Climate-change emissions from the shipping industry have been significantly underestimated and are racing ahead of those of aviation, a study has found.

The quantity of carbon dioxide pumped into the atmosphere by tankers and container ships is 50 per cent higher than was previously believed.

The findings, part of an investigation by the International Maritime Organization (IMO), come amid rising concern that the industry’s impact on global warming is being ignored. Aircraft and cars have borne the brunt of criticism by environmentalists who are concerned about the impact of emissions from the transport sector, but the new calculations are likely to focus more attention on ships.

The findings, seen by The Times, suggest that shipping is dirtier than was previously assumed and is causing significantly higher levels of damage to the environment.

The reputation of shipping as an efficient means of transporting 90 per cent of the world’s goods is unlikely to be lost, but the sector will be under pressure to reduce emissions.

Previous calculations have put global shipping emissions at about 800 million tonnes per year, compared with about 650 million tonnes for aviation. A new method of calculation, based on a reassessment of the quantity of marine bunker fuel used by vessels over 400 gross tonnes, puts shipping at 1.2 billion tonnes.

The figure is almost twice that of the emissions most commonly attributed to the aviation industry.

Research presented to the IMO by Intertanko, the International Association of Independent Tanker Owners, found that rather than the previously assumed 200-250 million tonnes of bunker fuel used annually, the figure was at least 350 million. This allowed the emissions total to be recalculated. The sizes of vessels, fuel efficiency and horse power were also taken into consideration.

Bill Box, of Intertanko, said that the industry recognised that it was lagging behind. “Planes, trains and cars have tightened up much more than shipping,” he said. “Shipping is the last to tighten up. It’s conscious it is the last and that things must be done – and must be done quickly.”Martyn Wil-liams, of Friends of the Earth, said: “It’s a bit of a shock. It’s not about good sectors and bad sectors. We need to calculate the amount we can safely put in the atmosphere.”