and China, in particular, had strongly resisted tougher IMO targets, arguing they cost poor, developing countries the most.

They are also strongly opposed to a flagship proposal for a global levy, or carbon tax, on shipping emissions.

French President Emmanuel Macron backed the idea at a recent climate finance summit in Paris, but said it would need backing from China, the United States and other European nations to work.

Green campaigners on Monday protested outside the IMO's headquarters.

Several dozen activists, including some dressed as jellyfish, urged greener freight to help tackle climate change and protect the oceans.

ved-bcp/rfj/ach