New research suggests that the impact of shipping on climate change has been seriously underestimated and that the industry is currently churning out greenhouse gases at nearly twice the rate of aviation.

Shipping, although traditionally thought of as environmentally friendly, is growing so fast that the pollution it creates is at least 50 per cent higher than previously thought. Maritime emissions are also set to leap by 75 per cent by 2020. The International Maritime Organisation, the UN body set up to regulate shipping, has set up a working group due to report this year. Research seen by the group suggests previous calculations, which put the total at about 600 million tonnes per year, are signifi-cantly short. The true figure is set to be more than one billion tonnes, according to a confidential report produced for the IMO by Intertanko, the International Association of Independent Tanker Owners.

In comparison, aviation produces an estimated 650 million tonnes. The old figures were based on 2001 estimates, but shipping has grown by 4.5 per cent on average annually. While other industries have come under pressure to clean up their acts, shipping has so far escaped. Bill Box, from Intertanko, said the industry knows it has been slow to respond. "Shipping has not yet been regulated and for politicians it is the last low hanging fruit," Mr Box said.

In California, the Attorney General has launched a petition aimed at forcing the Environmental Protection Agency to curb emissions of climate change gases from shipping in US waters. In the UK, the Government is under pressure to include shipping in emission targets for the Climate Change Bill next month. And new EU regulations come into force in November to compel ship owners to use cleaner fuel in coastal shipping lanes throughout continental waters.

"Shipping is an invisible industry," said Mr Box. "Ports are away from population centres and many people don't see a ship from one year to another."

The industry serves more than 90 per cent of global trade and as commerce has grown, so has the shipping fleet. At present it is more efficient to ship a container from Beijing to London than it is to transport it 100km by road. The world fleet of ocean-going vessels stands at 90,000, says Oceana, a US-based ocean protection organisation that is part of a coalition of environmental groups that has signed the California petition. The petition claims that the fleet generates emissions equivalent to nearly 190 million cars, all the vehicles in the US.

Michael Woods, co-chair of the UK Environmental Law Association's climate change working party, said government curbs on pollution were coming sooner than the industry realises. He said that shipping could be included in the European Emissions Trading Scheme. With land-based polluters already heavily regulated, the shipping industry could provide the most cost-effective way to reduce climate change gases.

Since the 1970s, the bulk of commercial vessels have run on heavy "bunker" fuel, a by-product of the oil refining process for higher grade fuels. One industry insider described it as "the crap that comes out the other end that's half way to being asphalt". It has potentially lethal side effects such as the release of sulphur dioxide, carbon dioxide, nitrogen oxide and sulphuric acid.

Recent studies in the US and the Netherlands showed pollutants from ships contribute half of the smog-related sulphur dioxide in Los Angeles. In Rotterdam, North Sea shipping lanes run within 25 miles of the shore, spewing pollution that can travel up to 1,000 miles. "If you want to improve air quality on land, you will have a larger effect from spending one euro at sea than you will have spending one euro on land," said Pieter Hammingh, from the Dutch environment agency.

(By Daniel Howden, The Independent, 10/10/2007)