Nordic ferries go gas-powered
The Finnish flag is fiercely clacking at the stern as the Viking Grace carves through spring ice, past scores of small islands on the route between Stockholm in Sweden and Turku in Finland.
A maritime revolution is taking place in this narrow waterway and its archipelago of hundreds of small islands. The Viking Grace, a brand new cruise ferry, is fuelled entirely by liquefied natural gas (LNG) and is the first of a new generation of green passenger ships.
"It's very important for us at Viking Lines to be a pioneer and save our environment," says Captain Magnus Thornroos on the ship's wide bridge.
Down in the bowels of the ship, the engines are running on 100% gas, although they are capable of using old-fashioned diesel as a back-up propellant if necessary.
"LNG is the cleanest of the fossil fuels we have on Earth," says First Engineer Victor Gingsjoe.
"Compared to running on diesel oils, the particle matter that we release into the atmosphere is virtually nothing. The sulphur oxide emissions are practically nothing. And also we can reduce the CO2 [carbon dioxide] by up to 30%."
But Dr Kaare Press-Kristensen, an air pollution expert from Denmark's Ecocouncil, adds a caveat.
"We know that LNG can significantly reduce harmful substances," she says. "However, if LNG escapes the engines without being burned, it will contribute significantly to global warming as well."
Viking Lines say its ship is fitted with the latest technology for monitoring the ship's systems.
By using LNG, the vessel is complying with new emission controls that come into effect in the Baltic Sea in 2015. Similar rules will begin simultaneously in the North Sea and along the east and west coasts of North America.
It is hoped the changes will make a significant difference to the ecology of the Baltic Sea, which is heavily polluted, in part from Russian ships coming from the east.
The bottom of the sea is said to be dying and the reason it is so dirty is that it is almost entirely enclosed by land and does not have a flow of fresh water to flush out the grime.
On deck, it is easy to see how still are the waters of the Baltic. As far as the eye can see in the Swedish part of the archipelago, the sea is covered in ice.
The project's supporters say the new regulations will not just benefit nature, but also public health.
"In Europe, we know that about 50,000 premature deaths are caused from air pollution from shipping," says Dr Presse-Kristensen.
"And the cost to society is about 55bn euros [£45bn; $72bn] every year, so it's a huge cost."
Inside the Viking Grace, a Bruce Springsteen video is entertaining passengers in the music bar.
On deck it is cold, and taking the air is Mohammed Hassan, from London.
"I have a carbon footprint," he says. "And I think it's being reduced because technically it's being driven by gas and it's very environmentally friendly as well. So I would say it's fantastic. I am being responsible by using less carbon."
Two new ferries, the Stavangerfjord and the Bergensfjord, both entirely powered by liquid gas, are currently being completed at Rissa, Norway, and they are due to start sailing between Denmark and Norway this summer for Fjord Line.
As is often the case when it comes to green technology, the Nordic countries are showing the way.